Rad1 Ological Defense

RAD1 OLOGICAL DEFENSE

VOI. IV

Manual

Prepared by the

Armed Forces Special Weapons Project

CUSSIFICATION CANCELLEDOR

CHANGEOTO

12b338b , ......

Radiological Defense, Vol. IV

RADIAC

An Introduction to Radiological

Instruments for Military Use

by D. C. Campbell, LCDR, USN

This document contains information affecting national defense within the meaning of the Espionage Laws, Title 18, USC, Section 793, 794. The transmission or revelation of its contents in any manner to an unauthorized person is prohibited by law

I i , *i-j81---.- -- _I TABLE OF CONTENTS Paw V vi 1

3 4 4

‘‘I CHAPTER 7‘ 7 8 9 9 10 11 12 I 12 13 13 14

CHAPTER 15 CHAPTER 19 19

CHAPTER 21 22 2 5 CHAPTER 27 CH.4 I’TE R 29 CHAPTER 31 31 32 33

35 35 36 39

41 41 43 43 iii 12b3388 Page 45

47 48 50 51 55 57

59 59 63 64 69 70 79 81 REFERENCES-- 83 APPENDIX I. 85 87 89

iv 1253389 -

45 , 47 A 48 : INDEX TO ILLUSTRATIONS 50 : Pare Page 51 Figure 1. Work is under way to develop satisfac- Figure 40. Checking meat for alpha contamination 55 . tory instriiments--_ ------VI11 n-ith a poppy-type portable propor- 57 Figure 2. Gamma ray absorption ______._---_-_4 tional counter ______49 Figure 3. Laboratory type electroscope ____ - - - - - _ 7 Figure 41. Geiger counter in use with beta shield Figure 4. Pocket dosimeter ______.______._____8 open to increase detection sensitivity 59 Figure 5. Reading the pocket dosimeter_.______8 in checking for ground contamination- 51 59 Figure 6. Charging a pocket dosimeter______. ___ 8 Figure 42. Ionization chamber being used for 63 Figure 7. Schematic drawing of quartz fibre survey gamma survey work by a shipboard instrument-_--__-_-_------9 damage control team ______- - 53 64 '. Figure 8. Personnel pocket chamber------10 Figure 43. Individual dosimetry.______53 69 Figme 9. Wearing a pocket chamber ______10 Figure 44. Helicopter ground monitor ______- __-_ 54 70 Figure 10. Charging and reading the pocket Figure 45. Decontamination- __ -.. . - - - -___------54

79 chamber ...... ~ .___10 Figure 46. Checking hand contamination ___-----_ 55 81 Figure 11. Alpha-Beta-Gamma portable ionization Figure 47. Laboratory- _____ - __ - ____ - - ____- - --_ 56 chamber survey meter _____ - - - - - ___ 11 Figure 48. Dosimeters and chargers ______-___-_60 83 Figure 12. Ionization chambers------.------12 Figure 49. Electrostatic dosimeter charger PP- 85 Figure 13. Ionization chamber circuit__-______13 3j4A/PD______-_------61 87 Figure 14. Electrometer tubes------.- - -.-. - - - 14 Figure 50. Pocket chambers and charger-reader- - 62 Figure 15, Resistors for electrometer circuits___-- - 14 Fipiirc 51. Victoreen minomeler type charger- 89 Figure 16. An ionization chamber survey meter reader_.______-_------62 goes ashore during landing maneuvers- 14 Figure 52. Nuclear Instrument and Chemical Com- Figure 17. Ionization chamber survey meter------15 pany model 2050 charger-reader. - - - 63 - Figure 18. Gas amplification ______-___--16 Figure 53. Radiac meter IM-7AIPD quartz fibre Figure 19. Counting chamber and circuit ______- 16 drift alpha, beta, and gamma survey I Figure 20. Pulse size as a function of voltage from a meter______-_--_-----_------63 chamber exposed to a constant energy Figure 54. 8S:PDR-T-1 gamma survey ioniza- source of radiation ______._--17 tion chamber ______-_--___---- 64 Figure 21. Portable proportional counter survey Figure 55. National Technical Laboratories ioni- meter_-______-_----_------. 20 zation chamber gamma survey meter, Figure 22. Parallel wire proportional probe------20 model hIX-6 (IM-40/PD)---. - _--- - 65 Figure 23. Geiger-Mueller tube pulse- .------.- .- 21 Figure 56. Victoreen model 2478 gamma chamber Figure 24. Geiger-Mueller tube characteristic curve- 22 survey meter (IM-B/PD)-.. ------65 Figure 25. Neher-Harper vacuum tube quench Figure 57. Tracerlab Cutze Pie (Ih1-5IPD) - - - - -_- 66 .. circuit-- __ - - -.- - - -.------23 Figure 58. National Technical Laboratories model Figure 26. Tubes for portable Geiger-Mueller hlX-2 beta-gamma survey meter-- - - 66 counters------.-----.- 23 Figure 59. Rauland Zeus _.__-__-____-______----67 Figure 27. Laboratory Geiger tubes ___.- -... - - -. . - 24 Figure 60. The AN/PDR-BO(XK-l), an experi- Figure 28. Diagrammatic sketch of a portable Geiger- mental model military .%?us______68 Mueller Survey Meter ___.__.___-_.- 25 Figure 61. Victoreen high-range proterimeter- - - __ - 68 Figure 29. Geiger-Mueller counkr in me.. - - - - -.- 26 Figure 62. AS/ADR-1(SN-2) Airborne radiation Figure 30. Simplified scale of two scaling circuit--- 27 detection system- - - -.- ______- - 69 Figurec31. Schematic diagram of a scintillation Figure 63. Original poppy type portable alpha counter _____ - - - - -.- - - -.- -.. - - - - - 33 proportional counter------.- - - - - 69

Figure 32. Film badge _____.._._.~ ._.-.~-~ ...-- 35 Figure 64. Xuclear Instrument and Chemical Com- Figure 33. Film badge carried in shirt pocket- - - - - 36 pany pee wee proportional alpha Figure 34. Schematic arrangement of a densitometer counter model 2111 ______- 70 used to determine film badge readings- 36 Figure 65. AS/PDR-IO poppy type proportional

Figure 35. Densitometer in use _____- ~ ----..--_-_ 37 alpha detector _____ - - _____- - __ ___ - - 70 Figure 36. Characteristic curve of a film badge Figure 66. El-Tronics model SM-3 Geiger counter emulsion - - - - -. - - - - -.------.- - 38 f.SN/PDR-26) - - - - -.- -. ------72

Figure 37. Medical records- ______.______.._~ - 38 Figure 67. Kational Technical 1,ahoratories model Figure 38. Existing equipment tried during field ?JX-5 Geiger counter (IM-39/PD) - 73 problems is found to be lacking in Flgure 68. Kuclear Instrument and Chemical Com-

many characteristics. ~ ~ ~ -.- - -~ - -..- 42 pany model 2610 Geiger counter Figure 39. Gamma calibration- _~____ - ______-_ 46 (.-1N/PDR-7) - - - -.. . - - - __ - ___-- - - 73

V Pap Pa@ Figure 69. Victoreen Instrument Company model Figure 75. Geophysical Instru,ment Company mod- 263A Geiger counter (AN/PDR-5) - - 74 el 600 monitor ______78 Figure 70. Recent commercial improvements in Figure 76. Kelly-Koett model K-240 hand and portable Geiger-Mueller survey foot counter (AN/UDR-3) ______-79 meters ______74 Figure 77. AN/UDR-10 five-channel counter for Figure 71. Geiger counters AN/PDR-S(series) ___ 76 detecting beta-gamma contamination Figure 72. Geiger counter AN/PDR-15 ______76 of the hands and feet ______--80 Figure 73. Radiac set AN/PDR-27 ______77 Figure 78. AN/PDR-ll(XN- ) alphasurvey meter.. 81 Figure 74. The AN/PDR-T-2 Geiger-Mueller sur- Figure 79. AN/PDR-18 gamma photomultiplier vey meter ______-______78 survey meters ...... 82

vi IZb33q I Page

.. . 78 .- 79 FOREWORD 80 81 This volume is the fourth of a series of Radiological Defense Manuals issued by the Armed Forces Special Weapons Project for training purposes in 82 the Department of Defense. The objective of Volume IT7 is to present certain phases of the radiological instrumentation program in such form as to assist defense personnel in preparing themselves for the complex detection problem which must be faced during atomic warfare. Aspects of the program are presented as seen today. It is anticipated that research ard development now under way will make many of the instruments herein described obsolete within a period of 18 months. The volume combines with the description of specific instruments a basic consideration of the mechanism of radiation detection and an indication of possible operational use, so that field personnel may be given a comprehensive picture of the role to be played by radiological instrumentation during atomic warfare.

K. D. NICHOLS Major General, USA Chief, Armed Forces Special Weapons Project . JANUARY1950

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viii

12b3393 m- a ., RADIATION INSTRUMENTS FOR MILITARY USE

Chapter 1 INTRODUCTION The development of the atomic bomb and the peutic use. radium radiographic and therapeutic possible development of radiological warfare use, isotope research and therapeutic use, cosmic agents require that future military plans contain a rav research. and investigations with high energy certain emphasis on radiological defense. Instru- accelerators. Military instruments in general ments are a basic requirement in any such defense require, in addition, an ability to withstand rough plan, since nature has not equipped man with usage under extreme weather, temperature, and senses capable of responding to nuclear radiations. geographic conditions. They should also be made Irreparable damage may be produced in high as simple rind foolproof as is possible within the ! intensity fields which cannot be recognized with- limits ol their detecting requirement. 1 out the use of suitable instruments. The field of radiological instrumentation, as it Since the first atomic bomb explosion, increas- applies to the defcnse establishment, has been ing emphasis and thought have been placed upon asqigned the namc “RADIAC”. This new word the development of instruments suitable for mili- for the military vocabulary has been taken from tary use. The instrumentation requirements are tlw initial lctters of-RAdiation, Detection, In- in many respects similar to those which hax7e been dication, And Computation. I encountered in X-ray radiographic and thera- I i I

I I I ! i I I

I I

0 i i 1 1 I 6 1 I 12b33~ I I ! I I I i ! ! i t

J i I; i i 3 t1: t 1 I >‘ i’” Chapter 2 RADIATION IN GENERAL

9.01 Introduction charged alpha and beta particles and to the Radiation, in the sense in which we are con- electrically neutral gamma rays. Of these radiations, the greatest emphasis is placed on measure- - cerned, means nuclear emissions and is not concerned with the radiations which are manifest ment of gamma rays. Table I gives some rough as radio waves, hkat, and light (1) (2).* It is comparisons of the characteristics of alpha and possible to separate these nuclear emissions into beta particles and gamma rays. electrically charged and electrically neutral The measurement of neutrons will become categories. important in conjunction with the operation of The electrically charged radiation consists of nuclear reactors for power production or the particles in motion such as: propulsion of ships or aircraft. Detection of neutrons involves some specialized applications beta (8) particles (electrons-e-) of the detecting principles which will be discussed. alpha particles (helium nuclei-He++) (a) However, a detailed description of neutron detec- protons (p) (hydrogen nuclei) (no military tion will be omitted, since neutrons at present are importance) of limited interest to the Defense Establishment. positron (positive electron) (no military It should be noted that there are certain importance) elements which give off pure alpha and pure beta The electrically neutral radiation consists of: radiations. Gamma radiations are produced neutron (n) only as an after-effect of either an alpha or a beta gamma rays (7) emission. With very minor exceptions, there is X-rays (not considered as a nuclear radiation) DO such thing as a pure gamma emitter, although Except in a few unique applications, military in some cases the alpha or beta emissions may be consideration is given to the measurement of the so weak as to be virtually indetectable.

