Industrial Radiography Manual. Education and Training; Officeof Education Atomic Energy Commission, Oakridge, Tenn

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DOCUMENT RESUME VT 006 293 ED 025 614 By-Richardson. Harry D. Industrial Radiography Manual. Education and Training; Officeof Education Atomic Energy Commission, OakRidge, Tenn. Div. of Nuclear CHEW, Washington. D.C. Div. of Vocationaland Technical Education. Report No-0E-84036 Pub Date Mar 68 Note- 179p. Office,Washington,D.C. 20402 Available from- Superintendent ofDocuments,U.S. Government Printing (FS5.284:840361 $1.25). Available from EDRS. EDRS Price MF-$0.75 HC Not *Textbooks, *Trade andIndustrial Descriptors-*Adult Vocational Education.Radiation. *Radiographers, Education *Nondestructive Testing Identifiers- Industrial Radiography, industrial This text was developedfor use by students in an80-hour course for (1) The Structure ofMatter, (2) Radiationand radiographers. Chapter headings are: Interaction of Radiation Machines, (3) NuclearReactions andRadioisotopes, (4) Radiation Detection andMeasurement, (6) TheNature and Radiation with Matter, (5) Organs and Consequences of RadiationExposure, (7) The Effectof Radiation on the Introduction to Radiography,(9) Elements ofIndustrial Tissues of the Body, (8) Interpretation Radiography, (10) RadiographicFilm, (11) RadiographyTechniques, (12) andTransportation ofRadiographs,and(13)GovernmentLicensing,Health, Radiography. A study guide(VT 006 294) andinstructor's Regulations for Isotope arrangement as this guide (VT 006 292) arealso available; each hasthe same topical text. (EM) INDUSTRIAL RADIOGRAPHY Manual

%oho' DISCRIMINATION PROHIBITED Title VI of the Civil Rights Act of 1964 states "No person in the United. States shall on the ground of race, color, or national origin, be excluded from participation in, be denied the benefits of, or be subjected to discrimination under any program or activity receiving Federal financial assistance." There- fore, any program or activity making use of this publication and/or receiving financial assistance from the Department of Health, Education, and Welfare must be operated in compliance with this law. von 01611V

U.S. DEPARTMENT OF HEALTH, EDUCATION & WELFARE EDO2b614 OFFICE OF EDUCATION

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THIS DOCUMENT HAS BEEN REPRODUCED EXACTLY AS RECEIVED FROM THE PERSON OR ORGANIZATION ORIGINATING IT.POINTS OF VIEW OR OPINIONS 0 STATED DO NOT NECESSARILY REPRESENT OFFICIAL OFFICE OF EDUCATION POSITION OR POI ICY.

INDUSTRIAL RADIOGRAPHY Manual

Developed jointly by the Division of V ocational and Technical Education of the U.S.Office of Education and the Division of NuclearEduca- tion and Training, U.S. Atomic EnergyCom- mission. Developed awl first published pursuant to a contract with the U.S. Atomic EnergyCommis- sion by Harry D. Richardson.

U.S. DEPARTMENT OF U.S. ATOMIC ENERGY COMMISSION HEALTH, EDUCATION, AND WELFARE GLENN T. SEABORG, Chairman JOHN W. GARDNER, Secretary Robert E. Hollingsworth, General Manager Office of Education HAROLD HOWE II, Commissioner March 1968

Superintendent of Documents Catalog No. FS 5.284:84036

U.S. GOVERNMENT PRINTING OFFICE WASHINGTON :1968 For sale by the Superintendent of Documents, U.S. Goyernmor' ?rintini Office Washington, D.C., 20402 - Price $1.25 Foreword

Nondestructive testing hasbecome an indispensabletool of industrial production. It resulted from arapid flow of technologicaladvances which and develop- are an outcomeof the large investmentin scientific research ment. Management inmodern industry canutilize one aspect of nondestructive testing, known asindustrial radiography, toreduce production costs and assure productquality in a. competitivemarket. Specifically, metallurgists, materials engineers,quality control engi- design engineers, testing neers, andmaintenance supervisors canapply the techniques of with X-rays and radioactiveisotopes to insure productreliability; prevent accidents and save humanlife; decrease losses ofproduction time; eliminate wastage of materials;decrease maintenance timeand costs; and maintain high industrialproductivity while achievingproduct integrity and serviceability. A vital factor in the growthof industrial radiographyis the technical personnel involved. They aretrained to understand thecomparative capa- bilities, advantages, andlimitations of X-rays andradioactive isotopes, and can safely andefficiently make specificapplication of these energy sources to all typesof industrial work. This resource manual hasbeen developed to assistin the training of industrial radiographers in an80-hour program. Traineesattending this program are expected tohave a formal high schooleducation. The training program, therefore,is most elementary, yetprovides the basic knowledge and skills required. The traineewill not become a proficientradiographer in this introductory program,hence, emphasis should beplaced upon understanding the basic principles.With a proper understandingof the principles he can improve hisabilities through experienceand by additional study of the materialscontained in the bibliography. In addition to this trainee manual,the material prepared andcoordi- nated for this course includes*: Industrial RadiographyStudentGuide and LaboratoryExercises Industrial RadiographyInstructor'sGuide The need for this course wasidentified by officials in theU.S. Atomic Energy Commission. The Commission'sfirst concern was to eliminate overexposures to workersengaged in radiography. Asecond interest was to increase the trained manpowerin this expanding field. Contentand format for the course were identifiedby a committee of industry repre- * Student Guide and LaboratoryExercises, Industrial Radiography, 0E-84035, available from Superintendentof Documents, U.S. Government Printing Office, Washington, D.C. 20402,price 55 cents. Instructor's Guide, Industrial Radiography,0E-84034, available from Superintendent of Documents, U.S. GovernmentPrinting Office, Washing- ton, D.C. 20402, price 40 cents. sentatives working with representatives of the U.S. Atomic Energy Com- mission and the U.S. Office of Education, Division of Vocational and Technical Education. The writing of the manual was performed by Harry D. Richardson, Louisiana State University, under contractual arrangements with the Division of Nuclear Education and Training, U.S. Atomic Energy Commission.

GRANT VENN RUSSELL S. POOR Associate Commissioner for Director, Division of Adult, Vocational, Nuclear Education and Training and Library Programs

iv Contents Page Foreword

Part IRadiation Physics xi

CHAPTER 1.The Structure of Matter 1 1-1Early Atomic Concepts 1 1-2Later Atomic Discoveries 1 1-3Particles of Matter 2 1-4Atoms and Elements 2 1-5Molecules and Compounds 3 1-6Fundamental Particles 3 1-7The Atom as a Solar System 3 1-8Atomic Number and Weight 5 1-9Isotopes 6 CHAPTER 2.ittxliation and Radiation Machines 9 2-1Radioactivity 9 2-2Discovery of Radiation 9 2-3Kinds of Radiation 10 2-4Properties of Radiation 10 2-5The Electromagnetic Spectrum 11 2-6Radiation Machines 12 CHAPTER 3.Nuclear Reactions and Radioisotopes 17 3-1Nuclear Reactions 17 3-2Nuclear Fission 17 3-3Chain Reactions and Crititality 18 3-4Fission Products 20 3-5Activation of Isotopes 20 3-6Nuclear Reactors 21 3-7Decay of Radioactivity 22 3-8The Curie 22 3-9Plotting Radioactive Decay 22 3-10 Decay Schemes 24 CHAPTkR 4.Interaction of Radiation With Matter 25 4-1Ionization and Ions 25 4-2Ionization by Particles 25 4-3Ionization by Electromagnetic Radiation 26 4-4The Roentgen 28 4-5Radiation Attenuation 28 4-6Absorption of Radiation 29 4-7Half-Value Layers 30 4-8Reduction Factors 33 4-9Principles of Radiation Safety 35 Page

CHAPTER 5.Radiation Detection and Measurement 39 5-1Radiation Detection and Measurement 39 5-2Radiation Measurement 39 5-3Dosimeters 39 5-4Survey Meters 42 5-5Instrument Characteristics 43 5-6Instrument Calibration 44

5-7Source Calibration . 44

Part IIThe Biological Effects of Radiation 47 CHAPTER 6.The Nature and Consequences of Radiation Exposure 49 6-1Radiation Health in Perspective 49 6-2Sources of Information About Radiation's Effect on Man 50 6-3Measurement Units of Radiation Doses 51 6-4 The Nature of the Radiation Health Problem 52 6-5Levels and Symptoms of Radiation Injury 53 6-6 Common Terms of Reference for Gross Effects of Radiation Injury 54 6-7 Summary of Biological Effects of Radiation 54 6-8Personnel Monitoring 55 6-9 Exposure for the Total Population 58 6-10 Physical Examinations 58 6-11 Instrumentation 58 6-12 Contamination 59 CHAPTER 7.The Effect of Radiation on the Organs and Tissues of the Body 61 7-1Radiation Effects on Living Matter 61 7-2Radio-Sensitivity 62 7-3Classification of Body Cells in Order of Radio-Sensitivity 62 7-4Types of Biological Effects of Radiation 63 7-5Factors Related to Somatic Radiation Effects 63 7-6Specific Effect of Radiation on Various Organs and Tissues of the Body 64 7-7Effects of Radiation on the Life Span 70 7-8 The Genetic Effects of Radiation 71

Part IIIIndustrial Radiography 73 CHAPTER 8.Introduction to Radiography 75 8-1The Process of Radiography 75 8-2 The Radiograph 76 8-3Applications of Radiography 76 8-4Industrial Radiography 77 CHAPTER 9.Elements of Industrial Radiography 79 9-1Sources of Radiation 79 9-2Geometric Principles 84 9-3Specimen 88 9-4Radiation Scattering 88 vi Page

Radiographic Film 91 CHAPTER 10. 91 10-1Introduction 91 10-2Radiographic Contrast 92 10-3Subject Contrast H & D Curve 92 10-4 Film Contrast, 94 10-5Radiographic Screens 95 10-6Film Processing 98 10-7Film ProcessingFacilities Radiography Techniques 101 CHAPTER 11. 101 11-1Introduction 101 11-2Exposure Calculations 109 11-3Exposure Arrangements 113 11-4Unsatisfactory Radiographs:Causes and Corrections Interpretation of Radiographs 117 CHAPTER 12. 117 12-1Basic Concepts ofInterpretation Specifications, Codes andStandards 118 12-2 125 12-3Radiographic Sensitivity Radiographs of Welds 126 12-4 128 12-5 Radiographs ofCastings 133 Part IVRegulations and Procedures CHAPTER 13.Government Licensing,Health, and Transportation Regulations forIsotope Radiography .. 135 135 13-1The Authority forAEC Regulations 13-2Licensing and PolicingAuthority of States and Other "Bodies" 135 13-3Requirements for a SpecificLicense to Use Byproduct Materials for Radiography 135 Conditions and Control ofLicenses 136 13-4 136 13-5General Standards forProtection Against Radiation Precautionary Procedures andRecords Required of 13-6 142 Licens :es Qualifications and Training ofRadiography Personnel 145 13-7 148 13-8Organizational Structure ofRadiography Programs Other Requirements forIndustrial Radiography 13-9 148 Operations 13-10 Transportation ofRadioactive Materials 149 13-11 Applying for aLicense to Use Radioisotopesfor 153 Radiography Appendix A.Glossary of Useful NuclearTerms in Industrial Radiography 155 Appendix B.80-Hour Schedule for RadiographyTraining Program 162 Appendix C.Tables of Squares and SquareRoots 163 165 Appendix D."Need to Know" Appendix E.Darkroom Don'ts 166 167 Bibliography 169 Index vii ILLUSTRATIONS

Figure Page

1.1 Molecules of Water ; 1120 3 1.2 The Atom and the Solar System 4 1.3 Particles in an Atom 4 1.4 Potassium and Chlorine Atoms 4 1.5 Electron Cloud Density and Energy Levels 5 1.6 Atoms of First Four Elements 5 1.7 Isotopes of Hydrogen 6 2.1 Identifying Three Common Types of Radiation 9 2.2 Wave Motion and Wavelength (A) 11 2.3 The Electromagnetic Spectrum 12 2.4 Van de Graaff Generator 13 2.5 Linear Accelerator 14 2.6 The Betatron 15 2.7 The X-ray Machine 15 3.1 Neutrons Released in Uranium Fission 18 3.2 Chain Reaction of U-235 19 3.3 Distribution of Fission Products 20 3.4 Production of Cobalt-60 21 3.5 Decay of Radioisotopes 22 3.6 Co-60 Decay Curve : Cartesian Coordinates 24 3.7 Co-60 Decay Curve : Semi-log Coordinates 24 3.8 Decay Schemes for Co-60 and Cs-137 24 4.1 Ionization 25 4.2 Ionizatien by Particle Radiation 25 4.3 Ionization by Electromagnetic Radiation 27 4.4 Variation of Radiation Intensity with Distance from Source; Cartesian Coordinates 28 4.5 Absorption of Radiation 29 4.6 Variation of Radiation Intensity with Lead Shielding; Cartesian Coordinates 30 4.7 Variation of Radiation Intensity with Lead Shielding; Semi- log Coordinates 31 4.8 Half-value Layers 32 4.9 Relative Efficiency of Shield'ing Materials 34 4.10Broadbeam Shielding for Absorption of Gamma Rays in Lead 35 4.11Broadbeam Shielding for Absorption of Gamma Rays in Iron 35 4.12Broadbeam Shielding for Absorption of Gamma Rays in Concrete 35 4.13Principles of Radiation Safety 36 5.1 The Lauritsen Electroscope 40

viii

_ Page Figure 40 5.2 The Pocket Dosimeter 41 Dosimeter Scales 5.3 41 'Types of Pocket Dosimeters 5.4 41 5.5 Condenser R-meter 45 5.6 Source Calibration Curve Estimated Average AnnualGonad Exposures in the 6.1 50 United States 52 6.2 Ionization Produced byRadiation Effect on Atoms Radiation "Banking" Conceptfor Radiation Workers 57 6.3 75 8.1 Radiograph Exposure Arrangement Diagram of X-ray Tube 79 9.1 80 9.2 Basic X-ray Circuit Continuous X-ray Spectrum atDifferent Tube Voltages 80 9.3 81 9.4 Characteristic X-ray Spectrumof Tungsten 9.5 Continuous X-ray SpectrumShowing High and Low Energy Limits 81 83 9.6 Early Capsule Designs Fusion Welded Capsule Designs 84 9.7 84 9.8 Double Encapsulation Shadow Formation 85 9.9 85 9.10Geometrical Unsharpness, thePenumbral Shadow 86 9.11Amount of GeometricalUnsharpness 86 9.12Distortion of Shadows 87 9.13Shadow Formation ShowingEnlargement of Image 88 9.14Sources of Scattered Radiation 88 9.15Back Scatter From Floor,Walls, or Objects 91 10.1 Film Density 92 10.2 Film Characteristic Curve 93 10.3 Relative Film Speed 96 10.4 Effect of Developing Time 102 11.1 Source to Film Distance 103 11.2 Source to Film Distance forLong Specimens 104 11.3 Gamma Ray Exposure Technique 11.4 Example-Specimen For ExposureCalculations 105 107 11.5 X-ray Exposure Curves 11.6 Filter Near Source of Radiation 108 11.7 Effect of Filter on Intensity of X-rayRadiation 109 110 11.8 X-ray Tube Beams 11.9 Gamma Ray Exposure Devices 111 11.10Welded Flat Plates 112 11.11Welded Joints of Pipe 113 11.12Radiographingy Welds of Larger DiameterPipes and Pressure Vessels 114 11.13Hemispherical Orange Peel Head 114 11.14Panoramic Exposure Arrangement 114 11.15Multiple Exposure or Multiple Film Technique 114 12.1 ASME Boiler Construction CodePenetrameters 119 12.2 ASME Porosity Charts Showing MaximumPermissible Porosity in Welds 120-121 12.3 API Standards for Field Welding of.Pipelines 123 ix Figure Page

13.1 Application for Byproduct Material License-Use of Sealed Sources in Radiography 137-138 132 Occupational External Radiation Exposure History 140 13.3 Current Occupational External Radiation Exposure 141 13.4 Radiation Symbol 142 13.5 Radioactive Material Sign (symbol in magenta on a yellow background) 143 13.6 Radiation Area Sign (symbol in magenta on a yellow background) 143 13.7 High Radiation Area Sign (symbol in magenta on a yellow background) 144 13.8 AEC Regional Office Locations 146 13.9 Red Label, Class D Poison, Group I or II 151 13.10Blue Label, Class D Poison, Group III 151

Table Page

1.1 Periodic Table of Elements 7 2.1 Properties of Nuclear Radiation 11 3.1 Decay of an Atom of Uranium 23 4.1 Dose Rate of Commonly Used Radioisotopes 28 4.2 Linear Absorption Coefficients 30 4.3 Dose Rate of Unshielded Gamma Radiation at Distances from One-curie Sources Commonly Used in Radiography 36 6.1 Estimated Average Annual Gonad 1 Exposures in the United States 49 6.2 Radiation Protection Guide 58 9.1 Characteristics of Gamma Radiography Sources 81 9.2 Metallic Pellet Dimensions 84 11.1 Relative Film Factor 101 11.2 Steel Equivalent Thickness of Metals (for gamma rays only) 103 11.3 X-ray Energies and Applications (A guide for inexperienced radiographers only) 103 11.4 Radiosotopes and Applications 103 12.1 Classification of Steel Casting to be Used with Radiographic Standards 123 12.2 Classification of Defects in Steel Castings to be Used with Radiographic Standards 123 12.3 Radiographic Standards for Steel Castings 124 13.1 Exposure Limits in Restricted Areas (In any calendar quarter) 139 13.2 Radioactive Materials Listed by ICC Commodity List 150 Part I Radiation Physics

Most persons entering training to becomeradiography technicians will have very little information and experiencerelated to ionizing radiations, and their properties and interactionswith matter. The reason is that these topics are not taught in many high school programs.Much publicity has been given to A-bombs and H-bombs, theirdestructive abilities, and their hazards to the human body. Relatively littleinformation has been published on the useful applications of radiationfor the technician. The first five chapters of this studydiscuss elementary concepts that are necessary for understandingthe radiography process andassociated safety practices. Each trainee should make a concertedeffort to gain a complete working knowledge of these topics. chapter 1 The Structure of Matter

the then 1-1 Early Atomic Concepts table of elements. He was able to place known elements in order starting withhy.dro- Speculations about matterextend back to gen, the one with thesmallest weight. Certain early Greek times. Thus wefind that Democ- properties of elements were repeated and they ritus, a Greek philosopher who livedabout 460 could be placed in groups. Since notall the ele- B.C., considered matter to be made upof very ments were known, gaps appeared inMen- small invisible particles. These hecalled atoms, deleev's table and he predicted that more ele- from the Greek work atomoswhich means ments would be discovered to fill the gaps.He something that cannot be cut. even predicted theproperties of these elements. Other Greeks did not accept this ideaand Many of his predictions were found to be believed that all substances were made ofearth, correct. water, fire, and air. Aristotle consideredmatter to be composed of mixtures of the fourqualities 1-2Later Atomic Discovr les hot, cold, wet, and dry. Thus, dryness andhot- The Greeks found that if a piece ofamber ness made fire, drynessand coldness made was rubbed withanimal fur it acquired the earth, and wetness and coldness madewater. ability to attract lightweight particlesof mat- Such theories as these persisted until the seven- ter. These effects came to be calledelectricity teenth century when scientific progress really because the Greek word for amberis "eleck- began. tron." Benjamin Franklin's famous kiteexperi- At about this time Cassendi ofFrance put ments with electricity are well known.In 1796, forth a theory that the tiny invisible ballsof Volta produced electricity chemically byusing matter had hooks by which they connectedto- two different pieces of metal between whichhe gether to form a substance. Newtonbelieved placed a piece of wet paper. that solids, liquids, gases, and light were com- Geissler, about the middle of thenineteenth posed of atoms or small particles that couldnot century, showed that electricitycould flow end of be further subdivided. through space. He sealed a wire in each Lavoisier in 1774 proved that air was com- a glass tube andexhausted the air from the posed of two substancesoxygen andnitrogen. tube. When the wires were connectedto an elec- He went on to discover and identifytwenty of trical source, there was a dischargethrough the elements. Later Priestly andCavendish the vacuum in the tube. It was foundthat rays showed that water was composed of twoele- of some kind came from the negativewire in ments that were normallygaseshydrogen the tube. They were first calledcathode rays, which means and oxygen. from the Greek word "kathodos" Then it was discovered that when certainele- negative. ments combined they always did so in afixed In 1895, Roentgen showedthat rays un- proportion by weight. John Dalton guessedthis known to him at that time,caused certain meant that elements must be made upof par- chemicals to become fluorescent andthat they ticles that cannot be divided. He alsodeveloped could penetrate solid substances.These were Becquerel, at some basic ideasabout atomic weight using called X-rays. Antoine Henri hydrogen as the standard. At about the timeof about this time, discovered rayscoming from Dalton it was discovered that water could be uranium salts which blackenedphotographic broken down by connecting two wires to abat- plates in their package. Then theCuries iso- tery and placing their ends into the water. lated from several tons of pitchblende ore, a Oxygen gas bubbled from one wire and hydro- small bit of material which they calledradium. gen from the other. The ability to produce rayswhich affected Mendeleev in 1869 developed the periodic photographic film was called"radioactivity." 1 Rutherford, in England, found that uranium 1-3Particles of Matter emitted two types of rays or radiation which he How do we know that a substance is made called alpha and beta radiation. He laid the up of numerous tiny particles?Some simple foundation for the modern concept of the atom examples lead us to the reasonableness of this that it is not a solid particle but mostly concept of matter. Table salt dissolves when empty space with a small solid core or nucleus. put into water and disappears. So do many sub- In 1900, Villard, a French scientist, found a stances when placed in water. Where does the third type of radiation which came from some salt go? There must be holes in the water for radioactive elements which he called gamma the particles of salt to go. A colored dye placed rays. These were found to be somewhat similar in a glass of water soon spreads throughout the to the X-rays discovered by Roentgen. water. The particles of dye must spread out Albert Einstein, in 1905, proposed his fa- and fill in spaces between the particles of water. mous theory of relativity, which was the real It is known that a quart of water mixed with beginning of modern physics. Many old con- a quart a alcohol is less than two quartsof cepts of classical physics were changed, and a mixture. The particles of one liquid occupy new approach to understanding energy, matter spaces between particles of the other liquid. If and time was made. Isart of his theory, the two very smooth edges of a bar of gold and a famous E = mc2 equation, related mass and bar of silver are placed together and left, it will energy in a new way and foretold the possibil- be found that some particles of each have ity of securing large amounts of energy from a mixed with the other bar. small amount of matter. This suggests that a smooth continuous sur- In 1913, Niels Bohr proposed a new theory face of matter is deceiving. Really there are al- about the forces which hold the atom together. most countless holes or spaces in all matter. This resulted in a better understanding of the This can be explained by thinking of matter structure of the atom. By 1932, many .of the as being composed of tiny small particles or particles making up the atom had been found. atoms with spaces between the atoms. Thompson had identified the electron, and Rutherford the proton. Chadwick explained a 1-4Atoms and Elements new kind of radiation by proposing the neutron as a new particle. Thus, the three important Substances such as hydrogen, oxygen, car- building blocks of nature were known. bon, gold, silver, iron, and many others are Discovery followed discovery in rapid succes- called "elements." Other substances such as sion. New particles were found. Nuclear science wood, rock, rubber,salt, and hundreds of was soon to make a great impact on the world thousands more are combinations of the com- with the explosion of an atomic bomb. Einstein paratively few elements. These combinations wrote his famous letter to President Roosevelt are called "compounds." and a crash program of nuclear research began. It took many years of work for scientists to In 1942, a nuclear chain reaction was produced find and isolate the elements. Many were known at the University of Chicago. In 1945, the first in ancient times, such as silver, gold, and car- atomic bomb was detonated at Alamogordo, bon. However, the people did know the ele- New Mexico. A few weeks later atomic bombs ments were different from other substances destroyed the Japanese cities of Hiroshima and such as salt or water. Some of the more famil- Nagasaki. iar elements with their chemical symbols are : In 1946, the Atomic Energy Commission was AluminumAl Copper CuNitrogenN set up to control atomic energy in this country. Calcium Ca Gold AuOxygen 0 Since then scientists have delved deeper into Carbon C HydrogenHSilicon Si the mysteries of the atom and have developed Chlorine ClIron FeSilver Ag new weapons of war and new peaceful uses of Cobalt Co Lead PbSulfur S this source of energy. Radiography, the use of penetrating radiation to make "photographs" The smallest particles of elements are atoms. of solid materials, has become an important For example, consider carbon atoms. Efforts commercial process. can be made to chemically change atoms by

2 mixing them with acids, alkalis, or other sub- tron microscope provides fairly clear pictures star ces. Efforts can be made to physically of some of the largest molectiles such as the change atoms by freezing or putting them proteins. These contain thousands of atoms per under great pressure. Even if carbon atoms ttre molecule. It is noteworthy that the first direct heated or burned to form a gas, the carbon photographs of molecules, looked in size and atoms can be converted bac:. to their original shape just as scientists had predicted they form. Atoms enter into many combinations would. with atoms of other elements to form many 1-6Fundamental Particles materials, but other reactions can always re- Even before the twentieth century, chemists claim the atoms back from these materials. knew that the concept of the atom as a homoge- Therefore, it seems that carbon is an elemen- neous tiny ball or particle was wrong.Atoms tary material. join together to form molecules. Balls do not By 1940, nearly 92 of these elementary sub- fasten together in combinations. Thus, oxygen stances had been found. Seven more were man- made as a result of the development of the can hold two hydrogen atoms, as in H20 or atomic bomb. The almost infinite variety of water. Carbon can hold two oxygen atoms, as materials in the world is made up of combina- in carbon dioxide, CO2. The bonds are often tions of these elements. spoken of as valences. Later it will be seen how the chemical union of atoms comes abotit. 1-5Molecules and Compounds Over a period of years, scientists have dis- Generally, materials which are not elements covered that atoms themselves are composed of are called compounds (consisting of two or tiny particles. The fundamental particles which more elements). The smallest is called a mole- are of primary concern in atomic theory are : cule. A molecule may be broken down into the (1) Protona particle carrying a unit atoms that compose it. Water may be broken positive electrical charge. Its mass is down into hydrogen and oxygen. Table salt may approximately one atomic mass unit.* be broken down into sodium and chlorine. (2) Neutronan electrically neutral par- Atoms making up a molecule of a substance ticle having approximately the same always combine in the same ratio by weight. mass as the proton. Thus, if a spark is shot through a tank of (3) Electrona particle carrying a unit hydrogen and oxygen, water will form. For negative electrical charge. Its mass is every ounce of hydrogen, eight ounces of oxy- 1/1840 AMU. gen will be used to form water. Each water (4) Positrona particle having the same molecule is composed of one oxygen atom and mass as the electron but with a unit two hydrogen atoms. positive electrical charge. 1-7The Atom as a Solar System Early in this century, Bohr and Rutherford developed theories that led to the nuclear concept of the atom. The atom came to be viewed as having a small, relatively heavy nucleus. About this nucleus, electrons revolve in path or orbit. The space in the atom outside the nucleus is very large as compared to the size of the nucleus or the electrons going around the nucleus.

Even/ wafer molecule i mode up of fwo atoms of The hydrogen atom has a single electron re- hydrogen joined fo one atom of oxygen. volving about a nucleus. The hydrogen atom is FIGURE 1.1.Molecules of Water; HIO. very small. Its diameter is about 1/200,000,000 Until recently, these concepts of atoms and of an inch. If the nucleus were enlarged to the molecules were mainly theories. No one had *An atomic mau unit (AMU) is an arbitrarily selected unit of seen an atom or molecule. However, the elec- mass which is Ihg the mau of an oxygen atom.

3 size of a baseball, the single electron would single electron on a potassium atom, and the be nearly half a mileaway. Thus, the volume two atoms are s ad to be united ina chemical occupied by an atom is almost emptyspace. reaction.

AN ATOM

Electron (Negative charge)

® Proton (Postive charge)

Neutron (No charge)

FIGURE1.3.Particles in an Atom.

THE SOLAR SYSTEM FIGURE 1.2.The Atom and the Solar System.

39 35 K CI *17 The hydrogen atom is the simplest of all Electrons 2-8-8-1 atoms and has the assigned atomic number 1.* Electrons 2-8-7 Other elements have atoms withmore protons *Refer to paragraph 1-8 for symbol nomenclature. in the nucleus ad more electrons in orbitabout FIGURE 1.4.Potassium and Chlorine Atoms. the nucleus. The electronsseem to revolve in shells about the atoms. For example, theele- Bohr's basic ideas about atomic structure ment potassium has 19 electrons arrangedin have been kept in about thesame form in pres- shells consisting of 2, 8, 8, and 1electrons. ent-day theory. His ideas led to the explanation These shells have been designated "K,""L," of many experim 3ntal results. Moremodern "M," "N," and soon. Chlorine has 17 electrons, concepts hold, however, that exact descriptions arranged in shells consisting of 2, 8,and 7 of the motion or paths of electrons in theshells electrons. The chlorine atommay seize the of atoms cannot be given. It is convenientto think of the .hells as clouds of varyingdensi- *The atomic number denotes the numberof protons in the nucleus, the number of positive charges inthe nucleus, and the ties, one inside the other with thenucleus inside number of orbiting electrons. all the cloud-shells. Across section cut of the varies tons in the nucleus. Thesuperscript refers to atom would reveal that each cloud-shell and protons in the nu- in density with the probability offinding the the sum of the neutrons electrons in the shell being highest where the cleus. Also, this superscriptis approximately cloud-shell was most dense (see Figure 1.5) the atomic weight. These shells are sometimes referred to as elec- The weight of one carbonatom has been tron clouds. Such a model or image doesnot arbitrarily set as 12 unitsof mass. On this give a precise orbit or path to electronsin a basis, the atomic weightsof other elements shell. Instead the most dense part of each shell have been determined. Examples : does correspond in radius to the paths de- hydrogen 1.008 cobalt 58.9 scribed in earlier static models of the atom. helium 4.003 lead 207.1 For convenience,pictures showing plane nitrogen 14.0 uranium 238 orbits of electrons about the nucleus of the atom may still be used. The path is not so im- Note that these are verynearly whole numbers. portant in some respects as are the energy Dalton's atomic theory cameearly in the levels of the electrons. Straight horizontal lines nineteenth century. It motivated asearch for may be used to denote energylevels of electrons elements which by the middleof the century in the shells. This is a useful way of visualizing resulted in the discovery of some75 elements. energy relationships of electrons. Study of these showed thatthey differed in atomic weight and that,furthermore, they could be placed in serial order.Also noted was the fact that some groupsof elements seemed to have similar properties.For example, lithium, sodium, and potassium weresoft shiny metals, easily tarnished inair. Their compounds were similar. Sodiumchloride, table salt, is a salty tasting white crystalwhich dissolves easily in water. Lithiumchloride and potassium chloride have the sameproperties. FIGURE 1.5.Eleetron Cloud Density and Energy Levels.

1-8Atomic Number and Weight neutron While the electron arrangement in the shells outside the nucleus of an atom is ofinterest to the chemist, the nucleus itself is ofinterest to the physicist. The nuclei of atoms are made up ELEMENT NO. I ELEMENT NO. 2 of protons and also neutrons (with thesingle (HYDROGEN) (HELIUM) exception of the simplest hydrogen atom) . The charge on the nucleus of an atom is determined by the number of protons in the nucleus.The 92 elements found in nature have been numbered from 1 to 92. Number 1 is hydrogen and number 92 is uranium. Symbols for the elements are commonly writtenwithsubscriptsandsuperscripts. Examples : hydrogen 11I1 oxygen 8016 ELEMENT NO. 4 helium 2He4 uranium 92U238 ELEMENT NO.3 (LITHIUM) (BERYLLIUM) The subscript is called the atomic numberand denotes the nuclear Charge or number of pro- FIGURE1.6.Atomsof First Four Elements. 5 Mendeleev, in 1869, arranged elements in a to 146 for uranium. In Figure 1.6 it maybe pattern called the Periodic Table (see Table seen that the nucleus of ahydrogen atom con- 1.1).This grouped together similar elements tains one proton and no neutrons. The next and enabled the prediction of new elements and element, helium, has an atom containing 2 pro- even the properties of new elementswhich tons and 2 neutrons. Thus, it is said that hydro- were then unknown. Using this table, the struc- gen has an atomic weight of oneand helium ture of the nucleus and the electron shells for has an atomic weight of four. Is there anything an atom may be visualized. Also the atomic with an atomic weight in between these ? number and weight may be found. Scientists found what was thought to be a The structure of the atoms of several ele- sample of a pure element containing identical ments may been seen in Table 1.1. Note that atoms. This wag really a mixture of atoms with the atomic number tells how many protons, or difierent atomic weights. These atoms had the positive unit charges, are in the nucleus and same number of protons in their nucleibut had how many electrons, or negative unit charges, different numbers of neutrons. The atoms re- are in the shells about the nucleus. tained the same chemical properties while differing in atomic weight. These atoms of the same element having different numbers of 1-9Isotopes neutrons were called isotopes of the element.

Atoms of an element are composed primarily HYDROGEN ISOTOPES of electrons, protons, and neutrons. The protons and neutrons are particles having approximately the same mass, and they make up the proton nucleus of the atom. The electrons are arranged in shells about the nucleus and at a relatively long distance from the nucleus. The number of HYDROGEN DEUTERIUM TRITIUM common rare (radioactive) protons in the nucleus (the atomic number) stable form stable form unstable form equals the number of electrons in shells about the nucleus. This number determines the chem- FIGURE 1.7.Isotopes of Hydrogen. ical properties of an element. The total num- Hydrogen was found to have two isotopes ber of protons and neutrons in the nucleus (the other than the ordinary hydrogf,n atom. By atomic weight) primarily determines physical cooling hydrogen gas to a liquid and allowing properties of an element. it to evaporate, a concentration of heavier Thus, all atoms with one proton in the nu- atoms remained. The nucleus of the "heavy" cleus are hydrogen. All atoms with 8 protons hydrogen (deuterium) atom contains a neutron are oxygen and all atoms with 27 protons are as well as the usual proton. Heavy hydrogen cobalt. If the number of protons in the nucleus atoms combine with oxygen to form "heavy" of an atom is changed, the resulting atom will water. Only about one hydrogen atom in 14;000 be a different element. The number of protons is a heavy atom. More recently a still heavier in atoms varies from one in hydrogen to 92 in hydrogen atom (tritium) has been discovered. uranium. Atomic work during and since World The number of isotopes for each element War II has resulted in producing several new varies. While hydrogen has three isotopes, tin elements which have atoms with more than 92 has 25 isotopes. Uranium has several isotopes. protons. Ona is called uranium-238. Its nucleus has 92 The number of electrons in orbit about the protons and 146 neutrons for a total of 238 nucleus of an atom ordinarily equals the num- particles. Another isotope, uranium-235, has 92 ber of protons in the nucleus of the atom. By a protons and 143 neutrons, or 235 particles. process called ionization, the number of elec- Both of these react chemically in the same way. trons may be changed but not the nucleus. It In all, more than 1,500 isotopes have been remains an atom of the same element as it was found. About 900 of these isotopes are radio- originally. active. This means they are unstable and they The number of neutrons in the nuclei ofwill change in some way to attain a stable atoms ranges from zero for the hydrogen atom condition.

6 Tam 1.1.-Periodic Table of Elements. INERT I IA HA 1118 IVB VB VIB VIII3 VIII 11B IIB IIIA IVA VA VIA VIIA HeliumGASES 2 Hydrogen LON 1H 4.003 He lithium 3 Beryllium 4 Boron e5 Carbon C6 Nitrogen 14.0 N7 Oxygen 16.0 08 Fluorine 13.9 F9 Neon20.1 N.10 6.94 LI 9.01 Be 10.8 13 12.0 14 15 16 Chlorine 17 Argon 18 Sodium 22.9 Na11 Magnesium 24.3Mg12 Aluminum 26.9 Al Silicon 23.0 Si Phosphorus 30.9 P Sutfur32.0 S 35.4 CI 39.9 A Potassium 19 Calcium 20 Scandium 21 Titanium 22 Vanadium 23 Chromium 24Cr Manganese Mn25 Iron26Fe Cobalt 27 Co Nickel Ni23 Copper Cu29 ZincZn30 Gallium Ga31 Germanium 72.5 Ge32 Arsenic74.9 As33 Selenium 73.9 S.34 Bromine 79.9 Br35 Krypton 33.8 Kr36 39.1 K 40.1 Cs 44.9 Sc 47.9 TI 50.9 V 51.9 54.9 55.8 58.9 58.7 63.5 65.3 48 69.7 49 50 51 52 53 54 Rubidium 37Rb Strontium 38Sr Yttrium 39 Y Zirconium Zr40 Columbium AllCb Molybdenum Mo42 Technetium Tc43 Ruthenium 101.1 44Ru Rhodium 102.9 45 Rh Palladium 106.4 46Pd Silver107.3 47Ag Cadmium 112.4 Cd indium114.8 In 113.6 TinSn Antimony 121.7 Sb Tellurium 127.6 Te iodine126.9 I Xenon131.3 Xe 85.4 87.6 88.9 91.2 92.9 73 95.9 74 (99) 75 76 77 78 79 80 31 82 83 Polonium 84 Astatine 35 Radon 36 Cesium 132.9 Cs55 Barium 137.3 Ba56 Lanthanum 138.9 La57 Hafnium 178.4 Hf72 Tantalum 180.9 Ta Tungsten 183.8 W Rhenium 186.2 Re Osmium 190.2 Os Iridium192.2 lir Platinum 195.1 Pt 196.9 GoldAu Mercury200.5 Hg Thallium 204.3 TI 207.1Lead Pb Bismuth 203.9, Bi 210Po (2:1) At 222Rn Francium 37Fr Radium 226Ra88 Actinium 227Ac89 (223) 53 59 Neodymium 60 Promethium 61 Samarium 62 Europium 63 Gado Ilnlu 64 Terbium 65 Dysprosiu 66 ni Holmium 67 Erbium 68 Thulium 69 Ytterbium 70 Lutetium 71 Lanthanum Series Cerium 140.1 Co Praeseody- 140.9mium Pr 144.2 bld (145)Pm 150.3 Sm 151.9 Eu 157.2 Gd j 158.9 Tb 162.5 DY 164.9 Ho 167.2 Er 168.9 Tm 173.0 Yb 174.9 Lu 97 93 99 100 101 102 103 Actinium Senes Thorium 232Th90 Protactinium 23191Pa Uranium 23892 U Neptunium (237) 93Np Plutonium (242) 94Pu Americium (243) Am95 Curium(245) Cm96 Berkelium (249) Bk Callforniu (249) Cf Einsteinium (254) Es Fermium (252) Fm Mendelevi (256) Md Nobelium (253) No Lawrenclu (257) Lw Chapter 2

Radiation and Radiation Machines

gamma alpha 2-1 Radioactivity

At about the turn of the century, it was beta found that the material containinguranium gave off some kind ofradiation that penetrated 0 or passed throughordinary materials. Also, Roentgen discovered that something cameoff magnetic feld the anode of a Geissler tube and passedthrough the glass. Whatever this was caused azinc sulfide screen held outside the tube tobecome lead container lead confrainer fluorescent. He called the things that were FIGURE 2.1.Identifying Three Common Types given off "X-rays" because they wereunknown of Radiation. to him. He knew they were not electronssince electrons cannot pass through glass or even a If a strong magnet is brought near thebeam, few sheets of paper. zinc Becquerel, in 1896, discovered that some there will be three spots glowing on the radiation from certain minerals could fog sulfide screen. Each glows le s?. intenselythan the single spot. If the magnet is removed,the photographic plates. Study revealed that those single spot reappears as before. The magnetic minerals containing uranium could give off this into radiation that could pass through ordinary ma- field caused the radiation beam to split three beams. There is one beam on either side terials. The Curies found that minerals con-of the original beam. It seems that perhaps taining uranium and thorium were radioactive by and that the radioactivity was proportional tothree different kinds of rays are given off the amount of these elements present. Later the radioactive material. These were called they found that pitchblende, an ore existing in alpha(a),beta (p), and gamma (7) rays. the earth's crust, though containing uranium, Further experimentation showed that the gave off more powerful rays thanuranium alpha rays were deflected in such an angle as alone. Several years of work resulted in the to indicate a positive charge. Since they were discovery of the new element, radium. Further only deflected slightly, it would seem that the experiments resulted in the discovery of still rays were probably composed ofrelatively more radioactive elements. What werethese heavy particles with a positive charge. Ruther- rays that such elements gave off? ford and others found the alpha particles to weigh about four times as much as the hydrogen atom. The inert gas, helium, has anatomic 2-2 Discovery of Radiation weight of 4. Thus, the alpha particle turned out Ernest Rutherford played an important role to be the nucleus of a helium atom. in discoveries about radiation. Experiments The beta rays were deflected in the opposite such as that illustrated in Figure 2.1 aided him direction to show a negative charge. Since the in determining the nature of radiation. Suppose amount of the deflection was much greater, it a bit of radioactive material, such as theele- would seem probable that beta rays were light- ment radium, is placed in a lead container with weight negatively chargedparticles.These a long round opening. The radiation fromthe turned out to be electrons, the same kind that material would travel up the opening in a nar- flowed from the cathode of the Geissler tube. row beam. If a zinc sulfide screen is placediii Theundeflected gamma rays were not front of the opening, the radiati on beam causes charged particles, but had the same character- a small circle to glow on the screen. istics as X-rays, discovered earlier.

/19 Thus it was found that the atoms ofradium product of frequency and wavelength is acon- and other radioactive elementsare continually stant. This constant is the speed of light. Also, emitting alpha particles, beta particles, and/or the energy possessed by the photons or quanta gamma rays. Experiments determined thepar- depends on the frequency or wavelength of the ticles were given off atvery high velocities, radiation. High frequency radiation has high which was evidence of great amounts ofenergy energy, while low frequency radiation has low locked up in the atom. energy. Thus, gamma radiation, which has very high energy (high frequency 2-3 Kinds of Radiation or short wavelength),penetrates matter much farther than It should be clear now that there are two does lower frequency ultraviolet radiation. The main types of radiation. One type is composed kinds of electromagnetic radiation ofconcern of tiny particles which move through space and to us include X- and gamma radiation. is called "particulate" radiation. The other type consists of very short waves called "electro- 2-4Properties of Radiation magnetic" radiation. Both of these kinds of Atoms and subatomic particles have been radiation may be given off by radioactive given an "atomic weight" determined bya atoms. Radioactivity refers to the disintegra- weight comparison with the carbon atom. Re- tion of unstable nuclei of atoms. Both kinds of member that the carbon atom was arbitrarily radiation convey energy throughspace. given an atomic weight of 12. Usually,approx- Particulate radiation is the movement of imations of the atomic weightsare given, tiny subatomic particles throughspace. The though they have been determined bymany ac- particles have mass (or weight) and, in most curate measurements to many decimal places. cases,an electricalcharge. They transfer Electrical charges andenergy levels are energy from one point to another. These par- given in descriptions of radiation. An electron ticles traveling at a very high speed may strike is said to havea unit negative electrical charge. and be deflected by other particles suchas or- (This has been measured to be 4.80 x 10-10 elec- bital electrons or nuclei of atoms,or they may trostatic units.) A proton hasa unit positive be stopped and captured by nuclei. As these charge. The energy of radiation is expressed in particles change speed, they change inenergy. ev's (electron volts). This is theenergy (equiv- When they are slowed or stopped, they release alent to 1.6 x 10-12 erg) acquired bya particle energy. When particles carry an electrical carrying a unit charge when it falls through charge, electrical or magnetic forces affect a difference in potential of one volt. their motion. When these fast moving particles Alpha radiation consists of relatively heavy transfer energy to atoms, theymay cause heat particles, each containing 2 protons and 2neu- and light to be given off and theymay cause trons. The particlesare identical with helium ionization to take place. The particulate radia- nuclei, except for their motion. Whenan alpha tion of concern to isotope applications includes particle slows down in itspassage through alpha and beta particles and neutrons. matter, it acquires two free dlectronsand be- Electromagnetic radiation consists of very comes an atom of helium. An alpha particle has short electromagnetic waves of energy having an atomic weight of 4.00277 and carries two no mass or weight. The radiation moves with unit positive electrical charges. Alphaparticles the speed of light (186,000 miles per second). are emitted from radioactive materials at Actually, eleetromagnetic radiation has been speeds of 2,000 to 20,000 milesper second. Be- described as small packages ofenergy called cause of their size and relatively low speeds, photons or quanta. In this respect, such radia- they travel onlya few centimenters in air and tion has some properties of particles. However, may be stopped by a sheet of paper. Thesepar- electromagnetic radiation hasa characteristic ticles are emitted withan energy ranging from wave motion and wavelength, and its frequency 4 to 10 million electron volts (Mev). can be determined. Frequency is measured in Beta radiation consists of particles identical number of waves per second and wavelengthis to high speed electrons. These particlescarry the distance between similar pointson the one unit negative charge and have a mass waves. For all electromagnetic radiation, the about 1/1,840, that ofa proton. They are 10 emitted at very high velocities approachingthe particles and radiation is presentedin Table speed of light. They have a range ofseveral 2.1. feet in air but may be stopped by a thinsheet TABLE 2.1.Properties of Nuclear Radiation of aluminum or a few sheets of paper.The energy of beta particles ranges upto 3.15 Mev, Radiation Kind Mau Charge Description with most particles having about 1 Mev. Gamma radiation consists of veryshort elec- Alpha (a)Particle 4 +2 Helium Nucleus Beta (13) Particle 1/2840 -±1 High Speed Electron tromagnetic waves of energy having no mass Gamma (v) Wave 0 0 Electromagnetic Wave or weight. Ithas very short wavelengths of Neutron (n)Particle 1 0 Uncharged Particle about 10-10 centimeters and extremelyhigh frequencies and high energy. The radiationtravels at the speed of light. These rays arehighly 2-5The Electromagnetic Spectrum penetrating and may be detected afterpassing Radiation or radiant energy is of great con- through several inches of steel. The energyof cern in modern atomicstudy. Light and radio gamma rays ismeasured in Mev. Gamma rays waves are the mostfamiliar forms of electro- emitted by natural radioactive elementshave magnetic radiation. These are seemingly very energies from about 0.04 to 3.2 Mev. different kinds of radiation. Energy fromthe X-rays and gamma rays are similar inthat sun comes to the earthmainly as light. How- both are electromagnetic radiation.However, ever, it is known thatwhat is called "sunlight" they differ in their origin. When thenucleus of contains radiant energy that is invisible.This ultraviolet radia- a radioactive atomemits an alpha or beta par- may be infrared radiation or ticle, the daughter nucleus frequently isleft in tion. In a similar fashion, radio waves are a excited state and the excess transfer of energy through space. This is in- a high energy or of energy is emitted as gammaradiation to bring visible radiation and usually the amount the nucleus to a more stable condition.Thus, energy picked up by adistant receiver is small. in the nucleus of Many experiments have verifiedthe wave gamma radiation originates A an atom. motion property of light and radio waves. X-rays, on the other hand, are produced when wave motionconsists of a series of crests and any stream of fast-moving(high-energy) elec- troughs. The distance between any two succes- trons is slowed down upon striking a suitable sive crests or troughs is called thewavelength target. Electron transitions between orbital of the radiation and is usuallydesignated by shells give rise to the photons or quanta of the Greek letter lambda (A) . Now, ifC desig- energy called characteristic X-rays. nates the speed of the radiation through space, The neutron is another type of particle which then the number of waves passing apoint in accompanies certain types of nuclear reactions. the unit of time will be C/A and iscalled the It is not found in natural radioactive decay, frequency of the wave motion. This is usually however. The neutron particle has about the designated by the Greek letter nu (u).Thus it same mass as a proton but is neutral sofar as should be noted that frequency times wave- electrical charge is concerned. It was found length equals the speed of propagationof that when alpha particles bombarded light radiation. elements such as beryllium and lithium, they frequency X wavelength = speed emitted neutrons. Because neutions have no v A =C electrical charge, they make good "bullets" to bombard the nuclei of elements. The positively A charged nuclei do not repel the neutron as they do other particles. Neutrons play an important role in nuclear fission, since the capture of a neutron by nuclei of atoms of certain elements causes the nuclei to split apart and form atoms of different elements. A number of particles and radiation have been identified. A list of the properties of some FIGURE 2.2.Wave Motion and Wavelength (x). 11 It is known that light, radio waves, and other They found that, if nitrogen is bombarded by radiationcalledelectromagneticradiation alpha particles, a proton or hydrogen nucleus is travel at a speed dependingon the medium formed as well as an isotope of oxygen. Thus, through which they pass. The speed usually the concept of "atom smashing" was begun. given is that for empty space. When measured in air, a small correction is mede. The radia- 7N14 2He4 1111 + 8017 tion travels at about 186,000 miles per second, an extremely high velocity. For scientific work, In only a few cases, however, is the nucleus this is usually stated in centimetersper second actually disintegrated. Usually there is simply and is rounded to 3.00 X 10" centimetersper a rearrangement ofprotons and neutrons second. among the nuclei concerned. The terms "nu- There are electromagnetic radiations having clear transformation" or "transmutation" are wavelengths both longer and shorter than light. preferred. Such changes may be called "artifi- At one extreme are the long radiowaves with cial" to distinguish them from naturally occur- wavelengths of hundreds of meters. Near the ring nuclear changes. other extreme are the gammarays and X-rays Early experiments in transmutations were withwavelengthsontheorderof10-4° carried out with alpha particles available from centimeters. naturallyoccurringradioactivematerials.

X-Rays

Visible

Ekcfric Radio Infra- Ultraviolet Gamma Waves Waves Red Rays

i I I Increasing Photon Energy, Electron Volts FIGURE 2.3.The Electromagnetic Spectrum. The electromagnetic spectrum isa continuous When calculations indicated that perhaps other band of radiation with a gradual shift from charged particles might be more effective as one type of radiation to another. Thus, the "bullets" to cause nuclear rearrangement, sci- longer gamma rays are identical with the entists began to think about building high shorter X-rays. Also, the shorter radio micro- voltage machines to accelerate protons and waves are the same as the long infrared waves. other particles. Brief descriptions ofsome of There is nosharpdivision between different these machines and the X-ray machine follow. "kinds" of electromagnetic radiation. 2-6.1 Van de Graaff Generator. The Van de 2-6 Graaff is an electrostatic, straight-line accelera- Radiation Machines tor. Electrons, protons, deuterons, and alpha In the early 1900's, itwas speculated.that the particles are commonly accelerated ina Van de nucleus of an atom could be altered by direct Graaff machine, but other charged particles collision with high speed particles. These in- may be used. A moving belt is used to transfer clude electrons and alpha particles suchas charges to an insulated hollow metal sphere. In those emitted by radioactive materials. Ruther- this way potentials of several million voltscan ford and Chadwick in the 1920's performeda be developed. This potential is used to accel- number of experiments which confirmed this. erate charged particles downa tube to a target.

12 Hydrogen, Deuterium, or Helium Gas Storage for High Voltage Dome Proton, Deuteron, or Alpha Particles

Charge Collector rf Ionization Oscillator

Insulated Belt Carrying Charges Focusing Accelerating 0 Electrodes

0 Porcelain Vacuum Electrostatic Tube Field Rings

Pressure Vessel

Charge Spray 0

Pressurized Dry Nitrogen

High Voltage 0 Charge Supply / Ground Analyzer Magnet

Belt Drive Motor ri-o--- Target

FIGURE 2.4Van de GraafGenerator.

13 Oscillator

Input Output

= o ) o 0 ) )

Vacuum Focusing Chamber Accelerating Gaps Electrodes Resonant Cavity Tube

Drift Tubes of Increasing Length

FIGURE 2.5.Linear Accelerator. 2-6.2 Linear Accelerator. This machine con- in a very short time. When these high speed sists of a number of cylinders of increasing electrons bombard thetarget,X-rays are lengths. Alternate cylinders are connected to- emitted. (Figure 2.6) gether. Thus, numbers one, three, and five are 2-6.4 X-ray Tubes. There are wide differ- connected to one terminal of a high-frequency ences in the structure of X-ray tubes. Some are oscillator, and numbers two, four, and six are air-cooled and some are oil-cooled. Some have connected to the other terminal. At any partic- a stationary anode while others have a rotating ular instant, alternate cylinders carry opposite anode. All tubes have an electron generating electrical potentials. On any half-cycle of the filament and a target anode enclosed in a high oscillator, for example, the odd-numbered cyl- vacuum. A positive charge is placed on the inders may have a positive charge and the anode or target so that the negative electrons even-numbered cylinders may carry a negative are attracted. When they strike the anode and charge. Positive particles passing through the are slowed down, they release some energy in first cylinder receiveno acceleration, but, upon the form of X-rays. This is usually referred to reaching the gap, there isa difference in po- as general X-radiation and covers a relatively tential and they are accelerated across thegap. wide band of wavelengths (these wide bands of If the lengths of cylinders are correct, the posi- X-rays are often called "white," "continuous" tive particle receives an accelerating impulse at or "heterogeneous"). The high speed electrons each gap. The target is at the end of the last also dislodge orbital electrons in the targetma- cylinder. In these machines, electronsmay be terial. Energy is imparted to the atom inre- accelerated to a velocity approaching the speed moving the electron. The excited atom attracts of light. Fast particles produced by thesema- an electron and returns to a stable state. Its chines are used to study nuclear structure and extra energy is then emitted as a form of X-ra- nuclear reactions, to produce radioisotopes, and diation. This is a narrow band of X-radiation, to provide a source of X-rays and neutrons. the wavelength of which is determined by the 2-6.3 Betatron. The betatron is an electron target material and the orbital location of the accelerator which uses magnetic induction to dislodged electron. accelerate electrons in a circular path. A vary- X-ray tubes require a high voltage electric ing magnetic field is used to provide the orbital circuit to supply a positive potential to the acceleration. This is provided by a large, lami- anode. These range up to millions of volts. Also, nated iron core in a transformer with themag- a filament circuit is required to heat the elec- net coils operating on various frequencies. tron-emitting filament of the tubes. These ma- Electron velocities are high and the electrons chines have a wide range of uee, ranging from make many revolutions acquiring high energies mecrcine to industry. (Figure 2.7)

14 Magnetic Field

FIGURE 2.6.The Betatron.