TABLEI.-Characteristics of nuclear radiation

~ Radiation Nature Energy Ionizing power in air Penetration Range in standard air -___

Alpha Par- Heavy positively High 40,00(t250,000 5.5Mev-4.06 x 7 Mev-6.0 cm ticle charged particle. ion pairs; 20,000- 10-3 cm in Al- 5 Mev-3.48 cm Helium nucleus 80,000 ion pairs uniium 2.0 Mev-1.0 cm He*+. Velocity 0 per centimeter 0.2 Mev-0.17 cm to 2 x IO’ cm/sec. ___- Beta Par- L i g h t negatively Up to Me- Medium 30-300 ion 0.15 hlev-1.0 mm; 0.2 Mev-37 cm

ticle a charged particle. dium High, pairs per centi- 2 Mev-3.5 mm 2 Mev--840 cm Electron e-. Ve- 0-3 Mev meter in Aluminum locities up to 99.7% that of light

Gamma Ray Electromagnetic ra- Low to Me- Low o+ Lower intensity Thickness to reduce diation. W a v e dium High, expot cn t ially intensity of 1 Mev length from 5 s 0.03 - 2.6 along its path to one-half: 10-10 to 4 x 10-8 Mev Air-350 feet cm. Cncharged Lead-0.9 cm

**Mev=Million electron rolts=amount of work done when one electron is accelerated by a potential difference of one million volts. Wumbcrs in parentheses indicate references on page 83 of this manual. 3 12b3395 * RADJAC

2.02 Electrically Neutral Radiation In some cases, photons of gamma radiation The fact that gamma (or X-rays) are uncharged behave like billiard balls and produce the effect means that it is not possible to detect them shown in figure 2b. Energy is absorbed from the directly with present types of measuring equip- incident photon to eject an electron. The scat- ment. Fortunately these radiations in their tercd photon has, as a result, lower energy than passage through matter produce secondary proc- the incident photon. This effect is important in esses which allow measurement. thc range of energies up to roughly 1 to 10 MeV. In order to understand the methods of measure- C. Pair Production ment of gamma rays, it is necessary to consider With high energies above 1 MeV, pair produc- the manner in which neutral radiation is absorbed. tion becomes possible, and becomes predominant It can be shown that absorption, or attenuation, in the region 5-12 Mev and ’above, being more takes place by several processes, the most im- important in absorbers of high atomic weight. portant being the following: Diagrammatically, this is shown in figure 2c where a high energy gamma photon is absorbed by pro- A. Photoelectric Effect ducing a pair of electrons. As shown all three As shown in figure 2a, an atom irradiated methods of absorption result in the production of with gamma rays absorbs the radiation by ejecting high energy electrons which are electrically charged an electron. This type of absorption is dependent particles of the same general type as beta particles. on the absorbing medium, but as a rough rule, is It should be reemphasized that only if un- only important with gamma rays having energies charged radiations are instrumental in producing below 0.1 Mev. charged radiations through some secondary proc- B. Compton Effect ess can they be detected or measured by the various means which will be discussed.

2.03 Electrically Charged Radiation Several possibilities present themselves for the PHOTON OF measurement of electrically charged particles. $ ENERGY llcthods employing gas ionization prove to be thc most convcnient and practical. When a a. Photoelectric absorption off1 gninrnn ray photon. chargcd particle enters a gas it may act on a ncutral gas atom or molecule with sufficient enwgy to remove one or more electrons. This process is called ionization and results in a single ncutral atom or molecule being split into two for niorc) electrically charged particles-the negativc PHOTON clwtron(s) and the positively charged remaining portion of the atom or molecule. The removal of b. Gamma rav photon absorbed through tke productmir of0 lo7~erenergy gamma a single electron produces what is called an ion photon and a recoil electron. pair. The energy required to produce ion pairs depends upon the particular gas involved.. In the casc of air, which is a mixture of gases, the average loss of enerqy by the electrically charged particle is about 32.5 electron volts for each ion pair pro- dared. This does not mean that 32.5 electron rolts go into the formation of the ion pair. c. Uamma photon being absorbed with the productinri oJ ail electron POIT. This Actually, only about half of this value is used only OCCUTS tn the iicinity oJthe iiuclens spwifically to strip off the electron in an ionizing Figure 2. Gamma rnij nbsorption. collision. The rcmainder of the 32.5 electron volts is givcn up in the excitation of gas molecules Three methods of gamma ray absorption are shown by means of schematic diagrams. It \rill tx rioted that a in inrlastic collisions which do not produce ions negative electron (e-) is produccd t)y each method. or in providing kinetic energy to the members of 12b339b -4

ei, RADIAC .diation -. an electrically charged particle will 'recombine e effect and ion pair if ionization is produced. We will of In the case air at *om the discuss later the excitation phenomenon in con- to form neutral molecules. of (le scat- nection with certain crystals, but for the moment atmospheric pressure the life of an ion pair is :y than ionization is of the greatest interest. believed to be in the order of five minutes. If, *. In the process of ionization, particles having tant in prior to recombination, the particles are subjected MeV. ' greater electrical charge will produce greater to an electric field, they will move under the in- ionization. Also, the more massive particles fluence of the field, the positive ions toward the I Iroduc- moving with lower velocities will present longer negatively charged cathode, and the negative ions minant periods of time in which forces can act and, as a toward the positively charged anode. A gas filled more result, will be more effective in producing ioniza- chamber containing electrons which have sufficient weight . tion than less massive particles. As an example, strength to collect all of the initially formed charge the transit in air of the negatively charged beta is called an ionization chamber. The electric field ;where 3y pro- particle will produce between 30 and 300 ion pairs strength required for charge collection in chambers 1 three per centimeter of path length with the higher generally is between 15 and 120 volts per centi- ation of ionization occurring for lower beta particle ener- meter and usually is not critical. This voltage harged gies. The heavier, doubly charged positive alpha corresponds to the field necessary to collect the .r ticles. particle will produce anywhere from 20,000 to ions prior to appreciable recombination and is not if un- 80,000 ion pairs per centimeter of travel. high enough tQ produce additional ion pairs as the lducing The ion pairs produced in a gas by the transit ions travel to the collecting electrodes. q proc- by the

for the rticles. to be %en a t on a fficien t This L single ,wo (or egative iaining oval of an ion n pairs In the ,verage )article ir pro- lectron I pair. s used mizing lectron lecules v ions bers of

5 12b3391 a

l2b3398 7

Chapter 3 IONIZATION CHAMBER

3.01 Introduction practice, form C is little more than an adaptation of the cylindrical condenser in B. With appropriate forms of chambers all ionizing The anode and cathode previously mentioned, radiations can.be detected (4). In the case of may take the form of electrodes in a simple elec- heavily ionizing radiations such as alpha particles troscope in which the chamber (container) forms (and in some cases electrons), separate ionizing events can be counted in a manner similar to that one electrode and the central wire and thin gold which will be described for Geiger-Mueller and foil form the other electrode as shown in figure 3. proportional counters. Design characteristics of The electrostatic field produced by the positive instruments are thoroughly entwined with opera- charge on the central electrode and the negative tional usage and the type of radiation involved. charge on the case exerts a force on the charge In general, the chambers are built around three on the gold leaves which causes the leaves to separate. Ions formed inside the chamber by basic forms: radiation will neutralize the charge on the gold A. Two parallel electrode plates, one highly foil leaves, and the leaves will move together. insulated and directly connected to the measuring part of the instrument. Thus, within certain limits, it is possible to read B. Cylindrical electrode with a coaxial collect- radiation dose as a function of position of the ing rod. sensitive element of an electroscope (3). An electroscope has no external voltage source, how- C. Rectangular box with an internal collecting ever, if the instrument used for the measurement network (sometimes called a Christmas tree). In of the electric charge collected in an ionization chamber utilizes a continuous external voltage for its operation it is called an electrometer.

3.02 Pocket Dosimeter A useful military instrument is the quartz jibre pocket dosimeter which is a modified version of the Lauritsen Electroscope (1). A dosimeter is pic- tured in figure 4. This instrument, about the size of a fountain pen, utilizes a metallic coated quartz fibre some five microns (0.0002 inch) in diameter as the sensitive moving element in place of the thin gold foil in our previous example. The instrument incorporates a small compound microscope for viewing the fibre against a calibrated scale. Some type of light source must be available in order to see the scale and fibre. These dosimeters, having a full scale sensitivity 0.2 roentgen (r),*are in common use for measuring integrated gamma ray exposures. Work is (POSITIVE CHARGE) undcr way to produce pocket dosimeters having full scale readings, perhaps as high as 200 roentgens. Pocket dosimeter reading and charging is Figure 3. Laboratory type electroscope. shown in figures 5 and 6.

Separation of leaves is caused by the repulsive force *See page 52 for an exact definitionof a roentgen. (This is a unit of measure- between two like charges. ment of gamma or X-ray dosage rate or absorption.) 7 i

RADIAC

CONTACT FOR CHARGING BOX END WINDOW \ /

'CHARGING TERMINAL

'INSULATOR

-QUARTZ FIBRE ELECTROSCOPE

/OUTER ELECTRODE FIXED METAL, LEAF

MOVEABLE FINE METAL ' COATED QUARTZ FBRE >OBJECTIVE LENSES

Figure 5. Reading the pocket dosimeter. A light source must be available to see the scale and fibre. Here a reading is made using sky light for illumination. in as a part of the instrument. Dosage rate is obtained by timing the rate of electroscope fibre movement. Timing is accomplished by the re- SCALE RETICLE petitive flashes of a neon lamp which appears t~ / the viewer just above the microscope scale. Since the instrument keeps its calibration over extended periods of time, it is used as a secondary standard.