IHigh Voltage Power Supply

() Cathode Electrons Anode (+) Power Supply

.11 MMIID 4/110 .111.

X-Rays

Fa(nian 2.7.The X-ray Machine. Chapter 3

Nuclear Reactions and Radioisotopes

3-1Nuclear Reactions trons. When it takes up a proton, it then has 4 Radioactive atoms which emit one or more protons and 4 neutrons and is in a very un- particles, and perhaps some energy in the form stable condition. It immediately breaks and of gamma rays, have been described. Another forms two helium nuclei(alpha particles), type of nuclear reaction results when the nu- each with 2 protons and 2 neutrons. Because cleus of an atom actually splits into two almost much energy is released, the two helium nuclei equal portions. In such a reaction neutrons and, fly apart at great speed. It was found that the in some cases, protons are emitted. This type mass of the two helium nuclei was less than the of reaction is called fission. Large amounts of mass of the lithium nucleus and the proton. released energy accompany the fission of nu- Some mass had been converted into energy. clei. The nucleus of each atom is held together This is a very poor way to release atomic by a force called binding energy. The heavy energy. A nucleus is very small compared to nucleus which is fissionable has more binding the rest of the atom, and a proton has a small energy than the two lighter atoms formed after chance of hitting a lithium nucleus. Also, since the fission ; therefore, energy is given up. the proton and lithium nucleus are both posi- When two light nuclei come together to form tively charged, they repel each other. Only a heavier nucleus, the process is called fusion. about one proton in 1,000 will hit a lithium This type of nuclear reaction also gives up nucleus. energy. Here, as in the fission process, there In the 1930's, shortly after neutrons were is a loss of mass in the form of energy. This discovered, Fermi used them to bombard nearly kind of reaction can be initiated only by heat- all the elements. Being electrically neutral, neu- ing to extremely high temperatures. By use of trons were not repelled by positively charged nuclearfission,these temperatures can benucH and more hits occurred. As a result, reached. Once started, the thermonuclear reac- Fermi discovered a large number of new radio- tion generates enough heat to sustain a chain active substances. Frequently, a nucleus would reaction. cipture a neutron. This produced a nucleus with too much mass for its charge and hence 3-2 Nuclear Fission an unstable one. The nucleus would emit a beta Physicists have long been interested in tie particle (electron) and return to a more stable structure of matter. The nucleus of the atom state. However, the nucleus was now one mass has been of much interest. Early efforts to study unit and one positive charge higher than the the nucleus have involved the bombardment of parent nucleus and thus was a different element. matter with alpha particles, protons, and deu- For example, cobalt is the 27th element with terons. Also of interest was the matter of the a mass of 59 units. Its symbol is 27Co59. This release of energy. One early experiment in- means that the nucleus has 27 protons and 32 volved directing a stream of protons at theneutrons. The cobalt nucleus may capture a metal lithium. From the lithium came alpha neutron to give cobalt-60. The process is writ- particles. It was found that for each proton ten as follows : that hit a lithium nucleus, there appeared two 27Co59 0n1 --> 27Co" alpha particles. A lithium nucleus has a charge of 3 and a mass of 7. A proton has a charge of Cobalt-60 is a radioisotope of cobalt. This iso- 1 and a mass of 1. The process is illustrated as tope emits gamma rays as it decays that make it commercially useful for radiography. follows : Fermi wondered what would happenif 3Li7 11-P > 2He4 2He4 uranium was exposed to neutrons. In 1934, The lithium nucleus has 3 protons and 4 neu- uranium was the 92nd or last element. If a /C/17 uranium nucleus should capture a neutron, ucts formed. The process may be written as what would happen? The most stable and fre- follows : quently found isotope of uranium has a mass of 92U235 0n1 56Ba188 &arm + 14o111 + energy 238. Its symbol is o2U238. When a nucleus of U-238 captures a neutron, the new atom emits In Figure 3.1, what happens to the neutrons a beta particle and becomes neptunium, the may be clearly seen. These released neutrons next heavier element after uranium. may be captured by other atoms of U-235 and cause more atoms to fission. 92U238 on1 > o2U289 -F e° > 93Np239 e° Because only a small amount of U-235 is contained in natural uranium, it was necessary Neptunium'is radioactive and also emits a beta to separate U-235 from the more plentiful particle to become element 94, plutonium. U-238. This was necessary in order to have the 93Np239 e° o4Pu239 e° U-235 fission process be self-sustaining. A self- sugitaining fission process is called a chain In both cases, a neutron in the nucleus has reaction. emitted an electron to become a proton. When the nucleus of a fissionable atom cap- U-235, an isotope of uranium, can capture tures a neutron and splits, it has been shown slow neutrons and fission or break into two ap- that a great amount of energy is released. Also, proximately equal fragments, Also,it was a number of neutrons are emitted fromthe nu- found that the new element plutonium would cleus. If only one of these neutrons caused an- fission. Of great importance is the fact that the other atom to split, and only one neutron from process of fission not only releases great energy, that nucleus caused another atom to split, and but also releases neutrons. These may, in turn, so on, then the fission process wouldjust main-- cause other nuclei to fission. Whenconditions tain itself. When a piece of fissionable material are correct, such a process causes a chain reac- such as U-235 or Pu-239 is below a certain tion or self-sustaining fissioning of the material. size, more neutrons escape from the surface of the piece than are produced in fission. There 3-3Chain Reactions and Criticality are always enough stray neutrons in theatmos- In addition to U-235 and plutonium, it was phere to cause some of the atoms to fisSion found that elements 90 and 91, thorium and however, an increasing chain reaction is not protoactinium, also were fissionable. When fis- built up in a small piece of the material. When sionable atoms split, it is into approximately a mass is large enough (and of correct shape) equal fragments. These turn out to be isotopes so that a .chain reaction is supported, it is of elements in the middle of the periodic table. called a critical mass. When several pieces are When uranium-235 fissions, it has been found brought together to form a critical mass, then that barium and krypton are among the prod- a nuclear explosion occurs. (Figure 3.2)

+ 0 + 14 Neufrons

Uranium -1- neufron Barium + Krypfon + Neutrons Atom Afom Afom

FIGURE 3.1.Nelltrons Released in Uranium Fission.

18 Fission of A Single Atom i

Fissionable Atoms

n U235

I 2 3

Generations FIGURE 3.2.Chain Reaction of U-235. 3-4Fission Products 1930's, however, a large number of isotopes 1 Uranium fission takes place inan unsym- have been obtained by scientists. Now,more metrical manner. The two nuclear parts have than 1,500 isotopes are known, most of them different masses. Itis known that the two radioactive. In fact, radioisotopes of all ele- groups of fission particles cluster around iso- ments have been obtained. For example, there topes of mass number 90 and 140. It has been areradio-carbon,radio-cobalt,andradio- mentioned that barium (Ba-138) and krypton cesium. (Kr-83) are frequently found fragments. Also The early production of radioactive isotopes found are strontium (Sr-90) and cesium (Cs- usually involved some kind of machine to shoot 137). fast subatomic particles v.t atoms of the various Figure 3.3 shows how the fission fragments elements. The cyclotronwas an early device of U-235 cluster around the twomass numbers used to secure high-speed partLles. Deuterons, 90 and 140. More than 95 percentof the U-235 alpha particles, and protonswere used as nuclei that fission give parts that fall intotwo bullets in the cyclotron. groups. One is a light group withmass num- Now, however, most radioisotopesare pro- bers from 85 to 104. The other isa heavier duced in nuclear reactorsor chain-reacting group with mass numbers frem 130 to 149. piles. The fission reaction itself ina reactor produces some radioactive products.Another 10 way is to insert a small mass of some element into the reactor pile and subject itto bombardment by neutrons. Neutron absorption isa process that frequently leads to a radicactive isotope.For example, the stable cobalt isotope27Co" may cap- It ture a neutron to become radioactivecobalt 27Co60. This is done by inserting theCo-59 into a reactor and bombarding it with neutrons. 10-7 The activation of atoms bombardedby neutrons depends upona number of factors. Among these are neutron density andthe nuclear cross section of the nuclei beingbombarded. The number of target nuclei beingactivated may be represented by theequation : A = Nfat where A = number of targetnuclei being actiVated 10-5

70 BO 90 100 110 120 130 140 150 160 170 N = total number ofnuclei in the target MASS NUMBER f = neutron densityper cm2/sec FIGURE 3.3.Distribution of Fission Products. 0. = nuclear cross section of target atoms (the probability thata neu- The two parts of a fissioned U-235nucleus tron passing through thetarget may be seen to contain too many neutrons and material will be captured bya so are usually unstable and emit neutrons. Most target nucleus) of these neutronsare emitted in an extremely t = time in seconds short time after fission. Thus,a chain reaction As some nuclei capturea neutron and become in a critical mass of U-235 takesplace in an radioactive, decaycommences immediately. The extremely short time. buildup in number of radioactivenuclei con- 3-5 tinues until the rate offormation and the rate Activation of Isotopes of decay are equal. After A few naturally occurring this point, there will isotopes are-radio- be no change in the numberof radioactivenu- active, such as radium anduranium. Since the clei present in the target. to convert water to steam and the steamis 3-6Nuclear Reactors used to drive electrical generators. The extra The first atomic pile, ornuclear reactor, was neutrons may be used to produce morefission- built by Enrico Fermi andother scientists at able material from U-238 and Th-232and to the University of Chicagoin 1942. They wished produce radioactive materials such at Co-60 or could be started that to see if a chain reaction Cs-137. would keep itself going. Thepile was made up The U-238 and Th-232 absorbneutrons and of blocks of graphite. Smallpieces of natural then decay into the highly fissionableiaotopes uranium in metal tubes were placedin holes in Pu-239 and 1J-233, respectively. Thus, a reac- the pile of graphite blocks.The graphite acted tor may act as a "breeder" to make newfuel slow down fast neutrons so as a moderator to and so on. more neutrons wouldenter U-235 nuclei and industrial In slots Co-60 and Cs-137 are used in keep the chain reaction self-sustaining. radiography as sources of radiation. Figure3.4 in the pile, pieces of cadmiummetal were radioac- acts shows how a reactor is used to create placed to control the reaction. Cadmium tive isotopes. For example, somestable Co-59 as an absorber ofneutrons. When the cadmium may be inserted in anopening in the reactor. strips are pulled out, the reaction speeds up. much As found in nature, cobalt has 27 protons and If the reaction becomes too fast and too 32 neutrons, or a mass number of 59.When the heat is generated, the strips are pushedback stable cobalt is bombarded by billions of neu- in the pile. trons, some nuclei capture a neutron andthen Fuels used in reactors are such fissionable have 33 neutrons instead of 32. Cobalt 60gives materials as 0-233, U-235, and Pu-239. Since radia- liberated off strong gamma radiation, some beta the mass of the fission fragments and tion, and has a half-life of 5.3 years. neutrons is less than the original fissionable atoms plus the neutrons which started thefis- Radioisotopes are obtained by two principal sion, mass is not conserved and energy is lib- methods : erated. The energy is given off as radiation and as kinetic energy imported tothe fission frag- (1) Fission products, that is thefission ments and fission neutrons. As the fission neu- fragments formed when heavy nuclei trons and fragments are slowed down and the split, are gathered and separated from radiation is absorbed in the surrounding ma- the waste materialinan atomic terials,thefission energyisconverted to reactor. thermal energy or heat. (2) The bombarding of atoms with neu- A reactor is, therefore, a source of both heat trons so that their nuclei capture neu- and neutrons. When a reactor is used as a trons and become radioactive without power plant, it is consideredprimarily as a changingtoanothermaterialor source of heat energy. This energy is usedthen element.

REACTOR

REMOVED

it It Mil 41 STABLE COBALT 59 Neutron Flux RADIOACTIVE COBALT 60 1+1+1+14014-14.141* or

Each Co 59 nucleus Some Co 59 nuclei have contains: 27 protons captured a neutron and 32 neutrons have become Co 60: 27 protons Note: Only a relatively few Co 59 atoms 33 neutrons become Co 60 depending on the time in the reactor and the magnitude of the neutron flux.

FIGURE 3.4.Production ofCobalt-60. 21 3-7Decay of Radioactivity by 4 because the atom loses 2 protons and 2 The nuclei of radioactive atoms are in an neutrons. However, when a beta particle is excited state or contain excess energy. The ex- emitted, the atomic weight remains the same, cess energy is emitted as radiation. The radia- but the atom changes to a new element. It was tion usually takes the form of alpha or beta found experimentally that the number of atoms particles and gamma rays. The naturally oc- of a radioactive element which decay in a unit curring radioactive elements at the high atomic of time is proportional o the total number of weight end of the periodic system fall into atoms present at that time. Since decay is a three rather distinct series. These are the thor- continuous process, the total number of atoms ium, the uranium, and the act,,nium series. present is changing and the rate of decay is Some radioisotopes, however, decay in one step changing. By use of calculus, an equation may to a stable state. The series may involve more be found to represent the decay which takes the than a dozen steps before resulting in a stable following form : isotope.Theresultingisotopesarecalled N = N.e-kt daughter products. where It is possible to follow one atom of uranium N. = number of atoms present at zero 238 through its series of disintegrations. An time atom of U-238 has 92 protons and 146 neu- e = base of natural logarithms = trons. In Table 3.1, the decay is sho wn step by 2.718. step as alpha and beta particles are emitted. A = decay constant of the 'radioisotope The final stable product is lead-206 which has t = time 82 protons and 124 neutrons. When an alpha N = number of atoms remaining after particle is emitted, the atomic weight decreases "t" time The constant A is related to a useful tarm, . the half-life of a radioactive element. This is the length of time necessary for half of the, DECAY OF A RADIOACTIVE SUBSTANCE atoms to decay. HALF.LIFE 4 HOURS 0.693 half-life Hours Hell. Relative Lives Activity, % The half-life is useful as a characteristic of a o o 100 radioisotope. From Figure 3.5, it may be seen' 4 1 so s 2 25 12 3 12.5 that, after six half-lives, the amount of decay- lb 4 4.25 20 s 3.125 ing atoms is reduced to las than 2 percent of 24 Is 1.562 the amount at the beginning. 3-8The Curie The number of disintegrations which a given amount of a radioisotope has during a given length of time is called the activity of the isotope. The unit of measure of activity is the curie. A curie is defined as the amount of any radioisotope that gives 3.7 X 10w disintegrations per second. For some isotopes, this is a rather large amount of material, so the units, millicurie and microcurie, are commonly used. (1) 1 curie = 1,000 millicuries (2) 1 millicurie = 1,000 microcuries 3-9Plotting Radioactive Decay 2T 31 4T ST iT Holf.Lives 4 I 12 lb 20 24 Haws Each disintegration of a radioisotope may FIGURE 3.5.Decay of Radioisotopes. be supposed to result in the ejection of a single

22 particle or photon. The rate at which these are decay curve is plotted on cartesian coordinate expelled per second from a radioactive source paper and on semi-log coordinate paper. Note may be measured by various detection devices that during each 5.3 years the count will have which measure or count disintegrations. The decreased by one-half. count per unit of time may be plotted against On the cartesian coordinate paper, the decay time and a decay curve obtained. curve is an exponential curve, while on the For example, consider a small amount of Co'-- semi-log paper the decay curve is a straight 60. Let the radiation count on January 1, 1963 line. The advantages of plotting on semi-log be 15,000 counts per minute. The half-life of paper are evident as only two points are needed Co.-60 is 5.3 years. In Figures 3.6 and 3.7, the to plot the decay curve.

THE URANIUM SERIES

Corresponding Radioelement Element Symbol Radiation Half Life

Uranium I Uranium Um a 4.51 X102 yr. * Uran* unn X1 Thorium Th234 0 24.1 days

Uranium X, Pntactinium 12a234 0 1.18 min. * Uranium II Uranium U234 a 2.48 X104 yr. * Ionium Thorium Th23° a 8.0 x104 yr. * Radium Radium Rang a 1.62 X103 yr. * 7.18 Ra Emanation Radon Rn222 a 3.82 days * Radium A Polonium P0211 aand p 3.05 min 99.98%1 0.02% + RadiumB-1, Lead Pb214 P 26.8 min. Astatine-218 Astatina Atm a 2 see. 't Radium C Bismuth Bi214 p anda 19.7 min. 99.96%1 0.04% 7 2 .4

Radium C' 1 Polonium p0214 1.6'X10-4 sec. 7261 Radium C" Thallium Tim 0 1.32 min. * Radium D Lead ph22. P 19.4 yr. if 7 -80 Radium E Bismuth Bills p anda 5.0 days f--100% 1 2 X10-4% Radium F 1 Polonium P0215 a 138.4 days Thallium-206 Thallium T1224 P 4.20 min. * Radium G Lead Pb2" Stable (End Product)

TABLE 3.1.Decay of an Atom of Uranium.

23 3-10Decay Schemes As radioactive materials decay, they follow 14 rather well defined schemes. Decay schemesare used to show the particles andgamma rays emitted as an unstable atom, decays toa stable 12 atom. In such schemes,a horizontal line is drawn to indicate the energy level ofa radioactive atom. Below this, another horizontal line 10 is drawn to indicate ground level for thestable atom. Arrows sloping down and to the right indicate emission ofa negative beta particle. Wavy lines drawn straight down indicate emission of a gamma photon. Decay schemes for 6 Co-60 and Cs-137 are given in Figure 3.8.No- tice that about 10 percent of the Co-60atoms emit a beta particle and then emita gamma 4 photon of 1.33 Mevenergy. About 90 percent of the Co-60 atoms emita beta particle and then emit, in turn,a gamma photon of 1.17 Mev 2 and one of 1.33. Mev. The finalproduct is stable Ni-60.

1463 1165 1967 1969 1971 1973 1175 TIME IN YEARS Unstable Co-40 Unstable CsI37

=957 FIGURE 3.6.Co-60 Decay Curve: Cartesian Coordinates. 5% Gamma 0.661 Mev. ,///. 20 Stable Ni-60 Stable Ra-137

FIGURE 3.8.Decay Schemes for Co-60and Cs-137. 10 About 5 percent of the Cs-137atoms emit a beta particle without emittinga gamma photon. 4 The other 95 percent emita beta particle before emitting a gamma photon of 0.669Mev. Stable Ba-137 is the final product. 2

1963 64 65 66 67 6/ 1170 71 73 74 75

Years

FIGURE 3.7.Co-60 Decay Curve:Semi-log Coordinates.

24 Interaction of Radiation With Matter

RADIATION 4-1 Ionization and Ions Atoms, molecules, and various subatomic particles which carry either a positive or nega- This electrically neutral atom tive electrical charge are called ions. Free elec- contains 3 ( ) and 3 ( ) charges. trons, not attached to any parent atom, are Radiation displaces an electron called negative ions. Other particles having causing a loss of I( ) charge. negative electrical charges are also negative Atom becomes a positive ion. ions. The alpha particle, a helium nucleus, carries two positive charges and so is referred to Displaced electron as a positive ion. becomes a negative ion Any action which disturbs the electrical bal- FIGURE 4.1.Ionization. ance of the atoms which make upmatter is referred to as ionization. Radiation, either parti- in what is called secondary ionization. This may cles or electromagnetic, has, the ability to ionize. continue, in fact, until the energy of the dis- A high-speed particle or a photon of energy lodged electron is below that necessary to drive which passes through matter will disrupt the other electrons from their orbits. atomic arrangement of the matter. For exam- The ionization process described here is the ple, an alpha particle may strike an orbital elec- principal reason behind the various biological tron in an atom and cause the electron to leave effects of radiation. The ionization of atoms its orbit. The electron may attach itself to an which make up the cells of the body have very atom. The first atom then has a positive charge serious effects on these cells and body tissue. and the latter atom a negative charge, and These are described in more detail later. these are referred to as positive and negative ions. Also they may be called an ion pair. 4-2 Ionization by Particles The charge on a particle moving through In ionization by a particle there is an energy matter also affects ionization. Thus the moving transfer from the particle to the orbital elec- particle may attract or repel an orbital electron. trons of atoms. In this process the moving par- Dislodged electrons may, themselves,cause ticle is slowed down. When the energy of the other electrons to be driven from their orbits particle falls below that needed to ionize (dis-

Negative Ion Electron Liberated (Free Electron) From Neutral Atom By Ionizing Particle Ionizing

Ionizing Path Particle

Positive Ion Atom Overbalanced with Positive Charge FIGURE 4.2.Ionization by Particle Radiation.

25 lodge orbital electrons), the particle still may ionization. It may fission and the resulting frag- impart some energy to, or excite, electrons. The ments may emit ionizing particles, or the nu- speed, mass, and charge of a particle all affect cleus which is a charged particle itself may re- the transfer of energy to an electron. In turn coil and produce some ionization.' the amount of energy received by the electron determines the amount of secondary ionization 4-3Ionization by Electroniagnetic Radia- caused by the electron. tion The number of ion pairs produced per unit Gamma and X-rays are not particles and length of a particle's track is called the specific have no mass or weight. Therefore they do not ionization of the particle. This is generally produce ionization directly by collision as do stated as the number of ion pairs produced per alpha and beta particles. Since these rays or centimeter of track in air. Differences in speed, photons of energy travel at the speed of l'ght, mass, and charge greatly affect the specific they do not lose their energy as readily as do ionization of particles. The total number of ion the particles. Gamma and X-rays lose their pairs produced by a particle, regardless of energy to atoms by three processes known as length of track, is called total ionization. photoeléctrical absorption, Compton scatter- Alpha particles travel only about Iwo inches ing, and pair production. When an atom ab- in air and may be completely stopped by a sheet sorbs energy by one of these three processes, it of paper. Thus high-energy alpha particles lose emits a charged particle, usually an electron. their energy rapidly. This means that they have The emitted electron then may produce ioniza- a high specific ionization which 'ranges from tion in a manner similar to that of other ioniz- 20,000 to 80,000 ion pairs per centimeter of ing particles. (Figure 4.3) air traveled. Alpha particles have energy rang- Gamma and X-rays are very penetrating, ing from about 4.0 to 10.6 million electron with a range depending upon their energy. It volts (Mev). The alpha. particle is relatively is not practical to measure the penetrating large and slow moving. These factors cause it power of these rays in feet or meters. Instead, to have a high ionizing effect. Also, its positive it is measured by the thickness of materials charge causes it to dislodge nearby electrons needed to reduce the rays to half their original due to coulombic attraction when there is no di- intensity. The process by which the direction of rect collision. incident radiation is changed is called scatter- A beta particle travels much farther in mat- ing. This may occur in several ways. Scattering ter than an alpha particle of the same energy. is of prime concern to the radiographer. This is true because the beta particle is very 4-3.1Photoelectrical Absorption Process. small, moves at a very high rate of speed, and When gamma or X-ray photons of low energy has less electrical charge than the alpha parti- penetrate matter, especially matter with a high cle. Being light in weight, the beta particle is atomic weight and many orbital electrons, the easily deflected so that distance from point of photon energy may be transferred to an orbital origin is not a good measure of distance trav- electron. Some energy will be used to dislodge eled. Beta particles have a low specific ioniza- the electron from its orbit and the remainder tion of 50 to 500 ion pairs per centimeter of will be used to give the electron kinetic energy air ; they may travel several meters in air and or a velocity. These are called photoelectrons, attain speeds up to 99 percent of the speed and the transfer of energy is called the photo- of light. Beta particles have energy ranging electric process. Only about 30 to 50 electron from 0.025 to 3.15 Mev. Both the speed and the volts are needed to dislodge an electron, so the range of the beta particle are proportional toremainder of the energy of the photon gives its energy. the electron a high velocity. The moving elec- The neutron having no charge does not ion- tron then loses its energy, producing ion pairs ize directly. A neutron passing through matter through ionization as previously described. The has a negligible effect upon orbital electrons in photoelectric effect usually occurs with low atoms of the matter. However, the neutron may energy gamma or X-photons of 0.1 Mev or less. strike the nucleus of an atom and cause reactions which will ionize. The nucleus may absorb 1 RCA Service Company. Atomic Radiation. Camden, New Jensen the neutron and then emit particles which cause 1957. P. 9.

26 Low-Energy Electromagnetic Ejected Electron Radiation

Ionization

Absorbers of High Atomic Weight

Medium-Energy Electromagnetic PHOTOELECTRIC EFFECT Radiation Electromagnetic Radiation of Longer Wavelength

Absorbers of any Atomic Weight

High-Energy -%...'.,%,..,,,.%..Libeated Electromagnetic COMPTON EFFECT Radiation 0 Ionization Ejected Electron

Ionization Absorbers of High Atomic Weight

PAIR PRODUCTION Ejected Positron

Ionization FIGURE 4.4.Ionization by Electromagnetic Radiation.

4-3.2 Compton Scattering. When electromag- into an electron-positron pair. A positron has netic radiation consists of photons of about 0.1 the same mass as an electron but carries a posi- to 1.0 Mev, Compton scattering occurs. In this tive charge. By Einstein's famous equation, process the photon does not lose all its energy E = mc2, it has been found that the mass of one to an orbital electron. Instead a part of the electron is equivalent to 0.51 Mev of energy. energy is transferral and a dislodged electron This explains the need for photons of 1.02 Mev is emitted at an angle to the path of the orig- so that the electron-positron pair can be formed. inal photon. Also a lower energy photon is Any energy above 1.02 Mev causes the pair of scattered at an angle to the original photon particles to have kinetic energy or speed. The path. This may be repeated until the original electron so formed may then cause ionization. photon is completely absorbed by the previously The positron may cause ionization, but has an described photoelectric effect. extremely short life. It combines with an elec- 4-3.3 Pair Production. Very high energy tron and disappears with the emission of two photons of 1.02 Mev or more cause ionization gamma photons of 0.51 Mev each. These will by a method called pair production. In this act as other low energy gamma photons and process a high energy photon approaches the may cause ionization by the photoelectric effect nucleus of an atom and converts from energy or by Compton scattering. 27 4-4The Roentgen The so-called "Inverse Square Law" isas An amount of radiation is not measured di- follows: rectly. Rather, the amount of ionization pro- Source duced by passage of the radiation through some 2 medium is used to measure radiation. The Tv roentgen (r) is a measure of ionization in air due to passage of gamma or X-radiation. One roentgen, or one r, is that quantity of gamma where :I = Radiation intensity at distance d or X-radiation that will produce 2.083 x 109 = Initial radiation intensity at dis- ion pairs per cubic centimeter of air gt stand- tance d. ard temperature and pressure (0°C and 760 d. = Initial distance from source mm mercury) . This is equivalent to 1.61 x 1012 d = Distance at which intensity is I ion pairs per gram of air and also is equal to It is possible to calculate the dosage rate at one electrostatic unit (esu) of charge. In stand- any point where emission constants are known. ard measures of energy one roentgen equals Example :Suppose the emission of a source of 83 ergs. The roentgen is a rather large amount of radiation is 100 roentgens per hour radiation. Therefore, a subunit is used for con- at I foot. What is the dose rate at 2 venience in measuring small amounts of radia- feet? At 4 feet? Source tion. This is the milliroentgen (mr),or one If thousandth of a roentgen. Thus one roentgen zo 100 r/hr do 1 ft. equals 1000 milliroentgens. d 2 ft. The roentgen measures a definite amount of gamma or X-radiation in terms of their ioniz- (1 \ 2 ing effect on air. Dosimeters measure a dose or Then I number of roentgens or milliroentgens. Also 100 useful is a dose rate concept. Ionizing rates are =100x(02= 100x= 25!Ow expressed in terms of roentgens per hour (r/ hr) or milliroentgens per hour (mr/hr). Emis- If 10 = 100 r/hr sion or dosage rate constants are useful to the do= 1 ft. radiographer when expressed as roentgens per d = 4 ft. hour per curie at a unit distance from the Then I (1)2 source. (See Table 4.1.) This term is called 100 \-47 emissivity and has unitsr/hr/c @ 1 ft. or 1 mr/hr/mc @ 1 ft. :=100 X(02=100 X = 6.25 r/hr.

TABLE 4.1.Dose Rate of Commonly Used Results of Calculations Radioisotopes. Distance Fmm Source Intensify Feet mr/hr Dose Rate 4,100 2 1,200 Radioisotope r/hr/curie at 1 ft. 3 533 Emissivity 4 300 5 192 5,000 Co-60,.. 14.4 4.2 4,000 Ir-192 5.9 Ra-226 9.0 3,000

2,000

4-5Radiation Attenuation 1,000 0

When a source of radiation is confined to 0 1 2 3 4 5 6 7 9 10 that it may be considered a point source, the Distance from Source. feet intensity of radiation is inversely proportional FIGURE 4.4.Variation of Radiation Intensity to the square of the distance from the source. with Distance from Source; Cortesian Coordinates. 28 Example: A 10-curie source of Co-60 is to be used The variation in intensity withdistance from at 10 feet from a group of workmen. source may be plotted (Figure 4.4). What dose rate will they receive? What Example: Suppose a radioisotopesource has an dose would they receive in 8 hours? emission of 6 mr/hr/mc at 1 foot. Ifan Note that the dosage rate for Co-60 is 800 mc source is used, determine the 14.4 r/hr/c at 1 ft. dosage rates at 2 ft., 3 ft., 4 ft., 5ft. If I = 10 X 14.4 = 144 r/hr = )2 d. = 1 ft. d or I = Io X(--2--) .d )2 d = 10 ft. N2 Then I 1 = 6 x 800 x()2= 4800 X 144 \iol 2 = 1200 mr/hr (Figure 4.4) I= 144 X 1 = 144 X1 6) 100= 4-6Absorption of Radiation 1.44 r/hr or 1440 mr/hr Alpha rays are completely stoppedby a few centimeters of airor a sheet or two of paper. In 8 hours the men would receive 8X Beta rays are stopped bya few meters of air 1440 mr/hr= 11,520 mr or a few millimeters of lead. Gammarays, Occasionally a known dosage rate is however,canpenetratethemostdense given and the distance from thesource materials. must be calculated. Gamma rays are diminished innumber by Example: In the above exampleat what distance any given absorber, but are not wholly stopped. would the group ofmen receive only If the number of monoenergeticgamma pho- 2 mr/hr? tons traversingan absorber is plotted against Ti I = 2 mr/hr the thickness of the absorber,an exponential = 144 r/hr = 144,000 mr/hr curve results. The intensity I of thegamma d. = 1 ft. rays after passing throughan absorber may be Then find distance d in the equation: calculated by the formula: I (do\ 2 I = P et where VT/ = initial intensity of gamma rays 2 1 e = base of natural logarithms 144,000 d2 u = linear absorption coefficientof ab- 2 d2 = 144,000 sorber for givengamma rays =72,000 t = thickness of absorber incenti- d = -V72,000= 268 ft. meters

GAMMA

0 0 0 0 0 0 0 0 0 0 0 0 0 00 0 0 O O O O E0 0000 0 BETA 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00 0000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00 0000 0

0 0 0 0 0 0 0 0 0 0 0 0 0 ALPHA 000000000000000000 0. .c

'EL al Mal& 4111119111111M

FIGURE4.5.Absorption of Radiation.

29 TAB= 4.2.-Linear Absorption Coefficients. Results of Colculdiens Lead Shield Thichsess Intemity Abeorption Coefficient. perCIS Centimeters ent/le

1 226 Ph F. Al H20 2 107.2 3 41.5 4 5 10.6 0.2 5.0 1.00 0.33 0.14 10 0227 0.6 1.7 0.63 0.23 0.090 210 1.0 0.77 0.44 0.16 0.067 1.6 0.57 0.40 0.14 0.057 2.0 0.51 0.33 0.12 0.043 200 LI 0.48 0.31 0.10 0.042 2.0 0.47 0.30 0.090 0.038 160 4.0 0.48 0.27 0.082 0.0/13 LO 0.48 0.24 0.074 0.030 100

Example :An unshielded point source emitting 1 Mev gamma rays produces an 0

emission of 500 mr/hr at 1 ft. What 0 1 2 3 4 5 6 7 II 9 10 will be the dosage rate if there are Lard Shield Thickness, Centimeters interposed lead shields 1 cm. thick, FIGURE 4.6.-Variation of Radiation Intensity with Lead Shielding; Cartesian Coordinates. 2 cm. thick, 3, 4, 5, and 10 cm. thick? or X-radiation, since a point is never reached To computeintensityofradia- when all such radiation is stopped. A Conven- tion for the 3 cm. thickness of lead ient measure is that amount of shielding which shielding, note that the linear ab- will stop half of the radiation of a given inten- sorption coefficient for lead at 1 Mev sity. This measure is called thehalf-value layer. is 0.77 (Table 4.2). The half-value layer of an absorber is related

Lead Absorber 2... am500 mr/br. to the linear absorption coefficient by the following equation : Source HVL =0.693 eLI Radiation Detector where HVL = half-value layer (centimeters) = linear absorption coefficient (in reciprocal centimeters) = /0e-nt 500 en" Example: Suppose there is a 1.0 Mev source of 500 e-211 gamma radiation. The linear absorp- = 49.5 mr/hr at 1 ft. tion coefficient of lead for 1.0 Mev radiation is 0.77. What is the half- Results from calculations of radia- value layer of lead? tion intensity passing through other 0.693 thicknesses of lead are tabulated on HVL = 0.90 cm Figure 4.6. 0.77 When the same data are plotted ou semi-log Therefore, nine-tenths of a centime- paper, note that the exponential curve becomes ter of lead will reduce gamma radia- a straight line. One advantage of using semi- tion of 1.0 Mev energy to one-half log paper to plot such data is that only two its intensity. points are needed to determine the straight line.(Figure 4.7) Example : A 10-curie source of Co-60 is to be used at 10 feet from a group of 4-7Half-value Layers workmen. How much lead shielding There is little use in trying to compute the would be needed to reduce the dose amount of shielding necessary to stopgamma rate to 2 mr/hr? (Figure 4.8)

30 Results of Calculations

Lead Shield Intensify Thickness mr/hr 300 Centimeters

1 225 200 2 107.2 3 49.5 4 23 5 10.6

100 90 80 70 60

10 9 8 7 6

1 10 0 I 2 3 4 5 6 7 8 9 Lead Shield Thickness, Centimeters Fi Guaz 4.7.Variation of RadiationIntensity with Lead Shielding; Sen li-logCoordinates. 81 Half-value Layers

1 First Second Third

Relative Number ---)10- 24 Rays *12 Rays 6 Rays of Gamma Rays i I IMAM"' 3 Rays rol pima www!MINI 1111111I Radiation 720 mr/hr 360 mr/hr 180 mr/hr Intensity 1,440 mr/hr Approximate Half-value Layers for Shielding Radiography Sources (including build-up)

Half-value layer thickness* in inches

Radiography source Lead Iron Concrete (147 lbs./cu. ff.)

1/2 1/2 1/2

Co-60 0.49 0.87 2.7 Ra-226 0.56 0.91 2.9 CsI37 0.25 0.68 2.1 1r-192 0.19 1.9

*The thicknesses for half-value layers provide shielding protection from the scattered radiation resulting from deflection of the primary gamma rays within the shield as well as protection for primary radiation from the source. FIGURE 4.8.Half-value Layers.

32 Since the energy of emission of Co- If buildup had been given consideration in 60 is approximately 1 Mev, the half- the preceding example, the results would have value thickness of lead would be .90 been : centimeters. From a previous example it was found that the dosage rate Example :One lead HVL for Co-60 radiation for the workmen was 1440 mr/hr. is 0.49" (refer to Figure 4.8) . 10 HVL X 0.49" = 4.9" lead required 1 HVL reduces 1440 mr/hr to 720 mr/hr This clearly indicates that buildup 2 HVL reduce 1440 mr/hr to is an important factor in shielding 360 mr/hr design. 3 HVL reduce 1440 mr/hr to 180 mr/hr Materials having a high atomic number ab- 4 HVL reduce 1440 mr/hr to sorb more gamma radiation than materials 90 mr/hr having a low atomic number. Some frequently 5 HVL reduce 1440 mr/hr to used shielding materials are lead, iron, concrete, 45 mr/hr and water. (Figure 4.9) 6 HVL reduce 1440 mr/hr to 4-8Reduction Factors 22 mr/hr The concept of a reduction factor is useful 7 HVL reduce 1440 mr/hr to in computing the amount of shielding needed. mr/hr The reduction factor is the dose rate of gamma 8 HVL reduce 1440 mr/hr to radiation reaching a point at some distance 5.5 mr/hr from a source with no shield divided by the dose 9 HVL reduce 1440 mr/hr to rate reaching the same point with some shield 2.75 mr/hr interposed. This reduction factor depends upon 10 HVL reduce 1440 mr/hr to the radiation energy (Mev) and the shield's 1.375 mr/hr atomic number, thickness, and density. Ten half-value layers of lead shield- Dose Rate Without Shield Reduction Factor ing would be required to reduce the Dose Rate With Shield dose rate to a value less than 2 mr/hr. Figures 4.10, 4.11, and 4.12 show the reduction factor for gamma radiation from Co-60, This would result in a shield thick- Ra-226, Cs-137, and Ir-192 plotted against ness : 10 X .90 centimeters = 9 cen- shield thickness for lead, iron, and concrete. timeters. The data on these graphs are for broadbeam Since 1 centimeter .4 inch, then radiation since it includes absorption of scat- the lead shielding would need to tered radiation caused by reflected primary have a thickness of gamma radiation, i.e., buildup is included. 9 X .4 =3.6 inches (not including buildup). Example :Suppose a Co-60 source of radiation As radiation passes through materials there has an intensity of 2,000 mr/hr at will be some radiation "scattered." The result is a distance of 10 feet. Workmen need that more radiation will pass through an ab- to be at that distance from the sorber than is indicated by the absorption equa- source but should receive only 4 tion. This increase has been named "buildup." mr/hr. How much lead shielding It depends upon the radiation energy (Mev) should be used? Iron? Concrete? and the atomic number (Z no.) of the absorber. 2,000 Reduction Factor = 500 Calculations involving buildup factors may be- 4 come quite complicated. For this reason, the calculations acceptable for radiography pur- Lead-4.6 inches poses can be made using half-value layers and Iron-7.8 inches reduction factors. Concrete-24.5 inches

33 It is very important for the radiographer imo to shield Ir-192, Cs-137, and to remember that the interaction of radiation Co-60. with matter depends upon (1) the gamma ray Radioisotope Lead Thickness energy (Mev) and (2) the atomic number Ir-192 1.9 1 (somewhat related to density). By referring to Cs-137 2.6 Figure 4.8, it is possible to consider the half- Co-60 4.8 value layer thickness variations with no change

1 in gamma ray energy. For example, observe Example : A radiographer plans to make a that : radiograph in a location where it is (1) The atomic number and density de- necessary for peopleto work pe- crease while reading across thetable riodically as close as 10 ft. to a columns from lead to iron to concrete. 500 me source of Co-60. He plans (2) For a selected radioisotope, e.g., Cs- to reduce the dose rate to 6mr/hr 137, the half-value layer thickness in- by placing a portable ironshield creases as one reads aexossthe table between the radiographic setupand 0.25" for lead to 0.68" for iron to the work area. What thickness 2.1" for concrete. shield would be needed to attenuate the gamma radiation to the required This is acceptable for calculations using level? heavy shield materials for high energy gamma rays. Similar conclusions can be drawnfrom Find the exposure rate at 10 feet data in Figures 4.10, 4.11, and 4.12. from the 500 mc source of Co-60. One curie of Co-60 has an exposure Example: To demonstrate the thickness varia- rate of 14,400 mr/hr at 1 foot. tion of a selected shielding material Therefore, 500 mc would have an when using energies from several exposure rate one-halfthis amount, radioisotopes, determine the lead or 7,200 mr/hr at 1ft. From the thickness at a reduction factor of equation : d.2 I° d2 the exposure rate at 10 ft. may be

These blocks show the relafive found thickness of several materials mosiired to absorb the same Steel amount of groom radiation having I (10 ft) = To 411. energy oppowdowetely I him (1 ft.)2 = 7,200 X (10 ft.)2 Ve44!;"...0 Goode = 7,200 X1 100 = 72 mr/hr

0%, The 72 mr/hr dose rate must be Earth reduced by the iron shielding to 6 mr/hr. 72 mr/hr Reduction Factor Water 6 mr/hr .11=ftap = 12 A reduction factor of 12 for Co-60 in iron from Figure 4.11 indicates Wood that an iron shield 3.5 inches thick is necessary to reduce the radiation FIGUIS 4.9.Relative Efficiency of Shielding Materials. to 6 mr/hr.

34 1111111 111111111 - !!!!! 111111111 1111 11111111111111111111 .-: egSGE._ --iMI11111 1111111111 6E11111INIIII NOM = 11111111NICK. -EVIIIIIIi1111111111116.1111EBY MW _ 111111 1111111111 111111111111111ISSCSIIIIILMIMI 1111111111 MIN 111171 1E1111 111111 111111111111111 1111111 0111101111111111 11111111 'Mg61.._ -MIIIIIII EINMIEN1111111111 ENO- 11111111IIIMEiii..- 11 IIII 11111111111111111M1111111 111111111111111111111 111111111111111111IMO. 11111111 MEI1111111M. MIMI Mgr MEM "9111111111111111 OM Ind 111111111n1111111MINIM 111111111111111111 111111111111M11111111111111 OM 1111111110111211111111111 11111111 11111111 OM MEM .0111.11901111 M. a Y a Dm 40. , . .. . DM 40. a 11111.11111 11111111 11111111 a a .. 40. DM , 11111111 f MP : ,M111111 11111111 1111111 111111111 a IND - 11111111i 11111111 DM r . . a 40. a , , .. 11111111111\MEN1MINOME '511H1111 11111111 1111111 111111111 111111111IIIIIIIIIIIIII 40. IND IIIIIIIII MEP 1111111_ MEM 11111111111 My - 11111111 NNE -19.111iHMO 111111111 Mb t 111111IL AD .. DM DM a MIMIMIIIIII1 111111111 7. MIL SHIM 1B11I I a2 MP .. a 1111111111MINN MM. 11111111111.1111111111111'EOM -MIS! DM MIMI! MI MIMI1111111111I11111111 MOM 1E111111111111111111 11111111IIM `NMISS TIME DISTANCE SWIEL.DINCo TO.

1., - sdremalIMENSIIK RADIATION SOUNICII RADIATION sousace LESS TIMff SPENToaEATeraDISTANCE NEAR SOURCE LESS FROM SOURCE... LESS FROM SOURCE -- LESS RADIATION RECEI VED RADIATION RECEI VIED RADIATION RECEI VED

FIGURE 4.13.Principles of Radiation Safety. radiography operations should be frequently tion and methods that permit the radiographer inspected to assure that the radiographer main- to calculate the radiation intensities at various tains the planned conditions associated with the distances from a source. Survey meters should source exposures. be frequently used to verify the calculations. 4-9.1 Personnel Exposure Time. Personal Table 4.3 tabulates useful data that verify the dosage received depends directly upon the time importance of working at various distances a person remains in theradiation field. He from gamma emitting sources. would receive only 3 mr in 2 minutes at a 4-9.3 Radiation Shielding. In the event that given point where he would receive 15 mr if working time is too long, and operating condi- he had remained 10 minutes. Limiting the tions prevent sufficiently long exposure dis- working time in a radiation field requires using tances, the radiographer may place shielding suitable instruments, paragraph 5-5, for de- material in the radiation beam to protect per- tecting and measuring the radiation intensity sonnel. Shields will not stop all of the radiation, and applying the equation : paragraph 4-6. Adequate shielding will attenuate the radiation to a value that will permit Allowable working time in hr/week = radiography operations without excessive or permissible exposure in mr/wk harmful personnel exposures. Using the absorp- exposure rate in mr/hr tion equation, page 29, half-value layers, or Table 13.1 in Chapter 13 lists personnel ex- reduction factor methods for shielding calcula- posure limits. A radiographer may usethe tions, will be adequate for radiographers. more convenient limit that 100 mr/week should In many industrial situations there will be be his "radiation protection guide." The work requirements to use high intensity sources to should be organized in such a way that no ra- produce the desired number of radiographs diation workers could receive more than 100 each week. mr/week. Limited space will be available. In these 4-9.2 Working Distances. Lower personnel cases, shielding will be necessary. Suitable pro- exposures will be received at longerdistances tection will require the radiographer to use from radiation sources. The inverse square law, time, distance, and shielding. This can best be paragraph 4-5, and the examples, give informa- illustrated with an example.

r/hr atvariousdistancesinft.from source Radioisotope 1 2 4 8 16 82

Co-60 14.4 8.6 0,9 0.28 0.06 0.014 Ra-226 9.0 2.3 0.6 0.14 0.035 0.009 Ir-192 5.9 1.5 0.4 0.09 0.028 0.006 Cs-137 4.2 1.1 0.26 0.07 0.016 0.004

TABLE 4.3.Dose Rate of Unshielded Gamma Radiation at Distances from One-curie Sources Commonly Used in Radiography.

36 Example : A foundry produces castings which ule the radiation require 50 radiographs each week. intensity below the allow- A 30curiecobalt-60sourceis able 20 mr/hr : needed to make each exposure in 6 1 HVL reduces 4,320 to minutes. Only a small shop floor 2,160 mr/hr area is available. Thisrequires that 2 HVL reduce 2,160 to the radiographer work within 10 ft. 1,080 mr/hr from the exposed source. Determine 3 HVL reduce 1,080 to the concrete shield thickness that 540 mr/hr must be provided to prevent the 4 HVL reduce 540 to radiation workers from receiving 270 mr/hr more than 100 mr/week. 5 HVL reduce 270 to Step 1 :Determine the length of 135 mr/hr time the sourcewill be 6 HVL reduce 135 to exposed : 67.8 mr/hr 50 exposures X 6 minutes 7 HVL reduce 67.8 to exposure = 300 minutes 33.9 mr/hr 300 minutes 8 HVL reduce 33.9 to 5 hours 16.9 mr/hr 60 min/hr. The HVL for concrete and Step 2 :Calculate the personnel ex- cobalt-60 is 2 7" posure rate in mr/hr which will allow radiographs to be 8 x 2.7 = 21.6" concrete made, but without the radi- which weighs 147 lbs/cu. ft. ographer receiving more For comparison, determine than 100 mr during the the shield thickness using week : the reduction factor : 100 mr/week Reduction factor = 5 hours/week = 20 mr/hr maximum ex- Dose Rate Without Shield posure rateallow- Dose Rate W ith Shield able for this situation 4,320 mr/hr Without Shield 20 mr/hr With Shield Step 3 :Determine the gamma field intensity at 10 ft. from the = 216 30curie cobalt-60 source : Using Figure 4.12, enter the curve sheet at R.F. = 216 in the left margin. Fol- low a horizontal line across tothecobalt-60curve. Fromthatintersection, move down and read the shield thickness at the bottom of the page. This value = 30 X14,400(1)2.4,320 mr/hr at 10' from is 21.5" concrete. 10 the source with no shield The results from the HVL Step 4 :Using the half-value layer method and the reduction concept, determine the con- factor method are compar- crete shield thickness that able. 37 Chapter 5

Radiation Detectionand Measurement

small doses of ex- Radiation Detectionand Measure- quently used for measuring 5-1 posure (1roentgen = 1,000milliroentgens). ment Instruments which measuretotal dose ex- Man cannot detect withhis senses radiation posure arecalled dosimeters. If aworkman is coming from radioactivematerials.. The bodyto be in an areawhere he is exposed toraffia . may be penetratedby high intensityradiation tion, he may want toknow his total dose ex- and feel no pain, eventhough it may be severely posure. Adosimeter would be usedto tell him injured by the radiation.This is similar to the his total dosage uponcompletion of his workin reaction of man to ultravioletand radio waves. that area. Examples ofdosimeters include the A person may be exposedto the ultraviolet rays Lauritsen electroscope,the pocket dosimeter, in sunlight and feelpain from overexposure the Rmeter, and filmbadges. several hours later.Likewise, a person receiv- Instruments used to measuredose-rate ex- ing an overexposure ofradiation may not be posure orradiation intensity arecalled survey aware of ituntil some time laterwhen radia- meters. A workman mayknow that an areahas tion sickness develops.Man must, therefore, radiation, but may not knowthe intensity of depend on some kind ofinstrument to detect the radiation. A surveymeter will tell himthe nuclear radiation that maybe of danger to him. dose rate and hencewhether it is safe to enter The term "detection"usually includes only the area or not.Examples of dose-rateinstru- a determinationof the presence ofradiation, ments include theGeiger counter and theion- whereas "measurement"includes both the de- ization chamber. tection and some measureof the amount of Except for photographicfilm techniques and radiation present. Radiationdetection or meas- a few specialmethods, all radiation-detecting urement instruments detectthe interaction of devices are based upon theionization produced radiation with some type ofmatter. Some in- in a gas by the radiation.When a high-speed struments are based on theionization produced particle or a photon enters a gas,it may act in the instrument by the passageof the radia- on an atom ormolecule with a forcelarge tion; in other instrumentsthe excitation of ma- enough to remove anelectron and form an ion terials is used to detect radiation.These are the pair of charged particles.Each charged parti- scintillation-type monitoring instruments. cle is accompanied by anelectric field that Chemical and photographicdetection tech- moves with theparticle. niques are also used. 5-3Dosimeters 5-2Radiation Measurement Several types of total dose exposureinstru- .Radiation measuring instrumentsusually ments are of interest tothe person working provide a measurement of dose orof dose rate. where radiation is present. An ionization The first measurementrefers to the accumu- 5-3.1 Lauritsen Electroscope. radiation over a period chamber is a closed vesselused for collecting lated exposure dose of high-energy radiation. A of, time. The second measurementrefers to an the ions formed by immediate measure of dose rate orradiation chamber usually consists of acylindrical con- insulated central elec- intensity. ducting shell with an is the roent- trode. The electrode consistsof two parts, one The unit of radiation exposure parts are elec- gen, which isbased on the effect gamma or fixed and one movable. The two X-radiation has as it passes throughair. This trically connected, andboth receive the same is a rather large unit formeasuring occupa- charge. Consequently thereis a force of repul- tional exposures, so themilliroentgen is fre- sion between them, and themovable part is de- 3r39 fleeted a distance proportional to the charge on When the instrument is brought into an area the electrode. As rays enter the ionization where there is radiation, ions are formed in- chamber and create ions in the gas there, the side the case as the result of the radiation. ions with a charge opposite that of the electrode Those ions which have a charge opposite that travel toward it. When they reach it, they give of the electrode travel to it and give up their up their charge and neutralize an amount of charge on the wire and the fiber. This reduces charge on the electrode. the repulsion between them, and as a result The amount of charge carried by any single the fiber returns toward its uncharged posi- particle is minute and has little visible effect on tion, the distance of return depending on the the electrode. As the radiation process con- amount of radiation and consequent ionization. tinues, the electrode is discharged appreciably, After the electroscope has been in the area and the change in position of its movable part to be surveyed for the desired length of time, can be interpreted in terms of roentgens. This the observer, looking through the eye piece and allows determination of the total dose of radia- noting the position of the quartz fiber T with tion absorbed by the electroscope (and the per- respect to a transparent scale calibrated in son carrying the electroscope) . One of the most roentgens, can determine the quantity of radia- useful instruments of this type is the Lauritsen tion received during the period of observation. Electroscope (Figure 5.1).In this instrument, 5-3.2 The Pocket Dosimeter and Pocket the electrode consists of a metal wire and a Chamber. Another useful quartz fiber instru- quartz fiber. The wire, bent into the form of ment is the pencil-type, or pocket, dosimeter an L,is mounted on the electroscope case (Figure 5.2) which is essentially a Lauritsen through an insulating bead of quartz or amber. electroscope modified so that it is about the Cemented to one end of the L is the quartz fiber, size of a large fountain pen. The electrode in made conductive by a thin metal coating. To the dosimeter consists of two quartz fibers, one make the position of this fiber visible through fixed and one movable, but each bent into a the eye piece of the instrument, a second quartz U shape. The two fibers are fused together at fiber is fused to its free end, forming a T. the ends of the U, and a microscope is focused Light comes in through a small window in one on the opposite end of the movable fiber. As end of the electroscope so that the head of the with the Lauritsen electroscope, the dosimeter T and a transparent scale can be seen through is charged from a separate source with a high the eye piece of the microscope at the other end. enough voltage to deflect the movable fiber to To prepare the electroscope for the meas- Glass Window urement of radiation, the L-shaped wire and Metal the conducting fiber are charged from a battery. Case

Both the L and the fiber then have the same Side View Showing polarity of charge, and the mutual repulsion Arrangement of Fixed between them causes the quartz fiber to deflect and Movable Fibers from the side of the L. The voltage to which they are charged is of sufficient magnitude to make the head of the fiber T coincide with the zero mark on the scale when viewed through the eye piece. A. Insulating Ring B.Charging Rod (Hollow to "L"-shaped "T" head attached to make moving wire quarh fiber visible Admit Light from Window) Quartz insulator C. Fixed Heavy Metal Coated Quartz Aber 01/119 D. Movable Fine Metal Coated Quartz Fiber Lens Charging terminal E.Metal Cylinder Transparent scale F.Transparent Scale G. Metal Support for Fibers PiEtee, Microscope focused on head of "T" Window I. if I for light leg! I I 11110 Moving quarh fiber FIGURE 5.1.The Lauritsen Electroscope. FIGURE 5.2.The Pocket Dosimeter.

40 scale. The presenceof plate is the barrel ofthe meter. The positive the zero point on the the electrode whichis radiation then producesionization, neutralizes plate of the condenser is movable fiber to re- mounted rigidly in a coaxialrelationship with the charge, and allows the the barrel and insulatedfrom it. Space be- turn toward the fixedfiber, a distance propor- the inner surface of tional to the quantity ofradiation absorbed. tween the electrode and the barrel is filledwith air. When X- or gamma Dosimeters can be madesufficiently rugged to the chamber, the air withstand the shocks of normalhuman activ- radiation passes through is ionized in an amountdirectly proportional ity, are small enough tobe worn comfortably, radiation. Free electrons and are useful formeasuring total exposure. to the quantity of the made such that 100 are collectedby the positivelycharged elec- Their sensitivity can be to the negatively produce about one-halffullscale trode. Positive ions travel mr will charged wall of the chamber.This action dis- deflection. charges the chamber indirect proportion to the quantity of radiationpassing through it.

Direct Reading Types of Dosimeters FIGURE 5.3.Dosimeter Scales. To prepare a pocketdosimeter for measuring Charging Device about 150 volts to radiation, it is charged to '50 100 150200 bring the image of the quartzfiber to zero on Milliroent ens the scale (Figure 5.3). Apocket dosimeter is Typical Scale charged by an external sourceof voltage. The ionization chamber is held atground potential and the metal frameand quartz fiber are Pocket Chamber the charger. The (Nondirect) charged to the potential of Reading Dosimeter fiber and metal frame repel eachother since Reading Device they are at the samepotential. The position of the fiber then varieswith the voltage dif- FIGURE 5.4.Types of PocketDosimeters. chamber and A. Movable fine quartz fiber ference between the ionization B. Bow to supply tension for Fiber A linear over the range C.Supports insulating Bow B and the fiber. The variance is Plate L from case Dosimeters with scales D. & E. Terminals which make contact covered by the scale. when detachable tube is inserted called direct-reading in chamber such as those shown are F.Ionization chamber dosimeters. Other types require areading de- Microscope to view G. Conductor between bow and plate fiber and scale placing L and A at same potential chambers (Figure H. Scale vice and are called pocket I. One disc of electrostatic generator grounded to case 5.4). J.Switch is an ion- K. Plate 5-3.3 The R-meter. The R-meter L.Insulators ization type of instrument which ismade in a M. Light variety of styles for radiationdetection under differing circumstances. In general,this instrument is composed of two maincomponents, one, a thimblechamber or roentgen meter, and the other, an instrument for charging and measur- Electrostatic ing the exposure to which thethimble chamber generator for Detachable ionization tube was subjected. Aroentgen meter is a special charging Fiber A form of electrical condenser.The negative FIGURE 5.5.Condenser R-meter. 41 The charged system of the charger andmeas- amount of radiation received by the person uring system also is the positive plate ofa wearing the film badge. Obviously, the badge condenser when it is isolated from the poten- should always be worn by the person when in tial of the electrostatic generator. The shell of a radiation area, and it should not be exposed the charging socket and the mounting barrel to radiation when not being worn by the that holds the quartz fiber electrometer is the person. negative plate. If the R-meter and the electrometer of the charger are charged to thesame potential (the zero potential of the electrom- 5-4Survey Meters eter) and the R-meter is then exposed toa quantity of X- or gamma radiationso that it is Although all instruments of the types pre- partly discharged ;the meter is then recon- viously described measure radiation exposure, nected with the charged system of the charger they cannot be utilized effectively in making a the charged system of the charger being first survey of a large area since too many such "zeroed" and isolated from the generatorpo- instruments and too much time would be re- tentialand the two condensers willcome to quired. To make a rapid survey of an area an- an equilibrium voltage. This will be indicated other type of instrument is needed, one that by the fact that the image of the quartz fiber instantly measures radiation intensity. Two will have moved from itszero mark on the suchinstrumentsareavailableionization reticle of the microscope. Each condenser R- chamber instruments with amplifier systems, meter is designed to havesome maximum and Geiger counters. measurable amount of radiation. 5-4.1 Ionization Chamber Instruments. Inan 5-3.4 Film Badges, A film badge consists of ionization chamber, when ionizationoccurs in a small piece of X-ray film inserted in a metal a gas in the presence of an electric field, the holder. It is wornon the outer clothing and is ions will move in opposite directions, eachgo- the most common type of total doseexposure ing to the electrode having the charge ofoppo- measuring devices. It is used mainly to detect site sign. If the electrodesare connected to a gamma and X-ray radiation and high energy battery, or other source, the ions reaching the beta radiation. The film badge does not react electrodes Will give up their charge and become to alpha radiation. neutral again, but at the expense of removing The badge consists ofa metal or plastic charge from the battery. This results ina cur- jacket in which a photographor nameplate rent flow through the battery and the external may be inserted. Inside the jacket area front circuit. This current flow, though extremely and rear filter composed of lead, cadmium,or small, can be measured and interpreted in some other shielding material. Between these terms of the radiation intensity required to are inserted one or more bits of film with produce the ionization. Instruments of this varying sensitivities. Inone portion of the type can be made small and portable, andare jacket there is a window to admit lowenergy used for health monitoring andsurvey work. gamma rays or beta rays. Their accuracy is plusor minus 15 percent of After the film badge has beenworn for a full scale and theyare therefore not suitable period of time, several daysor weeks, the film for accurate measurements. At the pointof is removed and developed by controlledphoto- measurement, this type of instrument indicates graphic techniques. The film will bedarkened intensityofradiation,aninstantaneous in proportion to the amount ofradiation re- measurement. ceived. The darkened filmmay be compared 5-4.2 Geiger Counters. Inareas where the with a set of control films ofthe same type radiation intensity is low, ionization chamber which have been exposed toa known amount type instruments are not satisfactory, for they of radiation. A densitometer isused to measure do not provide sufficient amplificationof the the density of the imageon the film. This ionization current to indicate it accuratelyon measure is then compared with densities of a meter. Low intensity measurementsare made known quantities of radiation ofgiven energies. with Geiger counters which attain theirgreater In this wayan estimate can be made on the sensitivity by taking advantage of all possible 42 amplification within the Geiger tube itself (gas veying. Their accuracy is plus or minus15 per- amplification)as well as thatprovided by cent of full scale and they are notintended to electronic amplifier circuits. make accurate measurements. These metersin- In the Geiger counter ionizing radiation dicate dose rates. creates ions by interacting with neutral atoms. Instrument Characteristics These ions strike other atoms and molecules, 5-5 and if the ions move slowly their collisions are The radiation measuring devices, previously elastic ;that is, they impart some of their described, all measure gamnia or X-radiation. energy to each of the gasmolecules with which Since particulate radiation is much less pene- they collide, speeding them up somewhat,but trating, the particles cannot pass throughthe producing no ionization. Another disadvantage walls of most of the devices, except those de- of ions with slow speed is the fact that it takes signed with a thin window. Such detectors usu- them a long time to reach the electrodes, and ally have a shutter that can be opened toadmit they have many opportunities on the way to particles. If the shutter covering the detector collide with oppositely charged ions, neutralize is opened, particulate radiation is admitted each other, and decrease the total ionization along with gamma radiation. Measurements within the area. If ions created by radiation made with the shutter both opened and closed move rapidly, however,they in turn strike allow a computation of the amount or intensity atoms and molecules with sufficient force to of particulate radiation. Also, film badges have knock electrons out and create other ions, thus an opening in thejacket and filter to admit increasingthetotalamount ofionization beta radiation. within the area. Such collisions are called in- Since both alpha and beta rays present a elastic collisions. minor external radiation hazard, and usually Since it is the ionization that is measured cannot penetrate the skin, their measurement is by most of the instruments used for measuring not of much importance to radiographers. How- radiation, the greater the ionization, the easier ever, radiographers should befamiliar with the it is to measure the radiation. One of the means characteristics of instruments and the type of of speeding up the ions is increasing the volt- radiation they detect or measure. age difference between theelectrodes and Instruments should have suitable ranges for thereby making the attraction of the ion for the radiation intensities to be measured. The the electrode greater. It is advantageous, there- AEC specifies that instruments used by radiog- fore, to secure as high voltage as possible be- raphers should measure as low as 1 mr/hr and tween the terminals in order to gain sufficient as high as 1000 mr/hr.Geiger counters are speed to produce a large amount of ionization. usually low level instruments and read only to Another way to speed up ions is to reduce the about 50 milliroentgens per hour. The ioniza- pressure. This increases the time between col- tion chamber type instrument measures high- lisions and gives the ions enough momentum levels of radiation. Commonly used types of to make collisions inelastic and produce more such instruments read up to 500 r/hr. ionization. Geiger tubes use these high voltages Geiger counters have a tendency to "block- and low pressures to gain gas amplifications out" in a high radtion field. This merins the within the ionization chamber itself, and each needle on the dial will not move above zero. particle or photon entering the chamber pro- Ordinarily, Geiger counters show a small read- duces an avalanche of ions. This process re- ing above zero due to background radiation. quires only a fraction of a thousandth of a sec- The person using this type of instrument ond, then the system is "quenched" to prepare should be careful not to accept a blocked the instrument for another ray and the result- Geiger counter reading of zero as meaning no ing avalanche. With further electronic amplifi- radiation is present. Special circuits may pre- cation circuits, each avalanche can deflect a vent this blocking. Ionization chamber type needle, produce a click, light lamps, or make survey meters will not block-out. If they are any convenient record desired. used in a radiation field whose intensity is Instruments using Geiger tubes as detectors greater than the instrument's range, the needle can be made small and portable for safety sur- will go beyond the highest scale reading. 43 Several important characteristics of survey source activity is 3.4 curies. (Co-60 meters should be considered in selecting an in- has a dose rate of 14.4 r/hr/c at one strument. These are summarized as follows : foot.) To check the instrument at (1) Instruments must detect the desired the 750 mr/hr point, determine the radiation. Survey meters for radiog- distance from the source at which raphy must detect X-ray and gamma the gamma radiation intensity will radiation. be 750 mr/hr. Then place the sur- (2) Survey meters must cover a suitable vey meter at that distance from the range of radiation dose rate. source. Source I (3) Instruments should be stable and hold do o calibration. ThenIo (4) Instruments should have an accept- do' able time constant. A short time constant is desirable; however, the time whereIo = 3.4 X 14.4 X 1000 mr/hr constant should not be such that the I = 750 mr/hr needlefluctuationswouldprevent do = 1 foot making measurements.(Time con- Solve for d. stant is an expression of the time re- \13A x 14.4 X 1000 quired for an instrument to respond 750 to changing signals.) .e,960 (5) Batteries must be replaced and there- 750 fore should be readily available. (6) Thesurveymetermanufacturer = V65; d = approximately 8 feet. should maintain a repair and calibra- At 8 feet the instrument should tion service. read 750 mr/hr ± 15 percent of 5-6Instrument Calibration the full scale reading or :I= 15 per- Radiographers should be able to determine cent of 1,000 = ± 150 mr/hr, this if the survey meters are operating properly. instrument is satisfactory if it,reads This involves (1) securing a source of radia- 750 + 150 = 900 mr/hr by 150 tion for which the intensity is known, (2) 150 = 600 mr/hr. placing the instrument at a distance computed to give a desired field intensity, and (3) read- 5-7Source Calibration ing the instrument to determine if it indicates Instruments are of great value in calibrating the proper value. Adjustments may then be a source of radiation. In this case the type of made on the meter to correct its reading ifradioactive material must be known to the necessary. The sarvey meter operation manual radiographer so that a decay curve may be will give instructions on how to make the ad- plotted. justments. It is considered good practice to make these calibration checks at two positions Example :Suppose a Co-60 source is to be on each instrument scale. One measurement calibrated. Charge a dosimeter to should be near the high end of the scale and some low value, e.g., 2 mr. (It is one should be near the low end of the scale. difficult to charge the dosimeter to zero because of electrode discharge Example :Suppose it is desired to check the upon remtival from the charger.) calibration of a survey meter which Expose the dosimeter to the source has a scale of 0-1,000 mr/hr. A suit- at a measured distance,e.g.,10 able check point is at 750 mr/hr on feet, for a measured length of time, the scale. Suppose that a Co-60 e.g., 6 minutes. Read the dosimeter. source of radiation is available, and Suppose the reading was 112 mr. from a calibration curve of the From the above information the sourceitis determined that the amount of Co-60 in millicuries may

44 be computed. The source emitted Assume this measurement was made on July 2, radiation that was absorbed by the 1962. dosimeter at the rate of 112 mr After making the source calibration meas- 2 mr = 110 mr in 6 minutes, urements, the radiographer should plot a decay which would be curve for that source. The curve sheet must 60 min/hr = 1,100 mr/hr also have information for complete and posi- 110 mr tive identification of the source. This identifica- 6 min at 10 feet tion can be made by specifying the radioiso- To compute the mr/hr at 1 foot use tope, the source manufacturer, and the source the inverse square law. serial number. Source Dosimeter A calibration of this type can be more accurately made with a condenser R-meter. (See 2 Figure 5.5.) Since these are very expensive, most radiographers will not purchase them. (cciro) Pocket dosimeters are not as accurate as R- Io = to be computed meters, but they are much more stable and ac- I = 1,100 mr/hr curate than survey meters. Dosimeters do have d = 10 feet acceptable accuracy for radiography source do = 1 foot calibration. d2 102 Io= X 1400 X The source activity can be determined on do2 12 any date by (1) entering the curve sheet at Io = 110,000 mr/hr at 1 ft. the selected date, (2) following a line verti- Since Co-60 has emissivity of 14.4 mr/hr/mc at cally to the calibration curve, (3) from that 1 ft., the millicuries of Co-60 may be found. intersection following a horizontal line to the 110,000 left ordinate, and (4) read the source activity = 7,650 me of Co-60 14.4 on the scale. (See Figure 5.6.) a. Source Calibration Date: July 2, 1962 b. Calibration By: J. Ray, Radiographer c. Source: Co-60 d. Serial Number: 347 e. Source Manufacturer's Identification: XYZ Co. 10,000 9,000 8,000 Source Activity is 6,300 mc on Jan. 2, 1964 7,000 6,000

5,000

4,000

3,000

2,000 1,912 mc at end of 2 half lives

1,000

CO Cr.

1%. r r Time, years FIGURE 5.6.Souree Calibration Curve.

45 Part II The BiologicalEffects of Radiation

It is to be expected that the firstquestion a student contemplatingtrain- ing in the use of radioactivematerials will ask is, "Whatdoes radiation do Ito people?" Thediscussions in Part II are desigaedto answer this question adequately for most nonscientists. By now the reader has seen thatit is possible to understandthe principles of radiation in a general waywithout extensive study ofadvanced physics and chemistry. Similarly, apractical knowledge of radiological safety may be ubtained by learning ofthe harmful effects of radiation on living tissues, andof the methods of protectionagainst radiation injury. Chapter 6 The Nature andConsequences ofRadiation Exposure

Part I dealt with certaintechnical aspects experience a biological effectranging from of radiation physics. It wasbrought out in a slight discomfort to death. Toharbor a morbid harmful to fear of these possibilities isfoolish, because general way that radioactivity was life. At man undercertain circumstances. Thischapter they have become a part of everyday acquaint the reader with (1) com- the same time, the potential hazardof automo- proposes to recog- mon types ofradiation exposure, and (2) how biles, disease germs, and electricity are refer to Chapter 7.) nized and proper safety measures aretaken. they are measured. (Also, which should be A short statement designed toplace the matter This is precisely the attitude of radiation health in properperspective serves assumed toward radiation hazard. as an introductionto these topics. The purpose of this and thefollowing chapter is to acquaint the reader withthe effects body, so that 6-1 Radiation Health in Perspective which radiation produces on the a proper attitude maybe developed. It was only a short time afterthe discovery By way of introduction, it may beobserved of X-rays and of radioactivesubstances that that all petIple are continuouslyexposed to radiation was identified as apotential health natural radiation. Cosmic radiationfrom outer hazard. space is ever present.At the same time, the The reports (usually dramatized)of illness earth's crust contains manyradioactive ele- and body damage sustained by personshan- ments which find their way intobuilding ma- dling, or otherwise exposed to,radioactive materials, foods, clothing, and many otheritems terials had created a vivid impression onthe for human use. When radiation formedical popular mind even before theNagasaki and reasons is included(X-rays, etc.), it can be Hiroshima bombs. Since that timethere has seen that humans can anddo tolerate consider- been so much publicity on theafter-effects on able radiation during the course of alifetime. the Japanese who were exposed thatit is not See Table 6.1 for average annual gonad(testes strange that many laymen tend toregard and ovaries or sex organs) exposuresin the radiation with awe and fear and to have an United States. exaggerated concept of radiation hazard. It is true that the biological effects ofradia- TABLE 6.1.Estimated Average Annual Gonad 1 fac- Exposures in the United States. tion can be serious, depending on varinus Natural Sources: MilUrema tors and conditions. However, it isjust as true (See paragraph 6-8.2 Rem) safe manner A. External to the body: that radiation can be handled in a 1.Cosmicraeiation 28.0 and can be made to perform usefulservices for 2. From the earth 47.0 8. From building materials 3.0 mankind. Since several nations have irrevoc- B.Inside the body: ably launched an atomic era, itbehooves all 1. Inhalation of air 2.0 persons to develop at least adegree of familiar- 2. Elements found naturally in people 21.0 Total,naturalsources 101.0 ity with radioactivity. Gross ignorance gen- Man-made Sources: erally results in one of two attitudes, bothof A.Medical procedures: 1. Diagnostic X-rays ...... 150.0 which can be deterrents to progress and safety. 2. Radiotherapy X-rays,radioisotopes -. 10.0 The first is a blind fear of radioactivity, and 8. Internal diagnosis, therapy 1.0 Subtotal 161.0 the second is complete lack of appreciationfor B. Atomic energy workers .... 0.1 radiation hazards. C.Luminous watch dials, television tubes, shoe fluoroscopes, radioactive industrial wastes, etc. 1.0 In the first instance the individual may be D. Radioactive fallout: reminded that daily living involves many health 1. External dose 3.0 2.Internaldose 1,0 hazards as great or greater than radiation. A Subtotal 5.1 person hit by an automobile, overcomeby a Total, man-made sources 166.1 disease germ, or shocked by electricity may I Testes and ovaries (sex organs). 4/1/49 control. In fact, control measures for individual and group protection are likely to be considerably more stringent for radiation bazards 603% than for electrical or fire hazards. 11111;111I1 ME ICAL PROCEDURES 6-2Sources of information About Radia- 111111111111H11 tion's Effects on Man 161 mrem A comprehensive body of informationon the biological effects of radiation has beenassem- OTHERS*5.1 mrem bled as a result of much study and research. 1.9% Since it is not possible to deliberately experiment on man with radiation, this information NATURAL CAUSES has been gleaned from other types of experiments and by chance. Four importantsources 131.0 mrem of data can be accounted for as follows. 37.13% 6-2.1Animal Experiments.All of the radiation effects which are produced inman can be produced in animals. Thus,many types of ex- *OTHERS periments have been conductedover the years 4.0 mrem Fallout from nuclear tests on many different animals and under all sorts 1.0 mrem Luminous watch dials, shoe fluoroscopes, of conditions. The published results of these TV tubes, radioactive industrial wastes, etc. 0.1 mrem Occupational exposures in atomkenergy work experiments form a virtual library of information. However, all animal experiments haveone 5.1 Mein major disadvantagethe dose-effect relations FIGURE 6.1.Estimated Average Annual Gonad cannot be assumed to be thesame as those for Exposures in the United States. man. Therefore, the data from animal experiments must be checked with human experienCe Since man lives withinan environment which before final decisionsas to exposure rates and has a natural background of radiation,expo- therapy can be made. sure hazard must be considered in terms of 6-2.2Occupational Experience.Before the degrees. A parallel may be drawn toexposure full effects of radiationwere known, certain from more familiar radiations, suchas heat workers received small doses of both X-and and light. Excessive heat results insevere gamma rays at fairly constant rates over long burns (often fatal), andoverexposure to di- periods of time. Scientists inmany instances rect sunlight produces, at the least, painful were able to study and fairly accurately cor- sunburn. Yet both heat and light haveex- relate biological changes in these individuals tremely beneficial effects inproper dosages. with rate of exposure. Inone example of this Injuries from ionizing radiations differ inna- type, individuals painting luminousdials on ture from heat and light radiations (theymay watches ingested paint containing radioactive penetrate beyond surface layers) but, likewise, material by pointing their brusheswith their are harmful only to the extent of overexposure. tongue and lips. Many of thesepersons devel- Radiation hazardsare thus much like all aped serious pathological conditions whichwere natural and man-made hazards. Theymust,be detected and studiedyears later. In other ex- considered in terms of the goalsor objectives amples, miners in uranium minesdeveloped sought. Hardlyanyone refuses to work in a lung cancer after/inhalinggases with high con- building because it is wired for electricity.This centration of radon. Personsworking with is true becausean unquestioning faith is held X-ray and similar equipmenthave also been that proper measures have been takento con- subject to study,as have individuals acciden- trol or harness thissource of energy. By the tally exposed to radiation inwork situations. same token, there is no reason whyone should However unfortunate theseinstances might be reluctant to work ina building housing have been for the subject, eachprovided cer- radioactive material whichis under proper tain information useful in appraisingthe ef- humans, and 6-3.1 Roentgen. The unit formeasuring pene- fects of this type of exposure on isthe aided mankind to this extent. trating externalradiation exposure half a cen- roentgen, which isabbreviated r (namedin 6-2.3 Medical Uses. For well over discovered 'X-rays in tury, X-rays and radium rayshave been used in honor of the man who certain diseases. 1895). The roentgen measures gammaor X-ray diagnosis and treatment of defined as the quan- Radioactive isotopes have beenadministered radiation in air only, and is for almost tity of X- or gammaradiation that will pro- internally for diagnostic purposes unit (esu) of charge, one-quarter ofaC century. Each time such ap- duce one electrostatic is afforded either negative or positive,in one cubic centi- plications are made, the opportunity standard temperature and to study carefully theeffects of radiation in meter of dry air at situations. The data pressure (0°C and760 mm Hg.). One roentgen controlled quantities and ability to produce an recorded from these studies haveprovided an of radiation has the the effects of amount of ionization whichrepresents the ab- invaluable source of knowledge of 83 ergs of energy radiation on humans. sorption of approximately Hiroshima and from radiation per gram ofair. (Ionization, it 6-2.4 Atomic Bombs. The creation of ion pairs, Nagasaki bombing provided furtheropportu- will be remembered, is the radiation on man. i.e., positively and negativelycharged parts of nity to study the effect of radiation on these Most of the bomb damage wasdone by fire and atoms, by the interaction of blast effect, but 15 or 20 percentof the effect atoms.) The roentgen canbe subdivided into called the milliroentgen,abbre- has been estimated to havebeen done by gamma a smaller unit of a and neutron radiations emittedduring the ex- viated mr, whichisone thousandth plosion. The United StatesAtomic Bomb Cas- roentgen. uality Commission has been studyingthe effects 6-3.2 Rem. Since the roentgen measures ra- of the bomb on the Japanesesince 1946, and diation in air only, it cannot beused to measure has amassed a wealth ofinformation.' the biological effects on man.The reason for In 1954, during the atomic bombtests at this is that the amount of energyrequired to Bikini, a heavy fallout of bombdebris was ex- prodtme an ion pair in animaltissue differs perienced by a group of natives on aneighbor- from the energy needed toproduce an ion pair ing island. This incident, whilecompletely acci- in air. The term used forthese purposes is dental and regrettable, made itpossible to called the rem (roentgenequivalent man). The study quite accurately, the effect ofvarying rem can besub-divided into a smaller unit doses of radiation on individuals.Studies of called the millirem andabbreviated as mrem, bomb victims continue andevoltually long-term which is one thousandth of a rem.A rem is effects will be known. defined as the quantity of ionizingradiation of 6-3MeasurementUnitsofRadiation any type which, whenabsorbed by man or any Doses other mammal, produces a physiologicaleffect It is impossible to measure aquantity of equivalent to that produced by theabsorption radiation directly sirce it can bringabout a of one roentgen of X-rays or gamma rays. change in matter only to the extentof the 6-3.3 Rad. The rad(radiation absorbed energy actually absorbedby ;this matter. A dose) has recently been accepted as aunit of given biological effect may also depend onthe measurement for radiation absorbedlocally by type and energy of theradiation, making pos- a person. It isdefined as the amount of radia- sible different effects from equal energyab- tion energy imparted to matter perunit mass sorption. For the above reasons, it is more con- of irradiated material. Thedose unit, the rad, venient and practical to measure exposurein represents an absorption of 100 ergs of energy purely physical terms, and then use anaddi- per gram of irradiatedmaterial at the place tional factor to allow for the relativebiological of exposure. It has been estimatedthat a rad effectiveness of different types and energiesof results in the ionization of approximately one radiation. The terms used in measuring radia- tissue atom in twenty billion. Obviously, thisis tion exposure are the following. a very small amountof energy. One rad can be 1 Glautone, Samuel, ed. The Effect of NuclearWeapons. Oak sub-divided into a smaller unit called the milli- Ridge, U.S. Atomic Energy Commission, 1957. 51 rad, abbreviated mrad, which is one thousandth radiation and is probably the most frequently of a rad. encountered hazard. The second type of expo- 6-3.4 RBE. Knowledge of the biological ef- sure is from material taken into the body fectiveness of radiation has considerableprac- through the body openings, through abrasions tical importance since it determines permissi- or cuts, and by skin absorption. This is known bleexposureratesformedicalusesand as internal radiation. One can see that these industrial radiation exposure. For example, al- different types of exposure constitutesepa- though both gamma and neutron radiationcan rate radiation health problems. Precautions produce cataracts, neutrons are approximately taken against one type will not necessarily be ten times more effective thangamma rays. effective against the second type. For this Values of RBE (relative biological effective- reason external and internal radiation are sepa- ness) have been worked out by the National rately treated in some detail. Committee on Radiation Protection basedon 6-4.1 External Radiation. There are two the X-ray as the RBE of one. commonly known types of external radiation In actual practice, the total biological dose hazards. Both have already been described. for several types of radiation (i.e., whena per- The first are the long-range, highly penetrating son receives radiation from several sources) is gamma or X-rays which, the student will re- converted to rem. The dose in rem equals ab- call, consist of very short waves of electro- sorbed dose in rads times RBE. This procedure magnetic energy having no massor weight. may be illustrated as follows : Assuming an The second are the short-range, less penetrat- individual received mixed radiation comprising ing beta particles, which are tiny particles of 0.4 rad of gamma, 0.3 rad of thermal neutrons, matter. Because of their low penetration, beta and 0.2 rad of fast energy neutron irradiation, particles contribute very little (excepting skin his total exposure would be calculated in this damage) to the total body effect of external manner : radiation. OXYGEN Example: NUCLEI HYROGEN Dose Dose NUCLEI Radiation in Rad RBE in Rem Gamma 0.4 X 1 = 0.4 Thermal neutron 0.3 X 5= 1.5 Fast neutron 0.2 X10= 2.0 Totals 0.9 3.9 In summary, the units of measurementof ionizing radiation of widest acceptanceare the roentgen, rem, and rad. The roentgenmeasures ionization in air due togamma or X-ray radia- Irak tion ; the rem measures the effectivenessof the different radiations in terms of biologicaldam- WNW) age and quantity of radiation. The rad measures the energy absorbed by radiation inany material. Values of RBE have been workedout ELECTRONS for all sources of radiation for computingtotal ATOMS OF exposure from a given dose. BODY TISSUE FIGURE6.2.--lonization Produced by Radiation 6-4The Nature of the RadiationHealth Effect on Atoms. Problem It is common to illustrate thewaves of The person who works around,or otherwise energy from gamma or X-rays as a continuous comes into contact with radioactive materials shower of tiny invisible bullets whichmay may be exposed in two entirely differentways. penetrate the body to some depth beforecaus- Radiation originating froma radiation source ing damage. (See Figure 6.2.) Suchan illustra- located outside the bodyis known as external tion is an oversimplification ofcourse, but it helps to emphasize the point that it is possible element which is carrying theradioactivity, for a gamma or X-ray to penetrate various dis- and not to the radioactivity itself. tances into substances (or all the way through) At any time radioactive materialsbecome before it hits anything, because of the empty lodged in the body organs (as the lungs or space between atom particles. When a rayhits liver)irradiation takes place. The damage one of the electrons which isspinning around which may be done depends on theactivity de- the nucleus of an atom, a transfer of energy posited, the radiation emitted, the RBE,and at results (the ionization process) .(See Figure least two other factorsbiologicalhalf-life and 6.2.) Ionization can be the cause of complex effective half-life. changes in the body chemistry which result in Biological Half-life. (The radioactive half- varying degrees of sickness or death, depend- life of source materials has beendiscussed in ing on the amount of exposure. Chapter 3.) The biological half-life of aradio- Neutrons may also produce an external active element is that period of timewhich it hazard, however, neutrons are less common to takes for one-half the element to beexcreted industry than gamma and X-rays. from the body by a natural process.Some ma- 6-4.2 Internal Radiation. The internal radia- terials are excreted quite rapidly and would tion exposure problem comes principally from not remain in the body long enough to domuch alpha particles. These particles do not present harm. Others are retained for long periods and an external radiation hazard becausethey have can do a great dealof harm. relatively short range and cannot penetrate be- Effective Half-life. In order to get a work- yond the outer layer of skin. The greatest risk ing measure of the harm which may cometo thus comes when such materials are taken into the body from an internal radiation source, the body. one must combinethe radiological half-life There are four common ways in which it is with the biological half-life and obtain what possible to get radioactive materials into the is known as the effective half-life of the ma- body :(1) by breathing ;(2) by swallowing ; terial in the body. The effective half-life of the (3) through breaks in the skin ; (4) by absorp- material may be explained simply as follows. tion through the skin. If a material has a radioactive half-life which After radioactive elements get into the body, is very short, then the effective half-life will the first question to consider is, "How long be more dependent on the radioactive half-life will they stay in the body ?" A high percentage since the isotope would decay before being ex- of everything which is inhaled is exhaled im- creted. If the radioactive half-life is very long, mediately. Materials which are swallowed and then the effective half-life will be more a func- which are not soluble in the body's digestive tion of the biological half-life since the isotope system may be dischargedratherquickly will remain active during its residence in the through the feces. However, if a material is body. soluble and goes into the blood stream, it will 6-5Levels and Symptoms of Radiation be carried around the body to the various Injury organs. Since the organs are chemical ma- A person receiving radiation injury exhibits chines, they chemically respond to the ma- symptoms according to the severity of his ex- terials. If the radioactive materials are rejected posure. Certain terms have comeinto common chemically by one organ, the blood stream usage to designate the "gross"condition of takes them along to another organ where they injury and to describe the levels of exposure. Al- may or may not be taken in. If no organ ac- though these terms represent arbitrary group- cepts the material, the blood takes it to the ings and classes, they make up a useful vocabu- kidneys and the kidneys dispose of it through lary for describing the level of injury received the urinary system. When an organ has use for andtheoverallconditionoftheperson the material, or if the chemicals of the organ irradiated. react to the radioactive substances as a ma- Doses of radiation are classified accordingly : terial, harmful results may come about. The 6-5.1 Mild Dose. A small dose of radiation point f.o remember is that the organs of the which produces no detectable clinical effects on body, initially, are reacting chemically to the the body is considered extremely mild. Such a

53 dose would hardly ever exceed 25 rem, al- fected. General disability may be accompanied by though it might range to 50 rem. Slightly drastic changes in the blood picture, including higher doses may produce some changes of a abnormalities in the red and white cells, plate- temporary nature in certain body cells, and lets, and hemoglobin. It is also probable that may possibly produce delayed symptoms. How- intractable anemia will develop, that sterility ever, it is improbable that serious effects would will result, and that cataract formation will result to the average individual, and this is the take place. Epilation will be permanent, and criteria used for classifying such dosages as many skin changes will take place, with the mild. possible malignant degeneration of some cells 6-5.2 Moderate Dose. Acute exposure with accompanied by cancer formation. doses ranging from 50 to 200 rem are classed 6-5.4 Lethal Dose. An acute exposure of 600 as moderate. When this dose is received there 800 rem or more to the whole body of man is are almost always observable phenomena, al- considered a lethal dose. Symptoms are nausea though the injury may vary from very slight and vomiting in one to two hours, then a short to serious. The important criterion in classify- latent period of about a week following which ing a radiation effect as moderate is that there there is diarrhea, vomiting, and inflammation be some but not excessive permanent damage. of mouth and throat. As early as the second At the lower limit of moderate exposure, symp- week, fever and rapid emaciation occur with toms inclnde blood cell changes, swelling, in- the probability of death. creased acidity and granularity of the proto- 6-6 Common Terms of Reference for plasm, crumbling of chromosomes, and halting of cell divisions. At the upper limits of mod- Gross Effects of Radiation Injury erate exposure symptoms include nausea, vom- 6-6.1 Radiation Sickness. This is a condition iting, malaise, and possible changes in the produced when a massive overdose of penetrat- blood. When dosages approach 200 rem, symp- ing external gamma radiation is received. Its symptoms are nausea, vomiting, diarrhea, ma- toms increasp to include epilation(lossof laise, hemorrhage, and a lowering of the body's hair),loss of appetite, sore throat, pallor, diarrhea, and moderate emaciation. These symp- resistance against disease and infection. If the irradiation is serious enough it can cause death. toms occur after a latent period of about one 6-6.2 Radiation Injury. Radiation injury is week (sometimes longer). Recovery from moderate doses of radiation the second term commonly used to describe is likely unless complications related to poor symptoms of radiation exposure and consists of health, injuries, or infections set in. However, localized injurious effects. Injury is most often delayed effects of moderate doses may shorten to the hand because contact is usually made life expectancy as muchs one percent and a with the hands. This type of sickness is recog- few individuals may die within two to six nized when injuries not unlike burns occur weeks alter exposure. along with loss of hair and skin lesions. Ge- 6-5.3 Median Lethal Dose. When acute ex- netic damage is also a form of radiation injury' posure results in a dosage from 200 to 600 which is usually permanent in nature. rem there is a possibility of up to 50 percent 6-6.3RadioactivePoisoning.Radioactive mortality. Injury and disability are certain at poisoning is illness resulting when dangerous higher exposures. Symptoms include nausea amounts of certain types of radioactive ma- and vomiting in one to two hours, followed by terials enter the body. This type of poisoning a latent period of perhaps as long as a week. may cause such diseases as anemia and cancer. After this period epilation, loss of appetite, and 6-7Summary of Biological Effects of general malaise accompanied by fever, are Radiation characteristic. Severe inflammation of mouth The biological effects of radiation were sum- and throat usually occurs near the third week. marized by the Federal Radiation Council in a The fourth week brings on a pallor, petechiae, report to the President dated May 1960. It is diarrhea, nose bleed, rapid emaciation, and re- apropos to quote the nine points made in this lated symPtoms. At the level of the body cell, re- report as a summary of the levels and symp- production (cell division)is permanently af- toms of effects of radiation on man.

64 (1) Acute doses of radiation may produce 6-8Personnel Monitoring immediate or delayed effects, or both. (2) As acute whole body doses increase The human senseshearing, seeing, tasting, above 25 rems, immediate observable smelling, and touchingcannot detect ionizing effects increase in severity with dose, radiations.Radiation penetrating the body beginningwithbarelydetectable causes no pain and a person canbe injured changes to biological signs clearly in- severely without realizing he is in danger. To dicating damage or death at levels of overcome this condition it is necessaryto pro- a few hundred rem. vide radiation detecting and measuring devices (3) Delayed effects produced either by to determine body exposures. To prevent undue acute irradiation or by chronic irra-body damage the exposure must be limited. diation are similar in kind, but the Permissible exposure limits have been esfab- ability of the body to repair radiation lished by regulatory agencies such as the damage is usually more effective Atomic Energy Commission and certain State the case of chronic rather than acute health departments. These limits are rigidly irradiation. enforced in all industrial radiography installa- (4) The delayed effects from radiation tions (see Part IV). In this regard, several are, in general, indistinguishable from types of devices have been designed so that the familiar pathological conditions usu- amount of personnel exposure can be detected ally present in the population. and measured (see Chapter 5). These devices (5) Delayed effects include genetic effects are required to be used andcareful records (effectstransmittedtosucceeding should be kept of radiation surveys and per- generations), increased incidence of sonnel exposures wherever radiation work is tumors,lifespanshortening,and performed. growth and development changes. The terms reviewed here are associated with (6) The child, the infant, and the unborn personnel monitoring and give something of infant appear to be more sensitive to the philosophy, as well as the practice, of pro- radiation than the adult. tection from radiation hazards. (7) The various organs of the body differ in their sensitivity to radiation. 6-8.1 Permissible Exposure. For practical (8) Although ionizing radiation can in- purposes, the assumption is made thatradia- duce genetic and somatic effects (ef- tion exposure has a "threshold" value, below fects on the individual during his life- which no particular effect is experienced by time other than genetic effects), the the exposed individual. Strictly speaking, there evidence at the present time is insuf- is no threshold dose for gene mutations, and ficient to justify precise conclusions some scientists thus reject the threshold con- on the nature of the dose-effect rela- cept completely. However, threshold values, tionship at low doses and dose rates. whether they are interpreted as points where Moreover, the evidence is insufficient Wk..; or no damage occurs, are the points of to prove either the hypothesis of a reference used by the government and other "damage threshold" (a point below agencies in establishing personnel exposure which no damage occurs), or the hy- limits. The official definition of permissible dose pothesis of "no threshold" in man at according to the National Committee on Radia- low doses. tion Protection reads as follows : "Permissible (9) If one assumes a direct linear relation dose may be defined as the dose of ionizing betweenbiologicaleffectandthe radiation that, in the light of present knowl- amount of dose, it then becomes pos- edge, is not expected to cause appreciable bod- sible to relate very low dose to an as- ily injury to a person at any time during his sumed biological effect even though it lifetime." 2 This definition may be further elab- isnotdetectable.Itisgenerally agreed that the effect that may actu- 'U.S. Department of Commerce, National Bureau of Standards. Permissible Dose for External Sources of Ionizing Radiation. ally occur will not exceed the amount (Handbook 69)Washington, U.S. Government Printing Office, predicted by this assumption. 1964. Pp. 26-27. 55 orated to indicate that appreciable body injury regulations because of their known resistance means any injury or effect that the average to radiation injury. The annual MPD has been person would consider objectionable, or that set as 75 rem for these parts of the body. medical authorities would regard s s being a Fluctuations in doses may be treated in the health detriment. same manner as whole body doses. Permissible weekly dose has also been de- (It may be noted that the Federal Radiation fined by the National Committee on Radiation Council has recommended that the term "max- Protection : "A permissible weekly dose of ion- imum permissible" not be used any longer. In- izing radiation accumulated in one week of stead, the Council w ould substitute for MPD such magnitude that, in the light of present the terms "radiation protection guide (RPG)" knowledge, exposure at this weekly rate for an and "radioactivity concentration guide (RCG)" indefinite period of time, is not expected to for maximum permissible concentration. The cause appreciable bodily inj ury to a person at latter terms are believed to state more clearly any time during his lifetime." 3 the intentions of the standards which have 6-8.2 Exposures Exceeding Permissible Ex- been set. Since most literature used by radiog- posure. The exposure limit of 100 mr/wk can raphers uses MPD, this terminology will be be routinely attained only by carefully pianned used in this radiography training program.) working procedures. There may occasionally be times when a radiographer needs to work Occupational exposure may not start before under conditions that require a personnel dose age eighteen. At any age beyond 18 years, the that is greater than 100 mr/wk. Under certain exposure limit is equal to five times the num- conditions it is acceptable for an individual to beia of years over age 18, provided no annual receive up to 3 rem of occupational exposure increment exceeds 12 rems. Thus, exposure of per calendar quarter while working in a re- personnel in restricted areas = 5 (N 18), stricted area. where N = a person's age in years. This requires that the licensee shall : 6-8.4 Radiation Banking Concept. The Na- tional Committee on Radiation Protection set (1) Obtain a certificate of informationre- quired on Form AEC-4, Figure 13.2. the permissible rate of radiation exposure just (2) Calculate the accumulatedexposure outlined in accordance with what is known as received by the individual and the the radiation banking concept. The idea or additional dose allowed for that in- model of a radiation bank is used to facilitate dividual who is likely to be exposed. the explanation of radiation exposure permitted in a lifetime. If his "Bank Account," paragraph 6-8.4, The banking comept considers that each permits, the radiographer can be exposed at man has a radiation "bank account" to which the greater rate of 3 rem in 13 weeks. he adds or deposits 5 rem each year of his life 6-8.3 Maximum Permissible Dose for Occu- pational Conditions. The National Committee after age 18. He can draw on this account at on Radiation Protection has established max- the rate of 12 rem per year. If he overdraws imum permissible accumulated doses to the his account slightly, no particular harm is done, whole body which it considers safe. These rec- but in order to keep down his exposure to ac- ommendations have been accepted by the AEC ceptable limits, he should be restricted from and have been written into the rules and regu- additional exposure until his account has been lations of this body, which built up by the passage of time. The following governs licensed example may be used to further illustrate this use of radioactive materials. These rules and concept. (Refer to Figure 6.3.)Say a man regulations are given in Part IV, Chapter 13. enters radiation work at the age of 23. Five The hands and forearms logicallyare likely to be exposed to more radiation than other years have passed since his eighteenth birth- parts of the body in an occupational situation. day. This means he has banked 25 rem in his It is permissible for the hands and forearms to radiation bank (5 rem per year).If he is al- receive considerably more radiation under AEC lowed to use up 12 rem of exposure his first year of work, he would then have an account 3 Ibid. balance of 18 rem, that is 25 rem minus 12

56 Bank Account (rems)

Deposits (Permissible Withdrawals Balance Age Dosage Accumulation) (Dose Received)

I. a. 5 yrs. X 5 rem/yr. 23 25 25 2. a. 1st year at work 12 13 b. 6th year over Age 18 24 +5 13 3. a. 2d year at work 12 6 b. 7th year over Age 18 25 +5 11 4. a. 3d year at work 12 1 b. 8th year over Age 18 26 +5 4 5. a. 4th year at work 12 8 b. 9th year crier Age 18 27 3 6. a. 5th year at work 0 b. 10th year over Age 18 28 +5 +2

60 FA 50 a No radiation work is ti , permissible until the 40 mi Accumulated exposure j,;v,mil 4th year bank balance exceeds should remain under F4i 12 rems the accumulated this line exposure 30 A SALM 3dear 20 12yrerins

2d year wi61111 I 0 5. A11-iii 1s4raerms ,,11111 12 rims 0

15 18 20 25 30 Age in Years

FIGURE 6.3.Radiation "Banking"Concept for Radiation Workers. rem plus 5 rem. At the same rate of exposure tional dose is not greater than, but preferably he would have a deficit in his banking account less than 5 rems. It should be noted that the by the end of the fourth year. This situation average annual exposure in AECplants and would prevent the man from doing radiation laboratories and industrial operations has been work until his "bank account" had accumulated controlled to approximately 100 mrem per a reserve. week or less. To prevent loss of employment, or job inter- The average long term exposure limit for ruptions, the radiation work must be controlled industrial radiographers should not exceed 114 over long time periods so the average occupa- rem per quarter. 57 6-9Exposure for the Total Population 6-10Physical Examinations

The whole body dose for the population of Every Atomic Energy Commission installa- the U. S. from all sources of ionizing radiation, tion has a medical support team. While this including medical as well as other man-made may not be true in certain industrial installa- sources and natural sources, has been set not tions, those places operating under AEC li- to exceed an average of 14 remsper individual censes should have the services of qualified over the period from conception to age 30. This medical practitioners available at all times. means an average of about 0.5 rem per year The important responsibility of the medical for the first 30 years. One-third this amount support personnel is to provide pre-employment may be added for each decade after age 30 dur- and follow-up physical examinations, both of ing the reproductive period. which are important in preventing radiation The above limits were established, keeping in inj ury. mind that, in the genetic picture, it is theav- The pre-employment physical examination is erage that counts despite very wide variations designed to determine the condition of thepo- among individuals. Present estimates place the tential employee's health. A worker ina lab or average dose per person, per generation of 30 shop where radiation is present should be in years, due to natural background radiation, at excellent physical condition. Certain physical about 4 reins, that due to medical X-rays and conditionsshould exclude individuals from other non-occupational artificialexposure at working with radiation. about 5 reins. Therefore, itappears that cur- Follow-up physical examinationsare often rently the average exposure is well below that recommended to assure the continued good considered permissible. health of the employee and to determine that The President approved the RadiationPro- radiation work is not likely to adversely affect tection Guide prepared by the Federal Radia- his health. After radiation injury, follow-up tiorA Council, and presented in its May 1960 examinations afford a way of keeping track of report which is reproduced below. The Council the ability of the body to respond favorably to recommended the guide be adopted for normal damage. peacetime use. 6-11Instrumentation

TABLE 6.2.Radiation Protection Guide. The common types of personnel-monitoring instruments currently used to measureaccumu- lated gamma radiation exposuresare the film Type of Exposure Condition Dose (rem) badge, the pocket chamber, and the direct read- Radiation Worker: ing dosimeter. These types of monitoring de- (aWhole body, head 6 times the number of vices have been described in Chapter 5, buta and trunk, active blood- Accumulated yearsbeyond 18at short review is presented here. Film badges forming organs, gonads, dose 5,000 mrem a year are or lens of eye 13 weeks 3 rem (3,000 mrem) packets of film (similar to dental film packets) (b) Skin of whole body worn in a special holder. The film is sensitive and tunoid Year 30 rem (30,000 mrem) to radiation in various ranges and when de- 13 weeks 10 rem (10,000 mrem) (e) Hands and forearms, Year 76 rem (75,000 mrem) veloped according to standard techniques will feet and ankles VI 25 rem (25,000 mrem) be darkened in relation to the amount of radia- Body burden 0.1 microgram of ra- (d) Bone dium 226 or its bio- tion received. The amount of radiation which logical equivalent the film badge has received is indicated when Year 15 rem (15,000 mrem) the darkening of film is compared to the dark- (e) Other organs 13 weeks ...... 5 rem (5,000 mrem) ening of similar films which have been exposed Population: to known quantities of radiation. The film (s) Individual, whole Year 0.6 rem (500 mrem) badge is a good indicator of exposure if it is body (b) Average, gonads 30-year-5 rem (6,000 mretn) worn continuously while at work and if it is not exposed to radiation when not being worn.

58 urements, a very smallamount of radioactiv- The pocket chamber anddirect-reading the accumu- ity is all that is neededto seriously affect dosimeters are devices which measure amount that maynot lative records of radiation exposurewhen work being performed, an and used. Dosim- be considered harmfulto. a person. properly calibrated, charged, radioactive contamination eters, after charging and exposure, canbe read The hazards from emanate from alpha, beta, orgammaradiation. directly by holding them up tothe light. Pocket its very short range chambers, after charging and exposure,must The alpha emitter, due to device provided forthe in air, will do noharm as long as it remains on be read in a reading such as a wall orfloor. However, it purpose. (Dosimeterssometimes give false Mgh a surface, may be takenfrom such places byair circula- nadings when dropped or damagedby electri- the body is customary in some tion or body contactand iogested into cal leakage. Therefore, it be done. Beta emitters operations to wear them inpairs.) where great harm may also present the possibilityof becoming airborn Survey meters, paragraph5-4, are used to high the and taken internally,but may also create survey theradiation fields to determine surface of the con- radiation intensities. Thesemeasurements will radiation levels near the calculating per- taminated area as well.Gamma emitters repre- give information required for for external radiation sonnel residence time inradiation areas. sent the greatest danger as contaminants. 6-12Contamination Greatcareshouldbetakentoavoid Wherever radioactivematerials are used contamination. that these ma- Contamination should neverbe a great prob- there is always the possibility if proper safety terials will be released andthe area become lem in radiography operations precautions are followed.Radiography sources contaminated. (Contaminationis the uncon- the radio- trolled release of the radioactivematerial. Ra- are designedand fabricated to sea walls of a capsule active material in acapsule to prevent con- diation emitted through the and procedures prop- is not contamination.) Like allother radiation tamination. If equipment k from breaking, problems, contamination may beminor or ex- erlyprotectthis 9ule the chemical corroding, and wearinthere should be no tremely severe, depending upon tests, called wipe nature of the material, the typeof radiation contamination released. Leak and require- tests, are made at intervalsnot exceeding six given off, the amount released, capsules have not rup- ments for use of the area. Forinstance, in a months to assure the laboratory doing very precise radiation meas- tured and releasedcontamination.