EYEPIECE LENSES

Fzgure 4. Pocket doszmeler. Shown is the dosimeter with the magnetic charging de- \ice recently developed by Dr. F. R. Shonka of the Argonne National Laboratory. A magnet in the charger repels the dosimeter magnet and move3 it into position so that the electroscope can be charged. Many dosimeters incorporate diaphragm charging terminals such as that shown with the pocket chamber in figure 8.

3.03 Drift Meter A medium sized portable gamma measuring, alpha and beta indicating, survey instrument has been built with a quart/ fibre system similar to that used in the pocket dosimeter. In some arcas this instrument goes under the name Landsoerk Electroscope. The unit has an enlarged cliarnb~r and is designed for portable but not pocket nsc. Since it is not a pockct dc>vicethe cliargrr is 1)uilt Figure 6. Charging a pocket dosimeter. 8 12b3400 I n d il- is re .e- to Figure 7. Schematic drawing of quartz $fibre survey instrument. ce . Thin windows in the bottom and end of the chamber case make possible the detection of beta and alpha radiations. cd d. The instrument can be made extremely rugged as as a result, less costly than the pocket dosimeters a gamma reading instrument. The problems ($5 as compared to $40). They hare a use in associated with thin windows necessary for alpha military operations where it is desired for one and beta admission to the chamber will be dis- reason or another to prevent the wearer from cussed later. Figure 7 shows a type of commer- knowing the dose he has received. A great num- cially available drgt meter. ber of pocket chambers are in use which have a total sensitivity of 0.2 roentgen gamma exposure. 3.04 Pocket Chamber Other pocket chambers are being constructed which have gamma sensitivities of 100 roentgens The charge on the chamber electrodes can be and there are considerations of chambers reading measured, and any decrease in charge over a as high as 1000 roentgens. Thewearing and reading period of time can be calibrated to give a measure of pocket chambers is shown figures 9 and 10. of the radiation dosewhich has produced the charge in decrease. For a number of years thimble chambers 3.05 Electrometers have been built to record X-ray dosages up to 2500 roentgens for energies between 0.08 and 0.25 Metal coated quartz fibres mounted on a torsion MeV. fibre between electrodes are used as electrometers The pocket chamber;figure 8, again about the for ion detection. Several forms hare been de- size of a fountain pen, is an instrument utilizing velopcd which have found some use in the labora- this principle. Usually the instrufnent required tory measurement of alpha particles and low to place the charge on the pocket chamber is used energy beta rays. The application of an external I at some later time to read any decrease in charge. potential to the electrodes produces +n instrument These instruments are more simply designed, and which is somewhat more sensitive than the elcc- \ 871745°-50-2 9 12b3401 RADIAC

POCKET CLIP

(INTERIOR SURFAC COATED WITH ALUMINUM CENTRAL ELECTRODE (COATED WITH GRAPHITE)

Figure 9. Wearing a pocket chamber. sible radiation dose (industrial tolerance level) POLYSTYRENE for one day, an average current of 3 x IO-'* amperes FLEXIBLE would be produced. Such minute currents require CHARGING the use of vacuum tube amplifiers and special DIAPHRAGM handling techniques in order to make proper measurements. These special electronic circuits are known as electrometer circuits. CAP .-a 3.06 Chamber Characteristics Figure 8. Personnel pocket chamber. The characteristics of a particular radiation I This is a non self-reading gamma dosage indicating which enter into ionization chamber design are device about the size of a fountain pen.

troscope. In most general use in this country are the Wulfand the Lindemann electrometers. How- ever, aside from possible laboratory usage the I quartz fibre electrometer has little military application. If radiations are allowed to produce ions in the space between two electrodes, as shown in figure 13, and an electric field is induced to pull the ions from the region in which they were created the positive ions will move toward the cathode (central wire), and thc electrons which are produced at the same time will move in tlic opposite direction toward the anode (chamber case). Current will therefore flow in the circuit 9 until all ions are collected. This ionization cur- b rent is very small. In the case of a one-litre I chamber having air under standard conditions of I temperature and pressurc the maximum permis- Pigure 10. Charging arid reading the pocket chamber. RADIAC the size of the source to be measured, and the TABLE11.-Range of beta particles in aluminum Energy Mea Thickneas range of dose rate anticipated. The physical mm rnglcml characteristics of the chamber which can be varied 0.15- __ ------______- - __ 0. 1 30 to meet various requirements are- 0.5_------0. 6 160 1.0______-______-_ 1. 5 409 1 Chamber Window 2.0-_--____-______--_ 3. 5 951 2 Chamber Wall Material 4.0 ...... 7. 5 2, 035 3 Pressure and Type of Chamber Gas It is customary in all types of nuclear work to meas- 4. Chamber Volume ure window thickness in mass per unit area (mg/cmz) since this gives a good practical unit of absorption that can be used for the measurement 3.07 Chamber Window of very thin films. These thicknesses indicate Gamma rays have penetrating powers which that there is only a moderate problem of getting eliminate the requirements of admission windows. beta particles into chambers for laboratory use. This is fortunate since the greatest number of The problem of making chambers with beta military instruments will be gamma-reading, windows capable of rough usage is another much and it is much easier to make a fully packaged more difficult problem. One form of alpha-beta- instrument rugged. This is not the case with gamma portable ionization chamber survey meter either alpha or beta particles. Beta particles are is shown in figure 11. characterized by a relatively low penetrating In the case of alpha particles there is consider- power. Beta particles having an energy of 2 Mev ably less penetration than with beta particles. A have a range of slightly greater than eight meters 5 hlcv alpha particle has a range of 3.5 centimeters level) in standard air. With aluminum as the absorber, in air; therefore, it is readily seen that there is a iperes maximum beta penetrations are roughly as shown real problem in getting an alpha particle into a equire in table 11. chamber. Few windows are sufficiently thin for pecial ,roper METER 1 rcuits

ADJUSTMENT iation n are BETA DISCRIMINATOR -WINDOW SLIDE CONTROL

LOOP FOR 0 CARRYING STRAP

\ALPHA DISCRIMINATOR WINDOW SLIDE CONTROL THIN MOVEABLE WINDOWS FOR ALPHA AND BETA RADIATION

BATTERIES FIGURE11. Alpha-beta-gamma portable ionization chamber survey meter. iber. Because of the thin window, this instrument type has a doubtful future as a military instrument. 11 12b3403 ?

RADIAC alpha admission. Thin mica and stretched nylon wdls with nonmetals of low atomic number and and rubber hydrochloride films about 5 microns writing specifications: thick and with a mass as low as 0.5 milligrams per 11 . . . . . the chamber will be air cquiralent square centimeter have been used with some suc- and wave length independent to within f20% cess. However, even with these extremely thin from 80 Kev to 1.5 Mev quantum gamma radiation.” films, the alpha particle will lose from one to two centimeters of range during its penetration. It Since the ultimate usage of these instruments is becomes apparent that alpha chambers stand little for health protection, it is desirable to hare the chance of developing into instruments for field use. inner wall coating approach the absorption of human tissue. Tissue is composed primarily of the light elements-hydrogen, oxygen, nitrogen, 3.08 Wall Material and carbon. Chamber walls therefore are made of bakelite or plastic containing a high percentage of The wall material is of little importance to carbon atoms or coated on the interior nith a chambers devoted to alpha and beta measure- layer of colloidal carbon. men ts ; however, the wall material becomes serious with gamma-measuring chambers since the gamma 3.09 Pressure and Type of Chamber Gas ray measurement stems from its absorption in the The thin windows required to admit alpha interior face of the chamber wall. Through the particles prohibit the use of any gas other than air mean gamma energies of 0.5 to 1.5 Mev the various and at any pressure other than that of the normal mechanisms of absorption produce a fairly uniform outside atmosphere. Little success has been secondary response. The process of photo-electric found in any gas other than air for beta measure- absorption becomes increasingly efficient for metals ments. It should be pointed out that aircraft at lower energies, and a metallic chamber will give transportability and possible use in the air pre- readings disproportionately hgh when subjected cludes the possibility of hermetically sealing at to low energy gamma rays. As a result, much normal atmospheric pressure ion chambers having effort is placed into coating the interior chamber thin windows. The minute currents to be dis-

Figure 12. lonixtion chambers.

From left, to right are the ionization charnhcr:: from (a) \’jetoreen 2478 (IAfG3/l’D) cut open to show the chamber interior, collecting electrode, and elcctrometcr circuit (top) ; (b) Kat,ional Technical 1,aboratory MS-F (Ih,I--IO PD) cut opeii to show the collecting electrode sgstcnr; (c) i-ictorccn Model 300 protesinieter (ANjPDIt-2) 1)roken opeii with only the anodc shoiving; (d) Iiellcy-lioett. mariufact itred AN/l’DIt-T-i in ivhich the sensitive clectroineter circuit, is housed in a. compartment adjacent to thc collecl :iig cliairiti(~r. This cornpart,ment is above the chainber iii the illustrat,iori. 12 12b3404 RADIAC