59 Chapter 7

The Effect of Radiation on theOrgans and Tissues of the Body

(It is not mandatory for the radiography Radiobiologists have determined that radia- technician to be tested on this material. How.. tion affects the living organism principally by ever, it is desirable for allradiation workers altering the ability of cells to reproduce nor- to be familiar with the body effects that can mally. In other words, the radiation damaged occur from unnecessaryexposure.) body cells do not reproduce in the same manner This chapter deals in a specific sense with as healthy cells. Thisalteration comes about the effect of radiation on the various parts of through the process of ionization. Ionization is the body. A brief review of the nature and com- the result of a transfer of energy whichtakes position of the various tissues and organs is place when radiation from radioactive ma- includedsothat the non-technicalstudent terialsinteracts with an electron spinning might better understand the rather complicated around the nucleus of an atom. Since each body processes involved. cell is made up of literally millions of atoms, radiation effects are produced by changing the 7-1 Radiation Effects on Living Matter structure or electrical charges of the atomsof The body of man, as that of all living or- the irradiated material. These changes inturn ganisms, is composed of cells. Cells are the affect the forces (valence bonds) which bind fundamental units of structure of living organ- the atoms together into molecules, and the isms, just as the atom is the fundamental unit latter break into parts, some of which are of chemical structure. It is not possible to de- charged. The charged parts react immediately scribe the make-up of various types of cells in with adjacent atoms and molecules while those a brief treatise such as this, butin general a not charged may interact chemically after a cell may be described as a restricted mass of while with the new molecules formed by the protoplasm differentiated into cytoplasm, nu- charged fragments. cleus, and a binding plasma membrane.' The above process may be illustrated as fol- It is well known that the bodies of living or- lows. Because living cells are mostly water, ra- ganisms have varying tolerances to all kinds of diation passing through a cell is most likely to injuries or abuses. The body is able to recoup strikewater molecules(H20). When this the damage done to it through a complicated occurs the bonds between thehydrogen and biological process known as mitosis. This is a oxygen atoms of the water arealtered and process whereby cell division takes placeand, breakdown products are produced which, when among other things, wornout ordamaged cells combined with oxygen atoms, produce bleaches. are replaced to make the bodyfunctionally Bleaches, such as hydrogen-dioxide (H02) and whole again, Mitosis is, of course, basic to all hydrogen-peroxide (H202) are powerful enough reproduction., but hereditary and other func- to break down the highly complex protein mole- tions are beyonid the scope of this chapter. cules in the body cells. The all-important en- Cell division is especially rapid in the earlier , zymes are made up of one class of protein years of life before full maturity hasbeen molecules, and the bleaches produced by irra- achieved. However, this process never ceases, diation remove the hydrogen atom from the though it' cdntinues at a slower pace after the sulfur-hydrogen-sulfur bond of the enzyme, ,individual Ills reached his adult stage. The dif- thus completely destroying its control function tferential rate of mitosis explains the difference in cell division. 'in' time whiCh is necessary for an older person It does not take a great deal of imagination ,and younger person" to recover from fractures to envision that even a small change in the and other types of organic pathologies. rate of cell division for a few cells can have Johnson, Willis H., Laubengayer, Richard A., and DeLanney, many serious effects. One outcome of irradia- Louis E. General Biology.(Revised edition) New York, Holt, Rinehirt, and Winston, 1961. Pp. 11-26. tion is for the cell to continue to grow until its a/61 size is abnormal. When suchan enlarged cell chemical changes occur in living cells),which dies there is no replacement to fill the void it lowers the cell's resistance to radiation. This is leaves in the tissue. Another effect is that the simply to state that working cells aremore cell is so altered that its daughter cellsare likely to be damaged by irradiation. A knowl- genetically different from it. These daughter edge of this fact explains why the resting cells cells may die before they reproduce themselves, in the blood-forming tissues and gonads, for or their rate of division may be higher orexample, are not as sensitive to radiation as lower than that of parent cells. In eithercase, the active cells in these places. an abnormality results. Undernourished cells (those shorton blood In summary, the effect of radiationon a liv- and food supply) react somewhat counterwise ing organism is produced at the cell level, and to what might be expected. Rather than pre- is both physiological and morphological inna- sent a high susceptibility in their weakened ture. In humans and other organisms, mily condition which might encourage radiation those rays which strikea target, that is an damage, these cells usually are less sensitive to electron, cause damage. The degree of damage radiation than normal cells. Their resistance is depends on many conditions and factors,as will accounted for in terms of decreased activity, be shown in the descriptions which follow. which means that chemical and other changes 7-2Radio-Sensitivity which radiation might aggravateare slowed down. It is well known that the different tissues and organs of the body differ ir nature, func- 7-3Classification of Body Cells in Order tion, and appearance. They also differ in their of Radio-Sensitivity response to radiation. This difference is defined A knowledge of the rank order in which cells as radio-sensitivity. Scientists have determined are likely to be injured is important to the that "the radio-sensitivity ofa tissue is directly therapist, who has in mind the special function proportional to its reproductive capacity and of each class of cells. It is also well thata per- inversely proportional to its degree of differ- son contemplating working with radioactive entiation." In simple terms, this finding estab- materials have some acquaintance with the lishes that the body cells whichare most active sensitivity of various body cells. The study of in reproducing themselves, and the cells which radiation damage to body cells has enabled the are not fully mature, will be most harmed by classification of cells according to their sensi- radiation. From this fact itcan be immediately tivity in a generalway. A partial list, including deduced that certain organs and tissues will be the most important cells, is given here. The more likely to receive damage after radiation function and importance of each class of cells exposure. The likelihood that children willre- will be elaborated in the discussion of radiation ceive more injury than adults also stems from effects on organs and tissues which follows. this knowledge. (1) The lymphocytes, the white blood cells Several factors besides reproductive capacity formed by the tissues of the spleen, are significant in radio-sensitivity. Among the lymph nodes, etc., are the most sensi- most important are :(a) the stage of cell divi- tive to radiation. These cellsare so sion, (b) cell activity, and (c) the bloodand sensitive to radioactivity that theyare food supply oi the cell. With regard to the first often used as indicators of radiation factor, cells are considerablymore sensitive to injuries. A sample of blood is taken radiation at certain stages of the mitoticproc- and a count of the number and type ess, i.e., while they are dividing. This phenom- of lymphocytes is made to determine enon can be understood in terms of the imma- variations from normality. ture *state of the daughter cells whichare in (9) The granulocytes, white blood cells the process of formation. The situationis formed in the bonemarrow, are also paralleledinanewbornbaby'sgreater high in radio-sensitivity. These cells susceptibility toexposure. are used to combat bacterial infections The greater vulnerability ofcells which are of one type or another, andany im- active is also easy to understand.These cells pairment of their functioncan be have a higher metabolic rate (therate at which critical to health. 62 considered in (3) The basal cells, so namedbecause they classes of biological effects are are the originatorsfor the more com- some detail onthe following pages. plex specialized cells ofthe gonads, 7-5Factors Related to SomaticRadiation the bone marrow, theskin, and the alimentary canal, also rank amongthe Effects radiation. Somatic radiation effects, asnoted, are those cells highest in sensitivity to individuals. These (4) The cells in the lungs whichabsorb experienced by irradiated air and release car- effects cannot be fully understoodwithout some oxygen from the the actual dose, bon dioxide from the blood arefairly notion of the factors, besides scale. which combine to produce thefinal reaction. high on the radio-sensitivity brought These cells are known as the alveolar Dosage is of great importance as was out in Chapter 6. cells. Dose is Admin- (5) The bile duct cells are intermediatein 7-5.1 The Rate at which the These istered. The living tissues ofthe body usually the order of radio-sensitivity. degree perform an important function begin repair processes as soon as some of damage, by whatever means,has been re- associated with digestion. of radiation ex- (6) The cells of the tubules of the kidneys ceived. This is true in the case posure. Up to apoint, the body can keep up are also affectedrather quickly by is re- radiation. The importance of the kid- with such damage, even though exposure ceived daily. When the body is ableto keep up ney is well known. change can be (7) The cells that line the closedcavities with damage received no visible the observed in the individual. Thisis why it is of the body, such as the heart and consider- blood vessels, and which are known as possible for a person to be exposed to able amounts of radiation over aperiod of time the endothelial cells, aremoderately the same radio-sensitive. without bae. aftereffects. However, (8) The structural cells of the tissues amount of radiation given all at oncewould which support the organs and other produce a violent reaction. It is thus the rateof specialized tissues of the body, known exposure that is the firstfactor to be con- cells, are more sidered in assessing the effects of radiation. as the connective tissue 7-5.2 The Extent of the BodyIrradiated. resistant to radiation than the endo- the thelial cells. Under circumstances of exposure where (9) The muscle cells rank next in order whole body receives a large or even amoderate and are quite resistant to radiation. dose of radiation, a severe reaction willbe ob- (10) The bone cells and the nerve cells are served and it is probable that furtherillness characterized by the least radio-sensi- will ensue. On the other hand if only asmall X-ray tivity of all body cells. fraction of the body is irradiated, as in therapy, the effects on the whole body are very 7-4Types of Biological Effects of Radia- mild, even for considerable doses. Localeffects tion may be quite noticeable,of course, with the Biological effects of radiation are grouped possibility of a degree of permanent' change in into two major classes. The first and most obvi- the affected tissues. ous effects are those which areexperienced by 7-5.3 The Part of the Body Irradiated. Cer- the irradiated individual. These effects, known tain portions of the body are more sensitiveto as somatic effects, include suchthings as dam- irradiation than others. In general, reaction is age to body tissz.,es. and organswhich impair much more severe if the dose is administered normal functions. The second class of radiation to the upper abdomen (and possibly to the effects does not concern the majority of persons spine) than elsewhere on the body. It is in this but is nevertheless profound. It includes the region, of course, that most of the vital organs genetic effects, or those effects which may be and tissues are found. Thus in considering the produced on future generations, if radiation condition of exposure of an individual, an at- produced changes in germ plasma which can tempt should be made to determine what part be transmitted to future generations. Both of the body received the damaging rays. 63 7-5.4 The Age of the Individual. It has been developed. It will be noted that the nerve tis- pointed out elsewhere that the physical matur- sue and muscular tissue (including the heart) , ity of the individual is importarA in radiation. are not discussed. The reason is that these tis- This is true because the cells of personsgrow- sues are generally insensitive to radioactivity. ing physically are in an accelerated stage of Studies have shown no significant 'effects on reproduction. For this reasen an exposure of a these tissues, other than small hemorrhages, given amount should be considered more seri- after lethal doses of radiation.2 ous for a young person than for an adult. 7-6.1 The Blood and Bone Marrow. Most of 7-5.5 The Biological Variation Among In- the different types of blood cells are formed in dividuals. Individuals differ in variousways in the red bone marrow. When these cells pass the make-up and functioning of their bodies. into the blood stream they travel to all parts of Therefore it is not unexpected that a set dose the body, through the arteries, capillaries, and of irradiation may produce a certain effect in veins. The blood itself ifs considered a tissue, one individual which may not be experienced to with the liquid part of the blood, the plasma, the same degree by a second person. (For ex- serving as a matrix for the formed elements ample, experiments have shown thata single or cells scattered in it.3 Adults generally have dose results in the death of a group of rats; from five to six liters of blood in their bodies. whereas some other rats will die from an ex- The formed elements or cells of the blood are posure of only half this strength.) classified under three general types :the red 7-6 blood cells or corpuscles known technically as Specific Effect of Radiation on Vari- erythrocytes; the white cells or corpuscles ous Organs and Tissues of the Body known as leucocytes; and platelets or throm- The point has been made that radiation in- bocytes. It has already been noted that the dif- jury depends upon the radio-sensitivity of cells ferent cells, including the blood cells, do not making up the organs and tissues of the body. react to radiation in the same manner, i.e., Level of injury is thus closely related to the they have different degrees of radio-sensitivity. organs and tissues which may be exposed to This difference, plus the difference in the life radioactivity. Radiationcan cause injury in span of the various cells, are important factors several ways :(a) There may be damage to a in radiation injury. tissue or an organ which results inan increase When the body is irradiated the first cells to or decrease in the production of its products, be affected, by a reduction in number, are the for example, hormones, enzymes, etc.; (b) leucocytes. It may be noted that these white Radiation maycause an alteration of the birth blood cells are typical cells with nuclei but con- rate of cells in the tissues or organs;(c) Ra- tain no coloring matter, thus their name. They diation may cause the complete death of tissues are far less numerous in the blood stream than or organs. the red cells, being outnumbered by the latter Whatever the effect, there is alwaysa chain at the ratio of 600 to 1. When the body becomes reaction with other parts of the body which diseased or injured the number of these white results in some change in non-irradiated tis- cells increases, apparently to counteract infec- sues and organs. For one thing, unless the tion. There are two main types of leucocytes, damaged tissue or organ is completely de- differentiated on the basis of whether they do stroyed it will begin a repairprocess. This or do not have granuks in the cytoplasm (the repair process, of course, affects the rest of the liquid surrounding the cell nucleus). Thegran- body because the balance of the body is upset ular leucocytes include the lymphocytes and to the degree to which tissue prodlctsare used monocytes. The lymphocytes are formed pri- in greater quantities during the repair period. marily in the lymph nodes and the spleen,as The organ and tissue growths whichare af- mentioned previously, and make up 20 to 25 fected most by radiationare treated briefly in percent of all white cells. Their function is the discussion which follows. In each instance, not too clearly established, but it is believed a brief review of the biological composition of that they may become connective tissue cells the organ or tissue is given in order thata per- 2 Behrens, O. F. AtomicMedicine.New York, Thomas Nelson and Sons, 1949. spective of its function to the body might be Johnson, W. ILet al. Op. cit.,PP. 173-190. 64 and play a role in scar tissueformation. Some general weakness of the individual. recent studies indicate that thelymphocytes It should be remembered that exposuresto give rise to one of the proteins ofthe blood radiation at less than permissiblelevels may plasma globulin, which is associatedwith im- not be serious. Under usualconditions cell mune substances orantibodies. production in the marrow and inthe'lymphatic The first cells to be reduced innumber after tissue will increase at least temporarilyto com- a person becomesirradiated are the lympho- bat infection, and after theinfection subsides cytes, because of their extremelyhigh radio- these tissues return to a steady,normal level sensitivity. Within a few days the granulocytes of production. However,repeated small radia- count iq also lowered. (There arethree classes tion injuries may overwork therepair proc- of granular-leucocyte's :eosinophils, basophils, esses and produce greatinstability in the blood- and neutrophils.) The lack of the necessary forming tissues. Such instability mayresult in number of white blood cellsbrings on the anemia or leukopenia or leukemia.The latter condition known as leukopenia which may or is an acceleration in productionof leucocytes, may not be serious. and is almost always fatal. Itis significant that The second part of the blood to beaffected repeated small doses of radiation maybe more by radiation is the platelets.These small struc- dangerous to a person than an acute exposure tures have no nuclei and are considered ascell which produces severe depletionof all blood fragments which originate from thegiant cells cells. The body will probablyheal from the of the red bone marrow. Plateletsdisintegrate latter if there is no further exposure,while in drawn or exposed blood and play animpor- injury from chronic exposure islikely to be tant part in blood clotting. permanent. Within a week after acute or severe radia- In summary, irradiation damage tothe blood tion, the platelets in the blood stream are re- and bone marrow may be said to comeabout duced critically in supply. This result comes because the functions of the bloodhave been about because of damage to the cellswhich impaired. These functions are carryingfood, produce platelets and because of injury tothe carrying oxygen, carrying wastes, fightingbac- platelets themselves. Irradiation serves firstto terialinfection,andbloodclotting.Said activate the platelets, producing a temporary another way, radiation effects on theblood and acceleration of blood clotting. Followingthis bone marrow are such as to :(1) make the phase, the platelets are severely reducedin body susceptible to ordinarily harmlessbac- supply and the blood clottingfunction is not teria, (2) prevent clotting and thusprolong performed as quickly. the healing of open wounds, and (3) bring on About seven weeks after irradiation, a loss a serious pathologicalcondition. of red blood cells (erythrocytes) occurs.In the 7-6.2 The Lymphatic System. Lymphis a adult, all red corpuscles (or cells) areformed liquid which is the same as the blood plasma in the red marrow of bone. They aredeveloped minus most of the blood proteins. It bathesall into typical cells with nuclei, althoughthe of the cells of the body and is oftenreferred nuclei of these cells are excreted just before to as the internal environment of thecells. All they are put into circulation It is hypothesized substances that are exchanged between the that the excretion of the nuclei allows the cells blood and the cells, and vice-versa, must bedif- to contain more hemoglobin, the important fused through the lymph. A lymphatic system oxygen-carrying pigment. Recent work with has evolved in all vertebrate types which car- tracer elements indicates that the redblood ries the lymph back into the venous circulation. cells may function in the blood streamfor In man, there are numerous lymph capillaries about 120 days. The total number of red cells which join to form even larger vessels (lym- in one person is normally about 35 trillion.A phatic vessels) most of which empty into a main lack of the proper number of red cells, or a lymphatic vessel, the thoracic duct. The tho- decreased amount of hemoglobin in the circu- razic ducts empty into the veins near the heart. lating bkiod, results in a condition known as Lymph is found not only in the lymphatic anemia. Anemia symptoms are pallor, short- vessels but also in various cavities of the body ness of breath, fluttering of theheart, and such as the coelomic, or main body cavity, the 65 pleural (lung) cavities, the pericardial (heart) Hair, then, grows from the bottom of the fol- cavities, and the cavities of the joints, where licle, not from its tip. it serves as a lubricant. Fingernails and toenails also develop from The lymphatic system performs the function inpocketings of cells from the inner layer of of purifying the lymph of tissue debris and of the epidermis. The nailsare composed of invading bacteria and passing it back into the densely packed dead cells which are translu- blood. The lymphatic vessels carry the con- cent. Oil a-nd sweat glands are also derived taminated lymph to the lymph nodes where from the inner layer of the epidermis by in- these foreign materials are out %.nd the pocketings which go deep into the dermis. Each supply of lymphocytes is replenished. hair follicle is asFociated with an oil gland. The spleen is the largest mass of lymphatic The skin has several important functions. tissue in the body. However it is involved in Perhaps the most vital, and certainly the most blood rather than lymph circulation, and is an obvious, is that of protecting the body against important source of lymphocyte cells, as men- all sorts of hazards associated with the external tioned before. This organ also removes dead environment. Since the skin is r,iatively tough blood cells from the blood and stores red blood and pliable, it shields the underlying cells from cells for use in an emergency. Contraction of mechanical injuries caused by pressure, fric- the smooth muscle in the spleen squeezes the tions, and blows of one type or another. Like- cells into the blood stream at a time of need. wise, the skin protects the body from certain disease-producing organisms and from the The functions of the spleen can be taken harmful ultraviolet rays of the sun. The latter over by other lymphatic tissues in an otherwise is accomplished through formation of a pig- healthy man. However, if there is radiation in- ment (tanning). The skin also helps preserve jury, all the lymphatic functions might be lost body moisture, and helps regulate the elimina- to the body. This means that the production of tion of heat from the body to maintain a con- lymphocytes would be stopped or reduced, and stant body temperature. In addition, the skin that the filtering of foreign substances out of contains a number of different sense receptors the lymph would be impaired. Such a develop- which allow us to feel pressure, temperature, ment would be associated with an increased and pain, and in general to discriminate be- activity of bacteria and would decrease chances tween the various classes of objects which may of recovery. be touched. Specialized glands such as the 7-6.3 The Skin and Hair Follicles. The skin sweat glands, oil glands, and mammary glands (or integument)is composed of two main are also located in the skin. parts, a comparatively thin outer layer known Everyone knows from experience with cuts as the epidermis, which is free of blood vessels, and bruises that the skin is easily injured but and an inner thicker layer, the dermis, which has a remarkable capacity for local repair. is packed with blood vessels and nerve endings. Fortunately for most of us, injury to the skin The epidermis is made up of several layers of is usually localized in a relatively small area, different kinds of cells which vary in number leaving plenty of normal tissue to promote in different parts of the body. The outer layers healing. of the skin are constantly peeling off and be- After irradiation, changes are recognizable ing replaced, a process everyone has observed in the skin within an hour, even when exposure on parts of his own body. has not been excessive. Skin reaction, observed The entire skin, except the palms of the microscopically, is one of the first clinical indi- hands and the soles of the feet, is equipped cations of radiation exposure. Intermediate with countless hair follicles. These are in- dosages of radiation will produce a reddening pocketing of cells from the inner layer of the of the skin known as erythema. This type of epidermis. Such cells undergo division and give reaction indicates the skin is in a partially rise to the hair cells, just as the inner layer of damaged condition, with some normal cells re- the epidermis gives rise to the outer layers. The maining among the damaged cells. The normal hair cells die while still in the follicle and the cells, under usual conditions, immediately begin hair visible above the surface of the skin con- repair, and a fairly rapid recovery may be ex- sists of tightly packed masses of their remains. pected. Large doses of irradiation (chronic or 66 formation of cancer- crete substances whichconvert food particles acute) may result in the It is noteworthy that ous cells on theskin. Skin cancer has been ob- into absorbable material. of careless, the processes ofdigestion begin fromthe ini- served in humans after four years continue to ultimate ex- over-exposure to gammaradiation. However, tial intake of food and taken, such a de- cretion. Also, the cells of thealimentary canal when proper precautions are being broken free by the passage velopment is extremely unlikely.Another skin are constantly premature aging. of food, and must be replacedcontinuoasly. symptom of irradiation is the first important This occurs only after over-exposurefor sev- Studies have shown that effects of irradiation on thealimentary canal eral years. juices and Irradiation of the cells liningthe hair fol- are impairedsecretion of digestive hair, or at best discontinuance of cellproduction. When cells licles can stop the growth of larger numbers of cause temporarybaldness (epilation) . Thehair of the canal break down, relatively large dose them are released from thewalls of the canal begins to fall out after a folds of the intestines of beta and alpha radiationand may continue and, consequently, the weeks. In most in- become cluttered with debris.The symptoms of to do so for one or two vomiting and nausea. stances epilation follows thenormal pattern of this kind of damage are ordinary baldness, with hair fallingout first Continued vomiting producesthirst. The cells be lost as aging exposed by the breakdown ofouter protective in the spots where hair would juices and pro- progressed. Interestingly, the leastaffected re- cells are irritated by digestive 'uce convulsions of theintestines and diarrhea. gions of the body usually arethe eyebrows, of blood eylashes, and beard. The other partsof the Diarrhea isaccompanied by loss affected to a through the bowels in severe cases.When ex- body, besides the head, may be done, ulcers may greate., or lesser extent. In thesmall group of tensive damage of this kind is Japanese survivors of the WorldWar II nu- be produced. 111.. Jr formationis seldom limited clear blast, 59 percent losthair from the to one area and causesfurther irritation to the scalp, 12 percent from thearmpits, 6 percent intestines, with even more celldamage. from the eyebrows, and 3percent from the It has been found thatcell repair processes beard. Even in the most severe amongthese following irradiation of thedigestive system cases, hair began toreturn within a few may not be normal.In certain instances excess of their tissues are formed. In otherinstances no cells months. However, the characteristics other new hair differed in someinstances from those are produced.All such developments, as of the hair which it replaced.For example, radiation damage, result in thedigestive sys- Japanese exposed to large tem functioning improperly.The vital nature some white-haired suggests the se- doses of radiation regenerated blackhair. The of this system immediately regeneration of gray hair is moretypical ac- riousness of danger to it. cording to studies made.4 7-6.4 The Digestive System. Man ischar- 7-6.5 The Liver and Gallbladder.The liver acterized by a tubular digestive tract orali- and gallbladder are important tothe digestive mentary canal which is differentiated intothe tract and can be thought of aspart of the di- been men- following regions :mouth cavity,pharynx, gestive system. The former, as has esophagus, stomach, small intestine, and large tioned, is the largest gland in thebody. The intestine. In addition, several glands make up liver is important to digestion becauseof its a part of thissystem, including the salivary secretion of bile. Bile is stored in thegall- gland, the liver, which is the largestgland in bladder, and when needed it passesthrough the the body, and the pancreas. The digestivetract common bile duct into theduodenum. There it is located in the body cavity or coelom, and is acts to c,..iulsify fats in thesmall intestine. held in place by the mesentery. The lengthof When the fats are broken intotiny droplets the canal in adult man is about 30 feet.The there is much more surface exposedto the fat- important many folds, especiallyin the intestinal part of splitting enzymes. The liver is also the canal, give it a large surface area.The for several other functions. One ofthe most specialized cells in the walls of the canal se- important is the conversion of glucoseinto glycogen and the storage of the latteruntil it Glasstone, Samuel, ed. The E ffecte of Atomic Weapons. (Re- into the vised edition) Washington, U.S. Government Printing Office,1960. is needed by the body. It is released 67 bloodstream to maintain a constant level of glands produce and store adrenalin which is sugar there. released according to the body's needs. Every Radiation damage to theliver and gall normal individual has present in his blood- bladder generally impairs digestion and thus stream varying amounts of adrenalin at all upsets this important function of the body. In- times. Upon stimulation the adrenal glands ternal radiation (from sources taken into the empty an extra amount of adrenalin into the body) is an especially great hazard because the bloodstream. This brings about the effects noted liver tends to concentrate many radioisotopes above. Blood pressure is raised by constricting within itself. Small doses of external radiation the blood vessels and stimulating the rate and (from sources outside the body) apparently force of the contraction of the heart. The ex- do not injure the gallbladder but may cause cess adrenalin also acts within the liver and alteration in the production of fatty acids in muscle tissues to cause increased sugar break- the liver, thereby altering the body's metab- down. Both of these processes provide extra olism. Large doses of external radiation may energy to the individual. After each instance have serious effects by producing small areas of stimulation, tissue function becomes normal of dead tissue and hemorrhaging in both the again and the supply of adrenalin which has liver and gallbladder. been depleted is restored over a period of time. The interval for this restoration of adrenalin 7-6.6 The Endocrine System. Three of the will be longer if the cells of the adrenal glands major classes of glands in the endocrine system have been damaged, as they can be through are especially prone to harm from radiation. irradiation. Thus the body functions less effi- These are the adrenal glands, the thyroid ciently, and the individual becomes more sus- gland, and the gonads. The integration of the ceptible to heat, cold, injury, and infection. activities of the various parts of the body is His heart beat may become irregular,his caused by the nervous system and by the prod- blood pressure drop, and the balance of salts ucts of the various endocrine glands. Secre- in his blood plasma may be upset. At this point tions of the endocrine glands are known as a note of caution is in order. The symptoms hormones. Hormones are carried by the blood noted above are not solely attributable to ad- all over the body, and each hormone serves to renal damage. Caution should thus be used in regulate a particular body process. All the hor- making a diagnosis. mones can be identified chemically as either The thyroid gland is located along the sides proteins, amino acids, or steroid compounds. of the trachea at the base of the throat in man. Hormones are powerful and exert their effects This gland secretes a hormone known as thy- even when present in very small amounts. They roxin. The general effect of thyroxin isto are necessary to the preservation of health. regulate the rate of metabolism. It may also be The adrenal glands are consideredfirst. noted that the functioning of the thyroid gland There are two adrenal glands, and in man one is associated with that of the pituitary and the is located on the top of each kidney. The main adrenal glands. Damage done te one of these hormone produced in these glands is adrenalin. glands will alter the functions of the others The importance of adrenalin is shown by the and have marked effects throughout the body. fact that an injection of this hormone produces The thyroid itself is not too sensitive to ex- marked effects on an individual, including an ternal radiation. However, it is the place in the increase of heart beat, a rise in blood pressure, body where iodine is concentrated. When radio- an increase in the glucose content of the blood, active iodine, which comprises about 5 perceht a decrease in the glycogen content of the liver, of the fission products from a reactor, is ab- and an increase in resistance to fatigue. An sorbed by the thyroid, this isotope continuously above-normal supply of adrenalin may produce bombards the cells of this gland with beta and symptoms such as dilated pupils, hair standing gamma radiation. The radiation damage to the on end, and the blanching of skin. thyroid causes a decrease in thyroxin produc- Leaving the other hormones besides ad- tion. This in turn affects the basal metabolism renalin, which is found in the adrenal glands, rate by decreasing it. The next effect is for aside for the moment, damage due to irradia- muscle tissue to fail to absorb needed oxygen tion can be shown as follows. The adrenal and the health of the individual becomes se-

68 the air goes to the verely impaired. larynx. From the larynx Although the pituitary glands are notextra trachea, which leads to theright and left lungs. sensitive to radiation and thus are notdis- The lungs are made up ofminute air sacs called cussed in detail here, it may be notedthey are alveoli. These sacs are connectedto small tubes, largertubes, affected by malfunction of otherglands. These bronchioles,thatleadinto glands regulate growth, act on the sex organs, bronchi, which are branchesfrom the trachea. other things. In the process of breathing,each air sac is ex- and stimulate the thyroid, among muscles of the The reproductive organs of man(ovaries and panded and compressed by the testes) are known as the gonads.R.adiation lungs and in this manner isfilled with air and the cells of these organs emptied. Air is absorbed throughthe walls of may severely damage (capillaries) and can produce sterility,although this is un- these sacs by tiny blood vessels usual. Moderate doses of radiation,however, which deliver oxygen into theblood and absorb will slow down the production of spermcells carbon dioxide and moisturefrom the blood. in males. Slowing down of spermproduction, Each air sac membrane isextremely delicate because of injury both to irradiated cellsand in order to permit the necessaryexchange of to the repair functions of nonirradiatedcells, gases, yet it is strongenough to hold back the results in only partial sterility.The sperms blood. If the membranes of theseair sacs break themselves are radio-resistant, andirradiation or have theirpermeability altered in some of the sex organs does not destroythem. manner, blood may enterthe lungs. Under modern conditions of occupational es- Radiation produces its effect on the lungsby cells posure, there is noevidence of any impairment damaging the air sacs or the maintenance to fertility. Permanent sterility isonly pro- which maintain the membranes.This type of duced in either man or woman by nearlethal damage may occur from externalradiation but doses to the reproductive organs. Sexualim- the greatest hazard is from internalradiation potency, the physical incapacity to engagein such as that emanating frominhaled dust and the sexual act, is not necessarilyrelated to vapors. Small particlesof radioactive materials sterility, and is not a usual occurrence. The enter the air sacs and mayremain there in- latter statement is emphasized becauseof a definitely. If they do not dissolve,they will great fear which many personsharbor. Indi- cause continuousdamage and eventually result viduals rendered completely sterile byirradia- in the formation of tumors. Solubleradioactive tion were impotent only while incapacitatedby materials pass through the air sacmembranes irradiation sickness. into the blood to cause damage in otherplaces After a relatively large dose of irradiation throughout the body. Although the aboveis the to the pelvic region, a pregnant woman may primary way in which radiationaffects the have a miscarriage or a still birth. This isnot lungs, damage may also occur fromtoxic by- always the case however. For example, of98 products created in other parts of the body as pregnant women in Nagasaki who werewithin a result of exposure.These substances are car- 1000 meters of the center of the explosion, ried to the lungs by the blood stream.Any about 23 percent of those who had severe radia- damage to the lungs is reflected in thefunction- tion sickness miscarried, compared to 4 percent ing of the body. of those who were not sick. It is possiblefor children irradiated inutero to be abnormal. 7-6.8 The Urinary System. The urinary sys- Howeihr, there is little information on this tem of man is made up of kidneys,ureters, subject. The genetic effects of radiation are so bladder, and urethra. The kidneys lieoutside profound that they are discussed under a sepa- the body cavity and are suppliedwith rather rate heading (paragraph 7-8) . large renal arteries and renal veins. Theureter leads from an indentation in eachkidney and 7-6.7 The Respiratory System. Man breathes isa duct whichempties into the urinary through his respiratory system which is chiefly bladder. The urethra is a tube which carries composed of the lungs. Normally air enters the urine from the bladder outside thebody for human system by way of the nostrils or mouth, disposal. The kidneys help regulate the con- passes through the nasalcavities into the centration and content of the blood byexcret- pharynx, through the glottis, and into the ing water and, waste products. 69 Both external and internal radiation may cause they absorb certain radioisotopes which damage the urinary tract. External radiation may come to them through the blood. Some breaks down the tissues and reduces kidney of these isotopes are so readily absorbed that functions. Internal radiation sources may be- they are called bone seekers. Such isotopes come concentrated in the kidneys and cause damage the bone cells, as well as the marrow extensive damage. This is especially true when cells, with their long-term bombardment of the radiation source is slow. When blood ap- radiations. Tumor production is possible under pears in the urine after irradiation, it is an these circumstances. indication that the kidneys have been injured. 7-6.10 The Eyes. When our eyes function This symptom is caused by hemorrhaging in the we experience sensations of light, color, and cells which line the kidneys. Lesser damage to form. The lens system of the eye forms images these tissues is indicated by an increase of on the retina, just as they are formed on a amino acids in the urine. Radiation damage screen by a projector. The iris acts as a dia- also breaks down the cells of the uterus and phragm in regulating the size of the pupil and the bladder. When large numbers of cells have controlling the amount of light which reaches died they feel much as the outer skin does after the retina. Of course, the brain rather than the a sun burn. The tubes (ureters) to the bladder eye interprets the picture that is received. may be blocked by clots of these dead cells Unlike other cells in the human body the with the resulting concentrations of wastes transparent lens cells cannot be replaced by causing damage. regeneration. These cells lose their transpar- A still further symptom of radiation injury ency when they become damaged Or die and to the urinary system is known as tenesmus,form what is known as a cataract. Although which is the urge to rid oneself of waste prod- cataracts form slowly, they eventually cause ucts without being able to do so. In some cases, the individual to lose his sight. Scientistsare which are extreme, the bladder may no longer not clear on this point, but it appears that only be controlled, possibly because of damage to one or two damaged cells are necessary to ini- cells, which normally act as signals to the brain. tiate a cataract. In some way, by releasing a Radiation damage to the kidneys does not toxic substance or by preventing a transfer of appear to be completely incurable, although food to other cells, other lens cells are affected symptoms of slight danzz'ge to this part of the by the damaged cells. body have been observed in persons chronically Radiation affects the eye by promoting the exposed to small doses of radiation over a pe- development of cataracts. However, it takesa riod of several years. relatively large dose for this to occur. Neutron 7-6.9 The Bones. Bones consist of living cells and gamma radiations appear to be the chief distributed in a matrix of fibers and bone salts. producers of radiation-induced cataracts. Sus- The fibers give the bones their tensile strength. ceptibilitytoradiation-induced cataractsis Salts give them their hardness. The cells are greater among younger persons, because their connected by fine channels which penetrate the lenses are still in the process of growth. Older matrix of fibers and salts. Larger channels in persons quite commonly develop cataracts from the matrix contain the blood vessels and nerves. natural causes. In most instances cataractscan The center of the bones is filled with marrow, be treated surgically by removal of the lens and either red or yellow. The red marrow, as the use of eyeglasses to do thenecessary focus- pointed out before, has blood-forming func- ing of light. Nevertheless, theperson who is tions and is restricted in adults to the skull, working with radioactive materials should be breastbone, ribs, pelvis, and spine. The yellow aware of this hazard. marrow wovides fat storage. Radiation represents a serious tIr2eat to the 7-7Effects of Radiation on the Life Span highly radio-sensitive red marrow of the bone cells, as has already been pointed out. However, A recurrent question among thosepersons external radiation has little effect on the bone who work with radioactive materials is, "What cells themselves or on the fibers and salts. In- is the effect of radiation exposureon the life ternal radiation can affect the bone cells be- span?" Unfortunately, a final answer is not

70 available at the present time. In this regard, a with brown eyes. This is truebecause the report that radiologists died at an earlier av- brown eye gene is dominantand the gene for erage age than the generalpopulation has been the blue eye is recessive. discounted because of unsatisfactory evidence. Occasionally a sudden change occursin a The information obtained from numerous gene and it fails toreproduce normally. The experiments performed with laboratoryani- abnormal form is called a mutation.Mutations mals (mostly rats and mice) indicates tliat ex- may be passed on tosubsequent generations. posure to radiation insufficient amount does Mutations, like genes, can be dominantand re- shorten life. These experiments gavepositive cessive. Dominant mutations may bepassed on results whether or not conditions of daily ex- by either parent, with the trait,while recessive posure or of singlewhole body exposure existed. mutations must await a situationwhen both It was pointed out before that theinterpreta- parents carry thetrait.Variations found tion of data from animal experiments mustbe among humans are in partthe result of heredi- made with great caution, insofar as manis tary variations coming from mutationswhich concerned. have occurred in past generations. Asfar as is Careful analysis of allevidence available known, all genes are subject to mutationand, suggests that exposure to permissible occupa- over the population as awhole, mutation is oc- tional dose rates from an early age doesnot curring at a constant although very lowrate. shorten life. Nevertheless, there is not suffi- The production of gene mutations byradia- cient evidence to make an unqualified state- tion has been carefully studied inplants and ment. It is therefore advisable to keep the animals and it has been found that the muta- permissible daily dose for lifetime exposure to tion rate is proportional to theradiation ex- penetrating radiation as low as possible. posure. There has been nosuch study among men (for obvious reasons)bat it is reasonable 7-8The Genetic Effects of Radiation to suppose that the same general patternwould The study of characteristics inherited in the occur.6 reproductive process is known as genetics. Sci- Radiation may also produce chromosome mu- entists have determined that in man and all tations. The reader will recall that chromo- higher animals every individual arises from F!omes are chains of genesand the radiation a single cell formed by thefusion of two germ effect is to break the chain. The chromosome cells, one from each parent. Geneticists have fragments may then recombine in such a man- discovered that such things as type and color ner as to produce translocationsof large groups of hair, eye color, stature, etc., are controlled of genes or other abnormalities, as loss of or by genes. Genes exist in all body cells, but only duplication of body parts. Also, normal chromo- in the germ cells do they play an essential role somes are unlikely to pairproperly with radia- in the reproductive process. The genes occur tion-altered chromosomes and the fertilized egg in pairs, with each pair having the ability of will not divide. In other words an offspring will producing a physical characteristic of the new not be produced. individual. In this regard, the cell division There are two effects on individuals in the re- (meiosis) by which the sperm and ovum are productive ages who receive a dose of radia- produced in the male and female, respectively, tion.6 The first effect is on their immediate results in each sperm and ovum receiving only offspring and the second is on their later de- one-half the number of genes that were present scendants, which is to say on the population as in the parent cell. Genes of the male sperm a whole. Although malformedchildren are couple with the genes of the female ovurii to cause for a great concern to immediaterela- produce the gene pair which determines the tives, it is more appropriate to a discussion particular characteristics of an offspring. Gen- such as this to consider the effect of extensive erally, for gene pairs, one gene will dominate radiation on the population as a whole. As a s Muller. H. .T. "The Manner of Dependence of a Permissible in producing a characteristic, such as eye color. Dose off Radiation on the Amount of Genetic Damage." Acta The combination of a gene for brown eyes from Eathologica, 41:5-20, January 1954. Quimby, Edith H.. and Feitelbert, SergerRadioactive Isotope. one parent with a gene for blue eyes from an- in Medicine and Biology.(Reviaed edition) Philaddphia, Lea and other parent nearly always results in a child giddier, 1968. Pp. 186-187.

71 -

matter of fact, it is quite impossibleto predict ling dose of radiation forhumans is not easy to what would occur toa given unborn individual answer. This is true because man is not because of the many chance a pure factors. In thisre- species like a pure strain of fruitflies or mice gard, it will takeyears to determine the effects or some other species which can tie studied on the children of the Japanese who received under laboratory conditions. Also,the time pe- radiation exposure from theWorld War II riod which elapses fromone human generation bombings. However, because ofknown prob- to another is such thatanswers to questions abilities,itis possible to estimate within must await the passage ofmany years. margins of errortheeffectson atotal Estimates as to what constitutesa doubling population. dose of radiationvary from 25 rads to 150 Roughly two percent of alllive births in the rads. The dose, however, United States have can be delivered at some sort of genetic de- once or in many small portions during there- fects, which are related tomutations. These de- productive period of the individual. fects range from epilepsy,idiocy, and congen- It is recomended thata period of at least six ital malformations, toother organic defects. months should be interposedbetween the time Should every one in the U. S.be subjected once of the radiation of the reproductiveorgans and to a doubling dose ofradiation (the amount the conception ofa child. This period permits which would eventuallycause the complete the formation ofsex cells which contain pro- doubling of gene mutations), the percentage of portionately smaller numbers ofgene mutations live births with defectscould be expected to than exist immediately rise in the first generation after irradiation. In as a result, but could this regard, the fearexpressed in the past (by be expected to return tothe normal equilibrium many reputable persons) that there would be later. However, if eachsucceeding generation a sharp increase in the frequency of of U. S. citizens received abnormali- a doubling dose of ties has not been validated.The childrencon- radiation, ina few generations the number of ceived in Japan after live births with defects the nuclear attacks by would rise to a double irradiated parentsappear normal for the most level, which in this instancewould meansome part. 200 million children born ill a generation with In concluding thisdiscussion, the reader defects.7 This rate ofincrease could theoreti- should be reminded that not cally be continued to all mutn,tions are a point which would have undesirable. In fact, naturallyoccurring muta- veryseriousimplicationsfora given tions are responsible population. for normal evolutionary The question processes. Radiation simply speeds theseproc- as to what represents a doub- esses, increasing the chances of undesirableas 7 Ibid. well as desirable changes.

72 Part III Industrial Radiography

The material in Chapters 8 through12 presents the technologyof the program. Radiographyis not an exact "science." Thetechnician will soon learn that many conditions cannot beaccurately predicted for his calculations. Rules and .approximations are suggestedto be used until the technician gains ability and confidence. Thenhe can proceed to make innova- tions that will improve performance withthe facilities available. The radiographer-trainee is encouraged tostudy the references listed in the bibliography. Chapter 8

Introduction to Radiography*

In 1895, Roentgen experimentedin Germany The three basic essentials in produciug a with cathode rays. He found, as aresult of radiograph are: these experiments, that the vacuumtube he was (1) a source of radiation, usually X-rays using to get cathode rays wasgiving off some or gamma rays kind of new ray. The new typeof ray caused (2) the object to be tested a glow to come from achemically coated paper (3) a cassette containing the film. near by. Furtherstudy showed that the invisible radiation, which he calledX-rays, could body, X-Ray or Gamma Ray penetrate paper, wood, books, the human Source of Radliafion and even pieces of metal. He alsolearned that the radiation could affect photographicplates in about the same way as light andthat the radiation could produce an image onphoto- graphic paper. After Roentgen's discovery, many scientists began studying X-rays. Soon the term radiography was used in reference to taking pictures of objects with X-rays. In 1898, the Curies discovered that radium was radioactive. Theinvisible radiation given off by radium was named gamma rays. No use, however, was made of radium as a source of radiation for radiography until the late 1920's. 8-1The Process of Radiography Radiography is a process of testing materials that uses penetrating radiation such asX-rays or gamma rays.This allows examination of the Cassette or Film interior of objects or assemblies that are Holder opaque to the light.Radiography is called a nondestructive method of testing since objects that are tested are not damaged by the test and Screens may still be used when the testingis completed. In passing through the material, some of the Alm radiation is absorbed or changed. The amount of absorption is dependent upon the thickness }WIRE 8.1.RadiographExposure Arrangement. of the material, the density of the material, The diagram in Figure 8.1 illustrates the main and the atomic number of the absorber. Some features in the making of a radiograph. The kind of detector such as film, a fluorescent X-ray tube or a then be used source of radiation may be an screen, or a Geiger counter may capsule containing a suitable radioisotope such to record the variations in intensity of the the radia- emerging beam as visual images or signals. as cobalt-60. Whatever the source, Industrial radiography is primarily concerned tion proceeds in a straight line from the source with recording images on film. to the object. Some of the rays pass through the object, some are absorbed by the object, and Extracts from Radiography in Modarn /nduatry published with some are scattered in all directionsby the ob- permissionof Radiography MarketsDivision, Eastman Kodak Company, Rochester, N.Y. ject. The amount of radiation reaching the 75 film in the cassette depends upon a number of of the film has an intensifying effect. Lead, factors. Among these are the nature of the upon being excited by radiation, emits elec- material being tested and its thickness. trons. Electrons expose the film just as the X- Suppose the object being tested is a piece of or gamma radiation ; in fact the electrons are steel and it has a gas bubble in the interior. more easily absorbed than the radiation. Also, There is a reduction in thickness of the steel fluorescent intensifying screens are occasionally through the area of the bubble. Therefore, used in X-ray radiography, but ae a rule are more radiation will pass through the section not used with gamma rays. These screens con- containing the bubble than through the sur- sist of a smooth layer of powdered fluorescent rounding metal. A dark 'spot corresponding to chemicals coated on a piece of cardboard or the projected position of the bubble will appear plastic. Such screens may lower the exposure on the film when it is developed. A radiograph needed to produce satisfactory radiographs by .is similar to the negative of a photograph. The a factor of more than 100. darker regions on the radiograph represent the Contrast of radiographs may be reduced by more easily penetrated parts of the object, scatter. Materials not only absorb radiation but while the lighter regions represent the thicker scatter radiation in all directions. Thus the or more dense parts of the object. film receives not only radiation from the primary radiation source, but also scattered ra- 8-2The Radiograph diation from the object being radiographed, the film holder, and the walls and floor of the The processed film containing the visible room. Scattered radiation tends to make blurry images caused by exposure to radiation is called the whole image on a radiograph. Scattering a radiograph. The darkening of the radiograph may be reduced by screens, masks, diaphragms, is referred to as density. This is sometimes re- and filters. ferred to as photographic density to distinguish it from the mass density of the object which 8-3Applications of Radiography was radiographed. Radiography is very useful in inspecting and Differences in density from one area to an- testing products of various kinds. It may be other on a radiograph are termed radiographic used to inspect finished products to determine contrast. The density of an area on a radio- their soundness or fitness and it may be used graph depends upon the amount of radiation to help develop production techniques that will the film emulsion absorbs in that area. The produce products that meet desirable standards. more radiation absorbed, the darker the radio- This method of testing may be used to examine graph. Within limits, the greater the contrast one or two pieces occasionally or it may be used or density differences in a radiograph, the to examine hundreds of pieces in a short period easier details may be seen. Too much overall of time. contrast can actually cause a loss in visibility Welding has become one of the important of some details at the very high and very low processes in the manufacturing of metal prod- density levels. ucts. Due to advances in this field, many high Sharpness of outline in the image on a radio- pressure, high temperature tanks or containers graph is called definition. If the change in are constructed by welding. Such equipment is densities between two areas is a gradual shad- now almostuniversallyexamined byra- ing without a sharply marked line, then there diography and other nondestructive testing is low definition of detail. Contrasts are more methods. Weld radiography is one of the im- difficult to detect in this case. Sharply defined portant applications of industrial radiography. images on a radiograph mean a high definition. One of the first industrial applications of When radiation strikes film, only avery small radiography was the examination of castings. portion of the energy is absorbed. Since the Most metal produced in the world is cast into darkening of the film is due to the absorbed a mold at some point in its processing: The radiation, a large part of the radiationenergy cooling of the liquid metal in the mold may be is lost. One way of using this lost energy is to accompanied by several undesirableeffects. use radiographic screens. These are also called Small pieces of sand from the mold may be- intensifying screens. Lead foilon both sides come trapped in the metal, gas bubbles may be

76 of source inroent- the metal. (b) Emission rate formed, and slag maybe caught in gens percurie per hourat one Also, the shrinkagecharacteristic of most 1 ft. for gamma solid may foot (r/c/hr at metals as they coolfrom a liquid to a at1meter for Many of rays)(r/hr lead to cracks, holes,and even breaks. X-rays) these may not benoticeable on the surfaceof the casting.Radiography may be usedto detect (2) The specimento be examined these flaws. (a) Mass densityof material (atomic Metal may be worked orshaped into desir- number or chemicalcomposition) able forms. Steelis usually forgedat high (b) Thickness orlength of absorp- temperatures becauseit becomes plastic to some tion path degree and is easierto form. Theexpansion or being forged maybe un- (3) The film to beused contraction of metal ability of the film even andthe stresses may causecracks or (a) Grain or the breaks at certainpoints in the metal.Radio- to resolve images (b) Speed andrelative exposure re- graphs will revealinternal defects. desired radio- Nonmetallic materialssuch as plastics, ce- quired to attain wood, textiles, and graphic density raMics, concrete, paper, and interpreta- food products are nowbeing inspected by ra- (c) Film processing diography. Assemblies arebeing inspected. tion working parts may bemade Study of internal principles and prototype stage as*well (4) Geometric during the design (a) Size of sourceof radiation as theproduction stage. (b) Source tofilm distance Other applicationsinclude pipe wallgaging, dimensions and shape radiography, microradiog- (c) Specimen high speed or flash (d) Specimen tofilm distance raphy andstero-radiography. (e) Projectedimages (geometric en- 8-4Industrial Radiography largement anddistortion) The subjects ihcludedin industrial radiog- (f) Calculations raphy are lWed below.The radiographer -these subjects, allof In addition to theseoutlined principles, every should be familiar with must know and prac- which will be morefully treated insucceeding successful radiographer chapters. tice these topics : (1) The source ofradiation techniques (a) The maximum energyof the (1) Radiography radiation in Key or (a) Exposurecalculations source of arrangements Mev, including the energy spec- (b) Exposure (2) Interpretation ofradiographs tral distribution Chapter 9

Elements of IndustrialRadiography*

Sources of Radiation transformer. The higher the temperature of the 9-1 filament, the more electrons it emits.X-ray Industrial radiography makes use of X- and tubes have a focusing cup around the filament gamma radiation. Thistype of radiation is toward the to to help direct the emitted electrons sometimes called "penetrating radiation" target. The small area of the target hit bythe electromag- distinguish it from other types of stream of electrons is called the focal spot. The netic radiation such as light or radio waves. stream of electrons from filament to targetis While X- and gamma radiation are very pene- ismeasuredin radiationis thetubecurrentand trating,theintensityof the milliamperes. changed by its passage through materialsand its The amount of tube currentis controlled by defects in materials. This is the basis for regulating the heating current supplied tothe testing. use in nondestructive filament. A rheostat in the primarycircuit of 9-1.1 Production of X-rays. When high speed control rays," the filament transfo-mer is the usual electrons, which may be called "cathode method. Much of the energy suppliedto the are suddenly slowedby striking matter, X-rays spot Equipment to produce X-rays X-ray tube is changed to heat at the focal are produced. on the target. Infact, in an X-ray tube with must provide a source of electrons, a vacuum 300 kv applied to the target oranode, only path along which the electrons may beaccel- about 3 percent of the electron energyis erated, and a metal target. The X-ray tube sup- the plies these requirements. In addition to the changed to X-rays. The remainder of energy appears in theform of heat. Since the tube, there must be an electrical power source producing give efficiency of the target material in to heat the filament of the tube so it will number, off electrons and a high voltage source to ac- X-rays is proportional to its atomic tungsten is most commonly used. It hasboth a celerate these electrons toward the metal target. high atomic number and a high melting point. Target Electrons (beam current) Some tubes have a metal rod connected to the (focal spot) Focusing Cup target which conducts the heat outside thetube \\. to cooling fins. Other tubes have a hollowanode so that oil or water maybe circulated to remove the heat.Still other tubes have a rotating anode which moves the target material so asto allow cooling. X-ray machines are designed sothat different voltages may be appliedbetween filament and target to fit the differing needswhich may arise. The higher the voltage, the greaterthe X.rays speed of the electrons to the target.High-speed electrons produce X-rays of shorterwavelength and higher penetrating energy thando low- speed electrons. The highest energyX-rays FIGURE 9.1.Diagram of X-ray Tube. emit are determined by the highestvoltage pr3duced in the power transformer. X-ray ma- The filament power source is a lowvoltage chines for low-energy levels may havefrom source which furnishes several amperesof cur- 10,000 to 100,000 volts of tube voltage.The rent. This power source is usually asmall tube wall must be thick to withstand thestress *Extracts from Radiography in Modern Industry published with created by the vacuum and this thick wallwill permission of Radiography Markets Division, Eastman Kodak Company, Rochester, N.Y. absoib the low energy radiation. Special win- 7,7 79 dows are provided to allowthe "soft" X-rays the energy potential applial to the X-ray tube to leave the tube itself. terminals. Kilovolts peak, Kvp, refers to the The 400kv X-ray machine isabout the high- maximum, or peak, energy of the appliedwave est energy machine touse the single section form.) tube. Such a machine produces X-rayswith all Radiation from an X-ray tubemay be con- the wavelengths produced by thelow-voltage sidered to consist of two parts. Theseare re- machines and also X-rays ofa shorter wave- ferred to as the continuous X-ray spectra and length and hence of a higherenergy level. These the characteristic X-ray spectra. Electrons in high voltage machinesare used to generate the beam impinging on the target material and X-rays to penetrate thicker, heaviermaterials. some electrons ejected from the target atoms Other types of X-ray generatorsare used for give up kinetic energy as they strike nuclei of operation at one million volts and higher. target atoms. The loss ofenergy results in Ammeter Filament Trani former X-rays. Since these electrons havea wide range of velocities, the X-rays generatedcover a wide band of wavelengths. The wavelength depends upon the energy given up by the electron. This provides a continuous spectrum of X-raysand is the radiation of mostuse in industrial radiography. Since the velocity of the impinging Autafransformer electrons dependsupon tube voltage, a high tube voltage not only increases the intensityof allthecontinuousradiation but produces X-rays of shorter wavelength thandoes a low r Switch tube voltage.

FIGURE 9.2.Basic X-ray Circuit. Higb The basic X-ray cir uit in Figure 9.2 shows a highly simplified diagram of a self-rectified circuit. Other basic circuits have rectifying tubes to supply the high positive voltage to the 90 anode or target of the X-ray tube. In this cir- to _ cuit it may be seen that thereare meters to measure the filament current and the tube cur- 70 rent. Also, there aremeans of controlling or 60 adjusting the filament current. There isan 50 autotransformer selector switch to choose the high voltage to be applied to the anodeor 40 -- target. This allowsan operator to choose low- 30 energy X-rays or higher energy X-raysas needed. Actual X-ray circuits containmany 20 other types of controls suchas switches, timers, 10 _ protect rs, and contactors. Characteristics of X-radiation. The energy .1 .2 .3 .4 .5 .6 .7 .8 .9 1.0 of radiation is often expressedin terms of Angstroms electron volts. Because this isa very small unit, FIGURE 9.3.Continuous X-raySpectrum at kiloelectron volts (key) andmillion electron Different Tube Voltages. volts (Mev) are the units mostfrequently Some electrons in the beam travelingfrom used. It has been noted thatas the wavelength filament to target strike anddislodge orbital f X-radiation becomes smaller,the energy electrons in atoms of the targetmaterial. The level (also penetrating power) ofthe radiation atom gains inenergy by this action, but the becomes greater. (The radiographerwill find orbital electron issoon replaced and the atom other terms in the literature.Kilovolts, Kv, is emits X-radiation ofa "specific" wavelength 80 characteristic of the element making up the target material. This material isfi equently tungsten. Being of specific wavelengths this X-radiation does not .ipver a band of frequencies. The energy of the characteristic spectrum is small compared to that of the continuous spectrum. Highest Key X-ray Determined by Power

Filters Absorb Looger Wavelength X-rays Which May Be Undesirable For Radiography

Wavelength Increasing

Key Increasing

.1 1.2 1.4 .2 .4 .6 1.o FIGURE 9.5.Continuous X-ray SpectrumShowing Angstroms High and Low Energy Limits. FIGURE 9.4.Characteristic X-ray Spectrum of Tungsten. 9-1.2 Sources of Gamma Rays.Radioisotopes for gamma radiography areavailable from : A broad energy spectrum is sometimesunde- sirable since the low energies are more readily (1) Naturally occurring materials(ra- scattered and absorbed. To overcome this, diunT-226) filters are placed over the tube window. Figure (2) Fission products (cesium-137) 9.5 shows that low energy (long wavelength) (3) Activation by neutronbombardment X-rays are successively eliminated from the (cobalt-60,iridium-192,thulium- beam by addition of filters 1 mm (millimeter), 170, etc.) 2 mm, and 3 mm thick. Beyond 400,000 volts, a different sort of Radium-226 isobtained by refining ores X-ray generator must be used. The single-sec- such as pitchblende andcarnotite. It is com- tion tube described here is not practical be- mercially available as the chemicalcompounds yond this point. The resonance-transformer radium bromide and radium sulphate. unit and the electro-static-belt generator are Paragraph 3-4 and Figure 3.3 provide a commonly used at the one and two million volt brief explanation of how nuclearreactors pro- levels. Beyond these levels linear accelerators duce fission products. Cesium-137is one of the and betatrons have been used to generate X-ra- most abundant radioisotopes inthe fission prod- diation of extremely short wavelengths and ucts. The cesium can be chemicallyseparated high intensity. from the other fission products.Since cesium TABLE 9.1.Characteristics of Gamma Radiography Sources. Specific Activity Isotope Symbol Ha lf-liie Gamma Energies Emissivity Emitted, mev R/C Hr @ 1 ft. C/gram

Radium-226 Ra-226 1,620 Years 2.20 to 0.24, 11 9.0 1 Principle Gammas up to 150 Cobalt-60 Co-60 5.8 Years 1.83 and 1.17 14.4 80 Years 0.66 4.2 up to 22 Iridium-192 Cs-137 up to 500 Cesium-187 Ir-192 75 Days 0.61 to 0.21, 12 5.9 Principle Gammas Thu lium-170 Tm-170 120 Days 0.08 and 0.05 ). Gadolinium-153 Gd-153 240 Days 0.10,0.07, and 0.04 Samarium-145 Sm-145 240 Days 0.06 and 0.04

81 is extremely active chemically in its elemental Item 7, sealing, is most important since re- form, it would be most difficult to handle. For lease of contamination and containment of the this reason cesium-137 sources are available radioactive material are dependent upon the as the compound, cesium chloride. sealing design and fabrication. (Careful leak All other gamma emitting radioisotopes now testing, described later, is required to assure being used for industrial radiography are pro- that the sealing has been properly accomplished duced by neutron activation as described in and continuously maintained.) paragraph3-5. Table9.1listsproperties Early capsule designs used screws, cements, ofgaanmasourcesusefulforindustrial crimping, and soldering techniques which did radiography. not adequately serve the industrial gamma radiography source requirements. An evolution- 9-1.2a Encapsulation of Radioisotopes. In ary process has replaced these with better cap- gamma radiography the energy emitted from sules and seals. While several types of seals decaying nuclei is used as described in Chapter may be proved acceptable, it is certainly true 8. The radiography equipment must be de- that fusion welding, properly done, will pro- signed to permit the gamma rays to escape, duce the desired quality. (Figures 9.6 and 9.7) but it is mandatory that the radioactive chem- Metallic sources of cobalt, iridium, and thu- icals (metals or compounds) be contained and lium are more easily contained than compounds not released into the environment where the of material such as cesium. Several unfortu- chemicals could contact or enter the human nate incidents have occurred with leaking ce- body. This containment isaccomplished by sium sources in industrial operations. For this sealing the radioactive materials in capsules reason the cesium sources are usually "double a process called "encapsulation." Encapsulation encapsulated." This means that the cesium is a highly specialized process requiring the capsule, after farication and leak testing, is most careful (1) design, (2) fabrication, and placed into and sealed in a second capsule (3) quality control to assure integrity of the which is also leak tested. Field experience of entire process. this capsule design has proved so satisfactory Selection of materials and designs for cap- that many sources, including metallic materials, sules must be based upon these criteria : are now made by the double encapsulation (1) Resistance to corrosion of the radio- technique. (Figure 9.8) active material Many source designs have been prepared for (2) Damage to capsule material caused special conditions or equipment. There is no by the emitted radiation doubt that 'others will be produced as equip- (3) Resistance to corrosion from the en- ment and techniques are developed. The radiog- vironment in which the capsule is to rapher should carefully evaluate sealed sources be used with respect to his service requirements and (4) Resistance to high or low temperas. the design criteria listed above. ture regions in which the capsule is to 9-1.2b Leak Testing Sealed Sources. After be used a capsule is sealed, a test is required to de- (5) Resistance to erosion or abrasion termine if the closure is complete. If the seal- (6) Structural stresses including impact, ing is not properly done, the by-product ma- vibration, creep, and fatigue loading terial will escape and contaminate other equip- (7) Sealing technique, e.g., screws, resins ment and the working area. After leak testing, or cements, crimping, soldering, silver the source exterior surfaces must be decon- brazing, shielded arc welding, elec- taminated to the degree thatno more than 0.005 microcuries of removable contamination tron beam welding, cold welding is present. Items 1 through 6 are deemed self-explana- 9-1.2c Characteristics of Gamma Radiography tory with the additional statement that the Sources. Radioisotopes for industrial radiog- wall thickness should be as thin as practical raphy have discrete energies emitted compared designs allow since this will minimize radiation tocontinuous energy spectra produced by absorption by the walls of the capsule. X-ray machines. The thickness of the specimen

82 CAP CAP

Length of Plug Length of Plug to Vary / to Vary With With Amount of Source Amount of Source Material Material 5 mil Metal Gasket

BODY

Dimension A to Vary With Amount of Source Material

0.0635 in.---vo BODY

0.500 in. Sources Source Sheath for Gamma Sources Source Sheath for Low Level DESIGN A DESIGN B

1/16 in. wide x 1/16 in. deep

CAP 0.125 in. (Mild Steel)

Screwdriver Slot

Cobalt Pellet

[0.0.250 in.