.' cussed in subsequent sections indicate the necessity and of maintaining high insulation between electrodes ; therefore, any breather holes, to maintain equilib- alent rium between internal and external pressure, must 20% mma contain drying compounds to prevent moisture from entering the chamber. In the case of an ionization chamber for gamma I Its is 1 e the measurement, there is some point to using a gas f' )n of other than air at perhaps some elevated pressure ly of in order to increase the effective gas cross section and increase the chamber sensitivity. Freon 12 R %en, Figure 13. Ionization chamber circuit. Lde of and argon have been employed in the chambers of portable instruments. Ige of since it is not possible to make measurements ith a 3.1 0 Chamber Volume across resistors having values of the order of mag- An increase in sensitivity is provided by an nitude of loll ohms In addition, if our example increase in chamber volume; however, with the were taken in the range of dairy tolerance intensities, say milliroentgen per hour (0.004 r/hr), the alpha majority of portable survey instruments, the 4 potential drop across would be 0.037 volts. an air operational desires are for smaller, more compact R ormal equipments. Three chambers from different por- Vacuum tubes therefore are required as a means been table survey instruments and one chamber from of amplifybg voltage and currents of this order of magnitude. mure- a group dosimeter are shown in figure 12. The rcraf t physical sizeand shapeof insulatorsare all that limit The common types of vacuum tubes have been rejected for ionization current amplifiers. The r pre- the smaller sizes of chambers. Large chambers are ng at limited by the high voltage required to insure ion normal tubes have an extremely small flow of cur- laving collection. Any type of corona discharge as the rent from grid to cathode, known as the grid cur- )e dis- result of high voltage will produce ions which will rent, which may be of the order of magnitude of give spurious readings. amperes, However, loF9 amperes when allowed to flow through a resistance of loll ohms mill 3.1 1 Electronic Characteristics produce a potential drop of some 100 volts. Elec- The simplest arrangements consist of a central trometer tubes, specifically designed with grid cur- collecting probe through the center of the chamber rents of 10-l~amperes or less are being manufac- as one electrode and the interior of the chamber turcd for use in ionization chamber instruments. case as the other electrode with a battery con- Lorn grid currents are obtained by operating the nected across the two. Under normal ionization tubes at low filament temperature and by placing chamber usage the negative terminal of the battery screen grids between the filament and control grid. is attached to the central probe, and the positive These screens are at a very slight positive poten- terminal to the chamber wall (note that the tial so as to collect the electrons normally surround- reverse is true for proportional and Geiger counters). ing the cathode. A group of electrometer tubes With the arrangement as shown in figure 13, it is are shown in figure 14. possible to determine the voltage across the resistor In addition to the low grid current characteris- R. Knowing the volume of the chamber, current tics, the electrometer tubes are designed to insure flow can be calculated, since a radiation dose rate extremely low leakage currents. These currents of one roentgen per hour causes a current flow of are held to a minimum by operating the tube at 9.28X1O-l4 amperes per cubic centimeter of cham- low plate voltage and current. Extreme care ber gas volume. For example, if we consider a must be taken in the handling of electrometer relatively large chamber having a volume of one tubes, since body oils deposited on or near the tube chambei litre and an extremely high resistance for R of base may cause serious leakage currents. -4O/PD) 10" ohms; then a current flow of 9 x lo-" amperes Special manufacturing techniques also are re- ,en open will cause a voltage across R of 9 volts per r/hr. quired to produce resistors up to ohms. Five rroineter This value is sufficiently high to be of some due. such resistors, carefully sealed in glass, are sho~vn itriiber iri In practice, the voltage is not utilized dkevtly, in figure 15. 12b3405 13 RADIAC

I C 0 1' 0 Figure 1.6. Electrometer tubes. a fi Shown is an assortment of subminiature triode, tetrode, and pentode electrometer tubes which are used for the amplification of the minute currents produced by radiation in ionization chambers. b C 0 ii ic

C e

t Figure 15. Resistors for electrometer circuit.% Shown is an assortment of resistors having values of 108 to 1014 ohms. The resistor is inclosed in a glass envelope I 1%inches long and 0.2 inches in diameter. E 3.1 2 Ionization Chamber Instruments Radiac instruments, sensitive to gamma radi- C ations, with 30 to 50 cubic inch chambers are useful as light weight, high dosc rate measuring instruments for field survcy work. Such an instrument is shown in use in figure 16, and diagramatically in figure 17. This is perhaps the most important of all military radiation survey instruments. Thin window survey chambers as previously discussed in corincction with figure 11 may be used to measure gamma radiation and give indications of alpha and beta radiations. Ionization chambers have many uses such as in the small pocket dosimeters and vhambcrs for lf7igiire 16. An ioriiralion chatnher szirvcy meter yots ashore individual closagc measurc~mcnfs and with lnrg~r tivl.inq/ Innding ~naneitcers. chambcrs for group dosagc rccording dcviccs. 14 12b340b h Chapter 4 GAS AMPLIF!CATION

Ionization chamber voltages are relatively weak. each particle entering the chamber will produce a However, if higher voltages are applied to the definite number of ion pairs, and these ions will chamber electrodes, a gas amplification can be be collected at the electrodes, thereby producing obtained (5). When the electron from an ion pair a pulse of current in the external circuit. is given greater energy than the ionization energy If the size of the pulse is plotted as a €unction of of the atom or molecule of a gas, it may produce the voltage applied to the electrodes, a. curve such additional ionization as shown diagramatically in as that shown in figure 20 is formed. .d for figure 18. Gas amplification also can be obtained Below a certain minimum voltage across the by reducing the energy required to ionize the chamber we do not collect all the ions which are chamber gas through the choice of a suitable gas formed, because in this region of low voltage, O-a, or by decreasing the chamber pressure so as to ions have an opportunity for recombination prior increase the mean free path and the energy of the to collection. At slightly increased voltages, u-b, ionizing particle. normal ionization chamber working conditions are If we consider the counting chamber and cir- reached. Above voltage a the pulse size becomes cuitry as shown in figure 19 with the chamber relatively independent of the voltage, since there exposed to a constant energy source of radiation, is it complete collection of all ions formed by the

SENSITIVITY ADJUSTMENT METER OFF AND ON AND RANGE SELECTOR (CHANGEABLE SCALES) INSSOR \ / SWITCH

"8" BATTERY HIGH RESISTANCE RESISTORS .elope I 1010- id4 OHM) ELECTROMETER TUBES IONIZATION CHAMBER WALL

1 BATTERIES

CHAMBER%w / CENTRAL - / ELECTRODE x I/ FILAMENT ashore BATTERIES Figure 17. Ionization chaniber survey meter. Gamma-measuring instruments of this type are probably tht: most important military survey instruments. 15 12b340-l RADIAC .. , ,-

Fzgure 18. Gns amplz$cafzon. Diagramatic representation of the avalanche type of gas amplification found throughorit the Geiger-Mueller tube and near the collecting electrode of a proportional counter. One initial ioniLing event may produce lo3 electrons collected in a proportional counter and 10 3 electrons collected in a Geiger-tube.

CHA..,,,,.M RFD - where: J PULSE N = Number o€ ions collected

f 1 c = Charge on the electron (coulombs)

Figure 19. Counting chamber and circuit. q = Capacity of the system (farads) passage of an ionizing particle. In the region If me assume the capacity of the system to be lo-" 0-a-b, only ions produced by the primary radiation farads and examine the voltage produced by 1 contribute to the pulse. In the region a-b tile centimeter of t,ravel of a 1 Mev alpha particle, pulse P in volts will bc given by the relationship: thm:

p= sc '1

16 12b3408 I RADlAC The same length of travel with a 1 Mev beta particle:

One would expect a slightly larger voltage, say 4 x lo-' volts to be produced as the result of the secondary electron produced in the absorption of a I hiev gamma ray. Assuming photoelectric absorption of the gamma ray, some energy is required for ionization, some energy will perhaps go into kinetic energy of the products of ionization, and there may be some excitation of other electrons in the ionized atom. At any rate, it would be expected that the photoelectron would be produced with very slightly less energy than the 1 Mev beta a b'C e particle and because of its lower velocity (see VOLTAGE - pagv 4) will produce a slightly greater number Figure 20. Pulse size as a junction of voltage from a cham- of ion pairs per centimeter of travel in the ber exposed to a constant energy source of rdiation. chamber. If the chamber is such as will expend a-b Ionization chamber region all Llie energy of the beta particle or photoelectron, b-c Proportional region the total number of ion pairs produced by the c-d Limited proportional region d-e Geiger region beta particle will be slightly in excess of those above e Continuous discharge region produced by the gamma ray photoelectron.

Miieller uce lo3

)e lo-" I by 1 article, its

17 12103410 c . Chapter 5 PROPORTIONAL COUNTER 5.01 The Proportional Region we are able, within limits, to differentiate between the pulses produced by alpha particles and the At some higher voltage b in figure 20 the above pulses produced by either beta or gamma radia- relationship would cease to exist, and pulses would tions. This means that the proportional counter be found larger than predicted. The region b-c is will have a limited military usage for alpha meas- the so-called proportional Tegion, because the out- urements. If the field strength is such as to form put pulse is directly proportional to the amount of beta-gamma to alpha ratio of lo6 or greater, primary ionization. The chamber operation in the a such as roughly approximates the case immedi- proportional region can be explained as follows: ately following an atomic bomb explosion, the In the region of a few electron mean free paths proportional counter not capable of eren- away from the central (anode) wire, a sufficiently is diff tiating between the combined effects multi- high field strength imparts to electrons, attracted of a tude of smaller beta and gamma pulses and the from the remaining chamber volume, enough large alpha pulses. The proportional counter energy to cause secondary ionization. The output has a definite use in decontamination work after pulse is therefore increased by the collection of the decay of the short half-life gamma and beta the additional electrons and is proportional to the magnitude of the initial ionizing radiation. emitters. A portable proportional counter survey If there are I ion pairs formed by collections as meter is sketched in figure 21. an electron travels toward the central electrode, Certain factors must be considered in order to then the size of the voltage pulse is given by- establisli good working characteristics for proportional counters. The gas used for tube filling may (I)(1.6 x 10-19) be chosen so as to accomplish the desired action. P= Pure argon, helium, neon and methane, and certain combinations of these gases have been found Here, “I” is defined as t8hegas amplification and to give satisfactory results. Other counter probes is the ratio of the number of electrons collected at are left open to the air. Strong electric fields the anode N to the number of ion pairs originally may be produced with moderate voltage by using formed in the gas No: two coaxial cylinders as the electrodes, and since the field strength varies logarithmically for a cylindrical configuration, the smaller the diameter of the anode, the higher will be the field strength It should be noted that the gas amplification fac- in the vicinity of one electron mean free path of the wire. tor varies from about 10 in certain photoelectric For this reason, extremely fine central cells to 103 in proportional counters and to lo8 in electrode wires are employed. It is readily seen Eome Geiger-Mueller counter tubes as shoIm in that the mechanical strength of a thin window the diagram in figure 18. tube with a 0.0005 inch diameter central wire is In the case of the proportional counter it is not such as to lend itself readily to field use. necessary that the secondary ionization (or am- 5.02 Proportional Counter Probe plification) occur less than ten electron mean free paths from the central wire. Otherwise strict, As previously stated, a counter for use in the proportionality ceases, and the limited propor- proportional counter region is restricted in the tional region c-d is entered where the gas amplifi- multiplication of electrons to somewhere in the cation factor has values from lo4 to lo7. order of ten generations. This can be obtained Since the total ionizatiorl produced by an ion- in the large electric field near the central wire in izing particle is dependent on the type of particle, the cylindrical arrangement described above. It it follows that in the proportional counter region follows that a parallel plate structure is excludrd 19 RADlAC 4FF &ON RANGE SELECTOR SWITCH

BATTERlES B HIGH VOLTAGE SUPPLY

HANDLE -+/,

THIN NYLON WINDOW

(SOMEHAVE APROBES PREAMPLIFIER MAY 2 - L${*;::E IN THIS END) ELECTRODE) Figure 81. Porfable proportional counter survey‘meter. This type of instrument \vi11 I)r used for alpha particle detection. for use in a proportional counter. It is possible to build proportional counter probes with large windows using a number of parallel mires. 11 satisfactory geometrical configuration has been found where the depth of the chamber behind the window is “x”, the wires we placed at a depth ‘‘42” and a distance “x” apart. In some probes, “x” has been chosen equal to one centimeter. Such a multiple wire probe is shown in figure 22. A single wire probe is shown in figure 21. In this Figure 22. Parallel wire proportional probe. latter example the probe case is not completely A satisfactory geometrical arrangernent has been found cylindrical since the window opening is cut longi- with x= 1 inch. tudinally along the side wall. Parallel wire counters having large sensitive hands. feet, clothing, filter paper samples, and openings (100-150 cn?) are used for the surrey of various surfaces. This is primarily a tool usctl in large areas. Proportional counters with probcls conjunction with a field laboratory and 11-ith are used for checking alpha contaniinatioll on dwontaminrttioll activities.

20 12b3412 I i' I i'

Chapter 6 GEIGER-MUELLER COUNTER

.O1 Avalanche Ionization If in our previous example (fig. 20) the voltage 5 raised still further above point c the gas amplification factor will continue to increase, but in the region c-d, the amplified pulses are no longer proportional to the initial ionization. This means that secondary ionization is started outside the distance of a few electron mean free paths from the central wire. There is still some difference in final pulse sizes so that this region c-d is known as the Tegion of limited proportionality. Tubes operated in this region have little application outside research laboratories. If the voltage is increased still further, a new . Time phenomenon occurs in which secondary ion Figure 23. Geiyer-Mueller tube pulse. multiplication spreads throughout the entire .4fter one pulse has started at w, no second event can chamber volume. This cumulative effect is known take place until the pulse reaches y. The time w-y is as Townsend or acalancge ionization and is shown the tube dead lime. diagrammatically in figure 18. When a chamber is used in this region d-e, it is called a Geiger-Mueller of their mass, the positive ions move slowly under I counter, and the pulse size is independent of the the influence of the electric field reaching the event which initiated it. Still higher voltages outer collecting electrode in perhaps IO-3 seconds. produce above point e a region of continuous arc The electrons formed during the Townsend discharge. While in effect this is not a continuous avalanche, being many orders of magnitude (lo') - discharge but a series of pulses so closely spaced lighter, are all collected in less than seconds, 6 to give that appearance. which is a long time before the positive ions reach It should be noted that for any particular the cathode. The result is a cloud of positive ions - counter tube, if the pressure is held constant and forming at a distance of several mean free paths the voltage is varied the instrument can be made from the anode and moving toward the cathode. to operate as either an ionization chamber, pro- This produces a positive space charge which for a en found portional counter, or Geiger counter. By holding time completely shields the anode and prevents the voltage constant a similar situation can be counter action. As the positive charge moves created by varying the mean free path through closer to the cathode, a limited counter action is es, and variations in gas pressure. allowed to occur. In this case the initial pulse usrd in An examination of pulses from a Geiger-Mueller will be of greater magnitude than that of the one id with tube reveals that pulses are of the same size only which follows. An examination of the pulse when spaced a good time apart. One would delivered by a Geiger-Mueller tube may be made expect all pulses to be of the same size, but an with the help of figure 23. examination of the action of the positive ion The pulse develops rapidly from w to x, due to reveals that this is not always the case. In tlic rapid collection of electrons. The pulse previous discussions of the operation of ionization dccctys more slowly from 5 to z, due to the longer chambers and proportional counters we have transit time of the positive ions and the time neglected the effect of the positive ions and con- constant of the external circuit. After one pulse sidered only the action of the electrons. Because 13213 started at time w, no second event can take 21 RADIAC

place until the pulse has reached y, due to the region 0-p is reached, and within the resolving viol time of the tube practically every particle entering shielding action of the positive space charge. bas The time w-y, in which no second event can take the tube which is capable of producing at least emi one ion pair in the tube gas is counted. Beta place, is called the tube dead time. This time in t: is very important, because it determines the particles which penetrate the tube walls will be a-ia maximum counting rate of the tube and its allied counted with almost 100% efficiency; on the It i. circuit. In portable survey instruments the dead other hand, gamma rays must produce ionization x-hi in the tube in order to be counted. The gamma time is approximately 0.0005 second which allows Thi a maximum counting rate of 2,000 pulses per counting efficiency usually is considered less than con- one per cent. The region of continuous discharge second. It becomes apparent that since the or 1 begins at p. maximum tube response is Vx; then pulses tub1 occurring after time y will have a minimum ampli- The Geiger portion of the characteristic curve A 0-p is known as the plateau. It is desirable, tude of Vx-Vy. This amplitude will increase prii with time to Vx at time z. Therefore, during the particularly in portable battery operated survey rolt time of pulse decay starting with the end of the meters, to have a long, flat plateau; since the an : dead period, there will be a period y to z with counting rate does not depend on applied voltage add pulses less than normal height. and, within limits, will not be affected by battery rec‘c If we assume a Geiger-Mueller tube to be aging. Tubes having plateau lengths from 100 to in t 300 volts and slopes showing an increase in counts exposed to a constant intensity source havinga cuc wide spectrum of energies of gamma photons or of only one to two per cent for a change of 100 is SI beta particles; then a typical Geiger-Mueller volts are in general usage. In many portable tim tube characteristic curve of pulses per second as a survrly instruments these tubes operate with the Y function of voltage may be plotted in figure 24. thwshold of the Geiger region in the neighborhood of t of 900 volts. In the laboratory equipment various tubes operate up to 2500 volts. Most of the I portable radiac instruments are necessarily re- n z stricted to batteries, and the higher the voltage, 0 w0 the larger and heavier the battery requirements. cn a Efforts are under way to develop satisfactory high W / a voltage suppliw* which operate from low voltage batteries. This is only a temporary expedient 3cn J until satisfactory low voltage Geiger-hfueller 3 a tubcs are developed. Constant voltage power supplics will reduce the requirement for a long plateau although tube aging with use many times causes voltagt. shifts in the characteristic curve VOLTAGE - whic.li makcs thrb plateau desirable. Figure 24. Geigpr-Mueller tube characteristic CUTve. m Curve threshold 6.02 Quenching the Discharge m-n Region of proportional counting o Threshold of Geiger region The approach of the positive ion cloud to the 0-p Plateau cathode cylinder will result in pulling electrons p Start of continuous discharge region from t,he cathode to produce neutral atoms or niolec,ules. The electron usually enters combina- There will be no response to the small pulses t>iori with the positive ion in an excited state. in the ionization chamber region where there is no Tlic process of transit to the ground state pro- gas amplification. A threshold m appears early dures a characteristic series of spectral radiation, in the proportional region. This region extends aid some of these radiations will be in the ultra- from m to n. As the voltage is increased, the *l’herc are cssrntially nine different types of power supply which can be gas amplification becomes increasingly niore im- USIYIto provide the high voltape required for Geiger counter operation: portant with more of the less energetic particles I3nttrvy, condenbcr, conrlenser-coiiinntator, vibrator, condenser-vibrator, rod1 rnciic fr~~~ucricy,fl~.t,ack, transformer (AC supply), arid multiplier (AC the being counted. At o the threshold of the Geiger >fl~l~d~). .ho 22 12b3414 RADIAC COUPLING ! region. This ultra-violet radiation usually COLLECTING ELECTRODE CONDENSER 1 sufficient energy to produce photoelectron I ssion from the cathode. These photoelectrons, $1 n, will have sufficient energy to start a second che, and the whole process will be repeated. I s therefore necessary to construct counters in the cycle is halted for each individual pulse. his process is called and can be ac- quenching I shed by using external electronic methods using special vapors inside of the counter

; curve All external quenching methods work on the Figure 65. Neher-Harper vacuum lube quench circuit. sirable, I inciple of lowering the collecting electrode survey it ge below that at which the counter can form tube grid potential. As the grid becomes positive ice the from its normal -4.5 volt bias, the tube conducts, voltage 9 an avalanche until such time as the danger of an additional avalanche is passed (3) (5). The thereby dropping the potential on the collecting battery .. recovery time for resistance quenched circuits is electrode. Other quench circuits in use are the L 100 to in the order of seconds. The Neher-Harper Nehcr-Pickering, Getting multivibrator, and a counts circuit, a good example of vacuum tube quenching, number of combinations and variations. of 100 is shown in figure 25. This circuit has a recovery Internally quenched Geiger-Mueller tubes utilize lortable time in the order of IOe4 seconds. small amounts of polyatomic vapor such as ethyl Vith the When current flows as the result of a discharge ether, amyl acetate, ethyl alcohol, etc., mixed with )orhood of the detector, the resistor raises the vacuum, the regular tube gas in order to cause the detectgr various R1 of the rily re- voltage, ements. )ry high voltage Ipedient Mueller power a long ~y times c curve