BODY 0.397 in. OverallLength (Brass or Aluminum) Before Crimping

DESIGN D

Cobalt Source Sheath DESIGN C

FIGURE9.6.Early Capsule Designs. 83 Capsule Cap penetrate the specimen. With respect to emis-

Fusion Weld sivity thereis some degree ofselectivity. Source manufacturers, upon request, willpro- vide information on the available specific activity, total activity, source dimensions, and capsule designs. Inert Spacer Metallic pellets activated for radiography sources are usually available in the shape of right circular cylinders with 'dimensions as Radioactive shown in Table 9.2. One or more pellets may Material be Sealed in a single capsule to make a gamma

41. Capsule ray, source.

FIGURE 9.7.Fusion Welded Capsule Designs. TABLE 9.2.Metallic Pellet Dimensions.

Dim. C Diameter 'Length 6.6 to 12.5 mm

1 millimeter 1 millimeter 1/26 inch 1/26 inch Outer Plug (Press fit) % inch % inch Type 410 Magnetic 1 centimeter ,1 centimeter Stainless Steel

9-2Geometric Principles Both X-rays and gamma rays obey the laws Dim. B of light. Since a radiograph is a shadow pic- 6.5 to 9.5 mm Outer Container ture of an object placed in a radiation beam, Type 316 Stainless Steel the common geometrical principles related to optics apply; to the making of a radiograph. Major differences include the facts that (1) all objects are more or less transparent to ra- Inner Plug (Press fit) Height Varies with Amount diation and (2) scattering of radiation pre-: of Cs137CI Dim. A Type 316 Stainless Steel sentsproblemsnotfoundinopticsor 23.5 to 40.0 mm ithotography. Inner Container Type 316 Stainless Steel 9-2.1 General Considerations. Since radia- Cs137CI tion beams used in radiography behave much like light beams, they form shadows of objects much as does light. If an object is placed between a source of radiation and a piece of FIGURE 9.8.Double Encapsulation. film, then a shadow will be cast on the piece of film (see Figure 9.9). Notice that the shadow Will determine the energy intensity required for is somewhat enlarged because the object is not penetration and film exposure. Isotopes used in contact with the film andan orthographic for radiography are listed in Table 9.1. projection is obtained. The amount of enlarge- In selecting a radioisotope for a particular ment will depend upon the relative distances of class of work the desired characteristics would the object from the film and from the source be (1) appropriate energy (mev),(2) high of radiation. If the object is lyingon the film, specific activity which would give smallsource there will be little or no enlargement. In fact size and high emissivity, and (3) long half-life. the ratio of the diameter of the object (Do) to Since half-life and mev emittedare physical the diameter of its shadow (Df) is equal to the constants for each isotope, there isno control ratio of the distance from thesource to the ob- by the radiographer. He can only select the ject (do) to the distance from thesource of the isotope having the energy (mev) required to film (d.). intensity of the source of radiation and the time which may be allowed for making the radiograph. 9-2.2 Sharpness of Shadows. The sharpness of a shadow depends upon the size of the source of radiation and upon the ratio of the source to object distance and the object to film distance. If the source of radiation has a definite area then the shadows east by the source are not perfectly sharp. Each point of the source may be considered as casting its own shadow (see Figure 9.10). These shadows overlap and produce a fuzzy image or shadow. No- tice that there is a fairly dark shadow sur- rounded by an ill-defined shadow. The ill-defined part of the total shadow is called the "penumbral" shadow. The penumbral shadow is also referred to as "geometrical unsharp- FIGTJRE9.9.Shadow Formation. ness." If a shadow the same size as the object is In order to minimize geometrical unsharp- desired then(:"..)the object should be placed ness, the specimen being radiographed should close to the film and (2) the source of radiation be as close to the film as possible and the source should be as far from the filmas possible. The of radiation should be as far from the filmas is latter factor, of course, will be governed by the practical (see Figure 9.10).

A I.Sketch A shows a small geometrical unsharpness (penumbra) when the object "0" is close to the film "F." 2. Sketch B shows much larger geometrical unsharpness when the source to film distance is thesame as in sketch A but the object to film distance is greater. 3. In sketch C, the object to film distance is the same as in sketch A but thesource to film distance is larger than in sketch A. The result is a smaller geometrical unsharpness in sketch C.

FIGURE 9.10.Geometrical Unaharpneas, the Penumbral Shadow.

85 The amount of unsharpness or fuzziness in since they will produce radiographs having less a radiograph may be calculated.In Figure geometrical unsharpness. 9.11, note that the triangle whose base is F In practice, tile radiographer controls the (the source size) and whose apex is A is sim- d/t ratio when selecting his exposure technique. ilar to the small triangle whose base is U The specimen thickness may be taken as "t" or and whose apex is A. Also note that d is the object to film distance. A rule of thumb is that altitude of the larger triangle and t is the alti- the d/t ratio should be 8 or more. The larger tude of the smaller triangle. Therefore : theratiothebetterthedefinitionon a radiograph. F d T 9-2.3 Distortion of Shadows. Object images on film may bedistorted for several reasons. or The plane of the object and the plane of the film may not be parallel. The radiation beam F X t may not be directed perpendicularlyto the surface of the film. where fP I I U = the amount of geometrical un- Point Source sharpness d = the source to object distance t = the object to film distance F = the physical size of source of radiation It has been reported that geometrical unsharpness as large as 0.01 inch may be acceptable on radiographs. F, the source size, is beyond the radiographer's control (except on some double focus X-ray machines) after the source is manufactured. Smaller source sizes are desirable

Film

Film in Tilted Plane

FIGURE 9.12.Distortion of Shadows. Also, note that the above distortions would apply to discontinuities in the object to be tested. 11 erefore, some unwise judgment about the size and shape of defects may be made. If the object is not in contact with the film some enlargement will take place. This could also cause some misjudgment about the size of the defect. In thick objects, there will be enlargement of images resulting from discontinuities which are not near the film. 9-2.4 Enlargement. Usually it is desirable to Radiograph Image have the srP.:4men and film as close together as FIGURIC 9.11.Amount of Geometrical Unaharpneu. possible In el.der to cut down geometrical un-

86 Point Source

Specimen

FHm FIGURE 9.13.Shadow FormationShowing Enlargement of Image.

radiation is (1) The radiation sourceshould be as sharpness. When the source of in a ra- very small (afraction of a millimeter) thisis small as possible. Definition extremely small diograph isclosely related to the not too important. With an thesourceof source of radiationthe film may be placed some physicalsizeof distance from the specimen.This will cause an radiation. enlarged image on the filmwithout too much geometric unsharpness. Enlargements upto (2) The distance from the source ofradia- three diameters may revealsmall defects not tion to the film should be as great as noticeable on regular radiographs.Microra- is practical. diography, using extremelysmall sources of radiation, has produced enlargementsof 20 to (3) The film should be as close tothe 30 diameters. specimen as possible. Usually, the cassette or film holder should bein con- Geometric enlargement has the addedadvan- tact with the specimen. tage of decreasing the amountof scattered radiation reaching the film. Theuseful image (4) The center ray of the radiationbeam formed on the film is the result ofthe direct should be perpendicular to the film. beam of radiation. Scattered radiationreduces This will minimize distortion ofthe the sharpness and quality of theimage. be specimen image and of flaws or de- Acceptable geometric enlargement can fects within the image. attained only if the source size is verysmall. of (5) The plane of maximum interest on 9-2.5 Summary. Geometric principles the shadow formation applied toradiography are the specimen should be parallel to the bases for the following : film. 9-3Specimen primary rays. The film receiVes some of this scattered radiation which will cause it to fog. Specimens radiographed in industry vary This serves to reduce the contrast on the film from thin low density plastics to thick high or parts of it and mayresult in a poor image of density metallic sections. Radiation interaction the object being radiographed. with and transmission through the specimen Source of Radiation depend upon the radiation energy(Mev), specimen atomic number, and density. Review of absorption coefficients in Figure 4.7 indi- 1111.M4 1.01111/1-o--- Diaphragm cates that : Sources of Primary Beam Scattered Radiation (1) For a selectedmaterial,radiation penetrates more easily as the energy (Mev) increases. (2) For a selected energy (Mev), the radiation penetrates more easily as Specimen the material density (atomic number) Film and Film decreases. r" Holder Using these coefficients in the absorption equation discussed in paragraph 4-6, it is determined that for a selected energy and subject FIGURE 9.14.Sources of Scattered Radiation. density, the amount of radiation transmitted is dependent upon thesubject thickness and Scattered radiation may come from any ma- atomic number. Thicker sections absorb more terial in the path of the primary radiation. For and therefore transmit less energy. The con- example, the specimen, film holder, floor, walls, verse is true of thin sections. Interrelations of or other objects receiving primary radiation radiation energy, specimen density, and speci- may be a source of scattered radiation. When men thickness are important in determining thick materials are radiographed, more scat- radiography exposure techniques (see Figures tered radiation may reach the film than pri- 11.1 and 11.2 and paragraph 11-2). mary radiation. Unless this scattered radiation These conditions suggest that high energy can be controlled or prevented from reaching radiation should be used to radiograph thick the film, the radiographic image may be of very dense specimens. Alternately, low energy ra- poor quality. diation should be used to radiograph thin low A Source of Radiation density subjects. Radiographic contrast (see paragraph 10-2) is partially dependent upon subject contrast Diaphragm (see paragraph 10-3).

Primary beam As radiation interacts with the specimen $ Bock-waHered there will be long wavelength scattered energy Radiation that may reach the film. This will decrease Specimen /5 S \ overall radiographic contrast. / Film and Film Holder hArffIrrAI 9-4Radiation Scattering

Radiation scattering occurs in radiography Wall with both X-rays and gamma rays. When a beam of either X-rays or gamma rays strikes an object, some of the radiation passes through the object, and some is absorbed by it. Also, \ some rays are scattered randomly as to direc- Floor tion. These scattered rays have longer wave- FIGURE 9.15.Back Scatter From Floor, length and so are less penetrating than the Walls, or Objects.

88 9-4.1 Types of Scatter. Generally, most scat- affects the edges of the specimen image. Such tered radiation reaching the film comes from scatter as this causes the condition known as the specimen being radiographed. This would undercut. be called forward scatter. Scattered radiation When primary radiation reaches objects be- seriously affects the edge of the image on the yond the specimen being radiographed, back- film. The result is an image with hazy or foggy scattered radiation occurs. Such scattered ra- edges. Also, any portion of the film holder that diation may come from the floor, walls, or table extends beyond the specimen may receive pri- top on which the specimen and film holder are mary radiation and so cause scattering which placed. (Figure 9.15)

89 Chapter 10

Radiographic Film*

Radiation Source 10-1Introduction Film is a prime essential for radiography work. While the general make-up of thefilm itself is relatively simple, its behaviorcharacter- istics are much more complicated. The latter are of concern to theradiographer, since the success and quality ofhis work will depend Specimen on his knowledgeand correct use of films Radiograph which are manufactured with manydifferent EA Ea properties. An industrial radiographic film is a thir, Light Intensity 10 Radiograph transparent, flexible plastic base which has Low DensityAreas been coated with gelatin containingmicroscopic Transmit Larger Amounts crystals of silver bromide. Some film have one Iluminator of Light-41 Emitting Diffused side and some have both sides of the base White Light coated with a layer, approximately 0.001inch thick, of this gelatin and crystals. The gelatin and crystal mixture is called an emulsion. This discussion is concerned with what has been termed the "sensitometric characteristics" Is. High Density Areas of radiography film. Said another way, this sec- Transmit Smaikr tion presents the properties of film which de- Amounts of Li9htI2 termine the exposure time required to produce FIGURE 10.1.Film Density. an image of adesired density on the film after chemical processing and the film's ability to Sometimes a high contrast radiograph willhave reveal structural details in the specimen. gradual shading of the gray areas andthe eye The human eye is the actual detector ofthe will not readily observe the image.Knowledge radiography process. The eye observes areasof of terms and characteristics related tofilms is the radiograph depending upon theamount of necessary to understandhow energy passing light passing through dark gray areas(de- through a specimen can be resolved intoimages scribed as having high density) , comparedto that can be "read" by the eye and interpreted the amount of light passing throughlight gray as identifiablediscontinuities in the specimen. Con- areas (low density)(see Figure 10.1) . 10-2Radiographic Contrast trast is a comparison of the light to dark gray A combination of subject contrast and film areas. If the radiographhas a large difference contrast, in density, the radiograph has highcontrast. contrastdeterminesradiographic If the radiograph has small density differences, which is defined as a comparison of densities on the radiograph has low contrast. The eye usu- developed film areas. Usually, finer details can be observed with greater contrasts; however, ally more easily discerns high contrast areas, loss of detail visibility may occur in the ex- but this can depend upon the "radiographimage sharpness," called definition.If the density treme high and low density areas. change is clearly outlined, the radiographhas Radiographic contrast resulting from a given good definition and is readily seen by the eye. set of conditions will depend upon: Extracts from Radiography in Modern Industry published with A. Subject Contrast permissionof Radiography MarketsDivision, Eastman Kodak (1) X-ray kilovoltage or isotope gamma Company, Rochester, N.Y. #/ ray energy 3.5 H and6Curve (2) Scattered radiation B. Film Contrast 3 0 (1) Screen type (2) Film contrast characteristics (3) Film density as determined by : 2 5 (a) Exposure (defined as radiation intensity multiplied by the ex- dB, posure time) -a (b) Chemical processing 2.0 dA, 10-3Subject Contrast Beginning with the fact that the radiation passes through a specimendepending upon the (1) specimen (subject) density, (2) specimen thickness, (3) specimen atomic number,and (4) radiation quality (energy spectrum) , itis 1 0 apparent that different amounts ofradiation dB, will pass through a solid area comparedto a dE, porous area of thespecimen. The ratio of radia- EA I I Ell Ei I I EH tion intensities passing through two selected Log Relative Exposure0 5 1 0 I 5 2 0 portions of a specimen is called subject con- FIGURE 10.2.Film Characteristic Curve. trast. Specimens having uniform thicknessand composition have very low subject contrast. The For convenience, this is expressed asthe base opposite is true if the specimen has large thick- 10 logarillm of E for plotting the H &D curve. ness changes. Film density, more correctly called thefilm Subject contrast varies according to the optical density, is defined mathematically, energy of the radiation andspecimen density thickness and atomic number (see paragraph D = logio 4-6 and Table 4.2).Careful consideration of energy absorption indicates thatsubject con- where trast can be increased by lowering X-ray kilo- D = film density voltage or using Ir-192 instead of Co-60 I = intensity of light incident upon sources, i.e., lowering the gamma rayMev. a film 10 intensity of light transmitted 10-4Film Contrast, H & D Curve through a film Film emulsion can be manufactured to give logo = base 10 logarithm different film contrasts as well as other proper- The eye can more readily interpretlarge ties such as speed and graininess. Radiographic density differences, or contrast. In fact,there sensitivity is dependent upon the ability of is a lower limit of contrast that cannot be ob- film to detect and record varying radiation ex- served by the naked eye. H & D curveshave posures as density changes. Thesedensity contours that increase contrast as the exposure changes, film contrast, are best described by increases and the overall film density increases. the characteristic curve, Figure 10.2, often On referring to Figures 10.1 and 10.2, it can called the H & D curve. This relates film den- be seen that film exposure EA at radiation sity to the logarithm of the radiation exposure. path A is less than the exposure EB at radia- Exposure of a film is defined as the product tion path B. For a low exposure El, the result of the radiation intensity, I, reaching the film is that film density dA1 will be less than film and the radiation exposure time, t. density dB1. The difference in film density E =Ixt dD1 = dB1 dA1. In the low density portion

92 of the H & D curve, i.e., density lessthan 1.0, graph 10-6). Radiation qualityhas very little the low contrast dD1 will probably not bedis- affect upon the shape of the H &D cbrve. cernible by the eye. 10-4.1 Speed. Mathematicallystated, the To improve the radiographic technique,the speed is inversely proportionalto the exposure exposure could beincreased tO E2. It is very required to attain a desired density.This means evident on Figure 10.2 that the densitydiffer- that a high speed (fast) filmrequires a low ence dD2 is greaterthan dD1 and the darker exposure, while a slowspeed film requires a film could be easily read by the human eye. long exposure to reach the samedensity. Generally, the contrast of industrial radiogra- Film speeds, Figure 10.3, areindicated by phy films increases continuously as theoverall the position of H & D curves alongthe log E film density increases. Good industrial radio- axis. The faster films are locatedtoward the graphs should not be exposed for density less left and the slower ones to theright. Radia- than 1.5, and the high density i s limited only tion quality partially determinesthe curve po- by the light intensity of the illminator. sition on the log E axis. Film processing, para- Figure 10.3 shows H & D curves for 3 differ- graph 10-6, affects the curve's position. ent films. Each has a different speed and a 10-4.2 Graininess. Film images are formed somewhat different film contrast. Higher speed by multitudes of microscopic silvercrystals, films are the curves toward the left on the log called grains. Groups of grains arevisible to E axis. Speed is defined as the relative ex- theeye,producinganoverallcondition posure required to attain adesired density. described as graininess. All filmshave this Film contrast is determined by the shape of condition.Some havelargegrains(high the H & D curve. graininess) and some have fine grains(low graininess). 3.9 Graininess is somewhat related to radiation 3 6 energy, although the relationis not clearly defined. It is also directly related to the degree 3.3 of development (longer developing timein- 3.0 creases graininess) , which inturn is governed by time, temperature, and the degree of exhaus- 2 7 tion of the developer. 2 4 Graininess is affected by screen type. Fluo-

E rescent screens increase grain size as energy 2.1 ii. increases. This condition prevents use of fluo-

cn u. foil 1.8 rescent screens at high energies. Lead en E LE screens have a very slighteffect on graininess In u 1.5 E 0. .2 In at any X- or gamma ray energies. Forthis 3 reason they are superior tofluorescent screens at higher energies. 0.9 Graininess is one of the factors which de- A termines the detail that can be perceived on a 0.6 pr film. A relative comparison can be made by 0.3 visualizing photographs in a newspaper compared to a slick paper magazine. The news-

0 0 3 0.6 0.91.2 1.51.8 2.1 2.4 2.7 3.0 paper photo is composed of large dots,widely LOG RELATIVE EXPOSURE spaced, and there is poor resolution of detail. FIGURE 10.3.--Relative Film Speed. This is comparable to high graininess film. In slick paper magazines, photos are composed of The shape of the H & D curve and its posi- small dots, closely spaced, and there is good tion along the log E axis, depend, primarily, detail resolution. This is comparable to low upon its design and manufacture.However, the graininess film. Desirable fine resolution sug- curve's position along the log E axis depends, gests that low graininess film should be used to some degree, upon developing (see para- for determining small specimen discontinuities. 93 10-4.3 Film Contrast, Speed, and Graininess. to improve quality. In radiography with gam- In non-destructive testing, the radiograph must ma rays the front lead foil needbe only 0.004 be of acceptable quality to resolve the specimen to 0.006 inch thick, a thickness insufficientto discontinuities which are likely to prevent the seriously absorb the primary radiation beam. specimen from performing its desired service. The back screen should be somewhat thicker Film contrast, speed, and graininess are inter- toreduceback-scatteredradiation.Such related so the radiographer must select films screens should be selected withextreme care. that can develop the desired contrast and image Although commercially pure lead is satisfac- sharpness, which depend upon graininess. Of tory, an alloy of 6 percent antimony and 94 course, it is desirable to make the exposurein percent lead is harder and stiffer and has bet- the shortest time. ter resistance to wear and abrasion. Tin coated Unfortunately, the fast films do not have the lead should be avoided under all circumstances, better contrast and graininess properties. Gen- since irregularities in the tin cause a variation erally, fast films have large grain and poor in the intensifying factor of the screen. Minor resolution, while slow films have fine grain and blemishes do not affect the screen appreciably good resolution. Practical aspects of these con- but large blisters or cavities do. trasting properties will be discussed in Chap- The intensifying action of a lead foil screen ter 11. iscaused by theelectronsemitted under gamma-ray (or X-ray)excitation. This ex- 10-5Radiographic Screens plains why the surfaces of screens must be Researchers made the discovery many years kept free of grease and lint, as they will pro- ago that when an X-ray or gamma-ray beam duce light marks on the radiograph because of strikes a film, it is seldom that more than 1 their high electron absorption. Grease and lint percent of the energy is absorbed. This high may be removed from lead foil screens with a loss of available energy presented a problem solvent, such as carbon tetrachloride, or may because the formation of a radiographic image be gently rubbed with a high grade of steel is primarily governed by absorbed radiation. wool. The shallow scratches left by the steel After experimentation with various methods wool will not produce dark lines on the photo- of more fully utilizing the energy wasted in the graph as deeper lines and other cuts and nicks radiography process, two types of radiographic will. Screens freshly cleaned with an abrasive screenslead foil and fluorescentwere de- should not be used for 24 hours, except when veloped. These screens were designed so as to they will be in contact with film for very short improve radiographic techniques without un- time intervals. This caution is necessary be- duly complicating the radiography process, cause the fogging action is increased by the The primary function of a radiographic screen cleaning process. is to intensify the photographic action of radia- In radiography with gamma rays,films tion on the film and thus to reduce time and other loaded in metal cassettes not equipped with exposure factors. Lead foil screens perform screens may record the effects of secondary additional functions of reducing the effect of electrons generated in the lead covered back scattered radiation, including back scatter, as of the cassette. These electrons produce a mot- well. Fluorescent and lead screens are described tled effect on the film, due to the structure of in some detail below. the intervening felt pad. Films loaded in lead- 10-5.1 Lead Foil Screens. The advantages of backed cardboard exposure holders may also lead screens are such that they are essential record the pattern of the paper separating the in practically all radiography with gamma rays lead and the film. These and similar effects may and some radiography with X-rays. Their func- be avoided with the use of lead foil screens on tion of removing scattered radiation is equally both sides of the film, as described previously. as important as their intensifying action. The When, for any reason, screens are not avail- latter reason is why they are recommended able, the film should be encased in a lightproof for use even in some cases (for X-ray) where paper or cardboard holder, without any metal they exhibit no intensifying action. backing. Lead foil screens are commonly used on both One iMportant caution must always be ob- sides of the film in industrial radiography so as served in the use of lead foil screens. This is

94 a careful checkto see that good contact is The exposure of film to ionizingradiations maintained between the film and screen.Other- creates a chemical change which can bemade wise, fuzzy images will result. visible through processing. In simpleterms, 10-5.2FluorescentScreens.Fluorescent the processing is designed to changechemically screens are made bymixing finely powdered the silver bromide on the film, sothat the chemicals, which have the ability toabsorb X- "radiation shadow" cast by radiationpassing rays and gamma rays andemit light(fluo- through the specimen radiographed canbe resce), with a suitable binder andcoating a seen. There are fivedistinct steps in the proc- special cardboard or plastic sheet with athin, essing of film: developing, stop bath, fixation, smooth glaze of the mixture. Films areclamped washing and drying. Each one is discussedin firmly between a pair of these screensduring some detail here, as eachwill become part of exposure. The photographiceffect is intensified the radiographer's routine work. because it is the sum of the effects of the source Certain general precautions apply tofilm radiation and of the light emitted bythe processing as follows :(1) For consistent re- screens. sults, it is necessary to maintain withinspeci- Industrial radiographers seldom usefluores- fied limits all chemical concentrations,solu- cent screens, since they are not employedwith tion temperatures, and processingtime. (2) high energy as a rule. The reason is thatthey Scrupulous cleanliness is necessary toavoid tend to give excessive graininess to theimage. streaks and spots on radiographs. (3)Tanks, They may be used on occasion in the radiogra- trays, stirring paddles, etc., should bemade phy of light metals or when economy demands from materials which resist attack bythe shorter exposure time, which their use allows. processing chemicals. Acceptable materials are Normally, fluorescent screens emit a blue type 316 stainless steel, hard rubber, glass, light when energized by radiation. They are and ceramics. Aluminum, zinc, copper, andtin used with film which has a high sensitivity to must not be used since these metalscontami- blue light. They are usually mounted in pairs nate the processing solutions and fog radio- in cassettes so that the fluorescent surface of graphs.(4)Suitable darkrooms should be each screen is in direct contact with the emul- equipped with subdued lights and filters which sion surface of the film. Poor contact results will not cause excessive "fog" on films. in blurred images. Protective surfaces, such as thin sheets of cellulose, should never be placed 10-6.2 Developing. Developing solutions have on screens. the ability to reduce the silver bromide crystals Care must be used in the mounting and stor- on the exposed part of films tometallic silver. age of fluorescent screens. The formeris such At the moment the exposed film is put into the a critical process that it isusually done by developer, the above process begins, and the commercial concerns. If screens are mounted longer the film is left in the developer, the more on the job, great care must betaken to avoid silver bromide is transformed and the denser unevenness resulting from adhesives, etc.Dust the image becomes. Rate of development is also and dirt particles must not be allowed to col- affected by temperature, with reaction increas- lect between the film and screen surfaces and ing as temperature increases. screens must be kept free from stains. The The radiographer will normally use com- sensitive surfaces of screens should never be mercially prepared developers in film process- touched. No cleaning should be attempted with- ing. These come in powder or liquid form, out consulting manufacturers' directions. which are dissolved in or diluted with water. Though more expensive, liquid developers are 10-6Film Processing usually easier to prepare, a fact which may 10-6.1 Introduction. Radiographic procedure be of importance in some laboratories. is only partially completed once the exposure The time-temperature system should be used has been made. The chemical processing of the in the processing of all radiographic film. Fol- film used for the exposure is an important and lowing this system, the developer is always exacting task. Improper processing may make kept within a certain narrow range of tem- it impossible to read film and render useless the perature, and the time of development is ad- most careful radiographic exposure work. justed so that the degree of development varies 95 slightly, at the most. The conti ast and density of development. The reason for this procedure normal y desired inindustrial radiography is that the reaction products of development films can usually be obtained with 5 to 8 min- have a higher specific gravity than the de- utes in a developing solution having a tem- veloper and thus flow downward, retarding perature of 68°F. or 20°C. Longer developing the development of the areas over which they time 's likely to produce chemical fog which pass. The correct procedure is to lowerthe film will decrease contrast. hangers carefully into the developing solution,

4.0 then tap the hanger bars (in tanks) to free air bubbles clinging to the emulsion. Sufficient agitation will result if the films are shaken 3.5 10 8 vertically and horizontally and moved from side to side in the solution for a few seconds 3.0 every minute of the development time. The second procedure which must be observed is the replenishment of developer solu- 2.5 tions. In the course of use a developer loses its chemical strength. This happens because of 2.0 the exhaustion of the developing agent in the process of changing silver bromide to metallic

14, 1.5 silver and because of the restraining effect of the accumulated reaction products of the development. Developer solutions should be tested 1.0 for activity at periodic intervals determined by use.

0.5 The easiest test for developer activity is to process film exposed in some standardized manner, and then to compare the density obtained

0 0.5 1 0 1.5 2.0 2 5 3.0 with that obtained in a film developed in a

LOG RELATIVE EXPOSURE fresh solution. For such a test, time and other exposure factors should remain identical. FIGURE 10.4.Effeet of Developing Time. The quantity of replenisher required can be Temperatures for developing solutions should determined by thesolutionmanufacturer's be checked immediately before the immersion directions. of films. Temperatures below 68°F. will retard 10-6.3 Stop Bath (Arresting Development). the action of the chemicals sufficiently to pro- Once the development process has been com- duce underdevelopment, while excessively high pleted, it is necessary to stop the activity of temperatures can fog the film or soften the the developer remaining in the film emulsion. emulsion on the film so that it will wrinkle This activity not only may result in uneven or wash off. development, but the alkali of the solution re- It is never an acceptable practice to use guess tained by the gelatin will neutralize some of work in developing film. For this reason, sight the acid in the fixer solution and shorten both development, the examination of film to deter- its effectiveness and life. The activity of the mine degree of development under safe light developer is arrested by an acid stop bath solu- conditions, is not recommended. Sight develop- tion. A stop bath may be made of 16 oz. of 28 ment may result in fogging because of exces- percent acetic acid mixed with enough water sive exposure to the safe light. With reliable to produce a gallon of solution. Stop baths can timingequipmentandthermometers,one also be made by mixing 41/2 oz. of glacial acetic should have no difficulty in developing. acid per gallon of bath. When glacial acetic Two relatively simple procedures, in addition acid is used, great care should be taken because to time and temperature control, complete good of the possibility of severe burns to the face development technique. First, it is necessary to and hands. The acid should be added slowly to agitate the film in order to secure uniformitythe water (never the water to the acid) while

96 Fixer solutions becomeexhausted through an stirring constantly. salts and by di-. The proper stoppingprocedure is to remove accumulation of soluble silver allow it to drain lution with rinse water orstop bath carried the film from the developer, to restore the solu- a few seconds(but not into the developer by the film. It is necessary the stop bath. tion at periodic intervalsdetermined by the tank), and then immerse it in fixation. Other- Care should be taken to preventthe developer interval necessary to produce into the stop bath. wise, abnormal swelling ofthe emulsion will from draining off the film be unduly pro- (One way to prolong the life ofthe stop bath result and drying time will is to briefly rinse thefilm in running water longed. The fixing solution maybe maintained prior to inserting it into thebath.) The film at a high state of activitythrough the simple for 30 to 60 process of addingsuitable quantities of its should be immersed in the bath of thumb is to seconds with moderate agitation.A stop bath component chemicals. A rule 70° F. should be replenish the solution when fifty14- by 17-inch temperature of 65° F. to fixed in 5 gal- maintained. films (or equivalent) have been If, for some reason, a stopbath cannot be lons of solution. At this time32 ounces of the used, the film should berinsed in running solution should be removed andreplaced with fixing chemicals, for 1 quart of undiluted fixingliquid, including water, free from silver or replenishments are at least 2 minutes. Moderateagitation is desir- hardener. Only two such the rinse tank recommended for best results.(Refer to the able if the flow of water in for replen- is not strong. solution manufacturer's instructions Five gallons of stop bath will treatapproxi- ishment recommendations.) 17-inch films (or 10-6.5 Washing. The next stepin film proc- mately one hundred 14- by running water equivalent).The use of exhaustedsolutions essing is thorough washing in will lower the quality of theradiograph. so that the fixerwill be diffused from the film. 10-6.4. Fixation. The developerdoes not Radiographic films should be washedin such change the unexposed silverbromide on the a way that theentire emulsion area willreceive film, which means that theunexposed silver frequent water changes. This canbe accom- bromide remains in the emulsionand will plished by completely covering thefilm hangers darken upon exposure to light.To prevent and maintaining the houily flowof water from this and the consequent ruining ofthe radio- 4 to 8 times the volume of thetank. graph, a "fixer solution" is usedwhich re- Washing tanks should be largeenough to moves the unexposedsilver bromide without handle the flow of films fromdeveloping and changing the silver deposits which composethe fixing solution. Films fresh fromfixing solu- desired image. The fixer solution also,hardens tions should ,e placed near theoutlet end of the gelatin on the film so thatit will stand wash tanks and gradually movedto the inlet drying with warm air. Such solutions areob- end as additional films are broughtin for wash- tained from commercial suppliers. ing. In this manner, the final partof the wash- The fixing time for film should be atleast ing process is done in freshuncontaminated twice the time it takes to clear theundeveloped water. silwz halide from the film (the clearingtime). Washing efficiency is closely related towater In a relatively fresh bath, fixing time isin the temperature with temperatures below60°F. neighborhood of 8 minutes. Longer intervals being very inefficient. Whenever possibletem- are needed as the bathis used. When times in peratures between 65°F. and 70°F.should be excess of 15 minutes arerequired, fixer solu- maintained. As soon as washing is completed, tions should be replenished to save timeand usually from 20 to 30 minutes, the filmshould maintain an adequate hardening action. be removed from the tank, asgelatin has a Films should be agitated vigorously when tendency to soften with prolongedwashing in first placed in the fixing solution. Thereafter, water above 68°F. agitation at two-minute intervals is advisable. 10-6.6 Drying. After washing, films must be Temperatures from 65°F. to 70°F, should be carefully dried. This is a relativelysimple maintained in the bath, with care exercised step, although caution must be used to remove to prevent warming in excess of 75°F. the small drops of water clinging to thesurface 97 of the emulsion. The latter cause distortionof essing rooms and/or operations intothree the gelatin and consequent changes inthe den- zones of light intensity :(1) the brightest can sity of the silver image. The best procedureis be normal white light forwashing and drying to immerse the washed film in a wettingagent film ; (2) the intermediate safelylighted space (obtainable commercially) for 1 or 2 minutes for developing and fixing film; and(3) the and then allow them to drain for anadditional dimmest safely lighted space for theloading 1 or 2 minutes. Wetting agents causesurplus bench. White light may be usedfor certain water to drain off the ffim more evenly, pre- activities, such as mixing chemicals,cleaning venting or greatly reducing water spots. tools, and unloading processing hangers. Radiographs dry best in warm, dry air that The "safeness" of a lamp depends onusing is constantly changing. Drying cabinets which bulbs of the correct wattage, with the proper circulate filtered and heated air give best re- filter, located at the proper distance fromthe &INS. If these are not available, the films, on film. A thorough study should bemade to their hangers, should be hung in a position apsure safe light conditions areestablished and where air freely circulates to dry uniformly maintained. A simple method of checkingillu- both sides simultaneously. mination is to expose to the safelight a partially protected sample of the fastest filmwhich 10-7Film Processing Facilities is to be used in the processing room. After a All radiography operations include film proo. time lapse equal to the maximum time needed essing facilities. For this reason the radiogra- for handling film, the test film should be run pher must know something about the room and through the standard processing procedure and equipment which, should be included in such a checked for greater density on the unpro- facility. The purpose of this brief discussion tected area. If the film shows no density in- is to describe the darkrooms and equipment crease, the light is safe. which have proved satisfactory for industrial The wall and floor covering of darkroomsis installations. Readers desiring more detailed more or less critical to the filmprocessing op- information should refer to the specialized ma- eration. Maximum reflectance of safelight is terials published on the subject, including the achieved with a cream or buff semi-gloss paint brochures of the various manufacturers of film on walls where chemicals are notlikely to be processing equipment. spattered. Walls near processing tanks should The location, design, and construction of a be covered with ceramic tile (free from radio- film processing facility will, of course, depend activematerials), structuralglasssheets, on the volume and character of the workwhich stainless steel, or certain plastics, to prevent has to be done. Such facilities may range from chemical attack and staining. Floors must be a single room to a series of rooms,individually resistant to chemical attack, as well as water- designed for each of the activities which have proof and slip-proof. Porcelain and natural clay to be performed such as loading, developing, tile or asphalt tile of darker colors are satis- drying, etc. Smooth, efficient operation and factory. Linoleum and the plastic cand rubber easy accessibility should be kept in mind when tiles stain or pit when processing chemicals are planning darkrooms. Estimates of the number dropped on them. and type of film to be processed daily at peak Darkroom entrances must be designed to operation should serve as a guide for the size accommodate the number of people who must of the room or rooms and equipment. It is just use the room and to utilize properly the amount as important not to overbuild and waste space of floor space available. A single door equipped as it is to build a large enough facility to pre- with an inside lock is, of course, most eco- vent crowding. nomical of space. However, when more than 10-7.1 The Darkroom. The first concern in one person is involved in film processing, it planning the construction of a film processing may not be practical. Two alternatives are pos- facility is the darkroom. Since excessive ex- sible : the light lock, made of double or revolv- posure of film to light will result in fog, great ing doors ; and the labyrinth or maze, which care must be exercised in the location and ar- effectively blocks outside light. rangement of lights. It is best to divide proc- 10-7.2 Equipment. Four major items of

98 equipment are standard in all filmprocessing Plumbing for processing tanks isalso a prob- cabi- lem because of corrosion.Drainage lines may facilities ; The loading bench, film storage waste solutions nets and bins, processing tanksand film dryers. be of galvanized steel when The so-called "dry" activities, such asthe han- do not remain in the pipes.One additional circum- dling of unprocessed film, loadingand unload- caution must be observed. Under no holders, and the stance should two metals subject toelectrolytic ing of cassettes and exposure connection. A com- loading of processing hangers areall done at action be used to make a the loading bench. Loading benchesshould be mon problem ofthis type occurs when galva, processing nized steel fittings are attached to copperpipes. located at some distance from the tech- tanks to avoid water and chemicals.The load- 10-7.3 Film Dryers. The recommended ing bench area willalso normally contain nique for film drying has beendiscussed else- facilities for storing processing hangersand a where. However, the location anddesign of light tight film storage bin. the dryer itself is one of themost important processing The "wet" operations (developing,stopping, considerations in planning a film fixing, and washing) are accomplishedin the facility. Several types of dryers areavailable, processing tanks. It is mandatory thattanks including hot air, infrared, and desiccanttypes. be constructed of material resistant toradio- Whichever model is chosen, it shouldbe fast- graphic chemical corrosion. (Most tanks are acting; at the same time it shouldnot overheat made of AISI Type 316 stainless steelwith 2 or the films. It is advisable, as aprecautionary 3 percent molybdenum and have beenfabricated measure, to use afilter on the air intake of in weld dryers, although this may require afan of in such a way as to avoid corrosion under areas.) large capacity. Removable drip pans The insert tank capacity is criticalbecause each film compartment are anaid to keeping it determines the maximum volumeof work the dryer clean. which can be done. A five-gallon developer tank can handle approximately 40radiography 10-7.4 Automatic FilmProcessing Equip- films an hour, at normal developing times.The ment. In large scale operationsit may be desir- stop bath tank should be the same size as the able to install automatic filmprocessing equip- developer tank, but the fivIr tank should be at ment. These automatic machines savetime and least twice as large and the washing tank four labor, and produce a very high degreeof film times as large. uniformity.

99 Chapter 11

RadiographyTechniques* Proper selection of equipment,safelights, and 11-1Introduction a darkroomarrangement as describedin para- The very large numberof, variables in the graph 10-7 will minimizefilm handling diffi- radiographic processrequires that well or- culties. Several manufacturers(see Appendix ganized techniques beprepared to interrelate E) prepare and/or supplydarkroom supplies conditions that can becontrolled by the radiog- and chemicals. To attainconsistent results, the rapher. Guess work andtrial and error meth- radiographer should select one groupof chem- ods are too costly andtime consuming for in- icals, (1) developer withreplenisher, (2) stop- dustrial operations.Background information bath, and (3) fixer withreplenisher, and then related to these variableshas been presented explicitly follow the manufacturer'sdirections in the preceding chapters on anelementary but for mixing, replenishing,film processing, and rather basic level. Suchinformation is neces- discarding depleted solutions.Any deviation sary for ageneral understanding ofradiog- can causetrouble. SCRUPULOUSCLEANLI- raphy. NESS is required in thedarkrooni to make The purpose of the followingsections is to good radiographs. present in.formation andtechniques that have 11-2,2 nms. Films are selectedaccording been proven useful andpractical in industry. to their speed andgraininess. If the shortest Use of these methods willenable a radiogra- exposure time isrequired, use high speed film. pher to attain reasonablygood results with These films have coarse grain andwill not give very littleexperience. A technicianhaving a the best subject detailresolution. If the best good knowledge andunderstanding of this ma- resolutionis required, the finegrain films terial can devise his ownshop practices when should be selected and the muchlonger expo- new specimens areto be tested. Improving sure time must beaccepted. Contrast varies practices and developing newtechniques to with film type and overallfilm density. Good secure high qualityradiographs depend both practice indicates the minimumoverall density on anunderstanding of generalprinciples of should be not less than 1.5,and darker films radiography and experience inthe shop and are desirableif the viewing equipmenthas laboratory. sufficient light intensity. of ra- 11-2Exposure Calculations "Relative film speeds" are statements diation dosage required to expose afilm to a More than 15 variables can beidentiled other film which must be controlled eachtime a radio- specified density compared to some with all of accepted as a standard. Table11.1 contains graph is made. Making calculations contrasts these variables is almost amathematical im- relative film speeds and comparative possibility and is certainly notpractical. As a of films used by industry. result of work by many laboratoryand industrial experimenters, it has been proven ac- TABLE 11.1.Relative Film Factor. ceptable for shop radiography that manyof the conditions can be established and held con- Density stant. Others can be selected fromtables and mathematically graphs. These can then be Film Type 1.5 2.0 2.5 8.0 related to the remaining variables.The following are some of the variables that maybe fixed, High Speed 0.8 1.3 2.1 2.4 graphed, or tabulated. (Coarse Grain) Medium Speed 3.6 5.1 5.6 15.0 11-2.1ChemicalsandFilmProcessing. (Medium Grain) Low Speed 15.0 21.0 27.0 84.0 Extracts from Radiography in Modern Industrypublished with (Fine Grain) permissionof Radiography MarketsDivision, Eastman Kodak Company, Rochester, N.Y. /od /1o1 11-2.3 Screens. In paragraph 10-5,the specimen shape, and (3) source dimensions as action of screens was discussed. One screen shown in Figure 9.11. It has been stated that should contact the film surface nearest the geometric unsharpness up to 0.010 is accept- source (front screen) , and one screenshould able. contact the other film surface (back screen) . Every source has physical dimensions which Fluorescent screens are acceptable under some will cast an undesirable penumbral shadow. conditions. At higher energies they may cause When the X-ray machine or gamma ray source undesirable graininess and lead-foil screens has been selected and delivered, the radiogra- are generally used. Up to approximately1 pher has no way to change source size. Gamma Mev, the front screen may be 0.005 inch lead- sources vary from 1/16 inch diameter to1 foil and the back screen may be 0.010 inch centimeter diameter. X-ray target dimensions lead-foil. vary from 8 millimeters square down to a frac- 11-2.4 Geonetry. Geometrical var,ables are tion of a millimeter. Target size and "permis- summarized in paragraph 9-2.5 and must be sible tube load" are interrelated. Both may be considered if acceptable detail resolution is to related to source costs ; therefore, the radiogra- be obtained. pher must carefully select equipment before Arrangement of the position of the radiation making purchases. source, specimen, and film willdetermirie the Specimen thickness and shapes will affect geometricunsharpness.Through judgment radiograph quality. If the specimen is long and experience, the radiographer must develop compared to the source to film distance, the a "feel" for the "geometry" of his techniques. extremities of the specimen will be under- Geometrical unsharpness is directly related to exposed because of the inverse square law and the (1) "source to specimen" distance,(2) the longer absorption path at the extremities.

Source

f = 2 X Wal I Thickness 8 X Specimen Thic.kness

Specimen Specimen Thickness Thickness

Film

For geometric unsharpness control, use source to film distance equal to or 3reaterthan 8 times the specimen thickness. (2) For calculating exposure time, use the length of radiation path "t." FIGURE 11.1.Source to Film Distance.

102 Two widely used rules for guides in arrang- Table 11.2 gives the steel equivalentthick- ing geometry of techniques are : ness of metalsfrequently used in industry. cal- (1) Thesourcetospecimendistance These values are acceptable for exposure should be no less than 8 times the culations using radioisotopes. specimen thickness. If the specimen TABLE 11.2.Steel Equivalent Thicknessof Metals is a pipe or irregular shape, this (for gamma rays only). thickness is defined as shown in Figure 11.1. Smaller ratios than 8 will cause Steel Equivalent undesirable distortion. Metal Density Thickness (2) The source to film distance should lbs. per cu. ft. (S.E.T.) never be less than the diagonallength Magnesium 108 4.64 of the radiograph. Beryllium 115 4.27 168 2.93 Diagonal length of Aluminum radiograph Iron (Steel) 492 1 Copper 557 0.884

11-2.6 Radiation Energy VersusSpecimen Specimen Thickness. The atomic number andthickness radiation energy Film of the specimen determine the (key or Mev) that must be used topenetrate A the subject and expose the film. Table11.3 for I.Path length B is longer than A, causing less radiation fc reachthe film at P. fhe film af B. give 2.The distance 5 to A is less than S to I, causing less radiation fo reach X-rays and Table 11.4 for gamma rays FIGURE 11.2.Source to Film Distance for information that has been proven useful. With- Long Specimens. in these ranges, 2 percent sensitivity(see paragraph 12-3)can be obtained.Outside 11-2.5 SpecimenSteel Equivalent Thickness. these ranges the sensitivity may not be as X-ray and gamma ray energy production were good as 2 percent but the radiograph maybe discussed in paragraphs 9-1 and 9-2. Their in- satisfactory, depending upon the specimen and teraction with matter was discussed in para- acceptable discontinuities. graphs 4-3, 4-5, and 4-6. In the energy range used for industrial gamma radiography, the TABLE 11.3.X-ray Energies and Applications gamma radiation interactionwith matter is (a guide for inexperienced radiographers only). somewhat related to subject density.Fill' this reason tables and graphs canbe simplified by Maximum Tube Voltage, KvpSteel Equivalent Thickness, Inches expressing metal thickness in terms of"steel equivalent thickness" (S.E.T.). As an example, 150 Up to11/4 250 Up toa the density of aluminum is 168 lbs. per cu.ft., 400 Upto 4 while the density of steel is 492 lbs. per cu.ft. 1,000 Upto6 2,000 Upto Therefore, the steel equivalent thickness of 24,000 Upto20 aluminum is: S.E.T. (Aluminum) = Density of Aluminum Density of Steel TABLE 11.4.--Radioisotopes and Applications. 168 492 Steel Equivalent Thickness, =.0.34 inch of steel Inches

radiation absorption Isotope Mev Minimum Maximum approximately equivalent to one inch of Co-60 1.17 and 1.88 1% Cs-187 0.66 8% aluminum (for the Ir-192 .4 Avg. a energy range most Tm-170 Gd-158 often used for isotope Sm-145 radiography) 103 EXPOSURE CALCULATION DATA for Co.-60, Cs-I37, and 1r-192 FAD 2 using equation: T where:

T =exposure time (minutes) F =film factor (from table) A =absorber factor (from curve) D =source to film distance (inches) S =source activity (millicuries)

Additional requirements Table of Film Factor"P' C -nsity Film Type 1) Lead intensifying screens to be used 1.5 2.0 2.5 3.0 0.005" front 0.010" back 2) Development 8 minutes at 68°F. 0.8 1.3 2.1 2.4 3) Emission values for determining High Speed source activity: (Coarse Grain) Co-60-- 14.4 mr/mc hr at 1ft. Medium Speed 3.6 5.1 6.6 15.0 Cs-137-4.2 mr/mc hr at 1ft. (Medium Grain) Ir-192-5.9 mr/mc hr at 1ft. Slow Speed 15.0 21.0 27.0 34.0 (Fine Grain)

500 400

300

200

100 90 80 70 60 50 40 Co,b°

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Steel Equivalent Thickness (inches)

FIGURE11.8.Gamma Ray Exposure Technique.

104 Darkening of the select an isotope appropriatefor that 11-2.7 Source Emissivity. thickness. Determine the sourceactiv- film is determined by the exposuretime multi- radiation reaching the ity, in millicuries, fromthat isotope's plied by the amount of calibration curve. film. It is obvious that theamount of radiation reaching the film must berelated to the radia- (2) Measure the longestdimension of the tion emitted from the source.For radiography specimen to be radiographed.Deter- isotopes, Table 9.1 givesthe emissivity ex- mine the source to filmdistance ac- pressed in the unitsroentgens per curie(or cording to paragraph11-2.4. milliroentgens per millicurie)hour at the unit (3) Select the film typeto the resolution distance of one foot. Every sourcehas its own required. From the table onFigure emissivity which is a constant.The total energy 11.3, select the film factor"F" in the emitted by any given sourceis determined by desired density column. multiplying its emissivitytimes the number of (4) From Figure 11.3,determine the ab- curies in the source. Atypical radiography sorber factor "A" by : source wouldcontain 30 curies of Ir-92hav- the sheet r/hr @ 1 ft. This must, (a) entering the bottom of ing emissivity of 177 at the appropriateS.E.T. value in some way, be includedin exposure calcula- paragraph 11-2.8 show (b) vertically followthat S.E.T. line tions. Figure 11.3 and selec;ed isotope that emissivity is accountedfor in the equation to intersect the by expressing the sourceactivity in millicuries. line For many reasons the endssionrates from (c) from that intersection,follow a X-ray machines cannot be aseasily stated as horizontal line across to theleft for radioisotopes. Energyemission rates from margin industrial X-ray machines be quite high, (d) where that horizontalline reaches requiring very carefultechniques to prevent the margin, read the valueof the personnel overexposure. Forexample, an X-ray absorber factor. machine operating at 300 Key and10 ma could (5) Calculate the exposuretime, "T," in emit 140 roentgens perminute at 0.5 meter. minutes, by substitutingnumerical (These are the units used mostoften in con- values into the equationshown on nection with X-rays.) In units usedwith iso- Figure 11.3, T = FAD2 S. topes, this would be anemissivity of 22,890 r/hr @ 1 ft., equivalent to the energyemitted Example : the specimen shownin Figure 11.4 from 3,880 curies of Ir-192. is to be radiographed.Selections of In exposure calculations forX-ray machines, technique details willfollow those a simplification isto express the energy emitted outlined in paragraph 11-2.8. in terms of milliampere-minutes(ma-min.). This means the tube current inmilliamperes is rSource multiplied by the minutes of exposuretime. The number of roentgens emitted isnot actually determined but is accounted for byinclud- ing milliampere-minutes in thecalculations 11.5. shown in paragraph 11-2.9 and Figure / 10" SFD 16"

11-2.8 Gamma Ray Exposure Time.The ex- Aluminum Specimen posure time must bedetermined for each radiograph. For gamma ray techniquesthis can be 4" done by using Figure 11.3 and thefollowing

steps : 4" Film (1) Measure the specimen absorption path thickness "t" and determine the steel FIGURE 11.4.ExampleSpecimenFor Exposure equivalent thickness. From Table 11.4, Calculations. 105 Step 1 : Thickness is 4". The speci- Measurements can easily be made of (1) source menisaluminum.Its to film distance, (2) tube current, £3) milli- steel equivalent thickness amperage, and (4) exposure time ; however, (S.E.T.) is 4" ± 0.34 = tube voltage is difficult to measure accurately. 1.36". From Table11.4, Designs of X-ray machines and their tubes select Ir-192. For this ex- vary between manufacturerssothatthe ample, assume the source amount and quality of energy emitted may be calibration curve gave 30.8 quite different, even though they are operating curies of Ir-192. at the same voltage and current. It is possible to prepare exposure technique Step 2 :(a) The longest dimension curve sheets that will reproduce conditions for toberadiographedis films, source to film distance, milliamperage, V102 + 42 = 10.6"; there- and exposure .time. Accounting for variance fore, the minimum source in kilovoltage settings often requires trial ex- to film distance must be posuretoattain thedesiredradiographic greater than 10.6" (b) the density. Exposure charts provided by the film specimen thickness is 4"; and X-ray machine manufacturers may be used therefore,theminimum as guides. The radiographer should make trial source to film distance must exposures to determine correction factors for' be 8 X 4"= 32" or greater the charts. A log book could be kept so the (c) use a 32inch minimum radiographer will have information for devel- source to film distance. oping techniques for new specimens. A typical X-ray exposure technique curve Step 3 : Medium speed film is ac- sheet is shown in Figure 11.5. Charts of this ceptable.From thefilm type are prepared for a specific set of condi- table on Figure 11.3, select tions as listed : the film factor "F," 3.6, (1) The X-ray machine is identified be- from the 1.5 density col- cause the amount of energy and the umn. energy spectrum will not be the same for all machines Step 4 : From Figure 11.3, deter- (2) The material and thickness of added mine the absorber factor filters "A" by (a)entering the (3) Film type and film density bottom of the curve at the (4) Source (target) to film distance S.E.T. value for the speci- (5) Specimen material men,(b)followingthe 1.36" line upward to inter- If any of the conditions are changed the radiog- sect the Ir-192 curve, (c) rapher must obtain or prepare a new chart or from that point following make some necessary corrections. a horizontal line to the left The curve sheet will permit accounting for margin and(d)reading the (1) specimen absorption path length, t, the absorber factor "A," (2) kv applied to tube, and (3) exposureex- 95. pressed in milliampere minutes, ma-min. An X-ray tube has an energy emission rate Step 5Calculate "T" in minutes : determined by the tube current, ma. Exposure is the product of beam intensity and time. Up FAD2 3.6 X 95 x 322 T = 11.3 min. to the maximum tube current specified by the S 30,800 mc manufacturer, the radiographer may selectany 11-2.9 X-ray Exposure Time. Calculation of milliampere, ma, value. This selectedma di- X-ray exposure time is not as simple as for vided into the milliampere minutes obtained gamma rays. The reasons for this are the com- from the curve sheet will determine theex- plex equipment, controls, and energy spectrum. posure time in minutes.