1 to the 4ec trons toms or ombina- d state. ate pro- Ldiation, le ultra- Figure 26. Tubes for portable Gi~~gu-Muellercounters. vhich can be T operation: The diagram indicates the difference between thin wall and thin end windox tubes. The Victoreen all metal thy- ser-vibrator, rode 1R85 is shown in thc lowcr left. The thin-end window tril)e is the 133-1 used for beta-gamma indication in ~ltiplier(AC the AKjPDR-8 series, -15 arid -27. The BS-2 for high rmige gamma detection in the same instruments is shown ill the lower right. Ai1 assortment of thin-walled tube,< from other portal~lecounters is shown. 23 lZb3415 RADIAC . 1 to quench itself after each discharge. These use are thin side walls of 30 mg/cm2 thickness. Geiger-Mueller tubes are known as self-quenching. Others have thin end windows in some cases 3 The primary function of the vapor molecules is mg/cm2 thick. Such tubcs are shown in figure 26. the absorption of ultra-violet photons, thereby Laboratory counter tubes range up to 3>6 inches forestalling any repetitive discharge. The major- in diameter with the length from two to ten times ity of the quenching gases are complex organic the diameter. Several laboratory Geiger-Mueller molecules such as alcohol or xylene which preclude tubes are shown in figure 27. The anode, thor- their use under subzero weather conditions. They oughly insulated from the cathode, is a fine wire also may show changes in sensitivity with changes from 0.0001 to 0.0010 inch in diameter running in temperature at room conditions. One of the down th'e cathode cylinder axis. To obtain a most severe problems presented by the quench satisfactory characteristic curve, the central wire vapor is in limiting the life of the tube. Some of must be manufactured carefully, free of die marks the quenching vapor is dissociated at each dis- and sharp protuberances. The tube must be charge, and eventually the vapor is completely cleaned carefully to remove all dust, grease, water used up and the tube goes into a repetitive dis- vapor, and oxygen; and special care must be charge condition. The better tubes in survey exercised in the selection of pure filling gases. equipment will have a life of 3 x loQcounts. For In addition, the filling gas pressure must be continuous operation in a field which will just chosen carefully. Most tubes used in radiac allow utilizing a second resolving time, the equipment of the portable survey type incorporate tube life will be only 100 hours. thin windon-s to permit some beta counting. Considerable work is under way toward the Kormnlly, this is a cylindrical section of tube wall development of Geiger-Mueller tube fillings which approximately 3 inches long at mid-tube length %I1 overcome the difficulties that have been as shown in figure 26 and having a thickness of 30 enumerated above. Halogen gas mixtures are mg/cm2. Provided the probe housing tube does among the most promising. Tubes have been not add additional shielding, the tube then will constructed with the Geiger threshold in the be sensitive to beta particles having energies neighborhood of 700 volts, having a virtually above 0.16 MeV. As previously stated, counter flat plateau of several hundred volts. These tubes may be employed with thin end windows tubes appear to have good temperature charac- such as that illustrated in figure 26. Tubes of this teristics and a life well in excess of that for tubes typc of construction are in more common use in generally employed in survey equipment. laboratory equipment than in equipment used for The majority of Geiger-Mueller counter tubes field survey work. Mica windows down to 0.5 presently employed in survey meters are $6 inch in rng/cm2 are available, although in normal labora- diameter and 53/$inches long. The cathodes vary tory work the thin windows run between 1.5 and from one to three inches in length. In common 4 mg/cm* in thickness.

Figure 27. Laborator!/ G'eiyer tubes. A number of tubes have been developed to cover thc wide range of requirements of laboratory counting. 94 IZb34 I b RADIAC mess. I A great majority of Geiger-Mueller tubes are peel off a once satisfactorily operating tube and ses 3 photosensitive. This undesirable feature has been introduce serious counting errors. re 26. overcome by coating the glass envelope with an 'I 'nches 3% *I %c opaque surface. Occasionally, pin holes in the 6*03 Geiger-Mueller Detector times '' thin opaque coating will cause spurious counts Geiger-hlueller counters, utilizing self-quench- ueller 1 thor- t when the tube is exposed to bright sunlight. In ing tubes, are especially useful as light weight I addition, the oprcque coating has been known to highly sensitive detecting instruments for field 5 wire nning ain a CALIBRATION wire ADJUSTMENT narks PHONE JACK /. METER ;t be water OFF AND ON AND \ HANnl F (CHANGEABLE SCALES RANGE SELECTOR # ;t be SWITCH pses. it be ;LIP adiac orate iting. wall ngth of 30 LOOP FOR does 1 will :rgies unter dows f this tse in sd for 0 0.5 bora- i and

PROBE

\ GEIGER\ TUBE BETA SHIELD THIN WINDOW SECTION OF TUBE BETA PORTS Figure 28. Diagramatic sketch of a portable Geiger-llfzrellrr sztrvey meter, The probe, foreground, has a descriminating slide which ma)- be used for beta indications. Indication is by the meter and by headphoIles (not shown).

25 r RADIAC

survey and decontamination work. Such an instrument is shown in figure 28. The pulses are of such magnitude that they can be heard in earphones without the necessity of much external amplification. At low intensity levels, a few multiples of ordinary background (30-50 counts per minute-roughly 0.01 mr/hr) aural indications are found in many cases to be more useful than observation of an indicating meter. The majority of field instruments place the counter tube in a probe at the end of a three- to five-foot length of cable so that the larger, heavier case containing power supply electronic circuitry, meter, etc., can be held in one hand or by a shoulder strap while a detailed examination is made with the probe Figure 89. Geiger-Mueller counter in use. held in the other hand. Afish-pole type of extended handle, which has been utilized \lth certain A fish-pole type of extended handle has been utilized with the ANIPDR-8 to hold the tube probe at a distance instruments to hold the probe at a distance from from the operator's body. the operator's body, is shown in figure 29

I I j

12b3418 Chapter 7 SCALING CIRCUITS Field laboratories will be used to evaluate chanical register which records the total number 1 than 4 ples of terrain, food, water, etc., to determine of 64 counts which have taken place. A greatly ijority < nature and extent of radiological hazards. simplified scale of two scaling circuits is shown in eina : s work requires that accurate counts be made. figure 30. Essentially, the two plates are joined gth of e best mechanical counters can be driven at by a relatively large capacitor C1 of the order of aining es of perphaps no more than 300 times per O.lufd. The two cathodes are tied together c., can second; therefore, other means are required to through the identical resistors R, and R, and held I while "'record the maximum Geiger-Mueller count in the ct some small negative bias. Because of the cross probe "neighborhood of 5,000 pulses per second. Elec- coupling by capacitor C1, the circuit will be in o€ ex- * tronically, it is possible to record pulses at rates equilibrium when either tube is cut off and the Zertain far in excess of the best counter tube output. other at maximum plate current. An impulse e from %me of these electronic arrangements are known having fired TI causes the grid of Tzto go negative as scaling circuits. with respect to the cathode and not fire. How- Scaling circuits are based upon a basic two- ever, the arrival of a second impulse gives a mo- tube circuit which divides the number of pulses mentary positive bias to the grid of T, and by two, and by constructing a series of such accordingly it fires. circuits, the pulses can be reduced by factors Certain difficulties are inherent in translating of 2, 4, 8, 16, 32, 64, 128, etc. The most common powers of 2 into multiples of 10; therefore, elec- scaling circuits in use utilize scales of 64. Record- tronic circuitry js being devised to give readings ing is accomplished by neon indicator lamps at of decades (units of lo), and all military field labo- each stage multiple of the circuit. The sum of all ratory equipment will probably be so constructed. indicator lamps will give the number of pulses Scaling circuits can be used in conjunction with counted. Since 64 or more counts per second are any tjjw of pulse detection. Many instruments not uncommon, the circuit is set to drive a me- are conhtructcd with high voltage power supplies

4- 250 V

OUTPUT

INPUT V PULSE 1 I

Figure SO. Simplajet1 scale of two scaling circuit. 27 12b3419 RADIAC which may be varied for proportional or Geiger tubes are discharged simultaneously or when one counter action. Scalers are built with special tube of a set does not discharge. Many circuits parallel plate chambers for alpha counting, and have been devised to provide the required dis- with proportional counters having a continuous. crimination and are known as coincidence and flow methane atmosphere for counting alpha anticoincidence circuits. These circuits have re- particles in the presence of high beta and gamma ceived considerable description in technical litera- activity. ture but have little potential use in military Occasionally in specialized fields of research radiological defense and are mentioned to assist such as the investigations of cosmic rays one may tlic reader with terminology. wish to record a couiit only when two or more

12b3420 Chapter 8 ;'h 1 I/ COUNT RATE METER 31, 11 'The normal portable Geiger-Mueller survey ing chambers, proportional counters, or Geiger per6 uses a count-rate meter in addition to aural counters. The laboratory count-rate meters 1 @&ation of pulses. This meter simply reads the usually are provided with terminals so that the hte of arrival of pulses and with rates above ten counting rate may be fed into some type of moving bmes normal background the rate is rapid enough paper recorder. In this manner sample decay 1 0 that a steady meter reading is obtained. In characteristics may be obtained by recordings bbboratory equipment it frequently is convenient made over a period of time. ;,to use a count-rate meter in placc of a scaling cir- Extc>rnalqiienching methods, such as the Neher- cuit. Considerable effort is placed in circuitry to Harper circuit previously discussed in connection provide the meter with pulscs of the same size so with figure 25, can be employed in conjunction &at all pulses give identical contributions to the with laboratory scalers and count-rate meters. meter reading. Space and weight considerations prohibit the use Count-rate meters can be used to indicate the of extcrnal quenching circuits with portable equip- rate of arrival of almost any type of pulse. Many ment,. Objections to use with portable equipment laboratory instruments are coilsLrnctcd with varia- may. in the future, be overcome by the use of ble voltage supplies that may be uscd with count- miniaturi et1 circuits.