106 rel 1000500 150 KV 10050 Industrial X-ray Machine 105 MediumSoftDensity36" 10Target-Film Aluminum maSpeed 1.5 Maximum Film Distance Tube Current

1 1.1/2 2 21/2 3 31/2 4 41/2 5 51/2 6 61/2 7 71/2 1/2 FIGURE Thickness in Inches 11.5.X-ray Exposure Curves. Scatter. Scatteredradia- Suppose that the ma-minvalue for 11-2.10 Control of Example : completely eliminated,but may an exposure wasdetermined to be tion cannot be be reduced tomihimize loss of imagecontrast. 24. The radiographercould select 8 reduce the amountof ma with acorresponding 3-minute Some of the ways to scattered radiationwhich reaches thefilm in- exposure time.An identical result (2) protection from could have been obtainedby select- clude (1) lead-foil screens, back scatter, (3)filters, and (4)masks and ing 6 ma with acorresponding 4- placed in direct minute exposure time. diaphragms. Lead-foil screens contact with bothsides of the filmdecrease radiation on the film. Example :The specimen inFigure 11.4 is to the effect of scattered Select the condi- The foil absorbs thelonger wavelengthscat- be radiographed. primary tions and use Figure11.5 to deter- tered radiation morethan it does the time. This speci- radiation. Also, itincreases the photographic mine the exposure of elec- men is 2"thick, aluminum. action of the film dueto the emission trons and secondaryX-radiation. Becauseof Step 1 : Medium speedfilm at den- this "intensifying"action, lead-foil screens may acceptable result in less exposuretime. By removingscat- sity 1.5 will give the resolution. tered radiation,however, they iinprove quality of the imageexcept at a very lowvolt- front foil Step 2 : From Table11.3 it is de- age. At asufficiently low voltage the termined that 150 kvis screen mayabsorb enough primaryradiation Some film holders or suitable. to lower image quality. cassettes provide for apair of thin lead-foil with the front Step 3 :(a) The longest dimension screens to bein direct contact toberadiographedis and back side ofthe film. V102 + 42 = 10.6"; there- Cp Source of Radiation fore, the minimum source / to film distancemust be ONEINEE-- Diaphragm the greater than 10.6" (b) Filter specimen thickness is2"; therefore,theminimum source to filmdistance must be 8 x 2" = 16" orgreater (c)use a 16"minimum source to filmdistance. \ Specimen th...ckness line Film and Step 4 : From the 2" \ Film Holder on the bottomof Figure 11.5, follow a line vertically 150 upward to intersect the Source of Radiation. kv curve. From that inter- FIGURE 11.6.Filter Near section, follow a horizontal Back-scattered radiation canresult in very line to the left marginat low quality images. Many exposuretechniques 2.7 ma-min. Select any ma provide a rather thick sheetof lead on the value which is not greater back side of the filmholder to prevent back than 10 ma, e.g., 3 ma. Ex- scatter from reaching thefilm. This is usually posure time =2.7 ÷. 3 = sufficient for X-ray radiographyusing voltages 0.9 minutes (not account- below about 100 kilovoltage.Above 100 k.v., ing for SFD) Correcting thicker lead is needed, up toabout 1/4 inch at Mev..Usually the table or floor onwhich speci- (1.6\2 placed is covered with the for SFD: 0.9\ 36 mens and film are 0.2 min. exposure time. lead. When film holders arefitted with the sheet

108 20 percent ofthe maximumsteel thickness of lead to preventback scatter, someprecau- when using gammarays gives good results. tions must be taken Up to 250 k.v.,filters should beplaced near or X-raysabove 200 k.v.Secondary radiation However, inmillion-volt ra- affect the imagequal- the X-ray tube. from the lead sheet may diography, filtrationat the tubedoes not seem film is enclosedbetween lead-foil Lead filters ity unless the to improve thequality of images. orintensifying screens. between thespecimen and thefilm have been Filters are sometimesused with X-ray ra- must be takento avoid copper, orbrass are found useful, but care diography. Lead, steel, defects in thelead filters lestthese show on used as filters. Afilter mounted nearthe X-ray specimen defects. and the specimen the film and bemistaken for tube between the source When a specimenhas highabsorption of serves a veryuseful purpose.Such a filter from external low-energy X-rays,scatteredradiation absorbs more ofthe "soft" or be high comparedto the primary "hard" or high-energyX-rays. sources may X-rays than the radiation reachingthe film throughthe speci- This helps prevent overexposureof thin areas results in a poorquality image. Also, such a filterreduces the men. This of the specimen. Such scatter maybe lessened bythe use of a undercut near the edgesof the specimen.Such the specimen. time or an in- mask cut out andplaced around a filtermakes a longer exposure sheet of lead maybe used as but this is usu- For example, a the creased kilovoltage necessary, a maskand an openingcut in the sheet ally not a problem. the specimen,but slightly thin sections adjacent same shape as If a specimen has very smaller. The leadreduces the radiationreceived to thick sections, orif the primarybeam may near thefilm and hence specimen, undercut may by objects around or A reach film near the the scatteredradiation receivedby the film. occur. Afilter placed near theX-ray tube will the source of the lead diaphragm maybe used near help prevent undercutand overexposure section of the primarybeam absorbing more of the"soft" to limit the cross thin sections. By to the shape orsize of the specimenin order radiation, lower subjectcontrast results. This Also, if only a partof the thicknesses to reduce scatter. permits a wider rangeof specimen specimen is to beradiographed, a leaddia- to be shown. Notables of filter thicknesses are to mask offunwanted of filter actionneeded phragm may be used available. The amount parts of the specimen. for a good imagedepends upon thematerial barium clay may bepacked specimen, upon the range In some eases, and thickness of the around a specimento serve the same purpose of specimen thicknesses,and upon the amount .01 inch diam- has as a mask.Also, metallic shot of of undercut likelyto occur. Experience eter or less maybe used withirregularly shown that in theradiography of steel, alead fill holes or cavitiesand filter about 3 percent or a copperfilter about shaped objects. These prevent overexposureof thin areas wherethere are alsothick areas to expose. Unfiltered Radiation 11-3Exposure Arrangements Proper location of the sourceand film, with Filtered Radiation respect to thespecimen, may determinethe quality of theradiograph. Withexperience, the radiographerwill become proficientat selecting the best arrangement. 4#0\N* General questions forthe radiographer to 41 keep in mind are : (1) Which arrangemer,*, will give the best radiographic contrast of thespecimen Wavelength area that islikely to contain manu- FIGURE 11.7.Effeet of Filter onIntensity of X-ray facturing discontinuities? Radiation. 109 (2) Which arrangement will give the best area, Figure 11.10A or B, is one of the simplest radiographic contrast of the specimen subjects to radiograph. Its critical area is'well area that is likely to fail under im- defined in length, width, and thickness. Sub- posed operating stresses? ject contrast is not excessive. (3) Which arrangement will allow the A welded Tee joint, shown in Figure 11.10B, shortest exposure time? presents a different problem. The weld root is the area most likely to contain weld defects. No convenient location for the film can be Target found that will give good weld root image resolution. Either of the arrangements can be used. It should be noted that the object film distance is quite large in view number 2, and in this circumstance good resolution can be attained only by using a very long source to film distance. A. Beam-Type Tube Radiography of pipe welds can require additional arrangements. If the pipe diameter is small, i.e., 1I/2 inches or less, the entire weld may be exposed on a single film. The source at A would project the images of both pipe walls onto the same film area. It would not be possible to determine which pipe wall contained a defect if one were present. A better arrangement is to place the source offset from

B. 360' Beam Tube the plane of the weld (see Figure 11.11 A.) The weld image *will be cast onto the film as an nay= 11.8.X-ray Tube Beams. ellipse, which will reveal the location of weld (4) Will the specimen contrast require discontinuities. (a) single film, On radiographing welds of larger pipe, the (b) double film, or radiographer will find difficulty determining (c) multiple exposure technique? the length of the radiation path through the (5) Can beam or panoramic radiations be specimen for calculating exposure time. In more appropriate? Figure 11.11 B, it is apparent that the thick- X-ray and gamma ray equipment can be de- ness along path P is much less than along the signed to emit the usable radiation in a beam, path near a tangent to the pipe. The radio- see Figures 11.8A, and 11.9A and B. Shielding graph along path P will be much darker than in the equipment is arranged to control the the tangential area. It is practically impossible radiation intensity in all directions except the to make an acceptable radiograph of larger beam. X-ray tubes are available which produce pipe on a single film. A better procedure is to a narrow, 3600 radiation beam. This is par- divide the weld circumference into 3or 4 seg- ticularly useful for simultaneously radiograph- ments and radiograph each with a separateex- ing several small pieces (see Figure 11.14) or posure. If the pipe has a diameter 12 inches or an entire circumferential weld(see Figure greater, and its interior is accessible,a widely 11.12). The gamma ray device in Figure 11.9 used arrangement is that shown in Figure emits its radiation with a 360° spherical beam. 11.12. This technique is most useful inpres- It is useful for the same application as the 3600 sure vessel radiography. X-ray tube. Also, the spherical beam has been All welds on spherical arid hemispherical used with a single exposure to radiograph all pressure vessels can be radiographed with a the welds on a spherical pressure vessel (see single exposure. Film holders cover all welds. Figure 11.13). The radioisotope source is placed at the geo- Several sketches will demonstrate applica- metric center, and the 360° beam front exposes tions of exposure arrangement. A flat weld all areas at the same time. This saves much

110 Control Rod/ Source (Extendable for Panoramic Shots) fLead Shield Type A Control Rod

Beam Opening

Source (Shielded Position

Lead Cylinders

Type B

Lead Shield Flexible Cable

360° Beam Radiation

Source Control Unit for Extending Source (Exposure Source Into the Flexible (Shielded Position)t Cable to Exposure Position Position) Type C

FICROUI11.9.Gamma RayExposure Devices. 111 Source

Specimen Weld

Film Film

A. Flat Welded Plate

Source \ Weld Root

Source

Film

B. Welded Tee Joint on Plate FIGURE 11.10.Welded Flat Plates. "set-up" time required for radiographing the radiographs, one for section A and many small areas covered by a beam forming one for section B. source. (Figure 11.13) (2) Place two pieces of the same type of When large numbers of small parts are to be film in the holder and make a single radiographed, a panoramic exposure arrange- exposure. During interpretation, read ment may be used (see Figure 11.14). a single film for section A, and super- Some specimens have very large subject impose the films on the viewer for contrast. The thickness range may not bepos- viewing section B. sible to radiograph on a single film witha (3) Place one high speed film andone single exposure (see Figure 11.15). In such slow speed film in the film holder for cases,severaldifferent techniques may be a single exposure. Read section A on acceptable : the slow film and read section Bon (1) Using the same type of film, make 2 the fast film.

112 A itsource

Plane of the Weld

A Mb 9 4. 0 \ IN/ Film Film

A. Welded Joints of Small Pipes

Source Source /I\ efi \ \ // //

Film Film

B. Large Pipe Welds

FIGURE 11.11.Welded Joints of Pipe.

11-4Unsatisfactory Radiographs: 11-4.1 High Density. An excessively high (1) overexpo- Causes and Corrections film density can be caused by : sure, (2) overdevelopment or (3) fog (tobe It is not unusual for a radiograph to be un- discussedlater). Overexposureisnormally satisfactory despite many laborious procedures. caused by an incorrect exposure factor and can The radiographer should try to locate the be corrected by decreasing exposure time by source of error and prevent a recurrence.This one-third or more. Meters and timers should section is designed to be of use in locating the be checked for accuracy if this trouble persists. more common faults which lead to poor qual- Sometimes an overexposed film can be reaLl ity radiographs. The characteristics of the well enough to be used,if illumination of unsatisfactoryfilmprovideaconvenient higher intensity is provided. reference.

113 Film

All Film Holders Exposed Simultaneously

I rL1

I / % / . \ I / \ / / Specimen \ \ I / / ./ . \ 1// . ' \ ' Source ./ /54/1iii .I

FIGURE 11.12.Radiographing Welds of Larger Diameter Pipes and Pressures Vessels. Fr: Overdevelopment isa function of one of two things: Too longa development time or too FIGURE 11.14.Panoramic Exposure Arrafigement. warm a developer solution. Simple checks will determine whether oneor both conditions should be corrected. /6\\ 11-4.2 Low Density. Thepresence of one or more of these conditions generally accounts for inadAnuate film density. First,exposure factors may be incorrect. When this condition issus- pected, an increase of 40 percentor more in exposure time is recommendee. Second, the Specimen with wide range of subiect film may be underdeveloped, foA. a number of contrast causes. Either the development time is too short, the developed solution istoo cold, or the developer solution is too weak. Suchconditions can be checked and corrected if found abnormal. Finally, it happenson occasion that an intervening material, suchas paper, is left between Film the screen and the film. Thispossibility should FIGURE 11.15.Multiple Exposureor Multiple Film be checked out if othererrors do not reveal the Technique. trouble. Film Holders To Cover 11-4.3 High Radiographic Contrast.When All Dotted Areas excessive radiographic contrastis apparent, determine whether high specimencontrast or high film contrast is thecause. The cause of the first condition is usuallya specimen thickness range is too great for the quality of radiation desired. Thismay be corrected by increasing the radiationenergy (key or mev).High film contrast is corrected by using filmof lower contrast characteristics.

Radioisotope Source 11-4.4 Low RadiographicContrast. Low radiographic contrast is causedby (1) low FIGURE MM.HemisphericalOrange Peel Head. subject contrast, (2) low filmcontrast, and/or (3) underdevelopment. The first iscaused by hangers are contaminated, (2) thefilm is im- radiation which is too penetratingfor the properly agitated, or (3) inspectionof film thickness range of the specimenand may be allows develGper to flow across thefilm before radiation energy fixation. During the drying process,streaks corrected by reducing the by use of (key or mev).The second, low film contrast, and water spots may be eliminated can be correctedby substituting film of higher a wetting agent inthe final water rinse before contrast characteristic. Underdevelopmentis a drying. matter of too short a developmenttime, too 11-4.8 Yellow Stain. Yellow stainscommonly cold a developer solution or adeveloper of too result from (1) prolonged developmentin old, low chemical activity. Appropriatecorrections oxidized developer, (2) the omissionof a stop should be made if these conditions arenot bath or rinsing, and (3) improperfixation. In correct. the first instance it is necessaryto replace the 11-4.5 Poor Definition. Radiographswith developer solution. Proper stop bathand rins- poor definition will notreveal detail possible ing procedures will alleviate the second cause within abilities of the process. Thiscondition and the replacement of thefixer solution will may be caused byseveral factors including (1) correct fixation stain problems. geometric exposure factors, (2) poorcontact 11-4.9 White Scum. The presence of amilky- between film and intensifying screens,(3) appearing fixer solution indicates thatthe solu- graininess or fluorescent intensifying screens, tion was mixed too warm, has beenmixed too (4) graininess of film. In the conditionsof rapidly, or that the develt Der has beencarried geometric factors excessive object-filmdistance over into the fixersolution. Each condition can can be corrected by decreasingthe distance be readily avoided once it has beendiscovered. between the object and film or, if this is im- 11-4.10 Physical Damage to Film Emulsion. possible, by increasing the focus-film distance. Puckered or net-like film surfaces, known as The second exposure problem results from reticulation, result from sudden extremetem- using too large a radiation source size and may perature changes during processing.The im- be corrected by using a smaller source size portance of constant temperatures hasalready or by increasing thedistance to the specimen. been stressed. (Source size means the actual shape emanating Another type of physical damage to thefilm the radiation whether itis the X-ray focal emulsion results when a warm orexhausted spot or a gamma ray source dimension.) fixer solution is used. This type ofdamage, Film holders should be checked to see that known as frilling (loosening of filmemulsion contact between the film and screen is uniform from its base) can be corrected by afresh over the entire area. Graininesscaused by flu- supply of fixation chemical. orescent intensifying screens is corrected by Excessive temperatures may cause the emul- chwaging to lead foil screens. Graininess of film sion to slough off from the backing. is reduced by using a finer grain radiographic 11-4.11 Miscellaneous Problems. There are film. various other conditions which lower thequal- 11-4.6 Fog. Films can develop fog from sev- ity of radiographs, all having to do with im- eral possible exposurns to light or radiation. proper technique. Crimpmarks are the result First, it should be determined that the film has of sharp bends being forced ontlie film while not received excessive exposure to light from being inserted into cassettes or film holders. leaks through walls or poor safelight filters. Pressure marks result from mechanical im- Next, film in storage should be checked for pact or pressure. Air bells can beeliminated excessive exposure to radiation, heat, humidity, by tapping the top bar of the film hanger and harmful vapors and gases. Finally, the film against the tank when first immersed in the processing procedure should be reviewed to developer. Light spots are often caused by eliminateoverdevelopmentandincorrectly chemicals being splashed on the film before mixed or contaminated solutions. development. Foreign materials on or in in- 11-4.7 Streaks. Streaks are discussed else- tensifying screens, or between screens and where in connection with a description of the film during exposure cause images which can film processing. Streaks result when (1) film be avoided by habits of cleanliness and care.

115 Chapter 12

Interpretation of Radiographs

Because of the varied materials and proc- The person interpreting radiographs will then esses which are subject to testing by radiog- be aware of the fact that he will be required raphy, the interpretation of radiographs is not to make judgments about the acceptability of a matter that can be made a routine procedure. discontinuities existing in the product being in- The many conditions under which radiographs spected. Thus, there is no single quality level are made make the interpretation of radio- applicable to all the great variety of pL'oducts graphsadifficultmatter.Thesuccessful and materials that will be subject to radio- interpretation of radiographs requires an under- graphic inspection. Each quality level must be standing of the general principles of radiog- evaluated and interpreted as it is related to raphy, knowledge of the materials being tested, the serviceability of the item and its contribu- and some practical experience in reading radio- tion to theeffectivenessof the completed graphs in order to relate the images of dis- product. continuities to the serviceability of the specimen. Thus, there is no formula or routine 12-1.2 Acceptable Quality Levels. The re- which can be set up for the interpretation of sponsibility for establishing quality levels is the radiographs. initial obligation of the engineering and scientific groups designing the product. In terms 12-1Basic Concepts of Interpretation of such factors as static and dynamic stress, Inspection by radiographic means is gener- operating temperatures, corrosion, creep and ally used to determine the presence of discon- fatigue, surface appearance, and many other tinuities in materials or parts and to inspect factors, specifications must be established for assemblies in which components may be miss- the acceptability of discontinuities. In almost ing or out of proper position. This inspection all cases the cost would be prohibitive if per- is done in order to determine whether to accept fectfinishedmaterials and products were or reject the part. It should be noted that the required. presence of some defects or flaws does not Quality levels are for the purpose of estab- mean that an item cannot serve its intended lishing some sort of standard or norm fora purpose. Therefore, the person who interprets particular job. If the end use of a product re- radiographs must exercise some judgment as quires that it be perfect then the standard to the degree of imperfection or discontinuity quality level should be established as such. that exists and whether the discontinuity or However, if the end use of an item does not re- imperfection will prevent the item from being quire perfection then upholding too high a used or fulfilling its purpose. standard will be inefficient and will handicap the manufacturing of the item. Obviously, hold- 12-1.1 General Ideas About Interpretation. ing to a quality level that is too high would be If absolute perfection was the required level of wasteful. Therefore, the quality level or norm quality for all materials and assemblies, then should be in keeping with the service require- the interpretation of radiographs would be ments of the article. relatively easy. The person interpreting the There are many borderline cases needing in- radiograph would simply declare that the prod- terpretation in radiography work. For example, uct or assembly was unacceptable if he found small gas holes may be a defect which will not any kind of discontinuity, flaw, or defect. How- cause the rejection of an ar ticle. Sometimes it ever, in most cases in industry something less is necessary to determine the streagth and than perfection is satisfactory for most prod- serviceability of an article with mechanical ucts.Engineering design specificationswill tests to determine whether certain kinds of establish quality guidelines for radiography. flaws or defects may be acceptable. When this is done, the interpreter will be able to make or charts include : better decisions about the acceptability of prod- American Society of Mechanical Engineers ucts in which certain kinds of discontinuities American Society for Testing and Materials or imperfections are seen on the radiograph. American Petroleum Institute Such a procedure will allow serviceable parts U.S. Army Ordnance Department to reach the assembly line and will help the U.S. Air Force production of the item to be more efficient. U.S. Navy However, the radiographer should call to the American Welding Society attention of the manufacturer the borderline Copies of the appropriate codes and refer- cases. In many instances the manufacturer may ence material should be available to the person be able to eliminate the defect by altering some responsible for interpreting the film. of his procedures. If the manufacturer does Many critical-system manufacturers set up not know of the borderline cases, then he is their own radiographic standards. They may unable to improve the quality of his product develop a general set of radiographs to serve even though the product may be of an accept- as an overall guide for evaluating discontinui- able quality. ties. In some cases, general radiographsare inadequate and a set of radiographs referring to 12-2Specifications, Codes and Stand- a specific casting or part may be required for ards proper interpretation. In many instances test reports are made available upon the testing of 12-2.1 Specifications, Codes, and Reference an actual part which has first been radio- Standards. In manycases the manufacturer graphed. This testing may be done under actual may use certain radiographic codes, references, or simulated service conditions. After complet- or specifications as the standard toward which ing tests, a standardmay be chosen and the he aims to manufacture his products. The inter- least acceptable standard fora particular prod- preter must familiarize himself with the stand- uct or part is set up and all further manufac- ards .and specifications in order to makeproper tured castings or partsmay be presumed to judgments about the evaluation of manufac- have a quality equal toor better than the one turers' products. The rules, specifications,or established as a minimum. standards upon which the interpretation of In many cases, as time passes andas cast- radiographs is basedmay serve two functions ; ings or parts are put intouse it may be found (1) they may serve asa guide for identifying that the parts may not need to beas good as types of discontinuities; or (2) they may spec- the standards first established. Then the quality ify or indicate acceptable and unacceptable level may be changed. On the other hand, it soundness conditions for products. Standards may be found that parts should be better than that function as a guide for the identification the standard first established andso the quality of discontinuities are often ofa pictorial na- level may be raised. ture. These may consist ofa series of radio- 12-2.2 Specific Interpretations. From the graphs or reproductions of radiographs which above it may be realized that the interpretation show various .types of discontinuities. Some- of radiographs may bea very difficult task in- times a description anda sketch of discontinui- volving to a great extent good judgmenton the ties are included. part of the interpreter. Ina specific instance, Specifications and standards that setup ac- however, interpretationmay be a fairly easy ceptable quality levelsare commonly called "ac- job especially whena radiographic standard ceptance standards." Theseare used to deter- has been selected fora specific process. For ex- mine whether or not parts, materials,or prod- ample, one may consider the welding ofone ucts are acceptableon the basis of evaluation piece of steel to another ina situation where it by radiographicmeans. Acceptance standards may be desirable to have radiographic exami- may be indicated pictorially or theymay be in nation. The engineeror designer who recognizes the form of written rules. the need for radiographic examinationis fa- Some of the organizations that have adopted miliar with the reason for the examination.He radiographic codes and referenceradiographs becomes the source of informationfor the 118 radiographic interpreter for thisparticular For the needs of this training program man- able to secure ual, the material presented willbe limited to weld. The interpreter should be ASTM, and a series ofradiographs of welds of thistype materials selected from ASME, which are of different qualities and compare API publications. these radiographs with thosetaken of actual 12-2.3 ASME Code. The ASMEpublishes welds. By working with theengineer-designer, a Boiler andPressure Vessel Code. One section the interpreter would be able toselect one or of the Code deals with unfired pressurevessels. more radiographs as thestandard which would This section includes standardsfor radio- indicate the least acceptable condition.All other graphic examination of weldedjoints and for radiographs then would be evaluatedin terms spot-examination of welded joints. Themain of these reference radiographs. provisions of the radiographiccode are as The interpretation of a specificproduct may follows *: be concerned with a casting, aweld, the inspec- radiographic tion of a radio tube, or various otherkinds of 1.,Welds requiring complete products. In many cases the problem ofinter- examination will be examined overtheir entire pretation is not a general problem so much as length by the X-ray or gamma-raymethod of one peculiar to theparticular company and the radiography. specific product. Thus, factorsrelated to in- 2. For butt-welded joints,weld ripples or spection standards must be developedby the surface irregularities, inside andoutside, .shall company itself andthegeneralreference be removed by any suitablemechanical means standards set up by societies or groups may so that radiographiccontrast due to these ir- not be of particular value in a case such asthis. regularities will not mask defects. The person doing the interpreting,therefore, must be reliable and assume properresponsi- 3. Welds shall be radiographedwith a tech- bility for his interpretations. Themanufac- nique which will indicate the size ofdefects turer would need to depend upon thegood judgment of the interpreter to assure that a .Extracted from the 1965editionof the ASME Boi/er and Pressure Vessel Code. Section 8: Unfired PressureVessels. (With product of proper quality would be reaching permission of the publisher, The American Societyof Mechanical his consumers. Engineers, New York.)

Identifying Number

I II 3.5 C) 40) 1/2"

4-H 1/2"-1 3/4"4-11/4"11/4"11/4+- 34"-P+-1/2"4-[4- 1/2"

For specimens over 21/2" in thickness For specimens 21/2" or less inthickness that of the specimens under Note I.The penetrometer shall consistof material substantially the same as examination. of the thickness of the specimen. Note 2.The thickness of the penetrometershall be not more than 2 percent the thickness of the penetrom- Note 3.The diameter of holes (left toright) shall be four, three, and two times eter, but not less than 1/16inch. the penetrometer; the numbershould The identifying number shallconsist of lead figures cemented to Note 4. the penetrometer may be used. indicate to two figures, the minimumthickness of fhe specimen for which FIGURE 12.1.ASME Boiler Construction CodePenetrameters.

119 ASSORTED ASSORTED

LARGE

MEDIUM :

MEDIUM

FINE

FINE ALIGNED I3OR MORE) --- 4T -

2T:ad

2T ALIGNED (3 OR MORE) ---- 4T I PLATE 1,4 INCH OR LESS 0 - 2T --

-"4I T

ASSORTED PLATE OVER-. 1/4 INCH TO 1/2 INCH

ASSORTED

LARGE

. 111

LARGE

MEDIUM

FINE MEDIUM

ALIGNED (3 OR MORE) 4T FINE

ALIGNED (3 OR MORE) 4T TO NEXT SPOT THIS SIZE

2T OA PLATE OVER 1/2 INCH TO II/4 INCHES I. 2T FIGURE 12.2ASME Porosity Charts Showing Maximum Permissible Porosity in Welds. PLATE OVER II/4 INCHES TO 21/2 INCHES 120 ASSORTED ALIGNED (3 OR MORE) 4T TO NEXT SPOT THIS SIZE --v.

2T TO NEXT GROUP THIS SIZE --IAD 01

2T TO NEXT GROUP THIS SIZE

LARGE

PLATE OVER 21/2 INCHES

FIGURE 12.2ASME Porosity ChartsShowing Maximum Permissible Porosity inWelds. (Cont.)

MEDIUM 7. When a complete circumferenceis radio graphed with a single exposure, fouruniformly spaced penetrameters shall beused. 8. Radiographs should be freefrom excessive mechanical processing defectswhich would FINE interfere with properidentificationof the a radiograph. 9. Identification markers whoseimages appear on the filmshall be placed next to the weld and their locations accurately andpermanently marked on an outside surface nearthe weld. appearing on a PLATE OVER 21/7 INCHES This serves to locate a defect FIGURE 12.2ASME Porosity Charts Showing radiograph. Maximum Permissible Porosity in Welds. (Cont.) 10. The job number, the vessel, the seam,and the manufacturer's name or symbolshall be plainly indicated on each film. having a thickness equal to and greaterthan 11. Radiographs shall be submittedto the 2 percent of the thickness of thebase metal. about tech- check on inspector with any information 4. Penetrameters shall be used to nique which he may request. the radiographic technique. (Adescription of radiography given in Fig- 12. Sections of weld shown by the penetrameters to be used is to have any of the followingtypes of imper- ure 12.1.) fections shall be unacceptable and shallbe re- 5. During exposure, the film shall be asclose paired as provided for in the Code. to the surface of the weld as practicable.This distance should not be greater than oneinch. (a) Any type of crack or zone ofincom- If s is the distance from the radiationside of plete fusion or penetration the weld to the source of radiation andif f is (b) Any elongated slag inclusionwhich the distance from the radiationside of the has a length greater than 1/4 inch for weld to the film, then the ratio gilshould be T up to 3/4 inch, Y3 T for T fromtY4 7 to 1 or greater. If the ratio is less than 7to inch to 21/4 inches, 3/4 inch for T over 1, the manufacturer should satisfy the inspec- 21/4 inches where T is thickness of the tor that the technique is adequate. Whenthe thinner plate being welded ratio s/f is less than 7 to 1, the ratio shallbe (c) Any group of slag inclusions in line clearly indicated on each film or attached that have an aggregate length greater thereto. than T in a length of 12 T, except 6. Penetrameters are usually placed on the when the distance between successive radiation side of the joint. They may be placed imperfections exceeds 6 L, where L on the film side if themanufacturer can satisfy is the length of the longest imperfec- the inspector that the technique is adequate. tion in the group 121 (d) Porosity in excess of that shown as where T is the thickness of the thinner acceptable in the standards (See Fig- plate welded. ure 12.2.) (c) If several imperfections within the above limitations exist in a line,the 13. A complete set of radiographs for each welds are acceptable if the sum ofthe job shall be retained by the manufacturer for longest dimensions of all such imper- at least five years. fections is not more than T in a length The ASME code also includes rules for spot- of 6 T and if the longestimperfec- examination of welded joints. Spot-examinations are separated by at least 3 L of tion may be used as a quality control measure. acceptable weld metal, where L isthe Such radiographs may be taken immediately length of the longest imperfection. after a welder or operator completes a unitof weld and they will show whether satisfactory (d) The maximum length of acceptable procedures are being used. If the work is un- imperfections shall be 3/4 inch. Imper- satisfactory, then corrections can be made if all fections shorter than 1/4 inch shall be radiographically disclosed defects are to be acceptable for any plate thickness. eliminated. A summary of ASME spot-exam- (e) Porosity is not a factor in the accept- ination rules follows : ability of welds not required to be fully radiographed. 1. Vessels or parts with butt-welded joints whicY are required to be spot-examined shall 4. Evaluation and retests be spot-radiographed to the following minimum (a) Spots acceptable under the above con- extent : ditions mean that the entire weld (a) One spot shall be examined in the first length represented by the spot radio- 50 feet and for each additional 50 graph is acceptable. feet of welding in each vessel. (b) When spots radiographed as above (b) Such additional spots shall be se- show unacceptable welding, then two lected so that each welding operator additional spots shall be radiographed shall have welds examined. in the same weld unit away from the (c) Each spot-examination shall be made original spot. as soon as practicable afterthe com- (c) If the two additional spots show pletion of the increment of weld to be welding meeting the above standards, examined. the entire weld unit is acceptable. De- fects shown by first spot-radiographs 2. Standards for spot-radiographic examina- may be repaired or allowedto remain tion include the following : at the discretion of the inspector. (a) The minimum length of a spot-radio- (d) If either of the two additional spots graph shall be 6 inches. shows welding not meeting minimum (b) Spot-radiographs may be retained or quality requirements, the entire weld discarded by the manufacturer after unit is rejected. The entire weld may the be removed and joint rewelded or the acceptanceofthevesselby weld unit may be entirelyradio- inspector. graphed and only the defective weld- 3. Acceptability of welds is judged as follows : ing corrected. Welds in which radiographs show any (e) Repair welding shall be performed us- type of crack or zone of incomplete ing a qualified procedure and the re- penetration shall be unacceptable. weldedjointshallbespot-radio- Welds in which radiographs show graphed at one location. slag inclusions or cavities shall be unacceptable if the length of any such The above standards for radiographing and imperfection is greater than2/8 T evaluating welded joints were adapted from the ASME Boiler awl Pressine Vessel Code, TABLE 12.2.Classification of Defects in Steel Castings section 8, 1965. For the complete standards to be Used with Radiographic Standards. refer to this publication. The standards described here are typical of standards adopted GROUP DEFECT by some other groups. A Gas andblowholes 12-2.4 ASTM Radiographic Reference Ma- Sand spots and inclusions terials.* The American Society for Testing and Internal shrinkage Hot tears Materials has a committee on nondestructive Cracks tests. This committee has prepared reference Unfused chaplets materials concerning recommended practices Internal chills for radiographic testing, controlling quality in radiographic testing, and radiographic refer- For example, there are six reference radio- ences for various industrial processes and ma- graphs showing gas and blowholes in steel terials. For example, it has comparison radio- castings. These are labeled Al through A6. For graphsforsteelcastings,aluminum and Class 1 service, castings with gas or blowholes magnesium castings,steelwelds, and steel that match radiograph Al are borderline cast- castings for aerospace applications. ings. Castings with defects that match radio- TABLE 12.1.Classification of Steel Castings to be graphs A2A6 are unacceptable. For Class 3 Used with Radiographic Standards. service, casting with gas or blowholes that match radiographs Al and A2 are acceptable, CLASS SERVICE those that match radiograph A3 are borderline, and those that match radiographs A4 1 High-pressure or high-temperature service castings, or A6 are unacceptable. In other words, a cast- both (wall thickness less than 1 inch). Machinery cast- ingssubject to high fatigue or impact stresses(wall ing with defects of a certain severity or extent thickness less than % inch). may or may not be acceptable depending upon 2 High-pressure or high-temperature service castings, or both(wall thickness 1 inch or greater). Low-pressure service castings (wall thickness less than 1 inch). Ma- chinerycastingssubjecttohighfatigueorimpact stresses (wall thickness of % inch and greater).

a Low-pressure service castings (wall thickness of 1 inch and over). Machinery castings subject to normal fatigue or impact stresses.

4 Structural castingsbless than 8 inches in thickness and subject to high service stresses. Machinery castings subject to low impact stresses or vibration.

5 Structural castings 8 inches or more in thickness and subject to high service stresses.

Machinery castings are dynamic parts or members in contact with working parts. bStructural castings are construction parts for machinery castings. The references suggest a classification of the service or use to be made of steel castings. Five levels of service are described andare numbered from one to five. Class 1 castings must meet the highest requirements while Class 5 castings must meet certain lower requirements. Also, seven types of defectsare identified and labeled A to G in Table 12.2. Several reference WM.LT WNW ESS OVER 1/2"7014" plates are made for each defect showing differ- MAXIMUM ent extents of the defect. DISTRIBUTION OF GAS POCXETS *Contents of Table 12.2 (ASTME 71-64) are published herein with the permission of the publisher, Amerkan Society for Test- FIGURE 12.3API Standards for Field Welding ing and Materials, Philadelphia. of Pipelines.

123 TABiz 12.8.Radiographic Standards for Steel Castings. PLATE CLASS CLASS CLASS CLASS CLASS NUMBER 1 2 a 4 5 GAS AND BLOWHOLES

Al BORDERLINE Acceptable Acceptable Acceptable Acceptable A2 Thacceptable BORDERLINE Acceptable Acceptable Acceptable A8 Unacceptable Unacceptable BORDERLINE Acceptable Acceptable A4 Unacceptable Unacceptable Unacceptable BORDERLINE Acceptable A6 Unacceptable Unacceptable Unacceptable Unacceptable BORDERLINE A6 Unacceptable Unacceptable Unacceptable Unacceptable Unacceptable

I SAND SPOTS AND INCLUSIONS

Ill BORDERLINE Acceptable Acceptable Acceptable Acceptable B2 Unacceptable BORDERLINE Acceptable Acceptable Acceptable 1311 Unacceptable Unacceptable BORDERLINE Acceptable Acceptable 34 Unacceptable Unacceptable Unacceptable BORDERLINE Acceptable BIS Unacceptable Unacceptable Unacceptable Unacceptable BORDERLINE 136 Unacceptable Unacceptable Unacceptable Unacceptable Unacceptable

INTERNAL SHRINKAGE

Cl BORDERLINE Acceptable Acceptable Acceptable Acceptable C2 Unacceptable BORDERLINE Acceptable Acceptable Acceptable C8 Unacceptable Unacceptable BORDERLINE Acceptable Acceptable C4 Unacceptable Unacceptable Unacceptable BORDERLINE Acceptable C5 Unacceptable Unacceptable Unacceptable Unacceptable BORDERLINE C6 Unacceptable Unacceptable Unacceptable Unacceptable Unacceptable

HOT TEARS

Dl Unacceptable Unacceptable Unacceptable BORDERLINE a Acceptable D2 Unacceptable Unacceptable Unacceptable Unacceptable BORDERLINE P5 Unacceptable Unacceptable Unacceptable Unacceptable Unacceptable

CRACKS

El Unacceptable Unacceptable Unacceptable BORDERLINE Acceptable E2 Unacceptable Unacceptable Unacceptable Unacceptable BORDERLINE ES Unacceptable Unacceptable Unacceptable Unacceptable Unacceptable

UNFUSED CHAPLETS

RI Unacceptable BORDERLINE Acceptable Acceptable Acceptable F2 Unacceptable Unacceptable BORDERLINE Acceptable Acceptable FS Unacceptable Unacceptable Unacceptable BORDERLINE Acceptable

INTERNAL CHILLS

Gl Unacceptable Unacceptable BORDERLINE Acceptable Acceptable G2 Unacceptable Unacceptable Unacceptable BORDERLINE Acceptable 08 Unacceptable Unacceptable Unacceptable Unacceptable BORDERLINE 04 Unacceptable Unacceptable Unacceptable Unacceptable Unacceptable

Acceptable only when the angle between the defect and the direction of the principal stress is notgreater than 20 degrees.

124 the service conditions. By making use of this As a practical matter, this percentage isesti- comparison set of radiographs showing seven mated by using a device known as a penetram-. types of defects and up to six levels of severity, eter whichisplaced on the object being quality for steel castings may be rather specifi- radiographed. cally described (see ASTM Book of Standards, 1961, Part 3).(Table 12.3) 12-3.2 Penetrameters. A penetrameter may 12-2.5 API Standards. The American Petro- consist of a small strip of the same material as leum Institute uses sketches and measurements the specimen and having a thickness which is to describe the severity of defects in pipeline in a definite ratio to the thickness of the speci- welding. For example, they have adopted specimen. For much routine workthis ratio is an fications for field welding of pipelines. These bitrarily set at 2 percent. The radiographic include a chart showing the maximum distribu- procedureisconsidered satisfactoryif the tion of gas pockets allowed in a field weld. The penetrameter edges and holes are clearly out- maximum distribution of fine, medium, large lined on the radiograph. The perietrameter and assorted gas pockets is shown in a sketch. sensitivity then is said to be 2 percent or better If the radiograph of a weld shows more gas (Figure 12.1). pockets than are shown on the sketch, then the Penetrameters also contain holes of various weld is rejected. Also shown are acceptable con- sizes. This aids in determining the quality of ditions for gas pockets that are aligned. (Fig- the radiographs even though a cavity in the ure 12.3) material may not be visible while a hole in the penetrameter of the same diameter as the cav- 12-3Radiographic Sensitivity ity may be visible. The reason for this is that A basic concern of the radiographer is secur- the penetrameter has holes with sharp bounda- ing radiographs that reveal small defects of ries while a cavity may have less well defined discontinuities in the material under inspec- boundaries. A penetrameter is therefore used to tion. The term "radiographic sensitivity" usu- indicate the quality and sensitivity o; a radio- ally refers to the ability of a radiographic pro- graph and not to measure the size of a hole or cedure to detect discontinuities. Because the cavity that may be detected. size, shape, and nature of discontinuities vary Some rules for radiographic examination so graatly it is not possible to measure sensitiv- state that radiographs will be used which will ity specifically in terms of defect or disconti- indicate the size cf defect having a thickness nuity detection. In practice, sensitivity is speci- equal to and greater than 2 percent of the base fied as the ratio of the smallest thickness metal. To assure this level of quality, pene- difference visible on the radiograph to the trameters of substantially the same material as thickness of the material being examined. This the specimen must be used for each exposure may be expressed as a percentage. and placed on the side of the specimen nearest 12-3.1PercentageSensitivity.Sensitivity the radiation source. They should be placed may be expressed as a ratio : parallel and adjacent to the weld at one end of Percentage Sensitivity = x 100 the exposed length, with the small holes at the outer end. The thickness of the penetrameter where : must not be more than 2 percent of the thick- s = smallest detectable thickness dif- ness of the specimen, Each penetrameter should ference contain three drilled holes two, three, and four t = thickness of material being exam- times the penetrometer thickness, but in no ined case less than 1A6 inch for X-rays and %2 inch Suppose the smallest detectable thick- for gamma rays. The smallest hole should be ness difference in a radiograph of a distinguishable on the radiograph. The pene- piece of metal 2 inches thick was .04 trameters shall carry numbers raised %2 inch inch. Then the radiographic sensitivity high which identify the material and indicate would be : the minimum thickness of the specimen. These numbersshouldappearclearlyonthe Percentage Sensitivity =.04x 100 = 2% 2 radiograph. 125 1244 Ibilismis et Weft Ann. tart aril WOW pallail twee ese op tleserally, detests is geoids esamet *her se aradlowds. mmiladime vatanses walsomPlab old thsi shag% Ow Mow asespisislie wide a void is do wold metal et as 11140111111 limb prosily Wham dmodord se eposollst has kw desalt, thas the 1111114010111 weM doe wart st the isterpersior Os mew hems* metal. Radiographs say shoo both Worm& bpi and external disesatistitios is mid& IstersalMahe fes ftM sr so mese him vary discontinuities umeally are the more serious. hut siamlarde f poresity. Y.other type of utmost discontinuities may be mime asd sew porosity may sot be impertantThee am may not be detected simply by impedesat interpreter et radimprmplio most seam atm* the surface. Not all discontinuities that appear infirmities sheet the use or semiee tar mas on a radiograph mak* a weld unacceptable.To Wale OW are welded. !Marmot a weld radiograph infonuation about 11-41 Weld SW issiardsos. Ills. are sew the welding procedure and the joint design any exudes prodosed by are m. They serve should be avallabk. This informstion will help to help take impotritias from des auks,metal in securing a better concept of how the weld and to tom a layer ever the weld to moire, should appear and in orienting the weld cos- cooling rates. Some gag may be trapped in the figurations to the radiograph. weIAI metal if it fails to remain molts* loss Internal discontinuities describod include: enough for the slag to rise to the earful*. In gas holes and porosity, slag inclusions, cracks welding requiring multiple passes, Wag nay be and breaks, lack of penetration, lack of fusion, lift on previous passes unless properly cleaned. and tungsten inclusions. External or surface Slag inclusions may be ;omitted along the Wow discontinuities described are as follows: underof the weld metal deposits and run in a line cutting, longitudinal grooves, eXCeslails pene- along the length of the weld. tration, concavity at weld root, incompletely Since the oxides making up slap are usually filled wild grooves, excersive reinforcement, of lower atomic weight than iron, they show up overlap,irregularitiesatelectrodechange as dark irregular shapes on radiogyaphs.Slag points, grinding marks, electrode spatter, and inclusions can occur singly, in clusters, or scat- welds with backing rings. tered randomly throughout a weld. They mot 12-4.1 Gas Holes and Porosity. Gas may be also occur In a linear distribution. The imago formed in fusion welding because of poor con- may have sharp, pointed ends and may beof trol of are current, technique used, electrodes variable density. used, and quality of parent metal. The term Slag lines appear along the edge of a weld "porosity" is used to describe gas inclusions as an Irregular or continuous dark line onthe that occur as rather spherical cavities In the radiograph. These are usually caused by insuf- weld metal. Gas inclusions may also occur as a ficient cleaning between weld passes. Voids left tube-likecavity sometimes referredtoas between passes by irregular deposits of metal "wormholes." Porosity may occur as single cause lines that have a similar radiographic cavities, in clusters of cavities, or randomly appearance. scattered cavities. Linear porosity may also ASME and ASTM reference standards may occur along with incomplete penetration and be used to determine acceptability of welds with is a series of cavities distributed along a line slag inclusions. As is the ease with other dis- that runs lengthwise with the weld. continuities,service requirements determine On a radiograph, porosity appears as round theseverityofslaginclusionswhizhis dark spots with rather sharp contours. They acceptable. may be of varying sizes and distribution. 12-4.3 Cracks or Breaks. Cracks in welds are Wormholes appear as dark rectangles if the usually produced by internal stresses caused by axis of the cylinder is perpendicular to the ra- shrinkage of the cooling weld. Cracks may be diation source beam, and as two concentric along the weld seam or they may be across the circles, one darker than the other, if the axis is weld seam. The latter cracks may extend into parallel to the radiation beam. Linear perosity the parent metal. Cracks are generally wavy is recorded on radiographs as a series of round or zigzag lines and may have fine hairline dark spots along a line with the weld. cracks branching off from the main crack.

126 f'r\ 12-4Radiographs of Welds ASME, ASTM, and other groups have set up Generally, defects in welds consist either of standards, including reference radiographs and a voitl in the weld metal or an inclusionthat charts, for judging the acceptability of welds with porosity. Whefe a standard isspecified, has less density than the surrounding weld the work of the interpreter is easier.Pressure metal. Radiographs may show both internal tanks for liquid or gas must have veryhigh and external discontinuities in welds. Internal standards for porosity. For other types of discontinuities usually are the more serious, but important. Thus an external discontinuities may be serious and usage porosity may not be may not be detected simply byinspection of interpreter of radiographs must secure much the surface. Not all discontinuities that appear information about the use or service for ma- on a radiograph make a weldunacceptable. To terials that are welded. interpret a weld radiograph information about 12-4.2 Weld Sktg Inclusions. Slags are usu- the welding procedure and the joint design ally oxides produced by arc welding. They serve should be available. This information will help to help take impurities from the molten metal in securing a better concept of how the weld and to form a layer over the weld to control should appear and in orienting the weld con- cooling rates. Some slag may be trapped in the figurations to the radiograph. weld metal if it fails to remain molten long Internal discontinuities described include : enough for the slag to rise to the surface. In gas holes and porosity, slag inclusions, cracks welding requiring multiple passes, slag may be and breaks, lack of penetration, lack of fusion, left on previous passes unless properly cleaned. and tungsten inclusions. External or surface Slag inclusions may be located along the edges discontinuities described are as follows : underof the weld metal deposits and run in a line cutting, longitudinal grooves, excessive pene- along the length of the weld. tration, concavity at weld root, incompletely Since the oxides making up slags are usually filled wild grooves, excessive reinforcement, of lower atomic weight than iron, they show up overlap,irregularitiesatelectrodechange as dark irregular shapes on radiographs.Slag points, grinding marks, electrode spatter, and inclusions can occur singly, in clusters, or scat- welds with backing rings. tered randomly throughout a weld. They may 12-4.1 Gas Holes and Porosity. Gas may be also occur in a linear distribution. The images formed in fusion welding because of poor con- may have sharp, pointed ends and maybe of trol of arc current, technique used, electrodes variable density. used, and quality of parent metal. The term Slag lines appear along the edge of a weld "porosity" is used to describe gas inclusions as an irregular or continuous darkline on the that occur as rather spherical cavities in the radiograph. These are usually caused by insuf- weld metal. Gas inclusions may also occur as a ficient cleaning between weld passes. Voids left tube-likecavitysometimes referredtoas between passes by irregular deposits of metal "wormholes." Porosity may occur as single cause lines that have a similarradiographic cavities, in clusters of cavities, or randomly appearance. scattered cavities. Linear porosity may also ASME and ASTM reference standards may occur along with incomplete penetration and be used to determine acceptability of welds with is a series of cavities distributed along a line slag inclusions. As is the case with other dis- that runs lengthwise with the weld. continuities,service requirements determine On a radiograph, porosity appears as round theseverityofslaginclusionswhichis dark spots with rather sharp contours. They acceptable. may be of varying sizes and distribution. 12-4.3 Cracks or Breaks. Cracks in welds are Wormholes appear as dark rectangles if the usually produced by internal stresses caused by axis of the cylinder is perpendicular to the ra- shrinkage of the cooling weld. Cracks may be diation source beam, and as two concentric along the weld seam or they may be across the circles, one darker than the other, if the axis is weld seam. The latter cracks may extend into parallel to the radiation beam. Linear porosity the parent metal. Cracks are generally wavy is recorded on radiographs as a series of round or zigzag lines and may have finehairline dark spots along a line with the weld. cracks branching off from the main crack.

126

f,rN POI

the lack of pene- I The radiographic image of a crack defectis of the plates being welded and a dark narrow line thatis usually irregular. If tration may be very severe. the plane of the crack is in line with the radia- The ASME standard for welded pressure tion beam, its image will be a fairly distinct vessels states that any weld shownby radiog- line. If the plane is not exactly in line with the raphy to have a zone of incompletefusion or radiation beam, a faint dark linear shadow may penetration is unacceptable and mustbe re- result. In thiscase additionalradiographs paired. Again, depending upon theservice re- should be taken at other angles. quirements of the product, lack ofpenetration Since cracks are a very serious weld defect, is usually a serious defect. additional radiographs should be made when 12-4.5 Lack of Fusion. Because oflack of in doubt. Fine grain films may be used,the heat or improper cleaning of thefusion face angle of the radiation beam changed, and per- of a weld bevel, the weld metal maynot fuse haps other kinds of non-destructive testing may properly with the parent metal.They may re- be used to supplement the radiographs. main separated by a thin layer ofoxide which By most standards cracks of any kind are causes a discontinuityalong the wall of the unacceptable. Certainly on welds that must bevel. withstand pressures or tensions, cracks are a The radiograph of a lack of fusion shows a very serious defect that couldmake a weld very thin straightdark line parallel to and on unacceptable. one side of theweld image. Where there is doubt, additional radiographs shouldbe made 12-4.4 Lack of Penetration. This defect with the radiation beam parallel tothe bevel occurs at the root opening at thebottom of the face. This will increase the possibilityof the welding groove or at the center of the weld for defect appearing on the radiograph. Alack-of- two-sided welding. It is caused by failure of fusion line is usually straight on oneside and the root pass to fuse properly with the parent irregular on the other. metal at the root. Root openings are used to This is a serious weld defect and, depending permit penetration of fusion to the bottom of upon service conditions, may cause aweld to be the weld opening or groove. Often tack welds unacceptable. are used to prevent movementof pieces being 12-4.6 Tungsten Inclusions. If the tungsten welded. Then one or more passes are made with electrode used in arc welding contacts the weld beads being laid over each other until the metal some small particles or splinters ofthe groove is filled. tungsten wire may become trapped in the metal If the root opening is too small for the weld that is deposited. Since tungsten has a very rod and the current being used, high melting point no fusion will occur. Tung- penetration may result. Sometimes poor bevel- sten has a higher atomic weight than iron and ing or preparation of the weld groove can cause so has a higher radiationabsorption than iron voids at the root area of the weld. Where pos- at the energies usually required for radiog- sible a cover pass on the back side of the weld raphy. Therefore, tungsten inclusions will ap- may fill such a void. pear on a radiograph aslight marks instead of The radiographic image of such a void ap- dark ones. pears as a straight dark line inthe center of Tungsten inclusions may appear as single the weld. The width may vary from a thin light spots or as clusters of small light spots. sharp line to a broad diffused line. Slag inclu- The spots are usually irregular in shape, but sions and gas holes may be found in connection sometimes a rectangular-shaped light spot will with a lack of penetration void. These may appear. cause enlargements of the primary darkline or 12-4.7ExternalDiscontinuities.Various may cause it to be accompanied by a sortof kinds of surface irregularities may cause den- dotted line. Slag inclusions may cause the pri- sity variations on a radiograph. As an aid in mary line to appear broad and irregular. interpretation these should, where possible, be Sometimes, lack of penetration may show on removed before radiographing the weld. Where a radiograph as a very narrow dark line.The it is impossible to remove surface irregulari- narrowness may be due to a drawing together ties, they should be considered during inter- 127 pretation to avoid mistaking their images for Weld grooves may be overfilled due to an ex- internal defects. cessive number of passes or an inadequate arc A common surface defect is undercutting current. The overfill is referred to as "weld which is caused by melting of the upper edge reinforcement." If the reinforcement is too of the beveled weld face. When insufficient weld high, the weld radiograph will show a lighter metal is deposited to fill the groove the parent line down the weld seam. There will be a sharp metal may be reduced in thickness at the point change in image density where the reinforce- of fusion on the edge of the weld bead. This ment meets the parent metal. results in a radiographic image showing a dark Sometimes when excess metal is deposited on line of varying width and density. The dark- a fin& pass, the excess metal mayoverlap the ness or density of the lineindicates the depth parent metal. There may be a lack of fusion at of the undercut. The density and sharpness of the edge of the reinforcement. While there will the image will help in judging the severity of be a sharp change in image density between the condition. In two-side welding, undercutting reinforcement and parent metal, the edge of the may occur on the back side of theweld, so this reinforcement image is usually irregular. condition should be identified where possible. Reinforcement thickness may be reduced on In multipass welds on horizontal positions a a cover pass at the end of a beadlaid with an smooth top surface may not be produced ifelectrode which is to be changed. Increased longitudinal grooves form in the surface of the thickness may occur at the point where the new weld metal paralleling the weld seam. These electrode is started. The extra reinforcement grooves may produce dark lines on a radio- forms a crescent shape with its convex side graph. These lines have diffused edges which nearest the reduced reinforcement area left by should not be mistaken for slag lines which are the first electrode. The radiograph shows a narrow and more sharply defined. Thesedark crescent shaped image of less density because lines are seldom straight, and they are parallel of extra metal. to the weld seam. Weld reinforcements may not be ground out Sometimes molten metal may run through completely smoothly. In this case image will the root of the weld groove and be deposited on show irregulardensitiesoften with sharp the back side of the weld. This may be caused borders. Improper electrodes or long arcs may by a wide root opening or by the unusually cause drops of molten metal to spatter about high temperature of the molten metal. Drops of the weld seam. These stick to the parent metal excess metal may form. This adds to the thick- and appearaslightroundspotsona ness cf the weld reinforcement and causes a radiograph. lowered image density in the center of the weld In pipe welding itis often impossible to image. Round light spots may correspond to make a cover pass at the root of the weld. Fre- hanging drops of metal on the back side of the quently a backing ring is inserted before weld- weld. ing and is then left inside the pipe. This ring is In overhead welding especially, there may be partially fused to the weld metal on the root concavity at the root of the weld. Since this pass. The ring produces a well defined image on means less weld metal at the root, the radio- the radiograph. This is a light band across the graphic image will be a dark line down the radiograph. The weld reinforcement shows up center of the weld. The line is broader and does as a still lighter line across this band. Many of not have sharp boundaries as do lack-of-pene- the usual weld discontinuities may still occur tration lines. where backing rings are used. Slag entrapment Weld grooves not completely filled appear may cause concavity at the root during the root as dark lines on a radiograph. If the lack of pass. Also, lack of penetration can occur. fill occurs at the bevel, the. dark line will be located on one edge of the weld image and will 12-5Radiographs of Castings have a sharp border on one side and an irregu- A 'casting is usually defined as a piece of lar border on the other side. If the incomplete metal formed in a mold which is a shaped cav- fill occurs in the center cf. the weld, the dark ity prepared to receive molteh metal. There is line will be rather wide and have diffused a variety of types of molds and ways of intro- borders. ducing molten metal into the mold. The radiog-

128 rapher to be of most use to a foundry or the part, or it may be highly stressed. Theeffects casting industry should become acquainted of gas, holes on the part as itfulfills its func- with their manufacturing methods. tions must be studied. The designer orengineer Radiography may serve the casting industry may have blueprintsshowing points of stress. in two ways. It may be used to inspect castings The safety factors in the design maybe con- to control quality of production. Internal de- sidered. The exact service requirements should fects may be found before more costly machin- be known and used in a reasonableinterpreta- ing operations are started. Also, defects not tion of radiographs showing defects or discon- uncovered by machining may be detected before tinuities such as gas holes. there are service failures. Also, radiography Generally, it is known that gas holes weaken may be used as an aid incasting design. Pilot a part. The amount ofweakening is based on castings may be examined to develop good the size of the gas hole or holes in relationto foundry techniques related to chilling, gating the cross section of the part in whichthey systems, risering, and venting. exist. Gas holes grouped closely may be con- The thoroughness with which a casting sidered as one larger hole. Gas holes may be should be radiographed depends upon the de- aligned in such a way as to represent a "propa- sign and use to which the casting will be put. gating" discontinuity. This is a serious defect Castings that must undergo high stresses and which renders a part unacceptable. This is es- which may not have a high safety factor may pecially true if the part is subject to repeated require extensive radiographing. Castings not vibration or shock stresses. Isolated holes may subjected to high stresses may require only a not be too important with regard to strength. minimum of radiography necessary to detect However, aligned gas holes may present prob- the most severe defects. lems in evaluation even when reference stand- Some of the common defects that appear on ards are available. radiographs are described in this section. Some 12-5.2.Porosity. A generally porous or of these defects are found in ferrous castings spongy condition in a casting iscalled "poros- and some are peculiar to light metal castings ity." Two kinds of porosity have been identi- and alloy castings. Those described are gas fied. These are caused by gas (gas porosity) holes, porosity, shrinkage cavities, inclusions, and by shrinkage (shrinkage porosity) .Gas cold shuts, cracks, core shift, hot tears, segre- porosity is caused by the release of gas from gation, microshrinkage, and surface irregu- the cooling metal and from green sand molds. larities. Inclusion of various kinds of impurities as well 12-5.1 Gas Holes. The entrapment of gas, as as high temperatures may also accountfor gas molten metal cools in a mold, causes the defect in a casting. Gas porosity appears on a radio- or discontinuity in castings known as"gas graph as very small round dark spots. These holes." The gas may have been dissolved in the may vary from very minute spotsclosely metal ; it may arise from the mold ; or it may bunched to single large round spots. Sonietimes have been trapped as the molten metal was in aluminum castings the voids in gas porosity "gated" into the mold. The holes may occur may be elongated instead of round. singly,incluster,or randomly distributed Shrinkage porosity is usually caused by lack throughout the casting. Gas holes appear on the of metal. As a casting cools, it takes metal from radiograph as dark areas with smooth borders. the risers. If the risers should cool first, no Sometimes gas holes may be machined off a molten metal would be available to keep the casting. Therefore the interpreter should have mold cavity completely filled. Thus, some or all information related to machining when evalua- of the casting may have some shrink porosity. tions are made. Sometimes if a cavity is re- Shrink porosity appears as a dark highly ir- vealed by machining, welding or more machin- regularly shaped image on a radiograph. It ing may make the casting acceptable. may be easily distinguished from gasporosity. In evaluating the effects of gas holes found Gas porosity of a minor severity does not by radiography, the end use of the product must greatly affect the strength of a casting. The be considered. For example : the part may be effect may be determined by testing a series of required to hold liquid, it may be a moving castings containing porosity of varlous degrees

129 of severity. If radiographs are first made of as rather well defined dark lines on aradio-. these test castings they may help the radiograph. Sometimes they are difficult to see. Cold graph interpreter evaluate porosity in castings. shuts may affect the serviceability of parts Also the findings may help the manufacturer which have highly stressed applications. For adjust his casting techniques. parts that are not under stress some degree of 12-5.3 Shrinkage Cavities. Shrinkage cavi- this defect may be allowed. Cold shuts may be ties are caused by an insufficient amount of evaluated in a manner similar to cracks. molten metal when the casting cools. They are 12-5.7 Cracks. Cracks may be caused by usually found along with shrinkage porosity. stresses in cooling of the casting, incorrect de- Early setting of metal in the risers may cause sign of the casting, or by rough handling of the a part of the casting to receive insufficient mold. A crack usually makes a casting unac- metal as the part sets. Shrinkage cavities ap- ceptable, unless it can be repnired by welding. pear on a radiograph as dark irregularly This is usually too costly except in large cast- shaped spots. These may vary considerably in ings. On a radiograph, cracks appear as dark, cross section areas, depending upon the size of irregular, intermittent, or continuous lines. If the casting. the plane of the crack is parallel to the radia- Shrinkage cavities and gas holes affect the tion beam, the lines are darker and more easily serviceability of a casting in much the same seen. Usually, however, a crack is very irregu- way. Since the cavity has sharp boundaries it lar and only a small part will be aligned with is a propagating type of discontinuity. This is any given radiation beam. Therefore, exposures a serious defect, especially for castings that from several positions may be necessary to de- must withstand vibrations and shock loadings. termine the extent of a crack or even to prop- 12-5.4 Inclusions. Inclusion is a term applied erly locate one. Other non-destructive methods to sand, oxide, slag, or any other foreign ma- should be used to supplement radiography in terial in a casting. Inclusions may appear as detecting cracks. light or dark spots on a radiograph depending 12-5.8 Core Shift. Some castings are made upon the relative densities of the inclusion and the base metal. If an inclusion is denser than by inserting a core in the mold to produce a the base metal it will appear as a light spot on void in the casting. If the core is not firmly a radiograph. In some cases inclusions do not fixed in the mold, it may shift when the molten harm the serviceability of a casting. In other metal is poured. A shift of the core is easily cases it may render an item unusable. seen on a radiograph since the void left by the core appears as a dark well defined area. Eval- 12-5.5 Misruns. A misrun occurs when uation of core shifts should consider the design molten metal fails to fill the mold completely. It may be a minor void which is t,xternally ap- allowances for machining of wall thickness. parent. Sometimes, however, a minor appearing 12-5.9 Hot Tears. As metal cools it contracts. misrun connects to a deeper cavity which may Sometimes, because of the shape and because of be seen on a radiograph. Misruns, being voids, the rigidity of the mold, stresses are set up in appear on a radiograph as dark areas with the cooling metal. If these stresses exceed the rather well defined borders. In large, costly strength of the metal, tears or cracks may ap- castings, misruns may be repaired by welding pear in the still hot metal. These are likely to or other procedures where the service require- occur at places where a thin section joins a ments will allow. thicker section of the casting. Impurities may 12-5.6 Cold Shuts. Sometimes streams of cause weak spots and contribute to the tear. molten metal entering a mold are split by cores Tears appear on a radiograph as dark lines that or chaplets and come together again. When the are ve,lr ragged and may have a number of streams of metal set to such an extent that they branch r. of varying densities. do not fuse into each other upon meetings,a 12-5.10 Segregation. When certain alloys are cold shut results. This may happen with mag- used for castings, the constituent metals may nesium, for example, because of the narrow tend to separate in spots. This separation will range of temperatures at which the metal flows show up as light and dark blotches on a radio- without oxidizing or setting. Cold shuts appear graph. Usually, castings with segregation are

130 rejected, except when relativelysmall areas graphs the casting should bevisually inspected and surface irregularitiesnoted. show this condition. irregularities 12-5.11 Microshrirkage. Magnesiumcastings Two common types of surface sometimes have a kind of porosityreferred to are surfacepits and excess surface metal.Sur- The radiographic image face pits usually appear asrather diffused dark as "microshrinkage." borders. Their radio- ofmicroshrinkageisusuallydarker and spots without well defined sharper than shrinkage porosity inaluminum. graphic image appears similar toinclusions. The image is one of fuzzy orfeathery streaks Some surface irregularities aresharply defined that outline a definite area. and may be difficult todistinguish from inclu- 12-5.12 Surface Irregularities. Surfaceirreg- sions or blowholes on aradiograph. ularities should be studied so thatthe inter- Excess surface metal appears aslight areas internal dis- corresponding to the dimensions ofthe excess preter can distinguish them from rather easy to continultiesofT'ariouskinds. A surface metal. This condition is usually irregularity may or may not beconsidered a identify because of the lightdensity of the defect. However, since they appear onradio- Fige.