99 1263421 - <

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h3 in bJ Chapter 9 CRYSTAL AND CHEMICAL DETECTION ~9.01 Excitation tage over detection by other methods of instrumentation, in that a single chemiCa1 method may As previously shown, an electrically charged be used to detect radiation over a wide range of particle in its passage through a gas may come intensity from a fraction of a roentgen to over close enough to an atom to exert sufficient force 1,000 roentgens. The problem involved in such remove an electron and ionize the atom. In to a method of detection is that of finding and con- .many cases the charged particle will not exert trolling a chemical chain reaction capable of multi- & enough energy to cause ionization, but will cause plying the radiation effect on a single molecule. + one or more of the atom’s electrons to be raised The special rgquirements are that the nuclear , to higher energy levels. The excited atom in radiation initiate a minimum chain length approxi- returning to its ground state will radiate char- a mately IO5 for visual perception and that it not acteristic series of spectral lines. Some liquids be initiated significantly by thermal radiation at . or solids subjected to ionizing radiation may give ordinary temperatures. Five possible ways in off a characteristic fluorescence which can be which multiplication may be achieved are: measured. In addition, the free electrons pro- A. Development reaction such as photo- duced in a solid or liquid by ionization may cause graphic d evelopment. changes in the electrical conduction of the sub- B. Explosive reactions such as benzoyl per- stance in which they are produced. This latter oxide triggered by nuclear radiation. process is sometimes referred to as conduction. photo C. Initiation of a free radical chain. Some crystals do not return immediately to a D. Psychological, such as a color reaction. ground state after being exposed to radiation. E. Thermoluminescence. This may manifest itself in a crystal color change. A few examples of many proposed systems In some cases shining light on the crystal will for accomplishing the above multiplication are release energy which has been trapped in the indicated below. crystal excited stage. Some crystals will en- Phosphors. The development of a dosage counter an effective change in electrical resistance indicating device in which a phosphor screen is when subjected to ionizing radiation. In some combined with a photo-sensitive layer. The cases chemical reactions which produce color phosphor absorbs the high energy photons to changes are initiated by the disassociation of which the photo-chemical layer is nearly trans- compounds, formation of free radicals or electron parent with the phosphor emitting an extremely attachments under the influence of radiation. large number of photons of ultra-violet light for With the exception of photographic film badges, each high energy photon absorbed. The photo- which will be discussed later, these various phe- chemical layer absorbs the ultra-violet emission nomena are of interest only in that some day they and in turn may be direct reading in shades of may be incorporated into a military dosage meas- grey or in colors after a development process. uring device. Much developmental effort is being This is an effective way to transform high energy placed on a dosage indicating tag which will radiation into a detectable form. change colors at various levels of exposure so as Colored Dyes. The formation of colored to be used for rapid determination of thc degree dyes on exposure to radiation of luecocyanides of field exposure. with pararosaniline. Halogenated Compounds. The radiation 9.02 Chemical Dosimeters decomposition of halogenated compounds can be It appears possible to detect nuclear radiations used to produce color reactions. by methods depending upon chemical change Pyridine Ring. The splitting and coupling induced by radiations. Detection of radiation of the pyridine ring under the influence of ionizing by chemical reactions possesses a possible advan- radiation may form colored compounds. 31 12b3423 RADIAC found that thio-Michler’s ketone can be used as a sensitive indicator for this reaction since it forms HC CH , deeply colored complexes with cuprous (Cu+) but not with cupric (Cu*) salts. II I Reduction of Molybdic Acid. Molybdic HC acid (H2Mo04)is reduced slowly to a blue com- \N//cII pound, molybdic blue (Mo206.nMo03)on irradiation. Much greater sensitivity is obtained if an organic acid such as lactic acid is present. Decomposition of Carb,on Tetrachloride. Reduction of Nitrates. Nitrates (NOa-) Carbon tetrachloride (CCl,) in the presence of are reduced to nitrites (NOz-) by radiation. The water and oxygen decomposes under radiation nitrite can be detected by the formation of azo into chlorine (Clz), carbonyl chloride (COCl,), dies. and hydrochloric acid (HC1). Tbe chlorine can be detected by the starch iodide reaction or by 9.03 Scintillation Counters more sensitive and stable indicators such as thio- Michler’s ketone. 0 ther chlorinated compounds Crystals such as Napthalene (C1,H,), anthra- such as DDT, chloro- and hexachloroethane react cene (C,H,:(CH)z:C,H,), calcium tungstate in manner similar to carbon tetrachloride. CaWOJ, silver chloride (AgCl), thallium-activated Reduction of Mercuric to Mercurous Salts. sodium iodide (NaI), thallium-activated potas- Mercuric chloride (HgCl,) or iodide (HgI,) is re- sium iodide (KI), and others have been found to duced to mercurous (HgC1 or HgI) and probably have a relatively high fluorescent yield. These to metallic mercury by radiation. An early crystals, in conjunction with light sensitive devices equilibrium is reached between the reduction such as high-gain photomultiplier tubes are in use products and the original salts, however, the re- as research tools, but as yet no successful survey action can be made to go forward by ha-iing instruments have been delivered; however, de- present an acceptor of oxygen. Such an acceptor velopment of such equipment is in advanced is tetramethyl diamino diphenylmethane which is stages. It is felt that the scintillation type counter oxidized to a deep blue diphenylmethane dye. A can be utilized to overcome many of the serious mixture of mercuric (Hg++) chloride and thio- problems of high resistance, insulation, arid thin compound therefore undergoes a change from windows associated with alpha counting by ioni- colorless to blue upon irradiation. There is a za tion chambers and proportional counters. In possibility that the mercurous salt (Hg+) or the addition, it is felt that scintillation counters may fine mercury formed in this reaction can be utilized provide a wide range instrument to replace the to catalyze some chemical reaction which would use of Geiger-Mueller counters for low intensity result in greater sensitivity. gamma detection and ionization chambers for high Reduction of Cupric to Cuprous Salts. dose rate gamma survey. Cupric chloride (CuC1,) or bromide (CuBr,) is Some problems are encountered with the reduced to the corresponding cuprous salts scintillation counter. There is a spectral sensi- (Cu2C1, or Cu,Br,) on irradiation. It has been ti\-ity problem such as that discussed in conjunc-

12b3424 forms J but : ybdic com- *adia- if an

(037 The f azo

Lthra- I /' PHOSPHOR ELECTRON MULTIPLIER TUBE Ftate vated Figure S1. Schematic diagram of a scintillation counter. botas- Radiation E iking the phosphor releases light which is picked up in the electron multiplier tube and is subsequently id to transformed into a meter reading or earphone indication. rhese :vices tion with ionization chambers. Satisfactory pho- 9.04 Other Possibilities n use toelectric tubes require in the neighborhood of 100 lrvey volts per stage and with 10 or more stages this Sevcral other processes have been examined for , de- presents the same high voltage problem discussed their possible use &s dosage-indicating devices. Lnced in conjunction with Geiger-Mueller counters. Electrets show some promise, but further investi- unter Since the photomultiplier tubes are light-sensitive, gation is necessary before their actual application Srious the tube and crystal must be encased in a light- to dosimetry may be used as a basis for long-range thin tight coating. planning. ioni- . In may e the nsity

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12b342b Chapter 10 PHOTOGRAPHIC DOSIMETRY

10.01 The Film Badge by a thin (1 mm) lead shield* designed to exclude Photographic films are in universal use for the beta particles, so that an examination of the film measurement of gamma ray dosage. As a personal blackening behind the lead or in the clear may badge, they are especially valuable since they give an indication of beta exposure. The lead shield also serves to enhance the darkening due to B: produce a permanent record which in many cases can bt; used for medical-legal purposes. As in the gamma rays because o€ a large number of electrons ' case of light, gamma rays produce developable ejected from the lead. images. Photographic materials find many labo- Placing an identification number on the outside ratory uses for the measurement of radiation, and of the film badge packet and transferring this as such may find their way into the field laboratory number to the light sensitive film presents some- (6). For the present, however, we will consider what of a problem. If this is done manually, the only dosimetric applications. time involved, except for minor numbers of badges, A film badge as shown in figure 32 usually becomes prohibitive. Some investigations are consists of a packet containing one or more photo- being made into the possibility of using X-rays to graphic films of dental size inches by 1Ti inches) expose a number punched out of a thin metallic wrapped in a thin material which is opaque. The sheet which would be incorporated into a section whole unit may be sealed in a waterproof paper or of the covering envelope. Today there is nothing cloth envelope. The sensitive emulsion consists of which can be considered as a satisfactory identi- a thin layer of a silver halide and gelatin spread on ficatjon system for military usage. a cellulose film base. The interaction of radiation 10.02 The Densitometer with the silver halide is understood to be some type of ionization which produces a developable latent A densitometer is used to measure the blacken- image. The developing process converts the ing of the film, and this is compared to the blacken- latent image into a deposit of black silver metal. ing of standard calibrated samples. The sche- Some sections of the film packet may be covered * Cadm~umhas had some use in film badge shields.

Figure S2. Film badge. Top left is the badge nith serial number on waterproof cover. Bclow are front and back views of packet with lead cross. Top center is an opened cover and lead cross; bottom, I)adgc opened to show paper dividers and films. At right are two processed films. 35 12b3421 / ? RADIAC In figure-36 the density is plotted against the log of relative exposure, and the characteristic Curve of a film emulsion is obtained.

10.03 Film Processing The characteristic curve will start with some minor density at A which the cellulose acetate backing contributes. Some exposure is required to overcome the inertia of the film in the toe portion A-B. The shoulder portion C-D shows that at some point continued exposure fails to make very much of a contribution to increasi6g the density. For the greatest accuracy only the linear portion of the curve B-C should be used, since the greatest change in density occurs with change in exposure. There is a limited range of sensitivity for any one emulsion; therefore, several emulsions may be combined into one film badge packet, to give an extended range (see sec. 15.08 on page 8 1 ). Figure 33. Film badge carried in shirt pocket. J'ariations in film processing can introduce possibilities of serious errors. The film density matic arrangement of a densitometer is shown in is a function of time and temperature of develop- figure 34 and a densitometer in use is shown in men t, developer solution strength, and the degree figure 35. of agitation in the developer. Every effort should The image of a small area of the film is allowed be made to follow a standard processing procedure to fall upon a photocell which in turn is connected such as that recommended by the film manufac- to a microammeter. Light falling directly upon turer. As a very rough rule of thumb, it can be the photocell will produce a rcading, I,. \Then stated that a one-degree change in developer the film is put in the light path, some absorption temperature can introduce a three to six percent will take place, and a lower reading, I, will result. mriation in the roentgen reading, and a sixty- 1,. second time variation may introduce five to The ratio _r is called the opacity, 0. The trans- ten percent variation. There are circumstances I when these variations can be much greater. Film parency, T, is the reciprocal of the opacity or -' IO processing is therefore very critical and must be The optical density, D, of the silver deposit on the controlled carefully. Under the majority of field photographic film is defincd by the relation: conditions it will be extremely difficult to maintain tlic required controls, and until automatic high D=log,o 0=10g,, IO slwtl developing and densitometric reading equip- film - FILM BADGE n A me "' I tha the den ni q SUPPLY for I LIGHT SOURCt fro1 LENS salt PHOTO CELL Lkih- seri Figure 34. Schfwalir arrangement of n densiio~iric r 1tscd lo dderiiizne film badge readings. 36 12b3t128 / RADIAC i I

the log I 'ic curve

h some acetate .equired toe por- ws that o make igg the e linear 1, since change sitivi ty ulsions ,ket, to ge 81). (roduce iensity svelop- degree should cedure ~nufac- can be .eloper lercent sixty- ve to tances Film ust be 'f field intain high Figure 3'5. Densitoiiirtcr 7n ust. 'quip- The density of each individual film badge must be obtained arid coinpared against the density of similar films calibrated against known radiation sources in order to deterrriirie dosage readings.

ment is put into use, the volume of film badges calibration be made for each batch. As in the ) that can be processed is limited seriously. From case of other photographic materials film badges the start of development to the completion of hare :i limited shelf life even under the best storage ZTER densitometric measurement using standard tech- conditions. There are also gradual changes in niques, a time of roughly one hour is required the film characteristics with time which requires for one film. tlitit c.ontinuous calibration checks be made. The It is found that no two hatches of the same film mctliotl of ctilibration will be discussed in chap- from the same nianufactur~cr have exactly the ter 13. same responsc to radiation. This can introduce Altliough thrrc are objections to film badges, seriniis difficiiltics if ignorctl and requircs that a they ii re a vcr- important dosage recording device. 37 tection of any military participation in future atomic weapon tests. Radiation exposure has become one of the standard entries in military health records (see fig. 37) and film badges, because of their permanence, are filed to substantiate any such entries.