131 Part IV Regulations and Procedures

Through ignorance, carelessness, or disregardfor safety and, in some cases, equipment failures,there has been a long series of unfortunateand unnecessary human overexposuresto radiation. In many incidentsthe cause was directlyattributable to failure on the part of aresponsible technician. An effort to eliminate this situation hasled government agencies to prepare regulatory control measures.These agencies have adequate authority to enforce compliance. Rather than viewing these as policing andenforcement matters, the radiographer could have a better workingperspective by accepting the regulations as safety guidelines. Some of the Nation'sleading authorities frequently review and revise the regulations. Therevisions give due consideration to the technician's operating requirements. It is advisable for the student to obtain andstudy, along with Chapter 13, a copy of the "AEC Licensing GuideINDUSTRIALRADIOG- RAPHY" referred to on page 135.

/32./ 133 Chapter 13

TransportationRekulations GovernmentLicensing,Health, and for IsotopeRadiography

plus the Chairmanof AEC Regulations tion, and Welfare 13-1The Authorityfor AEC and othersdesignated by thePresident) and Committee onRadiation Protec- The AtomicEnergy Commission(AEC) is the National which is tion and Measurements(comprised of notable the branch of theFederal government officials responsible for theatomic energy program.In scientists, physicians,and government its facilities, theAEC experienced inradiation) . TheNational Com- addition to operating International regulates and licenses usesof selected nuclear mittee cooperatesclosely with the establish Radiological Protection. materials. The powersof the AEC to C immittee on drawn to regulations and grantlicenses are pursuantto Regulations andsafety rules are radiation exposuresto a point the Atomic EnergyAct of 1954 (68Stat. 919) . limit personnel concerned with thevarious far below dangerlevels and toafford accept- This chapter is the general publicof the government regulationswhich apply tothe li- able protection for censing, use, andtransportation ofradioactive United States. radiog- of materials in connectionwith industrial 13-2Licensing andPolicing Authority raphy operations. pertaining to States and Other"Bodies" All discussions,except those Energy Act of 1954 wasamended transportation, are based onAEC regulations The Atomic in 1959 to permitthe AEC to enterinto agree- as publishedin the Code ofFederal Regulations allow R0, and ments with the governorof a State to (CFR), Title 10,Chapter I, Parts 20, Commission's portions most pertinentto the State to assumecertain of the 34, which are the regulatory authority.This authority isspecifi- radiographic operations.The "AEC Licensing and special Radiography" supplements cally limited tobyproduct, source, Guide for Industrial nuclear material inquantities not sufficientto these regulations.(It is availablefrom the should form a critical mass. Atomic EnergyCommission.) This guide accepted theseresponsi- be available to everyradiographer studying States which have bilitiesfrom AEC arecalled "Agreement this manual. Any personplanning to apply for Agree- should use this States." At this timethere are several an isotoperadiography license States are in the processof the license applicationform ment States. Other guide in preparing assuming such controls. and the supplementaryrecords and as anaid in carrying out therequired supplementary 13-3Requirements for aSpecific License procedures. Thediscussions ontransportation to Use ByproductMaterials for Radi- regulations. are based onfederal transportation ography These discussions arenot officialinterpreta- not be Specific licenses to usebyproduct materials tions of federalregulationg, and should successful simply illustrativeand are issuedto named persons upon taken as such. They are application to theappropriate agency.All per- explanatory notesdesigned to acquaintthe transfer, re- with the controlswhich sons who"manufacture, produce, reader in a general way ceive, acquire, own, possess,use, import, or cm- in effect. are currently port" byproductmaterial must havesuch a In actual practice,the AEC setsstandards for a license are for licensees on thebasis license. The requirements for its operations and summarized here anddiscussed in greaterde- of its own operatingand researchexperiences of the FederalRa- tail in sections whichfollow. and the recommendations The first step for aspecific license is filing diation Council (made upof the Secretariesof an applicationform. (See Figures13-1a, b.) Defense, Commerce,Labor, and Health,Educa- /31/ 135 This form must be completed and submitted to permission. This permission is not given until the appropriate regulatory body. the person to receive the license has fulfilled There are general requirements which must all the requirements for holding a license. be met before a radiography license will be is- Each license issued by AEC includes an ex- sued. The first is that applications must be for piration date, at which time it becomes invalid. a purpose authorized by the AEC Act. The sec- If and when a license becomes invalid all radia- ond requirement is that the applicant's pro- tion work covered by the license must be sus- posed equipment and facilities be adequate to pended. However, licensees are permitted to protect health and minimize danger to life and apply for renewal of their licenses. Such appli- property. Radiation protection standards are cations should be filed and submitted at least 30 used to determine whether or not this condition days before expiration of the old license. The is met. The third general requirement is that old license will remain in effect so long as the the applicant be thoroughly qualified by train- renewal application is pending. ing and experience to use the byproduct ma- The revocation or suspension of a license terial for the purpose requested and according may be done for two primary reasons :(1) the to the safety measures required. making of false statements in connection with Applicants who will be using sealed sources or in the application for a license ;(2) the dis- in radiography must also meet the following covery )f conditions in violation of the terms additional specific requirements to be approved of a license. In connection with the latter, the for licenses :(1) The applicant must show that licensee will usually be given an opportunity he has an adequate program for training ra- and time to make whatever changes are necek.- diographersandradiographers'assistants. sary for compliance, with one exceptioncases (The type of training program required is out- of willful violation. lined later in this e,hapter,)(2) The applicant The regulations grant the power to withhold must indicate that ratherdetailedrecords or recall . byproduct material from licensees showing the receipt, transfer, export, and dis- when it is felt the latter are not equipped to posal of byproduct materials will be kept and carry out necessary safety precautions. Viola- that these reports will be available for inspection of safety and other regulations is also tion. (3) The applicant must include satisfac- cause for the withholding or recalling of such tory written operating and emergency proce- materials. dures and an internaltest and inspection The regulations provide that when the Com- system in his application.(4)Finally, it is mission enters into an agreement witha State, specifically required that a description of the the licenses issued by the State will be recog- overall organizational structure of the proposed nized by the Commission within certain speci- operation be submitted with the application. fied limits. These limits apply whenan Agree- These requirements are elaborated upon later ment State license does not limit radiography in this chapter. to one address, but rather provides for field When it has been determined that an appli- use at temporary job sites. cation complies with licensing requirements, an appropriate license will be issued. 13-5General Standards for Protection Against Radiation 13-4 Conditions and Control of Licenses It has been brought out that radiationcan The provisions of the AEC Act define vio- be safely used in production, research, and de- lations of any of its licensing requirementsas velopment applications. At thesame time, it a crime punishable by fine and imprisonment. was made clear that rather rigid safety stand- Such strong penalties are necessary because of ards must be maintained for protection against the health consequences of violations. Atany radiation hazard. Regulationsare designed to time that a violationoccurs or appears immi- control the receipt, possession, use, and trans- nent, the Commission may obtain.tri injunction fer of licensed material by licensees in sucha or court order and take punitive action against manner as to prevent individuals from receiv- the offender. ing radiation exposure inexcess of the pre- The regulations do not allow transfer ofa scribed standards. These standardsare con- license to another person, except with written sidered adequate to safegua: d the radiation

136 ww., .... UNITED STATES ATOMIC ENERGY COMMISSION Form AEC-313R APPLICATION FOR BYPRODUCT MATERIAL LICENSE Form approved (9-62) Midget tureen Ntl 38-1I37 1--- USE OF SEALED SOURCES IN RADIOGRAPHY 7=/ SEE ATTACHED FORM AEC-313R INSTRUCTIONSUSE SUPPLEMENTAL SHEET WHERE NiCESSARY BE SURE ALL ITEMS ARE COMPLETED AND THAT ALL NECESSARY ATTACHMENTS ARE FURNISHED.IF ANY PORTION OF THE APPLICATION IS NOT APPLICABLE SPECIFICALLY SO STATE. DEFICIENT OR INCOMPLETE APPLICATIONS MAY BE RETURNED WITHOUT CONSIDERATION.

Iso) NAME AND ADDRESS OF APPLICANT 2. PREVIOUS LICENSE NUMTIELib) (Indicate if application is for renewal sr amondmen of an eisisting byproduct meterial license.)

3 LOCATION(S) WHERE SEALED SOURCES WILL BE USED AND/OR STORED (II use 1(b) APPLICANT IS: An individual A partnership A Corporation An will be made in states other then named in 1(o), they should be listed here ) Unincorporated Association Li Other 111 If op& licant is other thanon individ vol. the applicable section on therrrrr se side must be completed.

4. SEALED SOURCES TO SE USED IN RADIOGRAPHY

BYPRODUCT MATERIAL MAXIMUM ACTIVITY SOURCE MODEL NUMBER NAME OF MANUFACTURER NUMBER Of SOURCES (E lement and Mass No.) PER SOURCE

A. A.

C. C C. C.

5. RADIOGRAPHIC EXPOSURE DEVICES AND/OR STORAGE CONTAINERS TO SE USED WITH SOURCES LISTED MOVE

MODEL NUMBER NAME OF MANUFACTUREA (II custom mod*, attach complete design spetifkation.)

I S.

C C. 6. THE FOLLOWING INFORMATION IS ATTACHED AS A PART OF THIS APPLICATION: (Checkop/marble blocksandettacts information celled ktr inIhtt Mori/diens with this lone.) Net Applicable Aitoclard Previously Submitted

(a) Description of radiographic focilibes (Instruction 6-o) . . . . . on 0 (oAtt) (b) Description of radiation detection instruments to be used (Instruction 6-b), . 0 "(it)om (c) bstrument colibrotion procedures (Instruction 6-c) . I 0 0 en (d) Personnel monitoring equipment (Instruction 6-d) . ... . 0 0 (...) (e) Operating and emergency procedures (Instruction 6-e) . . il en (I) Training program (Instruction 6-f) ... 0 ___. (Dm) 1 (0) Internal inspection system or other management control (Instruction 6-.) ...... 0 (we) (h) Overall organizetional structure (Instruction 6-h) . 0 (Dm) (i) Leak testing precedures (Instruction 6-i) en (OATS) CERTIFICATE (This itm must be completed by ap licant) 7. THE APPLICANT AND ANY OFFICIAL EXECUTING THIS CERTIFICATE ONBEHALF OF THE APPLICANT NAMED IN ITEM I, CERTIFY THAT THIS APPLICATION IS PREPARED IN CON- FORMITY WITH TITLE 10, CODE OF FEDERAL REGULATION, PART 30,AND THAT ALL INFORMATION CONTAINED HEREIN,INCLUDING ANY SUPPLEMENTS ATTACHED HERETO, IS TRUE AND CORRECT TO THE BEST OF OUR KNOWLEDGE AND BELIEF

Applicant Named in Nem 1

DATE Title of Certifying Official WARNINO.-111 U.S.C., Section 1001, Ad of Jun* 25, I94C 62 SIM. 749r makes it a criminal offense b mrkewillfully fake statement er repruentatien to any department or agency af the United States as te any matter within its jurisdictian. -- FIGURE13.1.Application for Byproduct Material License-Use of Sealed Sources in Radiography.

137 FORM AEC-313R (9-62)

LEGAL STRUCTURE OF APPLICANT

If applicant is a cc rporation, complete Items 8 through 11; if applicant is a partnership, ccmplete Items 12 through 14; if applicant is onunincorporated association or a legol entity other than a partnership or corporation, complete Items 15 and 16.Attich separate sheets where space provided proves inadequate.

CORPORATION

S. STOCK OF APPLICANT CORPORATION

NO. OF SHARES NO. OF SHARES NO. Of SHARES ,, TOTAL NUMBER Oft AUTHORIZED I ISSUED SUBSCRIBED (a) Stockholders (b) Subscribers

1--- 9. Is applicant corporation directly or indirectly controlled by ensther co welkin or other legal entity? YES NO If answsr is "YES" give nom* and address of other corporation or ether Noel entity end describe how such control exists end the extent thereof.

10. (a) Identify by name end address any individual, cmporetien, or other legal entity (1) owning 10 percent orMOMof the stock al applicant cmperotioo issued end outstanding tor (2) subscribing m 10 percent or more of the outherixed lout unisvmd'stesk of the corperstion. (b) Identify by neme and oddress ell officers and directors of the ceoperstien,

I I. Identify tfie State, District, Territery, or penessien under dm lows of which the opplicont is incerporMitd.

PARTNERSHIP 12. Name and oddrem isf each individual or Meal entity owning pertnorship intered in the opplicont.

13. State rho percent et ewnership of the epplicent partnership held by each of the individuals or legol entities lister; is Item 12.

14. Identify the State. District, Territory,Ofpossession under the lows of which the emplicont partnership I. orgoolled.

, OTHER. I S. Describe the nowe of the epplicent and identify the State, District, Territory, or poisession under the laws of which it is orgenissid.

16. State me Imol number of members m persons holding en ownership in the @pelisse', ideetify moth by name end address, end indiosto the ownershipinterest thereof.

FIG. 13.1.Application for Byproduct Material License-Use of Sealed Sources in Radiography (reverse).

138 public. They are also rems per calendarquarter provided the radiog- worker and the general not exceed flexibleenoughtoallowforindustrial rapher's accumulated dose does 6-8.3).Before operations. 5 (N-18) (refer to paragraph The standards for personnelprotection are permitting an individual to receivesuch expo- quite specific. Each of the rulesis precise in sure, each licenseemust record on suitable forms outlining the quantities of radiationwhich can each period of time theindividual has been precautionary meas- occupationally exposed since his 18thbirthday be tolerated and certain prepared. ures to betaken. Since these standards have and have the individual sign the form been included in the industrialradiography li- (See Figures 13.2 and 13.3:) Whenfor some sections will be re- reason the individualhas no record of his oc- censing guide, only selected the viewed here. cupational exposure, the licensee must use 13-5.1 Definitions. Since federalregulations arbitrary rates prior to January 1,1961, of 11/4 rems are legaldocuments, care must be taken so 33/4 rems or after January 1, 1961, that technical words will notbe misinter- per calendar quarterfor periods prior to this preted. Such terms as "byproductmaterial," time. Note :if doses computed in this manner "calendar quarter," "individual,""occupational show exposure prior to January 1,1961, to ex- dose," "person," "radiation,""radioactive ma- ceed 5 (N-18) the excess amountneed not be terial," "restricted area,""unrestricted area," used in further computations ofpermissible "dose," "radiographer,""radiographer's assist- rates of exposure. ant," "radiographic exposuredevice," "radiog- 13-5.3 Permissible Levels ofRadiation in raphy," "sealed source," and"storage con- Unrestricted Areas. With proper controls, it is tainers" have specified definitions forregula- are permissible torelease radiation into unre- torypurposes.Although theseterms stricted areas which does not exceed thefollow- defined in v.zious places in this text,the ra- 2 with the ing limits :0.5 rem in one calendar year, diographer shoald familiarize himself millirem in one hour, or 100 millirem in seven glossary. precise definitions which appear in the consecutive days. 13-5.2 Exposure of Individuals toRadiation It is believed that if an individual were con- in Restricted Areas. In radiographyoperations tinuously present to receive these accumulated prevent some it is impractical or impossible to dosages there could be no body harm. exposure of individuals toradiation. For this reason radiographymust always be performed 13-5.4 Exposure of Minors. Radiation dam- in restricted areas. Equipmentdesigns and age is more severe togrowing organisms. For controlled procedures will permit theradiog- this reason no individual under 18 years of age rapher to work without receivingexcessive is permitted to receive dosages exceeding10 radiation doses. percent of the limits specified in Table13.1. Limitations on individual dosage havebeen There is a special regulation to protect per- set according to Table 13.1. Thedosage should sons under 18 years of agebecause of their always be kept to a minimum. A generalguide greatersusceptibilitytoradiationinjury. to follow is that the maximum averagedose of Under normal conditions, such persons will not 100 mr/wk will not exceed the "tolerancedose." be involved in operations licensed forradiog- raphy. When they are, permissible exposure is TABLE 13.1.Exposure Limits in Restricted one-tenth that for persons over 18 years of age. Areas (In any calendar quarter) . 13-5.5 Symbols and Signs. Regulatory re- (1) Whole body; head and trunk; active bloodforming organs; lens of eyes; or gonads 124 rem quirements ih many instances have created a (2) Hands and forearms; feet and ankles. 18,4, rem 71/2 rem public awareness of standardized safety colors, (8) Skin of whole body symbols, and signs. Radiation warning symbols On occasion, certain operations requirethat and signs of a certain type are alsorequired an individual workerbe exposed to radiation for specific situations. The design andother doses in excess of the limits shown above.This specifications of these symbols and signs are fact has been recognized and aprocedure discussed in paragraph 13-6.4 and are illus- worked out which allows exposures up to3 trated in Figures 13.4, 13.5, 13.6, and 13.7. 139 FOAM AEC-4 Form Approved. (HO Bureau of Budget No. 36-R119. Expiration Date: June 30, 1961, U.S. ATOMIC ENERGY COMMISSION OCCUPATIONAL EXTERNAL RADIATION EXPOSURE HISTORY Sete Instructions on the Back

IDENTIFICATION 1, NAME (PR1ATLAST, FIRST, AND MIDDLE) 2. SOCIAL SECURITY NO.

3. DATE OF NIRTH (MONTH, DAY. YEAR) 4, AGE IN FULL YEARS (N)

OCCUPATIONALtouposunarnsvious HISTORY

PREVIOUS DOSE HISTORY 5. PREVIOUS EMPLOYMENTS INVOLVINGRADIATIONEXPO. I. DATES OF EMPLOYMENT SURE--LIST NAME AND ADDRESS OF EMPLOYER (rmoNTo) 7, PERIODS OF EXPOSURE S. MIME BODY 4, INSERT ONE: (nrk) RECORD OR CALCULATED

II, REMARKS II. ACCUMULATED OCCUPATIONAI. DOSETOTAL

13. CALCULATIONSPERMISSIBLE DOSE 12. CERTIFICATION: I CERTIFY THAT THE EXPOSURE HISTORY LISTED IN COLUMNS 5. 4, AND 7 IS CORRECT AND COMPIZTE TO ME BEST OF MY KNOWLEDGE AND BELIEF. WHOLE BODY:

(A) PERMISSIBLE ACCUMULATED DOM 5(14-111)

EMPLOYEE'S SIGNATURE DATE (111) TOTAL EXPOSURE TO DATE (FROM ITEM 14) NEM

M. NAME or LICENSEE f,C) PERMISSIBLE DOSE REM

FIGURE 13.2.Occupational External Radiation Exposure History.

140 FORM AEC-5 Form approved. (NO) Bureau of Budget No. 35-R120. Expiration date: June 30, 19W. U.S. ATOMIC ENERGY COMMISSION Current Occupational External Radiation Exposure See Instructions on the Back IDENTIFICATION I. NAME (PRINTLast. first, and middle) 2. SOCIAL SECURITY NO.

3.DATE OF BIRTH (Month, day. year) 4. AGE IN FULL YEARS (N)

OCCUPATIONAL EXPOSURE

5.DOSE RECORDED FOR (Specify: Whole body; skin of 6.PERMISSIBLE DOSE AT BEGINNING 7. METHOD OFMONITORING(e.g.,Film BadgaFl; of whole body; or hands and forearms, feet and ankles.) OF PERIOD COVERED BY THIS SHEET Pocket ChamberPC; CalculationsCalc.

13. RUNNING TOTAL FOR S.PERIOD OF EXPOSURE DOSE FOR THE PERIOD (rem) (Fromto) CALENDAR QUARTER (rem) 1. GAMMA 10.BETA II. NEUTRON 12. TOTAL

LIFETIME ACCUMULATED DOSE

14. PREVIOUS TOTAL IS. TOTAL DOSE RECORD-16. TOTAL ACCUMULATED 17.PERM. ACC. DOSE ItPERMISSIBLE DOSE ED ON THIS SHEET DOSE rem rim rem 5(N = rarll rim I.NAME OF LICENSEE FIGURE 13.3.Current Occupational External Radiation Exposure.

141 13-5.6 Limits on Levels of Radiation for and records kept of the location of sources and Radiographic Exposure Devices and Storage of field intensities where personnel are likely Containers. Certain regulations are designed to to be exposed. After each exposure is com- protect workers from radiation emanating from pleted, and after sources are "stored," surveys radiographic exposure devices. The standards must be made to determine. if the source has which must be met for sealed sources in the been properly shielded. In effect,radiation shielded, i.e., "off" position for the separate hazards incident to radiographic operations classes are as follows : must be surveyed and evaluated, and records Radiographic exposure devices measuring of these findings must be keft on file for review. less than four (4)inches from the sealed 13-6.2 Storage of Licensed Material. The ra- source storage position to any exterior surface diographer must make sure that unauthorized of the device shall have no radiation level in personnel do not have access to stored material excess of 50 milliroentgens per hour at six (6) at any time. inches from any exterior surface of the device. 13-6.3 Personnel Monitoring. Each radiog- Radiographic exposure devices measuring a raphy licensee must provide film badges and a minimum of four (4) inches from the sealed dosimeter (or pocket chamber) for each radiog- source storage position to any exterior surface rapher and radiographer's assistant to wear of the device, and all storage containers for while performing radiographic operations. sealed sources or for radiographic exposure de- 13-6.4 Caution Signs, Labels, and Signals. vices, shall have no radiation level in excess of The necessity for clearly marking radioactive 200 milliroentgens per hour at any exterior materials and exposure areas is obvious as a surface, and ten (10) milliroentgens per hour precautionary procedure. However, since con- at one meter from any exterior surface. cepts of adequate signs, labels, and signals 13-5.7 Radiation Survey Instruments for vary, and because standardization has advan- Radiographic Operations. It is also required tages, the established rules are outlined here. that calibrated and operable survey meters be Licensees must place radiation caution sym- used to survey radiation fields at operation bols, Figure 13.4, and signs in a conspicuous sites. The instruments used must have a range 60° capable of reading as low as 2 mr/hr and as high as 1,000 mr/hr. (It is not mandatory that this entire range be measurable on a single instrument.) 13-5.8 Tagging Sources. Some sealed sources are not fastened to or contained in a radio- 00 graphic exposure device. Such sources are required to have permanently attached a durable tag at least one inch square upon which is printed the radiation caution symbol and the instruction "DangerRadioactive Material Do Not Handle. Notify Civil Authorities if Found." 13-6Precautionary Procedures and Rec- ords Required of Licensees Certain rules and regulations are enforced with regards to safety which are strictly precautionary procedures. These may be briefly stated as follows : i4- A 13-6.1 Surveys. Radiation surveys arere- A 4I./IL2 quired in the interest of safety. It is desirable, I Iy before using sources, to make calculations of the dose rates into restricted and unrestricted areas. During exposures, surveys must be made FIGURE 13.4.Radiation Symbol.

142 FORM AIEC4N3 place in all exposureareas, and on all con- CIL111 tainers in which radioactive materialsare transported, stored, or used. Each area, room, and containerin which radiography sourcesare used or stored must be conspicuously posted with signsbearing the CAUTION radiation symbol and the words CAUTI(Px(or DANGER) RADIOACTIVE MATEiviAL (Figure 13.5). CAI/ 0

e RADIATION AREA

FIGURZ 13.6.Radiation Area Sign (symbol in magenta on a yellow background).

body could receive a dose exceeding 100 parem RADIOACTIVE MATERIAL in any one hour. Each high radiation area must be conspicuously posted with signs bearing the caution symbol and the words : CAUTION (or DANGER) HIGH RADIATION AREA FIGURE 13.5.Radioactive Material Sign (symbol in (Figure 13.7). magenta on a yellow background). In addition to radiation warning signs, high radiation areas must be equipped witha control Radioactive material containers must havea device which, upon entry byan individual, tag or label stating the (1) kind of radioactive shall : material therein, (2) quantity, and (3) date of measurement. (1) reduce the radiation intensity to less Radiation area means any area accessible to than 100 mr/hr, or personnel in which radiation exists at such (2) energize a conspicuous visibleor au- levels that a major portion of the whole body dible alarm so the entering individual could receive in any one hour a dose exceeding and the individual responsible for the 5 mrem, or in any 5 consecutive daysa dose in high radiation area will be alerted excess of 100 mrem. Each radiation area must that someone has entered the area. be conspicuously posted with signs bearing the radiation symbol and the words: CAUTION In the event thata high radiation area is (or DANGER) RADIATION AREA (Figure established for a period of less than 30 days, 13.6). the control device is not required; however, it High radiation areameans any area accessi- is most desirable that a responsible individual ble to personnel in which radiation exists at stand gum d to restrain individuals from enter- such levels that a major portion of the whole ing the radiation field.

143 FORM AIC.21114 (3) Operating procedures applyingto the work under the license (4) Figure13,8 AEC RegionalOffice Locations. CAUTION If it is impractical to post thedocuments they may be kept availablefor employees' examination upon request. 13-6.6 Waste Disposal. The continued svfety of the public demands safe disposalof radioactive wastes. However, since decayedradiog- raphy sources have such high activitythe only practical means of disposal is to send the source to an authorized disposal company.Radiog- raphy Sources are usually returnedto the source vendor. Ali Licensees must not bury, incinerate, discard into the ocean or otherwise finally disposeof waste materials without license authorization. HIGH RADIATION AREA 13-6.7 Security. Security regulations require that a radiographer or radiographer's assistant shall maintain a direct surveillance of each radiographic opr ation to protect against un- FIGURE 13.7.High Radiation Area Sign (symbol in authorized entry into a high radiation area. The magenta on a yellow background). only exceptions to thisrule as previously brought out, occur when :(1) the high radia- 13-6.5 Instruction of Personnel and Notices tion area is equipped with a control device or to Employees. Regulations in and of themselves alarm system or (2) the area is locked to pro- are only partial answers to safeguardingthe tect against unauthorized or accidental entry. personnel of licensed operations. It is necessary 13-6.8 Records, Reports, and Notification. that all personnel be familiar with the hazards Mention has already been made of some of the and the safety precautions for them. Conse- records which are required of licensees. All quently, all licensees are required to : records and reports are studied periodically and (1) Inform every individual working in must be carefully kept. It is also necessary to restricted areas of all radiation haz- notify the proper authorities of thefts and mis- ards present ; haps ana to provide employees and former em- (2) Instruct all such individuals in the ployees with reports of their occupational ex- necessary safety practices and proce- posuretoradiation.The most important duresforthetypesofhazards records are : present ; (3) Instruct all personnel in the applicable (1) Records of personnel monitoring must provisions of regulations and licenses be kept which provide the information which apply to their protection; specified in Figure 13.3. (4) Advise employees of copies of radia- (2) Records of surveys must be prepared tion reports which they may request. toshowlocationsofradioactive sources, radiation field intensities, and In addition each licensee must post in a con- protectivemeasurestosafeguard spicuous place, and at a place where employees individuals. pass on their way to and from work : (3) Records of quarterly inventory. (1) Current copies of the AEC regulations (4) Records of receipt and shipment of relating to standards for protection sources. against radiation (5) Records of source utilization. (2) A copy of the radiography license (6) Records of leak tests.

144 Reports and notifications which must be made a period of 24 hours, wouldexceed include : 500 times the limits specified for such materials in Appendix )3, Table II of (1) Reports of personal dosage, ifre- Part 20 of CFR ; or quested, shall be made to former (3)A loss of one day or more of the op- employees. eration of any facilities affected ; or (2) Reports, if requested, shall be made to (4)Damage to property in excess of employeesoftheannualdosage $1,000. received. (3) Reports of theft or loss of byproduct 13-7Qualifications and Training of Radi- material shall be made to the nearest ography Personnel AEC Regional Office listed in Figure 13.8. Two types of radiography personnel, i.e., Immediate notification must be made to the persons engaged in the actual handling and use manager of the appropriate AEC Regional Of- of sealed sources of radiation and related fice of incidents involving : equipment, are recognized by the AEC. A radiographer is defined as any individual who (1) Byproduct source or special nuclear either performs radiography himself or who is material which has causedor in attendance at the site of use and personally threatens to cause exposure of the supervises radiographic operations. The radiog- whole body of any person to 25 rems rapher bears the direct responsibility to the li- or more of radiation, exposure of the censee's management for compliance with regu- skin of the whole body of any individ- lations and license conditions. A radiographer's ual to 150 rems or more of radiation, assistant is defined as a person who manipu- or exposure of the feet, ankles, hands, lates equipment and material related to radiog- or forearms of any individual to 375 raphy under the direct and personal supervision rems of radiation. of a radiographer. A radiographer's assistant (2) The release of radioactive material in must be under surveillance at all times by a concentrations which, if averaged over radiographer. The radiographer's assi6tant can- a period of 24 hours, would exceed not exercise independent judgment in work re- 5,000 times the limits specified for lated to radiography. The duties and responsi- such materials in Appendix B, Table bilities of a radiographer may not be delegated II of Part 20 of CFR ; or to a radiographer's assistant. (3) A loss of one working week or more Because sealed sources used in radiography of the operation of any facilities af- are hazardous if not properly used, persons who fected ; or aspire to positions as radiographers or radiog- (4) Damage to property in excess of rapher's assistants must meet certain minimum $100,000. training and experience qualifications. In fact, For lesser incidents, the licensee is given 24 it is mandatory that each applicant for a li- hours to notify the manager of the appropriate cense to use byproduct material have an ade- AEC Regional Office (see Figure 13.8) by tele- quateprogramfortrainingradiography phone or telegraph. Incidents which fall in this personneL class are : 13-7.1 Training Programs. Training programs normally consist of four phases which (1) Exposure of the whole body of any may be elaborated as follows : individual to 5 rems or more of radia- 13-7.1a The Initial Training Program. The tion ; exposure of the skin of the whole initialtraining program for radiographers body of any individual to 30 rems or must cover five major categories of subjects. more of radiation ; or exposure of the The list of subjects is : feet, ankles, hands, or forearms to 75 rems or more of radiation ; or I.Fundamentals of radiation safety. (2) The release of radioactive material in A. Characteristics of gamma radia- concentrations which, if averaged over tion.

145 Form AEC-3 ioCFsssS (6-45) UNITED STATES OF AMERKA ATOMIC ENERGY COMMISSION Washington, D.C. 20545 In Port 20 of its RulesNOTICE and Regulations, the Atomic Energy againstTO Commission radiation EMPLOYEES hazardshas established from radioactive standards mattrial for your under protection license issued by the Atomic Energy Commission, STANDARDS FOR PROTECTION AGAINST RADIATION YOUR EMPLOYER'S RESPONSISILITY REPORTS ON YOUR RADIATION EXPOSURE HISTORY 2.Your Post1. employerApply or otherwise these is requiredAEC make regulations to-availableAEC license regulations, and to you theto all condition:a copywork license:, underof theof andthehis license. operating procedurv I. The in theployeesofyou anylicense. a written applicable arc set report forth limit inif yousection as setreceive 20.101,forth an in exposure 20.103,the regulations and in excess20.104AEC or regulations require that your employer give The basic limits for exposure to em- In legion I I YOUR RESPONSIIILITY whichAStheir A WORKER apply provisions to work to you. you arc engaged in, and explain 2. If you work where personnelpursuanton exposureof monitoringradioactivethe toPart Sectionto 20 radiation material regulation.is 20.202:required and in air.exposure Thew sections to concantrPtions specify limits viaciw ..,r) 60 IS. provisionstoAECYou the should regulations, work for familiarizeyou your arc and ownengaged the yourself protectionoperating in. with procedures and those protection provisions which of applyof your the You should observe their (a) your employer must give you a writtenof yourtion report ofradiation your employment exposures uponif you the request termina- it, and HAWAII L.,0.1111111111 I I WHATco-workers. IS COVERED BY THESE AEC REGULATIONS AllINSPECTIONS activities under the license are subject to inspection(b) your by employer must advise you annuallyyour exposure of to radiation if you request it. 0I. awelisn S)4.13 V CANAL IONS 4.3.2. CautionPersonnelMeasuresI. Limits signs, ontomonitoring, exposurebe labels, taken andafter tosurveys radiation safetyin accidental restricted and interlock and equipnunt; exp3sure;radioactiveand equipment;unrestricted material areas; sentInquiriesINQUIRIESrepresentatives to the dealing United of theStateswith U.S. the Atomic Atomic matters Energy Energy outlined Commission Commission. above can Com- be UNITED STATES ATOMIC ENERGY COMMISSION COMPLIANCE OFFICES I" logien I I 6.5. RelatedExposure matters. retords and reports; and plant,pliance as Office shown having on the inspectionmap at the right.responsibility over your REGION Region I, D6ision et Compliance, USAEC ADDRESS 212-9N-1000 11A117MC A A ?MIMI212-949-1000 Aft NOLIBATIIi POSTING REQUIREMENT III New374Regien HaimYork, II,NewStreet Division York 10014of Cusp lime, USAEC 404-535-5791 401-534-5791 anyMCplacesCopies oreportion inconducted,of every this of notice aestablishment restricted to permitmust bearea postedwhere to observe activitiesin a sufficient a copy licensed on number the by way the of employees working in or frequenting III SalmAtlanta,50 SeventhRegion 410, Cow& III,°skim&Stmt. Division 30323 Northeast l'refeesiesal et Comm Mang&KM MEC 312-144-11110 312-739-7711 to or from their place of employment. IV OakDenver,IONReg/en Brook West IV,IllinoisOs DivisionWageColfax 112215 Armee of Comp &sof, USAEC 60523 303-2974211 303437-50% Mau 18.8.AEC Regional Office Locations. V 2111RabeRegion Rawl& ley, V. CaliforniaWay Divide. et Compliance USA= 94704 CO 1011 155 415-141-5110 415451-5430seedas-oase-ma aro B. Units of radiation dose(mrem) A review of the list ofsubjects required indi- ofradioactivity cates that a givenapplicant for a license may andquantity knowledge (curie). not have employeeswith sufficient of of radiationprinciples to provide the necessary C. Hazards of excessive exposure the applicant radiation. instruction. If such is the case, from licensed may specifythat initial trainingwill be per- D. Levels of radiation consultants, schools, or material. formed by qualified E. Methods of controllingradiation commercial companieswhich provide training dose : courses forradiographers. 1. Working time 13-7.1b Periodic Training.It has been em- 2. Working distances phasized elsewhere that thefield of nuclear sci- 3. Shielding ence is rapidlychanging. Insofar asradiog- II. Radiation detectioninstrumentation to raphy is concerned, changesin equipment and be used: technology are constantlyoccurring which re- A. Use of radiation surveyinstru- quire revisions inoperating and emergency ments. procedures and the learningof new techniques. 1. Operation This is why the radiographypersonnel must re- 2. Calibration ceive updated instructionwhenever changes 3.Limitations. occur in theradiography program.The licensee B. Survey techniques. is made responsible fordetermining that both C. Use of personnelmonitoring equip- radiographers and radiographers'assistants ment have an understandingof all changesaffecting 1. Film badges their work and are competentto use new equip- 2. Pocket dosimeters ment, instruments, andprocedure 4. 3. Pocket chambers. 13-7.1c On-the-job Training.The necessary III. Radiographic equipmentto be used : competency in the handlingand use of expo- A. Remote handlingequipment. sure devices,sealed sources, etc., oftrainees B. Radiographic exposuredevices. can only bedemonstrated on the job.For this C. Storage containers. reason on-the-jobtraining is considered avital IV. The requirements ofpertinent regula- aspect of trainingradiography personnel. Li- tions. censees mustprovide sufficient time ofthis na- V. The licensee's writtenoperating and ture in their training programsto assure that emergency procedures. trainees will have ampleopportunity to learn how to handle all theequipment involved in Each category of subjects mustbe separately license, and the their programs. identified by the applicant for a Determining Qualiftca- scope of plannedtraining fully explained in the 13-7.1d Methods for tiont; of Personnel. The lastrequirement, with license application. radiographers, relates The training philosophy isthat such pro- regard to the training of radiographer a practical to the determination ofcompetency. Procedures grams should give the comprehensive written and/or approach to the understandingof the nature may range from radiation. To this end, oral examination to personalobservation. The and potential hazard of submit copies of training programs normally wouldinclude both applicant for a license may experience. typical examinations ordescribe the scope of formal instruction and on-the-job questions. Evidence Instruction must deal specificallywith the ra- testing, including sample radiographic must also be inchzded toindicate that a stand- diation detection instrumentation, examination will not equipment, and operating and emergency proce- ard, unchanging type of be used over a long periodof time. The require- dures to be used in the applicant'sradiography personnel may be work. Prospective radiographypersonnel must ments for radiography in the operational summed up, as follows. No person canact as a also be instructed thoroughly assistant with- procedures of the exposuredevices they will radiographer or radiographer's the event of equip- out successfully completing theprescribed train- use, incl'ng what to do in of licensees ment malfunction. ing program. It is the responsibility 147 to see that such training is received and that transferofradioactivematerialsprocured every radiographer is supplied with (1) copies under the license. It is especially designed to of Parts 20 and 34 of the AEC regulations, (2) see that radiographers and radiographers' as- the operating and emergency procedures per- sistants follow the operating and emergency taining to the radiography operations, and (3) procedures specified in the license application. the AEC license under which this operation is There are, of course, many different types done. Radiographers' assistants are only re- of radiography programs. The particular pro- quired to have copies of operating and -emer- gram will establish the frequency and scope of gency procedures, but may profit from copies of the internal inspection system. The adequacy the pertinent regulations and licenses as well. of the system will be reviewed relative to the radiography programs proposed. Part of any 13-8Organizational Structure of Radiog- such system will be continued review of rec- raphy Programs ords relating to receipt and disposal of licensed material and other records such as personnel Regulations require that an applicant submit monitoring, leak tests, quarterly inventories, a description of theoverallorganizational utilization logs, and surveys. Such inspections structure of his radiography program. This is are expected to be on both an announced and an required because active control over the radiog- unannounced basis. raphy program must be exercised by personnel in positions of authority. In the preparation of 13-9.2 Operating and Emergency Proce- this application, it is necessary to show specifi- dures. Paragraph 13-3 made reference to the cally how authority is established and responsi- fact that operating and emergency procedures bility delegated for operation of the program. had to be prepared for a specific license applica- This enables the identification of each individ- tion and for the information of radiography ual in the chain of command by name and title personnel. The procedures which should be fol- and of the duties and responsibilities he will lowed and the items which should be covered have in the radiography operations. are briefly described here. The types of duties which may be performed The first and most important fact to remem- by management personnel vary a15 do the titles ber is that operating and emergency proce- given such personnel. Some individual must be dures should be prepared so as to fit the pro- responsible for performing radiographic opera- gram which is proposed by the applicant. tions. Except in very small organizations, it is Among the specific items which must be pro- preferred that an additionalindividual be vided are : charged with management safety functions and be designated as a Radiation Safety Officer. (1) Step by step instructions on the handling of exposure devices and related 13-9Other Requirements for Industrial equipment. Radiography Operations (2) Instructions on the operation, use, limitations, and malfunctions of the After reading paragraph 13-3, the student specific survey instruments which will will be aware that there are several other be used. requirements which must be met before the li- (3) Descri ption of methods for control- cense is issued for radiographic work. In addi- ling atmess to radiographic areas, in- tion to information already presented, knowl- cluding ways forestablishing and edge of these requirements is necessary for the controlling restricted and unrestricted preparation of an application for a license. areas. 13-9.1 Interned Inspection System. Appli- (4) Instructions on the detail of methods cants for a radiography license must establish and occasions for locking and secur- and submit a satisfactory internal inspection ingexposuredevicesandsealed system to assure that applicable regulations sources. will be followed. This system must provide for (5) Instruction on personnel monitoring active control over receipt, possession,use or devices to be required.

148 Instructions to personnel on proce- proper applicationof federal regulations relat- dures to follow in the event ofacci- ing to transportation ofradioactive materials. dent or malfunction. Persons responsible for shipmentsof radioactive Review of the records required. materials should familiarize themselveswith Description of the signs which will the pertinent regulationsof the Interstate be used by radiographic personnelarid Commerce Commission (ICC), theCivil Aero- instructions. nautics Board (CAB), the U. S. PostalServiqe, Instructions for transporting radio- or the U. S.Coast Guard. graphic sources. There is no attempt here to discussintraBtate regulations, as these vary among the 50States. For intrastate transportation, localauthorities 13-9.3 Leak Testing. It is not frequentthat a must be consulted. radioactive contamination problemdevelops in the use of a sealed radiography source.How- ever, as a precautionary measure,it is required 13-10.1 ICC Regulations. Alltransportation that each sealed source be tested forleakage at of radioactive materials movingin interstate intervals not to exceed six months. Thetest commerce by rail,water, or public highway made must be capable of detecting the presence (except for TJ. S. mail)is regulated by the of 0.005 microcurie of removablecontamination ICC. Certain States extend ICCregulations to on the sealed source.Records of leak testing intrastate transportation as well. must be kept to identify the (1)specific source, The ICC regulations covering theTrans- (2) date tested, and (3) results of thetest. A portation of Explosives and OtherDangerous sealed source received from othersshould be Articles include seven parts (Parts71-77) of accompanied by a certificate showing an accept- Title 49 of the Code of FederalRegulations. able date and result of its last leak test. Ifsuch Individuals using their private automobilesfor a certificate ismissing, the source may not be transporting personal property are not subject used until another test has been completed.De- to .these regulations so long as theproperty tails on leak testing are presented in paragraph transported is not to be used in connection with 9-1.2b. a commercial enterprise. ICC regulations have one major purpose 13-9.4 Radiological Assistance. There is al- "to minimize the dangers to life and property ways the possibility that anaccident will occur incident to the transportation of explosives and which involves licensed material and threatens other dangerous articles by common carriers public health and safety. The Interagency Ra- engaged in interstate or foreign commerce." To diological Assistance Plan was dcveloped by the this end, a philosophy has been adoptedwhich Interagency Committee on Radiological Assist- represents a workable compromise between no ance as a means of providingrapid and effec- shielding and gross overshielding. In the appli- tive assistance in the event of such an occur- cation of this philosophy, shielding is specified rence. Upon receiving a requestfor assistance, which provides "i3asonable protection" to un- appropriate emergency assistance is provided, developed films in transit and entirely adequate including radiation monitoring personnel and protection to humans. qualified medical personnel. Requests for assistance should be sent through theAECD.O.D. Joint Nuclear Coordinating Center. If radiolog- 13-10.1a Materials CVisidered Dangerous. ical assistance is required, notify the nearest Radioactive materials (poison D classification) AEC Regional Office shown in Figure 13.8. considered dangerous are listed in the Federal Register. The purpose of this listing is to provide shippers with the (1) proper shipping 13-10Transportation of Radioactive Ma- name, (2) maximum quantitywhich can be terials shipped in an outside container, and (3) label The comments included in this section are which must be used for transportation pur- designed to be helpful in the interpretation and poses. Those materials of special interestto 149 radiography work have been excerpted from The b asis for the rather low limits for ex- the ICC list and are listed here. emptions are explained in this manner. Not only must the possibility of accidnntal contami- TABLE 13.2.Radioactive Materials Listed by nation under normal conditions be avoided but, ICC Commodity List. in the event of a wreck, survivors and rescue workers ingesting or inhaling a substantial Label Maximum quantity in Article Classed as required one outside container portion of the contents a the package must not by rail express be injured. Parcel wrappings must be free from external radioactive contamination which Cobalt-60 Poison D Poison 300 curies might be transferred to other parcels or per- Radioactive Red sons. They must also be thickenough to absorb Cadum-137 Poison D Poison Radioactive 304 curies all alpha and beta rays emitted within the materials package so that adjacent film packages will not Red aidima-192 Poison D Poison 300 curies be damaged. Radioactive 13-10.1c Packing and Shielding. All con- materials Red tainers whose radioactive content or radiation Radioactive Poison D Poison emission exceeds permissible limits must be materials Radioactive ems. (not materials specially labeled and packaged. In addition, otherwise Blue or red each container has to carry proper markings specified) and descriptions and certification. Two criteria are accepted for specifying conditions forade- 13-10.1b Exemptione. ICC regulations are quate packing and shielding : intended to apply only to radioactive materials which represent a potential hazard during (1) Under normal conditions the degree transportation. Arbitrary limits are therefore of fogging of undeveloped film must prescribed below which ICC regulations are not not exceed that produced by 11.5 milli- applied. All packages whose radioactive content roentgens of penetrating gamma rays exceeds these limits must be packaged and of radium filtered by one-half inch of labeled in accordance with ICC regulations. lead. The tests for determining whether or not a (2) There must be no significant radio- package is exempt may be paraphrased as active surface contamination on any follows: part of the container. (1) Packages mutt be rugged enough to Radioactive materials used for radiography withstandconditionsofordinary are sealed in metal capsules which prevent transportation without allowing leak- spread of contamination. This leaves only elec- age of radioactive material. tromagnetic radiation to be controlled for ship- (2) The total activity of the package con- ping purposes. Some practical considerations tents must not exceed 0.1 millicurie for container and shielding designs are : of radium or polonium, or that amount (1) Gamma radiation intensity must not of strontium 89, strontium 90, or bar- exceed 200 mr/hr at any accessible ium 140 which disintegrates at a rate container surface. of more than 5 million atoms per sec- (2) Gamma radiation intensity must not ond; or that amount of any other exceed 10 mr/hr at one meter from radioactive substance which disinte- any accessible container surface. grates at a rate of more than 50 (3) All outside dimensions of the ship- million atoms per second. ping container must be equal to or (3) The package must be so prepared greater than 4 inches. (This dimen- that no significant alpha, beta, or neu- sion will prevent personnel from at- tron radiation is emitted from the ex- tempting to carry containers in their terior of the package and the gamma pockets. Also, lead shielding is most radiation at any part of its surface often used for radiography sources must be less than 10 milliroentgens and the weight would be sufficient to for 24 hours. eliminate unnecessary handling.)

150 (4) Containers for radiography sources A package of radioactive materials whose must be evipped with a tamper seal. surface radiation is less than 10 mr/24 hr Even though itis not mandatory, (0-0.4 mr/hr), but whose radioactive content many shipping containers arede- is too great to qualify under the exemption signed with locks and/or bolts to clauses is required to. have a so-called "blue secure the covers. label." This label is lmown technically as a (5) No more than 300 curies can be Class D Poison label, Group III. shipped in a container without special arrangements with the ICC. (6) The container must be rugged enough to withstand shocks and loads encountered in ordinary transportation. 13-10.1d Labeling. Requirements for radioactive materials labels apply to all shipments HANDLE CAREFULLY which do not qualify for exemptions. These re- MADNIETIVE MATERIAL EMITTING CORPUSCULAR RAYS ONLY quirements are briefly as follows. For gamma ray (Group I) emitters, the shipper must at- Name of Wats tach to the outside of the package a Class D CLASS D POISON Poison, Group I or Group II label. GROUP RI mai is be merry dist tke sontesta at dr package are properly darreal by lure mad me packed mad marked and are in pram serlition 1tranapartatian scowling to tke regu- leirdzerrar Atzteittra=4.Cemmeroe Commlation Thu shipment is %Orin tke limitatiow prescrflwa procapper-carryirig aircraft.

SiarPtel NNW Vellein4 hell= kg INV° WI* by IMME=11. EMUS HANDLE CAREFULLY Radioactive Material CLASS-D POISONGroup I or II FIGIURR13.10.Blue Label, Class D Poison, Group III. Ns perm Ai mai wain 3 int of this embitter meossesrily D. Nat place sealerekped f withi. 15 fastI this caetsim Blue labels must show the name of the con- priasipal takilleactive caettet Aativity prerars tents of the package, i.e., "carbon-14," "sul- Naming ndietiee free phur-35," etc., and thq shipper's name. Nat maw tbra 41 =its shall be loaded le one car or one molar raids er hold at one location When Group I or Group II materials are nir k to swift Ileit emeftsle of tk whop are props& dwidlead by ors and sr ward seml Paaebol anal re placed in a mixed package with Group III ma- la row sandltion I leerwristias standbr be dr Ilardnalsr prwribal by dr Ws& rats Crowson Ornsiatier terials, both a red and a blue label must be used. Blue label packages do not require segrega- Ildregea Mae hIVOMI klr INF MIEN by tion from either film or personnel. However, MMUS , av the regulations regarding fire, accident, break- eq" age, proximity to explosives, and notification FIGURZ13.9.Red Label, Class D Poison, Group I or IL of shipper and Bureau of Explosives are the same as for red label packages. Such a label is commonly referred to as a Certain detailed instructions are included in "red label." The shipper must fill out the label the ICC regulations to guide shippers and car- so that it specifies: (1) the name of the prin-riers. These instructions forbid the use of cipal radioactive element ("radium," "cobalt- radioactive-type labels on packages which are 60," etc.) ; (2) the activity of the contents ofnot subject to labels, and the use of labels the package in disintegrations per second (dps) which might be confused with standard cau- or in curies ;(3) the number of "radiation tion labels, or which do not conform to size, units" from the package (for purposes of these color, and printing specifications. regulations, 1 unit equals 1 mr/hr at 1 meter 13-10.1e Placards and Markings. The ICC in all practical cases) ; and (4) the shipper's prescribes that placards must be, applied to name. railway cars, and motor vehicles transporting

151 any quantity of radioactive materials. For blue labels are prohibited on empty containers. railway cars the placard must be diamond These labels must be removed, obliterated or shaped, measure 108/4 inches on each side and completely covered by an "empty" label. The bear these words in red letters, DANGEROUS latter is the third regulation which applies to RADIOACTIVE MATERIALS. empty containers. Such labels must be white, Motor vehicles and trailers carrying radio- not less than 6 inches on each side and bear active materials must be marked or placarded the word "empty" in letters.not less than 1 inch on each side and rear in letters not lessthan high. 3incheshighonacontrastingback- 13-10.11 Violations and Accidents. Violat o ground as follows : DANGEROUSRADIO- of ICC regulations and accidents must be re- ACTIVE MATERIALS. ported to the ICC. Violations should be re- 13-10.1f Shipping Orders and Bills of Lad- ported as quickly as possible, and in full detail, ing. ICC regulations are to the point with re- to the Bureau of Explosives, 50 Vesey Street, gard to the descriptions which must be used New York, N. Y. on shipping papers. Shippers ofradioactive In case of motor vehicle accidents involving materials by all usual modes of transportation the breakage of, or unusual delay of, shipments must do two things: (1) use the name appear- of radioactive materials, the package or ma- ing in the ICC Commodity List (Table 13.2) terial should be segregated as far as possible in describing the articles on shipping orders, from human contact. Great care should be bills of lading, and other shipping papers ; and taken to prevent contact with, or inhalation of, (2) show thereon the color or kind of label ap- radioactive material by humans. Both the plied to the package. It is permissible to add shipper and the Bureau of Exposives must be further descriptions consistent with the ICC notified immediately. Commodity List; however, abbreviations of 13-10.2 Civil Air Regulations. The Civil any kind are expressly forbidden on shipping Aeronautics Board has regulatory authority papers, because of the possibility of misinter- over the transportation of radioactivematerials pretation. It may be noted, as a reminder, that by air. Its Civil Air Regulations (CAR) cover- instructions included with the Commodity List ing the Transportation of Explosives and Other indicate that all radioactive materials should Dangerous Articles constitutes Part 49 of Title be entered on shipping papers as "radioactive 14 of the Code of Federal Regulations. These materials" and the p-oper group classification regulations were revised in 1949 to admit Class added. D poisons, i.e., radioactive substances. 13-10.1g Certification. The legal responsibil- Except for storage aboard aircraft, the CAR ity of shippers is usually assured through a are essentially the same as ICC regulations. certification procedure. Shippers offering radio- Some airlines have additional restrictions and active materials for transportation by rail ex- the radiographer must determine these from press must show their names on the package the specific airline concerned with his service. labels. Both red and blue labels contain a state- Certification requirements are imposed by ment to this effect : the CAR as follows. No shipment may be made This is to certify that the contents of this by air without a clear and plainly visible state- package are properly described by name and ment to the effect that all CAR regulations are packed and marked and are in proper con- have been complied with. This statement must dition for transportation according to the regu- be signed by the shipper or his authorized lations prescribed by the Interstate Commerce agent, and attached to the package. Shippers Commission. must also certify that radioactive material on 13-10.1h Empty Containers. Three precau- passenger-carrying aircraftfallwithin the tionary regulations apply specifically to empty limits prescribed for such aircraft. Passenger containers. First, all containers and accessories aircraft are not allowed to have dangerous which have been used for shipments of radio- cargo in their cabins. active materials must be sufficiently free of 13-10.3 U. S. Postal Regulations. Postal reg- contamination to be classified as exempt from ulations relative to mailings of radioactive ma- packaging and labeling under the regulations terials are included in the U. S. Postal Manual. as previously outlined. Second, ICC red and The important fact for radiographers contem-

152 plating the mailing of radioactivematerials is to the shipper and the DistrictCommander of that only those parcels exempt fromICC speci- the U. S. Coast Guard. fications packaging and labeling are acceptable in the mails. Red or blue label packages are 13-11Applying for, a License toUse nonmailable. Radioisotopes for Radiography Postal regulations state that any label re- When an individual or companydesires to agencies quired by Federal law or any Federal use radioisotopesfor industrial radiography, it must be pasted on the outside ofradioactive is required to apply for and receive alicense packages. The nature of the contents mustalso before procuring the radioisotope orusing the be plainly shown on the outside ofthe package both radioisotopes. along with the full name and address of The U. S. Atomic Energy Commissionis the the mailer and addressee, in ink, orrubber national authority for this licensingactivity. stamp, unless printed labels with thisinforma- Several States have accepted theresponsibility tion are glued to the package. from AEC for radiography licensing.If the ap- A package containing radioactivematerials plicant does not know the proper agency or must not emit from its exterior anysignificant his state, it is proper the person to contact within alpha, beta, or neutron radiations and to write to : gamma radiation at anysurface of the package must be less than 10 milliroentgensfor 24 The Division of Licensing and Regulations hours. U. S. Atomic Energy Commission For regulatory purposes, thereis no distinc- Washington, D. C. 20545 tion between the various classesof mail. Thus, packages which are "excluded fromthe mail" This Division will provideinformation on are ineligible forsecond class mail, airmail, licensing requirements, procedures,and the and parcel post, as well as firstclass mail. proper responsibleauthorities. 13-10.4 U. S. Coast Guard Regulations.For The radiographer is again advisedto obtain transportation by water, there is adivided re- a copy of the"AEC Licensing GuideINDUS- sponsibility. ICC regulations determinepack- TRIAL RADIOGRAPHY." This isavailable for aging and labeling requirements,but the ac- 65 cents from the : ceptability, handling, and storageaboard ship are the responsibilityof the U. S. Coast Guard. Superintendent of Documents The U. S. Coast Guard regulationsgoverning U. S. Government Printing Office the transportation of radioactive materials are Washington, D. C. 20402 included in Title 46, Part 146, of the- Codeof Federal Regulations. It may be notedthat This bulletin is a guide onradiation safety Coast Guard regulations, like CAR followICC considerations to be used in the preparationof regulations very closely ; however, theyapply license applications. Careful preparationof the to shippers making shipments of dangerous ma- license application along the formatof this bul- terial by vessels and to the persons who own, letin may save time in reviewingthe license. control, or work aboard vessels. The bulletin will certainly assist thecareful In the event of accidents and violationsof reader to evaluate all facets of hisradiation regulations notification should be submitted safety program. Appendix A

Glossary of UsefulNuclear Terms inIndustrial Radiography

which neutrons BARNa very small unit of areaused in meas- AcTivATIoNthe process by of atoms, nuclei, bombard stable atoms tomake them radio- uring the cross sections electrons, and otherparticles. One barn is active. which has ac- equal to 10-24 squarecentimeter. The term AGREEMENT STATEA State probability that a given cepted regulatory authority overbyproduct is a measure of the nuclear reaction will occur. materials from the USAEC. Ray)an elementary ALPHA PARTICLEA positivelycharged particle BETA PARTICLE (Beta materials. It is particle emitted from a nucleusduring radio- emitted by certain radioactive electrical charge made up of two neutronsand two protons, active decay. It has a single of a helium and a mass equal to %840that of a proton. hence it is identical to the nucleus stopped by a thin atom. Beta particles are easily indivisible by sheet of metal. A negativelycharged beta AToma particle of matter 'ical to the elec- chemical means. It is thefundamental build- particle is physically ide? tron.Ifthe betaparticleispositively ing block of chemicalelements. Beta radia- ATOMIC NUMBERdenotes thenumber of pro- charged, it is called a positron. tons in the nucleus, thenumber of position may cause skin burns, andbeta emitters tive charges in the nucleus,and the number are harmful ifinhaled or ingested. BETATRONan electron acceleratorwhich uses of orbiting electrons. electrons in ATOMIC WEIGHT (Atomic MassUnit AMU) magnetic induction to accelerate the mass of an atom. Thebasis of a scale of a circular path. atom, and the BODY BURDENthe amount ofradioactive ma- atomic weights is the oxygen animals. commonest isotope of thiselement has arbi- terial present in the body of man or weight of 16. BREmssTRAHLuNGelectromagneticradiation trarily been assigned an atomic when they are Hence the unit of the scale is I-A0the weight emitted by charged particles the mass of the slowed down by electricfields in their pas- of oxygen-16, or roughly Literally "braking proton or neutron. The atomicweight of an sage throughmatter. element, therefore, is approximatelyequiva- radiation" in German. protons and neu- BONE SEEKERa radioisotopethat tends to lent to the total number of introduced into trons in its neucleus. lodge in the bones when it is AUTORADIOGRAPHY (see also radiography) a the body. picture produced upon a sensitivesurface, BurLD-uPan increase in radiationtransmitted film, by the rays from a through material because of forwardscatter. e.g., a photographic law, radioactive substance containedwithin the BYPRODUCT MATERIALin atomic energy any radioactivematerial (except source or specimen to be examined. the process BACKGROUND RADIATIONtheradiationof fissionable material) obtained in man's natural environment,consisting of of producing or using source orfissionable the nat- material. Includes fission productsand many that which comes from cosmic rays, in nuclear urally radioactive elements ofthe earth, and otherradioisotopesproduced also reactors. from within man's body. The term may films and mean radiationextraneous to an experiment. CASSETTEa light tight carrier for BACKSCATTER-z-radiation scattered fromthe screens. element floor, walls, equipment, and otheritems in CESIum-137--a radioisotope of the the area of a radiation source. cesium. BANKING CONCEPTan idea or modelused to CHAIN REACTIONa reactionthat stimulates facilitate the explanation of radiation ex- its own repetition. In a fissionchain reaction, posure permitted in alifetime. a fissionablenucleus absorbs a neutron and fissions, releasing more than one additional DENSITY, PHOTOGRAPHIC (film density, optical neutron. These in turn can be absorbed by density) the darkening effect of a radio- other fissionable nuclei, releasing more neu- sensitive emulsion after exposure to radia- trons. A fission chain reaction is self-sustain- tion and chemical processing. ing when the number of neutrons released DETECTORa devicewhich determinesthe in a given time interval equals or exceeds the presence of radiation. number of neutrons absorbed. DEUTERIUMan isotope of hydrogen having COBALT-60a radioisotopeoftheelement mass equal to two AMU. cobalt. DEVELOPERa chemical solution which reduces COLD SHUTa defect caused by streams of exposed silver halide crystals to metallic metal meeting in a casting but not properly silver. flowing together. DISCONTINUITYa term generally referring to COMPOUNDa chemical combination ofele- any kind of flaw, defect, or lack of continuity ments. in a material. COMPTON SCATTERINGa process in which a DosEthe amount of ionizing radiation energy photon transfers a portion of its energy to absorbed per unit mass of irradiated ma- an orbital electron in matter and a lower terial at a specific location, such as a part of energy photon is scattered at an angle to the the human body. Measured in reps, rems, and original photon path. rads. CONTAMINATIONthe presence of unwanted DOSE RATEthe radiation dose delivered per radioactive matter, or the "soiling" of ob- unit time and measured, for instance, in jects or materials with "radioactive dirt." rems per hour (see also dose) . CONTRAST, RADIOGRAPHICdifferences in den- DOSIMETERa device that measures radiation sity from one area to another on a radio- dose, such as a film badge or ionization graph are termed radiographic contrast. chamber. CONTRAST, SUBJECTthe ratio of radiation in- ELECTROMAGNETIC RADIATIONradiation con- tensities passing through selected portions sisting of electric and magnetic waves that of a specimen. travel at the speed of light. Examples : light, CRACKa discontinuity which has a relatively radio waves, gamma rays, X-rays. All can large cross section in one direction and a be transmitted through a vacuum. small or negligible cross section when viewed ELECTRONan elementary particle with a unit in a direction perpendicular to the first. negative electrical charge and a mass Y1840 CROSS SECTIONa measure of the probability that of the proton. Electrons surround the that a nuclear reaction will occur. Usually atom's positively charged nucleus and deter- measured in barns, it is the apparent area mine the atom's chemical properties. presented by a target nucleus (or particle) ELECTRON VOLTthe amount of kinetic energy to an oncoming particle. gained by an electron when it is accelerated CURIEthe basic unit used to describe the through a voltage difference of 1 volt. intensity of radioactivity in a sample of ma- ELEMENTone of the 104 known chemical sub- terial. One curie equals 37 billion disintegra- stances that cannot be divided into simpler tions per second, or approximately the radio- substances by chemical means. Examples : activity of 1 gram of radium. hydrogen, lead, uranium. DECAYthe spontaneous radioactive transfor- ELEMENTARY PARTICLEoriginally a term ap- mation of one nuclide into a different energy plied to any particle that could not be fur- state of the same nuclide. Every decay proc- ther subdivided ; now applied only to protons, ess has a definite half-life (see also half- electrons, neutrons, antiparticles, and strange life). particles, but not to alpha particles and DECONTAMINATIONthe removal of radioactive deuterons. contaminants from surfaces, as by cleaning EMISSIVITYthe energy emission rate usually and washing with chemicals. expressed as r/c/hr @ 1 ft or mr/mc/hr @ DEFINITIONsharpness of the image on a 1 ft. radiograph. EMULSIONa gelatin and silver bromide crys-

156 transparent film origin. Gamma radiationusually accOM- tal mixture coated onto a always base. panies alpha and beta emissions and ENCAPSULATIONthe process of sealingradio- accompanies fission. Gamma rays are very contamination. penetrating and are best attenuatedby dense active materials to prevent uranium. EXPOSURE, FILMradiationintensity multi- materials like lead and depleted GEIGER COUNTERa radiationdetection and plied by time. contains a gas- EXTERNAL DISCONTINUITIESsurfaceirregu- measuring instrument. It larities which cause density variations on a filled tube which dischargeselectrically when with the ionizing radiation passes throughit.Dis- radiograph. These are observable the radia- naked eye. charges are counted to measure FILm BADGEa package ofphotographic film tion's intensity. by workers in the nuclear GENETIC EFFECTS OF RADIATIONeffectsthat worn like a badge organisms industry to measure exposure toionizing ra- produce changes in those cells of diation. The absorbed dose can becalculated which give rise to egg or spermcells and by the degree of film darkeningcaused by therefore affect offspring of theexposed the irradiation. individuals. for films GOVERNMENT AGENCYmeans anyexecutive FILM HOLDERa light tight carrier estab- and screens. department, commission, independent FISSIONthe splitting of a heavy nucleusinto lishment,corporation,whollyorpartly two roughly equal parts (which arenuclei owned by the United States ofAmerica United of lighter elements) , accompaniedby the re- which is an instrumentality of the lease of a relatively large amount GA. energy States, or any board, bureau, division, serv- and frequently one or more neutrons.Fission ice, office, officer, authority, administration, can occur spontaneously,but usually it is or other establishmentinthe executive caused by the absorption of gamma rays, branch of the Government. neutrons, or other particles. GRAININESSthe subjective impression ofir- FISSION PRODUCTSnuclei formed by thefis- regularity of the silver deposit on aphoto- sion of heavy elements. They are of medium graphic material. atomic weight ;almost all are radioactive. HALF-LIFEthe time in which half the atoms Half- Examples : strontium-90, cesium-137. in a radioactive substance disintegrate. FISSIONABLE MATERIALany material readily lifes vary from millionths of a second tobil- fissioned by slow neutrons, for example, lions of years. uranium-235 and plutonium-239. HALF-LIFE, BIOLOGICALthe time required for FIXERa chemical solution which dissolves un- a biological system,such as a man or an exposed silver halide crystals fromdeveloped animal, to eliminate, by natural processes, has film emulsions. half the amount of a substance which FLUX (neutron) the intensity of neutron ra- entered it. diation. It is expressed as the number of neu- HALF-VALUE LAYERis that thickness of ma- trons passing through 1 square centimeterin terial required to absorb one half ofthe 1 second. impinging radiation. FORVVAIW SCATTERradiation scattered in ap- HIGH RADIATION AREAmeans any area, acces- proximately the same direction as the pri- sible to personnel, in which there exists radi- mary beam. ation originating in whole or in partwithin FUSIONthe process by which two light nuclei licensed material at such levels that a major combine to form a heavier nucleus. portion of the body could receive in any one GADOLINIUM-153a ralioisotope of the element hour a dose in excess of 100 millirem. gadolinium. HOLESany void remaining in a specimen as a GAMMA RAYShigh-energy short-wavelength result of improper manufacturing process- electromagnetic radiation emitted by a nu- ing. Often called gas holes, cavities, or air cleus. Energies of gamma rays are usually locks. between 0.010 and 10 Mev. X-rays also occur HOT CELLa heavily shielded enclosure in in this energy range, but are not of nuclear which radioactive materials can be handled manipulators ceived, possessed, used, ortransferred under remotely through the use of special license issued bythe and viewed through shieldedwindows so that a general or there is no danger to personnel. Atomic Energ Commiosion. contained in LINEAR ACCELERATORa devicefor accelerat- INcLusIoNany foreign matter high velocities welds or castings. ing charged particles to very for producing Lrays. INDIviDuALmeans any human being. neutrons and INDUCED RADIOACTIVITYradioactivitythat is MASS NumBERthe sum of the with neu- protons in a nucleus. The massnumber of created by bombarding a substance nearest whole trons in a reactor or withcharged particles uranium-235 is 235. It is the number to the atom's actualatomic weight. produced by particleaccelerators. (MPD) that INVERSE SQUARE LAW(at adistance from a MAXIMUm PERMISSIBLE DOSE point source) the intensity ofradiation re- dose of ionizing radiationvenich competent of the authorities have established asthe maximum ceived varies as the inverse squae undue risk to distance of the source. that can be absorbed without IoNan atom or moleculethat has lost or human health (see also radiationprotection gained one or more electrons. Bysuch "ioni- guide). zation" it becomes electricallycharged. MEvone million electron volts. IONIZATIONthe process of addingelectrons to, MIcRoa prefix that divides abasic unit by electrons from, atoms or mole- one million. or knocking basic unit by cules, thereby creating ions.High tempera- MILLIa prefix that divides a tures,electricaldischarges,andnuclear one thousand. MINORany individual under 18 yearsof age. radiation can cause ionization. when the IONIZATION CHAMBERan instrumentthat de- MISRUNa condition that occurs casting mold. tects and measures ionizingradiation by ob- molten metal fails to fill the serving the electrical currentcreated when MOLECULEa group of atoms heldtogether by radiation ionizes gas in the chamber,making chemical forces. The atoms in themolecule it a conductor of electricity. may be identical : H2,S2, S8 ; or different: IONIZING RADIATIONany radiationthat di- H20, CO2. rectly or indirectly displaceselectrons from NEuTRONan uncharged elementaryparticle the orbital shell of atoms.Examples : alpha, with a mass nearly equal to that ofthe pro- beta, gamma radiation. ton. The isolated neutron isunstable and IRIDIum-192--a radioisotope of theelement decays with a half-life of about13 minutes Neu- iridium. into an electron, proton, and neutrino. IRRADIATIONexposure to radiation, as in a trons sUstain the fission chainreaction in a nuclear reactor. nuclear reactor. ISOTOPEatoms with the same atomicnumber NONDESTRUCTIVE TESTINGtesting to detect in- materials (samechemicalelement)butdifferent ternal and concealed defects in atomic weights. An equivalentstatement is using techniques that do not damage orde- that the nuclei have the same numberof pro- stroy the items being tested. tons but different numbers ofneutrons. NUCLEAR REACTIONa reaction involving an Thus, 6 C12v el 13, and 614 are isotopes of the atom's nucleus, such as fission, neutron cap- element carbon, the subscripts denotingtheir ture, radioactive decay, or fusion, asdistinct limited to common atomicnumbers, the superscripts from a chemical re:iction, which is denoting the varying atomic weights. changes in the electron structure surround- LACK OF FUSION (incompletepenetration) ing the nucleus. failure to properly fuse the base metalin a NUCLEAR REACTORa device by meansof weld. which a fission chain reaction can be initi- LEAK TESTa test on sealed sources to assure ated, maintained, and controlled. Its essential that radioactive material is notbeing re- component is a core with fissionable fuel.It leased. usually has a moderator, a reflector, shield- LICENSED MATERIALsource material, special ing, and control mechanisms. nuclear material, or byproduct material re- NUCLEUSthe small, positively charged core

158 of an atom. It is only about1/10,000 the di- PITCHBLENDEan ore which containsuranium. ameter of the atom but containsnearly all POROSITYa defect which consistsof a collec- hydrogen, all tion of small holes in amaterial. the mass. Except for ordinary charts for com- nuclei contain both protons andneutrons. POROSITY CHARTsstandard exists for paring porosity size andspacing. NuCIADEany species of atom that POSITRONan elementary particlewith the a measurablelength of time. A nuclide can electron but charged positively. be distinguished by its atomicweight, atomic mass of an It is the "antielectron." It isemitted in some number, and energy state. The termis used is produced synonymously with isotope. Aradio-nuclide radioactive disintegrations and in pair production. is a radioactive nuclide. with a single of an PRoToNan elementary particle OCCUPATIONAL DOSEincludes exposure positive electrical chargeand a mass ap- individual to radiation (1) in a restricted proximately 1840 times thatof the electron. area ; or (2) in the courseof employment in The atomic number of anatom is equal to which the individual's dutiesinvolve expo- the number of protons inits nucleus. sure to radiation ;provided that "occupational R-METERan ionization typeinstrument de- dose" shall not be deemed to include any ex- signed to measure radiationdose. posure of an individual toradiation for the RAD--radiation absorbed dose. Thebasic unit purpose of medicaldiagnosis or medical of absorbed dose ofionizing radiation. One therapy of such individual. rad is equal to the absorptionof 100 ergs of PAIR PRoDUCTIONthetransformation of a radiation energy per gram ofmatter. high-energy ray into a pair ofparticles (an RADIATIONthe propagation of energythrough electron and a positron) duringits passage matter or space in the formof waves. In throgigh matter. atomic physics the term hasbeen extended PARTIcLEa minute constituent ofmatter with to include fast-movingparticles (alpha and a measurable mass,such as a neutron, pro- beta rays, free neutrons,etc.). Gamma rays ton, or meson. and X-rays, of particularinterest in atomic PENFTRAMETERa small strip of the same ma- physics, are electromagneticradiation in terial as a specimen and having athickness which energy is propagatedin packets called which is in a definite ratio tothe specimen photons. thickness. RADIATION AREAmeans any area,accessible PERIODIC TABLEa tabulararrangement of ele- to personnel, in which thereexists radiation, ments according to theirproperties. originating in whole or inpart within li- PERsoNmeans (1) any individual, corpora- censed material, at suchlevels that a major tion, partnership, firm,association, trust, portion of the body could receivein any one estate, public or privateinstitution, group, hour a dose in excess of 5millirem, or in any Government agency other than theCommis- 5 consecutive days, a dosein excess of 100 sion, any State, any foreigngovernment or millirems. nation or any politicalsubdivision of any RADIATION PROTECTION GUIDEthetotal such government or nations, orother entity ; amounts of ionizing radiationdose over cer- and (2) any legal successor,representati,re, tain periods of time which maysafely be agent, or agency of the foregoing. permittedtoexposedindustrialgroups. PERSONNEL MONITORINGEQUIPMENTmeans These standards, established by theFederal devices designed to be worn orcarried by an Radiation Council, are equivalentto what individual for the purpose ofmeasuring the was formerlycalled the "maximum permis- dose received (e.g., film badges,pocket cham- sible exposure." bers, pocket dbsimeters, film rings,etc.). RADIATION SAFETY OFFICERanindividual en- PuaronEcrRIc EFFECTa process bywhich gaged in the practices ofproviding radiation electromagnetic radiation imparts energyfo protection. He is therepresentative ap- matter. pointed by the licensee for liaisonwith the PHOTONa discrete quantity ofelectromag- Atomic Energy Commission. momentum but RADIOACTIVEatoms which are energetically netic energy. Photons have condition by no mass orelectrical charge. unstable and decay to a stable 159 emitting radiation are said to be radioactive. RADIUMa radioactive element with the atomic RADIOACTIVE MATERIALincludes any such ma- number 88 and an atomic weight of 226. In terial whether or not subject to licensing nature, radium is found associated with control by the Commission. uranium, which decays to radium by a series RADIOACTIVITY CONCENTRATION GUIDEthe con- of alpha and beta emissions.,Radium is used centration of radioactivity in an environment as a radiation source. which results in doses equal to those in the REDUCTION FACTORdose rate without a shield radiation protection guide. This Federal Ra- divided by the dose rate with a shield inter- diation Council term replaces the former posed between a source and a poiht at which "maximum permissible concentration." radiation is measured, RADIOBIOLOGYthe study of the scientific prin- REFERENCE RADIOGRAPHSa group of radio- ciples, mechanisms, and effects of the inter- graphs containing images of discontinuities. actionofionizingradiation with living These can be used as comparison "standards" matter. for acceptability of materials. RADIOGRAPHERmeans any individual who per- RELATIVE ISIOLOGICAL EFFECTIVENESS (RBE) forms or who, in attendance at the site where the relative effectiveness of a given kind of the sealed source or sources are being used, ionizing radiation in producing a biological personally supervisesradiographic opera- response as compared with 250,000 electron tions and who is responsible to the licensee volt gamma rays. for assuring compliance with the require- REMroentgen equivalent man. A unit of ab- ments of these regulations and the conditions sorbed radiation dose in biological matter. It of the license. is equal to the absorbed dose in rads multi- RADIOGRAPHER'S ASSISTANTmeans any in- plied by the relative biological effectiveness dividual who, under the personal supervision of the radiation. of a radiographer, uses radiographic expo- REProentgen equivalent physical. An obsolete sure devices, sealed sources or related han- unit of radiation dosage, now superseded by dlingtools,orsurveyinstrumentsin the rad. radiography. RESTRICTED AREAmeans any area to which RADIOGRAPHIC CoDEa code for specifying access is controlled by the licensee. minimum standards related to radiographic RGENTGENa unit of exposure dose of ionizing practices. radiation. It is that amount of gamma or X- RADIOGRAPHIC EXPOSURE DEVICEmeans any rays required to produce ions carrying 1 elec- instrument containing a sealed source fas- trostatic unit of electrical charge in 1 cubic tened or contained therein, in which the centimeterofdryairunderstandard sealed source or shielding thereof may be conditions. moved, or otherwise changed, from a shielded SAMARrum-145a radioisotope of the element to unshielded position for purposes of mak- samarium. ing a radiographic exposure. This may also SCATTERINGa process that changes a par- refer to machines which produce ionizing ticle's or photon's trajectory. Scattering is radiation. caused by collisions with atoms, nuclei, and RADIOGRAPHYmeans the examination of the other particles. If the scattered particle's structureofmaterials by nondestructive energy is unchanged by the collision, elastic methods utilizing sealed sources of byproduct scattering prevails ; if there is a change in materialandothersourcesofionizing energy,theprocessiscalledinelastic radiation. scattering. RADIOISOTOPEan unstable isotope of an ele- SCREENS, RADIOGRAPHICmetallic or fluores- ment that decays or disintegrates spontane- cent sheets used to intensify the radiation ously, emitting radiation. More than 1300 effect on films. natural and artificial radioisotopes have been SEALED SOURCEmeans any byproduct material identified. that is encased in a capsule designed to pre- RADIoLoGYthat branch of medicine which vent leakage or escape of the byproduct uses ionizing radiation for diagnosis and material. therapy. SENSITIVITY, PERCENTAGEa ratio of the small-

160 est detectable thickness difference dividedby SURVEY METERa portable instrument which the thickness of material being examined. measures dose-rate of exposure orradiation SENSITIVITY, RADIOGRAPHICa term usually re- intensity. ferring to the ability of a radiographic pro- THuLIum-170a radioisotope of the element cedure to detect discontinuities. thulium. SHIELDa layer or mass of material usedto TRACERan element or compound that has reduce the passage of ionizing radiation.. been made radioactive so that it can beeasily SHRINKAGECAVITIEScavitiesincastings followed (traced) in biological and industrial caused by lack of sufficient molten metal as processes. Radiation emittedby the radio- the casting cools. isotope pinpoints its location. SLAG INCLUSIONincluded slag in a weld or TRITIUMa radioactive isotope of hydrogen casting. with two neutrons and one proton in the nu- SOURCEa radioactive material packaged so as cleus. It is heavier than deuterium(heavy to produce radiation for experimental orin- hydrogen). Tritium isused in industrial dustrialuse.Inthis manual the term thickness gages, as a label in tracer experi- "source" also refers to the "target" of an ments, and in controlled fusion experiments. X-ray tube. TUNGSTEN INCLUSIONSinclusions in welds re- SOURCE MATERIALin atomic energy law, any sulting from particles or splinters of tung- material, except special nuclear material, sten welding electrodes. which contains 0.05% or more of uranium, UNDERCUT, RADIOGRAPHYan effect from scat- thorium, or any combination of the two. tered radiation that causes fuzzy edges of SPECIAL NUCLEAR MA :TRIALin atomic energy images on radiographs. law, ine.ludes plutonium, uranium-233, ura- UNDERCUT, WELDINGa surface defect caused nium containing more than the natural abun- by melting the upper edge of a beveled weld dance of uranium-235, or any material arti- face. ficially enriched by any of these substances. UNRESTRICTED AREAmeans any areainto SPEED, FILMFilm speed is inversely propor- which entry is not controlled by the licensee, tional to the exposure to attain a specified and any area used for residential quarters. density. UNSHARPNESS, GEOMETRICALthe fuzziness or SPILLthe accidental release of radioactive lack of definition in a radiographic image re- liquids. sulting from the source, size, object to film SPOTEXAMINATIONlocalexaminationof distance, and the source to object distance. welds or castings. VAN DE GRAAFF GENERATORan electrostatic STABLE ISOTOPEr---a nuclide that does not under- machine in which electrically charged par- go radioactive decay. ticles are separated mechanically by a mov- STOP BATHa mild acetic acid solution used ing belt to build up a high potential on an to arrest film development. insulated terminal. The particles are then STORAGE CONTAINERmeans a device in which accelerated along a discharge path through sealed sources are transported or stored. a vacuum tube by thepotential difference SURFACE IRREGULARITIESany change in ma- between theinsulated terminal and the terial surface which renders the specimen opposite end of the machine. unserviceable. WASTE, RADIOACTIVEequipment and materials SURVEYmeans an evaluation of the radiation (from nuclear operations) which are radio- hazards incident to the production, use, re- active and for which there is no further use. lease, disposal, or presence of radioactive X-RAYpenetrating electromagnstic radiation materials or other sources of radiation under emitted when the inner orbital electrons of a specific set of conditions.When appropri- an atom are excited and release energy.Thus ate, such evaluation includes a physical sur- the radiation is not nuclear in origin and is vey of the location of materials and equip- generatedinpractice by bombarding a ment,andmeasurementsoflevelsof metallic target with high-speed electrons radiation. (see paragraphs 2 and 3 on page 11) .

161 Appendix B

80-HOUR SCHEDULE FOR RADIOGRAPHY TRAINING PROGRAM

1-Hour Simko) lat Day 2nd Day 3rd Day 4th Day 5th Day 6th Day 7th Day 8th Day 9tb, Day 10th Day Number

General Review Review Review Mid-Term Review % of Review 1 Instruc- SGL-1,2, IGL-9 SGL-7,8, SGL- 6,6 Exam SGL-11 SGL-12 LE-16 tions 3,4 9,10 SGL-13

2 IG-Intro. LE-1 LE-2 LE-3 LE-7 Mid-Term LE-10 LE-12 LE-14 LE-14 Exam

$ IGL-1 LE-1 LE-2 LE-3 LE-8 IGL-11 LE-10 LE42 LE-14 LE-16

4 IGL-2 IGL-6 LE-4 IGL-10 LE-8 IGL-11 LE-10 LE-12 LE-14 LE-16

6 IGL-3 IGL-6 LE-4 r..5 LE-8 LE-9 % of IGL-12 Review ' Final IGL-13 SGL-12 Exam

6 IGL-4 IGL-6 LE-4 LE-5 LE-6 LE-9 LE-11 IGL-12 LE-13 Final Exam

7 SGL-1 SGL-5 IGL-7 LE-6 LE-6 LE-9 LE-11 SGL-12 LE-13 Final SGL-2 SGL-6 IGL-8 Exam

8 SGL-3 SGL-5 SGL-7 SGL-9 LE-6 SGL-11 LE-11 SGL-13 LE-13 Final ISGL-4 SGL-6 SGL-8 SGL-10 Exam

IGL = Instructor's Guide Lesson LE = Laboratazy Exercise SOL = Student Guide Lemon 1

Appendix C TABLE OF SQUARES AND SQUARE ROOTS

Mx and Square Nix and Square No. and Square No. and Square No. and Square No. and Square or or or or or or Square Square Square Square Square Square bio. Root and No. Root and No. Root and No. Root and bro. Root and bi4). Wet and

16626 186 84596 248 61504 811 64721 1 1 68 8969 125 187 84969 249 62001 212 97844 2 4 64 4096 126 15876 188 85344 250 62600 8 9 65 4225 127 16129 189 85721 261 68001 813 97969 4 16 66 4866 128 16884 252 68504 814 98596 6 25 67 4489 129 16641 253 64009 315 99226 6 86 68 4624 190 86100 191 86481 254 64516 816 99856 7 49 69 4761 180 16900 266 66026 317 100489 8 64 181 17161 192 86864 198 87249 256 66686 818 101124 9 81 70 4900 182 17424 319 101761 71 5041 188 17689 194 87636 257 6600 195 38025 258 81664 10 100 72 5184 134 17956 196 88416 259 67081 320 102400 11 121 78 6329 185 18225 88809 321 103041 12 144 74 6476 186 18496 197 198 89204 260 67600 322 103684 18 169 75 6626 187 18769 199 89401 261 68121 323 104i29 14 196 76 6776 188 19044 262 68644 324 104976 16 225 77 5929 189 19321 200 40000 268 19169 826 105625 16 256 78 6084 40401 264 69696 326 106276 17 289 79 6241 140 19600 201 202 40804 265 70225 327 109929 18 324 141 19851 203 41209 266 70766 828 10/584 19 861 80 6400 142 29164 71989 829 108241 81 6561 148 20449 204 41616 267 42025 268 71824 20 400 82 6724 144 20786 205 42486 269 72261 880 108900 21 441 83 6889 145 21025 206 42840 881 109661 22 484 84 7056 146 21816 207 270 72900 882 110224 28 529 85 7226 147 21609 208 48264 209 48681 271 7V" 333 110889 24 576 86 7896 148 21904 272 78,1, 884 111556 26 625 87 7669 149 22201 210 44100 278 74529 235 112225 26 676 88 7744 211 274 75076 336 112898 27 729 89 792t 150 22500 44621 44944 275 76626 387 118689 28 784 151 22801 212 218 276 76176 838 114244 29 841 90 8100 162 28104 46860 839 114921 91 8281 153 28409 214 45796 277 76729 278 77284 80 900 92 8464 154 28716 215 46226 216 46656 279 77841 340 115600 81 961 98 8649 155 24025 47089 841 116281 82 1024 94 8886 156 24886 217 280 78400 842 116964 88 1089 95 9026 157 24649 218 47624 281 78961 848 117649 84 1166 96 9216 158 24964 219 47961 282 79524 844 118886 $5 1226 97 9409 159 25281 220 288 80089 845 119025 86 1296 98 9604 48400 284 80656 346 119716 37 1869 99 9801 160 25600 221 48841 285 81226 847 120409 38 1444 161 26921 222 49264 286 81796 848 121104 89 1621 100 10000 162 28244 223 49729 121801 101 10201 163 26569 224 60178 287 82869 349 82944 40 1600 102 10404 164 26896 225 50626 288 226 289 83521 850 122500 41 1681 103 10609 165 27225 51076 351 123201 42 1764 104 10816 166 27666 227 51529 51334 290 84100 852 128904 43 1849 105 11026 167 27869 228 291 84681 363 124609 44 1986 106 11286 168 28224 229 62441 292 85264 864 125316 46 2026 107 11449 169 28561 280 52900 298 85849 855 126025 46 2116 108 11644 231 68361 294 86486 356 126736 47 2209 109 11881 170 28900 232 53824 295 87025 357 127449 48 2804 171 29241 233 54289 296 87616 858 128164 49 2401 110 12100 172 29684 234 64756 111 12821 173 29929 285 66225 297 88209 859 128881 298 88804 60 2500 112 12544 174 80276 236 56696 299 360 129600 51 2601 118 12769 175 80625 237 56169 89401 180821 62 2704 114 12996 176 80976 288 56644 861 800 90000 362 181044 58 2809 116 18225 177 81829 289 67121 801 868 181769 54 2916 116 18456 178 81684 90601 802 364 182496 66 8026 117 18689 179 82041 240 57600 91204 808 365 133225 66 8186 118 13924 241 58081 91809 304 366 133966 57 8249 119 14161 180 82400 242 68564 92416 58 8864 181 82761 248 59049 805 98025 367 184689 806 185424 59 8481 120 14400 182 88124 98686 868 121 14641 244 59586 807 94249 869 186161 186900 60 8600 122 14884 183 28489 245 60025 808 94864 370 61 3721 123 16129 184 88856 246 60616 899 96481 871 187641 62 8844 124 16876 185 84226 247 61009 810 96100 872 188884 163 TABLE OF SQUARES AND SQUARE ROOTS (Continued)

No. and Square No. and Square No. and Square No. and Square No. and Square No. and Square or or or or or or Square Square Square Square Square Square Root and No. Roct and No. Root andNo. Roct and No. Roct and No. Roct and No.

479 229441 878 189129 894 155286 415 /,72225 486 190096 458 209764 374 139876 895 156025 413 118056 487 190960 459 210681 488 210400 375 140625 896 156816 417 173889 488 191644 481 211361 376 141876 897 157609 418 174724 489 192721 460 211600 482 212324 877 142129 898 158404 419 175561 461 212521 488 211289 378 142884 899 159201 440 198600 462 218444 484 234256 379 148641 420 176400 441 ' 194481 468 214869 485 225225 400 160000 421 177241 442 195864 464 215296 486 216196 380 144400 401 160801 422 178084 448 196249 465 216225 487 237169 381 145161 402 161604 428 178929 444 197136 466 217156 488 238144 382 408 145924 162409 424 179776 445 198026 467 218089 489 219121 383 146689 404 163216 425 180625 446 198916 468 219024 490 384 147456 405 240100 164025 426 181476 447 199809 469 211961 491 385 241081 148225 406 164886 427 182829 448 200704 386 148996 407 402 242064 165649 428 188184 449 201601 470 220900 499 387 149769 408 248049 166464 429 184041 450 202500 471 221841 494 388 244086 150544 409 167281 451 208401 472 222784 495 389 151821 246025 480 184900 452 204804 478 223729 499 410 246016 168100 481 186761 468 206209 474 224676 497 390 152100 411 247009 168921 482 186624 454 206116 475 226625 499 391 152881 41P 248004 169744 483 187489 455 207025 476 226576 499 392 158664 41 J 249001 170569 484 188856 456 207936 477 227529 393 154449 414 171396 435 189225 457 208849 478 228484 500 250000

164 Appendix D

"Need to Know" A successful and competent radiographer needsto know all of the basic subject material presented in this Manual PLUSadditional published subject matter. He must also have long experience inthe shop and field performing industrial radiographic operations with manydifferent types of gamma ray and X-ray sources onmultitudes of various specimens. Since this Training Program has been outlined forpresentation in 80 hours, it is not deemed possible to learn all of thesubject matter in this Manual. For this reason a "priority" list follows whichsuggests the instructor and student place primary interest on learning thesetopics. The knowledge gained from studying these items will permitthe beginning radiographer to safely. make radiographs. Continuedstudy and experience will lead to competence. Topics That Must Be Learned TOPIC NUMBER TITLE Par. 2-4 Properties of Radiation Par. 3-7 Decay of Radioactivity Par. 3-8 The Curie Par. 3-9 Plotting Radioactive Decay Par. 4-1 Ionization and Ions PEr. 4-4 The Roentgen Pa r. 4-5 Radiation Attenuation Paz. 4-6 Absorption of Radiation (Know concept only. It is not mandatory to be able to solve exponential equations.) Par. 4-7 Half-value Layers Par. 4-8 Reduction Factors Par. 4-9 Principles of Radiation Safety Par. 5-1 Radiation Detection and Measurement Par. 5-2 Radiation Measurement Par. 5-3.2 The Pocket Dosimeter and Pocket Chamber Par. 5-4 Survey Meters Par. 5-5 Instrument Characteristics Par. 5-6 Instrument Calibration Par. 5-7 Source Calibration Par. 6-1 Radiation Health in Perspective Par. 6-3 Measurement Units of Radiation Doses Par. 6-4 The Nature of the Radiation Health Problem Par. 6-8 Personnel Monitoring Par. 6-12 Contamination(Refer to Laboratory Exercise 15 for information on leak testing.) Chapter 8 Introduction to Radiography Chapter 9 Elements of Industrial Radiography Chapter 10 Radiographic Film Chapter 11 Radiography Techniques Chapter 12 Interpretation of Radiographs Chapter 13 Government Licensing, Health, and Transportation Regula- tions for Isotope Radiography

165 Darkroom Don'ts

DON'TSRULES WHYREASONS WHAT TO DOACTIONS

General Genera/ General 1 Don't use a darkroom without adequate Lead protects ihe film from fogging andInsist upon adequate lead protection, usually, lead protection. the technicians from X-ray exposures. 1.5 mm of lead. 2. Don't permit the darkroom to become A hot room makes the regulation of solu-Use electric fans and outside ventilation if too hotabout 75 F. tion and temperatures difficult. possible. 2. Don't guess at processing times. Most individuals can not estimate time ac-Always use darkroom timer or clock. curately enough for darkroom requirements. 4. Don't store large quantities of films. Films deteriorate with age. Keep a small surplus; renew your supply frequently. 5. Don't keep boxes of films lying fiat. Staticchargesofelectricity may collect Stand film boxes on end. from pressure.

Cassettes and serfs's. Cassettes and screens Cassettes and screna

6.Don't permit screens to become dirty. Dirt reduces screen sensitivity, resulting inWash screens monthlyuse pure grain alco- spotted films. hol and lint-free cloth. 7,Don't load, unload, or leave cassettes near Drops of liquid may be splashed on theKeep loading bench far away from solutions. processing tanks. screens, reducing their sensitivity. 8.Don't leave cassettes open. Exposes screens to damage by dirt, liquids,Keep cassettes closed when not in use. and other objects. 9.Don't rub or scratch screen surfaces. Decreues screenlife by destroying pro-Brush screen surface lightlyuse soft mate- tective coat. rials, such as a camel's hair brush. 10. Don't touch screen surfaces with your Theoilinfingerprintsreduces screenWhen exchanging screens, touch only the fingers. sensitivity. edges.

Dry films Dry It /me Dry film* 11. Don't bend, crease, pros, or buckle films. Black, half-moon marks may occur. Handle films carefully to keep surfaces fiat and smooth. 12. Don't scratch films with finger nails or Scratches appear as light or dark strealmUse finger tips and not nails when handling other hard objects. on films. films. 13. Don't slide or shuffle dry films over flat Films may become scratched; staticelec- When films are moved, free them from all surface. tricity may develop. supporting surfaces. 14. Don't leave film boxes uncovered. Films become fogged with irregular mark- Keepfilmboxes closed and in a darx cabinet ings. when not in use. 15. Don't pile films on top of one another Static electricity may be developed. When filmisremoved from the cassette, before mounting on the hangers. place it on a hanger immediately.

Chemicals and solutions Chemicals and solutions Chemicals and solutions 16. `Do,n't use same paddle to stir developer Developer may become contaminated withHave one paddle for developer; another for and hypo. hypo. hypo. 17. Don't mixdeveloperinvesselsother Other materials contaminate the solutions Use glass, stainless steel, enamel, or earth- than glass, stainless steel, enamel, or and destroy their action. enware vessels for mixing solutions. earthenware. 18. Don't use scouring powder to cleanse Scouringpowderisdifficulttoremove. Use stiff brush and water to cleanse tanks. the tanks. May "spot" films. 19. Don'tleavesolutionsuncovered when They may become contaminated with dirt.Keep processing tanks covered with semi- not in use. There may be loss of water by evapora- tight lid when not in use. tion. Bibliography

Information on industrial radiography has been published in many pro- fessional and technical journals, a few texts and handbooks,and several "codes." Selected references have been footnoted in thismanual. Most of the subject matter has been drawn from the materialslisted below. Grate- ful acknowledgement is made to these publishersand authors for permission to quote from the titles listed. American Society of Mechanical Engineers. Rules forConstruction of Unfired Pressure Vessels. New York, ASME, 1959. American Society for Testing and Materials. StandardReference Radio- graphs for Steel Welds. Philadelphia, ASTM, 1963. Eastman Kodak Company. Radiography in Modern Industry.(2nd edition) Rochester, N. Y., 1957. Frazier, P. M., Buchanan, C. R., and Morgan, G. W. RadiationSafety in Industrial Radiography with Radioisotopes. Oak Ridge, U.S.Atomic Energy Commission Office of Technical Services, 1954. McGonnagle, Warren J. Nondestructive Testing. New York, McGraw Hill Book Co., 1961. McMaster, Robert C., ed. Nondestructive Testing Handbook. New York, Ronald Press Co., 1959. Naval Medical Research Institute, U.S. Naval Radiological Defense Laboratory, and Brookhaven National Laboratory. Some E'ffects of Ionizing Radiation on Human Beings. Washington, U.S. Government Printing Office, 1956. "Nondestructive Testing." Journal of the Society for Nondestructive Test- ing, November-December, 1959. Overman, Ralph T. Basic Concepts of Nuclear Chemistry. New York, Reinhold Publishing Corp., 1963. RCA Service Company. Atomic Radiation. Camden, N.J., 1957. U.S. Department of Health, Education, and Welfare, Office of Education U.S. Atomic Energy Commission. Peacetime Radiation Hazards in the Fire Service. Washington, U.S. Government Printing Office, 1961.

167 Index

Absorption coefficients, 30 Definition, 76, 91 Absorption, radiation, 29-37 Densitometer, 42 Accelerator, linear, 14 Density, 76, 92 Activation, 20 Detection, 39 Agreement States, 135 Determining qualifications of personnel, 147 Alpha radiation, 2, 9, 10, 11 Deuterium, 6 American Petroleum Institute, 123, 125 Deuterons, 20 American Society for Testing and Materials,123 Developing, 95 American Society of Mechanical Engineers, 119 Diaphragm, 88 Artifacts on radiographs, 113-116 Distance, source to film, 102, 103 Atom, 1, 3 Distortion of shadows, 86 Atomic Energy Commission Licensing Guide,153 Dose, 139 Atomic mass unit (AMIJ), 3 Dose, maximum permissible, 56 Atomic number, 4, 5 Dose rate, radioisotope, 28 Atomic weights, 5 Dosimeters, 39, 40, 41 Drying, film, 99 Backscatter, 89 Barhun clay, 109 Electromagnetic radiation, 10, 11, 12 Beta radiation, 2, 9, 10, 11 Electromagnetic spectrum, 11, 12 Betatron, 14, 15 Electron, 2, 3 Bills of lading, 152 Elements, 1, 2, 7 Biological half-life, 53 Emergency procedures, 148 Buildup, 33 Emission, 77 Byproduct material, 139 Emission, gamma ray sources, 28 Emissivity, 28 Calendar quarter, 189 Emulsion, 91 Cassette, 75 Encapsulation of radioisotopes, 82 Cavities, 130 Examination, spot, 121 Cesium-133, 20, 81, 84, 104, 105 Exposure, 92 Chain reaction, 2, 18, 19 Exposure limits, personnel, 139; minors, 139 Chamber, ionization, 42 External radiation, 52 Characteristic curve, film, 92 Charts, exposure, 104, 107 Film, contrast, 91, 94 Cobalt-60, 17, 21, 22, 24, 81 Film holder, 75 Codes, 118 Film processing, 95 Cold shuts, 130 Fission, 17 Commodity list, ICC, 150 Fission products, 20 Compounds, 3 Fixation, 97 Compton scattering, 27 Fixer, 97 Concrete shielding, 32, 35 Fluorescent screens, 76 Containers, empty, 152 Fog, 115 Contamination, radioactive, 59 Forward scatter, 89 Contrast, film, 91, 94 Fusion, 17 Contrast, radiographic, 76 Contrast, subject, 92 Cracks, 130 Gamma radiation, 11 Crimp marks, 115 Gamma ray, 9, 11, 12 Curie, 23 Gas holes, 129 Curve, film characteristic, 92 Geiger counters, 42 Geometric principles, 77, 84, 87 Darkroom, 98 Geometrical enlargement, 86 Decay, 24 Geometrical unsharpness, 85 i7169 Geometry of shadow formation, 84, 85 Procedures, operating and emergency, 148-149 Graininess, 98, 94 Proton, 2, 3 Half-life, 28 Quality levels, 117-118 Half-value layers, 30 H and D curve, 92 Rad, 51 1 Holes, gas, 129 Radiation, 189 Hypo, see fixer Radiation, absorption of, 29 Radiation area, 143; high 143 ICC regulations, 149 Radiation banking concept, 56 Illuminator, 91 Radiation safety officer, 148 Inclusions, 130 Radioactive, 6 Industrial radiography, 153 Radioactive material, 139 Inspection system, 148 Radioactivity, 9 Instrument calibration, 44 Radiographer, 139 Instrument characteristics, 43 Radiographer's assistant, 139 Intensifying screens, 94 Radiographic contrast, 92 Internal radiation, 53 Radiographic exposure device, 139 Interpretation, basic concepts of, 117 Radiographic screens, 76 Inverse square law, 28 Radiographs, unsatisfactory: Ionization chamber instruments, 42 causes and corrections, 113 Ion pair, 25 Radiography, 75, 139 Ions, 25 Radiological assistance, 149 Iridium-192, 81 Radium, 10, 81 Isotope, 6 RBE, 52 Records, 144 Labeling, 151 Reduction factor, 33 Labels, 142 Reference standards, 118 Law, inverse square, 28 Regulations, Civil Mr, 152 Lead foil screens, 76, 94 Regulations, U.S. Coast Guard, 163 Lead, shield, 29, 30, 32, 85 Rein, 51 Leak testing sealed sources, 82, 149 Reports, 144 Levels, 142 Restricted area, 139 License application for radioisotopes for radiography, R-meter, 41 153 Roentgen, 9, 28, 51 Linear accelerator, 14 Safe light, 98 Microcurie, 23 Scatter, 76 Millicurie, 23 Scattering, 26 Minors, 139 Screens, 75 Misruns, 130 Screens, fluorescent, 76, 95 Molecule, 5 Screens, lead foil, 94 Sealed source, 139 Negative ions, 25 Sealing, 82 Neutron, 3, 11, 17 Security of sources, 144 Notices to employees, 144 Sensitivity, 125 Notification, 144 Shadow formation, geometry of, 84, 86 Number, atomic, 4, 5 Shielding, radiation, 29 Shrinkage cavities, 130 Occupational dose, 139 Signals, 142 Orders, shipping, 152 Signs, caution, 142 Organizatinnal structure of radiography programs, 148 Slag, 121 Solution, developer, 95 Packing and shielding, 150 Solution, fixer, 97 Pair production, 27 Solution, stop bath, 96 Particles, 2, 3, 11 Specifications, 118 Penetrameters, 119, 120 Speed, film, 77, 93, 94 Penumbral shadow, 85 Spot-examination, 121 Periodic table, 1, 6, 7 Standard radiographs, 118 Permissible dose, maximum, 56 Steel equivalent thickness, 105 Person, 139 Stop bath, 96 Peraonnel, instruction of, 144; qualifications of, 147 Storage containers, 139, 142 Personnel monitoring, 142 Subject contrast, 92 Photoelectric process, 26 Surface irregularities, 131 Pitchblende, 1 Survey, 142 Placards, 151 Survey meters, 39, 42-43, 142 Porosity, 120-122, 129 Symbols and signs, 139, 142 Positron, 3 Postal regulations, U.S., 152 Tagging sources, 142 U.S. Coast GuardRegulations, 153 Time, developing, 95 Time, fixing, 97 Tritium, 6 Time, washing, 97 Tubes, X-ray, 14 Tolerance dose, 139 Training radiography personnel, 145;initial training Undercut, 89 program, 145; on-the-jobtraining, 145; periodic Unsharpness, 85 training, 145 Transportation of radioactivematerials, 149; Van de Graaf, 12 Interstate Commerce Commission,149: Certifica- tion, 152; empty containers,152; labeling, 151; Waste disposal, 144 packing and shielding, 150; placardsand mark- Wavelength, 11, 12 ings, 151; shipping orders andbills of lading, 152; violations and accidents, 152 Civil Air Regulations, 152 X-ray, 1, 9, 10, 11, 12, 79 U.S. Postal Regulations, 152 X-ray tubes, 14

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