Figure 36. Characteristic curtie of a film badge emulsion.

The size, weight, record permanence, simplicity, and cost when compared with the various disadvantages, may outweigh the use of more Figure 37. Medical records. complicated electronic devices which require Radiation exposure has become a standard entry in considerable upkeep and adjustment. It is cer- military health records; and film badges, because of their tain that film badges will be used for health pro- permanence, are filed to substantiate any entries. tars Chapter 11 L ause ’ CLOUD CHAMBERS AND ACCELERATORS any The cloud chamber is one of the most useful tools and extent of the vapor trails can be utilized to for the scientific examination of the properties of give indications of charge, velocity, mass, etc., of the atomic nucleus and of the various particles and the initiating radiation. 1 radiations. Such an instrument has no fore- Another group of machines called accelerators I seeable military applications ; however, the cloud are used as tools of the physicist in his examina- i chamber is advertised widely, and a brief state- tion of the structure of matter. Descriptions of ment is considered essential to give a well-rounded the linear accelerators, van de Graaf generator, description of radiac instruments. cyclotron, synchrocyclotron, betatron, synchro- Ions caused by a charged particle may act as a tron, Bevatron, etc., may be found in most nucleus for condensation in a supersaturated modern physics texts (2) (7). They have no vapor. Radiation passing through such a vapor application to the problems of military radio- - will produce ions which .will cause droplets of logical defense. It should be noted that a number vapor to form that may be seen by the naked eye of the radiac instruments herein described were or photographed by a camera under certain condi- developed for the health protection of personnel tions. When such cloud chambers are used in employed in the vicinity of high energy accelera- conjunction with magnetic fields, the curvature tors.

I y in ,heir

39 12b3431 12b3432 t 9.01 Introduction So far only one attempt has been made to deviate No attempt will be made in this article to dictate from the ordinary shoulder strap and handle military characteristics for the various radiac type instrument. This deviation is the AN/PDR-8 instruments and equipments, but a slight indica- Geiger counter which is built to fit over the stom- tion of the degree of evolution is considered of ach, with the carrying strap running around the some value to personnel who are unfamiliar with back of the neck. Several tests indicate that the field. this method of carrying the instrument may have The portable instruments now available to the some slight advantage in going through hatches military are, in most instances, laboratory equip- and up and down shipboard ladders. For any ments which have been altered to hand carrying other type of use, it is found that the neck rapidly cases. They have undergone enough develop- tires, making the neck strap less satisfactory ment so that they can render satisfactory military than a strap which crosses the body over one service as training instruments and, in the event shoulder. Also, the stomach-carried instrument of emergency, would no doubt give good service does not lend itself to ease in being hand-carried. within the continental limits of the United States. As in the case of everything else that one may It is doubtful, because of the peculiarity of be required to transport, the ultimate goal is construction and lack of standardization of zero weight and zero size; however, this not being certain components, such as high resistance practical, there are some immediate goals which resistors, Geiger tubes, electrometer tubes, and the may be set. It has been found that a rectangular like, whether these interim instruments would be shape, roughly eight inches long, five inches wide, entirely suitable in oversea military operations. and six inches high, weighing not over eight Such instruments have not yet reached a point of pounds, can be carried by hand or by shoulder service acceptability by either field or landing strap for extended periods of time. In any opera- forces. It is anticipated that the development tion where instruments must be handed from programs now under way will produce satis- person to person, such as from ship to small boat, factory equipment within the next 12 to 18 months. or in and out of vehicles, etc., a rigid handle has It is certain that if the necessity arose tomorrow, been found more desirable than the hinged suit- the interim instruments could be used to caw type. It should be obvious that a broad advantage. shoiilder strap is desirable for comfort in instru- merit carrying. although some instruments come 12.02 Physical Characteristics equipped with straps only slightly wider than a The great majority of the portable radiac shor string. instruments of the types in which we are interested One of the most important considerations is the are housed in rectangular metal cases of roughly .location of the instrument’s center of gravity. 250 to 500 cubic inches. Carrying has been by Too many instruments have a tendency to fall means of a handle on the top of the instrument on their sides &en carried on the seat of a jeep and by a carrying strap attached to eyes on the or placed on the deck of a boat. Experiments ends of the instrument case. The instrument indicate that the minimum angle from the vertical weights run between 7 and 15 pounds. to which the instrument can be tilted prior to Field tests during atomjr weapon test explosions falling over is 35 degrees. (8) have givcn us some critcria for the design of Disposable transparent plastic covers have been hand-carried instruments. Thc.rc are virtually used to prevent instrument contamination. In no indications as to proper form factor for instru- many cases these covers were more of a nuisance ments carried by pack, attac.licd to tlie belt, ctc. than they were worth. The majority of instru-

97174s -50-4 41 12b3433 RADIAC ments now have smooth hard finishes from which meters, the following range scale colors have been. contamination may be washed. Future designs accepted: should consider the elimination of any unneces- 0-500 r/hr fire engine red 1 sary protuberances, such as meter housings, which 0-50 r/hr light magenta would be contamination collectors. 0-5 r/hr orange Many of the high range instruments will be 0-500 mr/hr yellow used by personnel wearing gloves, and this fact 0-50 mr/hr white has been overlooked in the placing of knobs and 0-5 mr/hr green-yello w switches on a great number of instruments. 0-0.5 mrjhr light blue There is also the possibility that some of the It is anticipated that a color patch scheme instruments will be used by personnel wearing will be standardized for dosage recording instru- gas masks and, therefore, meter markings should ments, film badges, etc., which will match that be such as to present no opportunity for mis- of the rate meters somewhat as follows: reading. Scale numbers which change with a. change in the range scale, along with distinguishing 500 r or higher fire engine red colors, are certainly rwommended. Also, a means 50 r-499 r light magenta 5 r-49 r orange for illuminating the scale for night operation is 500 mr-4.9 r yellow recommended. 50 mr-499 mr white Military radiac equipments will, in all prob. ability, have changeable scale markings with An experienced field soldier, on examination changes in scale ranges. In addition, the scales of the better commercial Geiger-Xueller detectors, will have distinguishing colors. For gamma rate may be appalled at the bright chromium-plated

Figure 38. Existing eqrizpment tried during field problems is found io be lacking in many characteristics.

42 t 2b3434 RADIAC

tube probe; or a marine may complain that it subject to many temperature problems. Most would be impossible to drag any of the ionization organic quenched Geiger tubes will cease to chamber instruments along when involved in function a few degrees below zero Fahrenheit. 4 jungle fighting. Others, depending on their Ion chamber instruments are subject to many F missions, will find faults with any of the present difficulties with changes in pressure due to use or 9 equipments. This is the state of development. transport by air. Military gamma measuring To date, the greatest emphasis has been placed on chambers require constant reading over a change in qbtaining proper instrument response with the elevation from sea level to 36,000 feet. Efforts are idea that once this has been achieved, some of the being directed toward covering the temperature other characteristics will receive attention. range of -40 to +125' F. gcheme D. Saturation Effects instru- 19-03 Electrical Characteristics To prevent an erroneous assumption as to the absence of radiation, the instruments should show .h that Characteristics will, of course, vary from no effects of saturation of the detector component instrument to instrument and will depend some- until radiation intensities of at least five times the 1 what upon the use for which the instrument is maximum reading of the instrument are en- intended. Some of the more important character- countered. istics which are somewhat unique to radiac instruments will be indicated. 1 2.04 Radiological Characteristics A. Ability to Zero in Field ination The electronic circuit should be so designed On page 12 an indication is given of the spectral Lectors, that it will zero automatically on high dose rate sensitivity problem. It is felt that gamma -plated of the instrument under background radiation rrsponse in roentgens should be held within It20 intensities less than 0.05 mrjllr. percent of air equivalent over the range 80 Kev to 5 MeV. At the same time, the instrumental B. hletering Time Constant inaccuracy should not be more than f 10 percent Depending on'the purpose for which the of the scale reading for any point above 10 percent instrument is used, after an initial warm-up of the scale for energies between 1 Mev and period the time constant should bo such that 95 3 hlev. percent of t,he final reading is reached after a For beta survey purposes, wall thickness of 30 maximum period of one second. For low intensity mg/cm2 are recommended. Thinner windows of ranges such as 5 m/hr this time constant may tlic> order of 3-4 mg/cm2 will be required for beta be longer. ad mission during certain decontamination proc- C. Pressure and Temperature Effects esses. The majority of commercial instruments Instruments for alpha detection must record having non-military standard batteries may be particles having a minimum range of 3 centimeters.

43 12'03435 .i

12b343b r.

Chapter 13 CALIBRATION

A problem which at first appears of little conse- effects and absorption of the beta particles. A quence is that of instrument calibration. Actually. good number of standards are made by depositing this is an extremely serious problem to designers, on a foil a known amount of uranium oxide manufacturers, and to users whether in laboratory (U308). The foil having a density of 25 mg/cm2 or field work. There are two calibrations which will absorb all alpha particles and only about five must be considered: prrcent of the beta particles. Strontium 90 is a. Spectral sensitivity, and also used as a het8acalibration source. It should b. Dosage rate. be rioted that the methods of alpha and beta The first is a function of the materials, configura- cali hrations are not entirely satisfactory and that tion, etc., of which the instrument is made. Mili- work is under way to develop better means of tary radiac equipment is checked for spectral calibration. response by the X-ray section of the National Radium encased in platinum and cobalt 60 are Bureau of Standards, and it is considered usctl as gamma radiation sources for calibration. that they are not likely to change unless the Sources are calibrated at the National Bureau of instruments are damaged or altered. Unfortu- Standards at periodic intervals. Information from nate]~~the instrument evolution has not progressed the source calibrations allows a calciilation of to the point where one is willing to use them per intcnsity at one centimeter from the source. se without continuous rate calibrations. Intensities at othcr distances are found by use If errors, some serious, are to be eliminated from of the inverse square law. quantitative dose rate measurements, then it is In the case of radium, the following relation- necessary to expose the instruments in substan- ship exists: 8.4m tially the same manner in which they are cali- IRa=C/Z brated. This does not mean that qualitative indications cannot be obtained when an instrument where I is the dose rate in roentgens per hour at a is not calibrated €or a specific radiation. In the dist’ance d cent,imeters from a source of mass m case of the portable Geiger-Muellcr counter the milligrams. The half life* of radium being rel- instrument is calibrated for gamma radiation but atively long (1,600 years), there is little worry is satisfactorily used to locate beta surface con- ahout, changes in source n-eight over periods of tamination. An extremely complex beta calibra- months. Cobalt 60, on the othcr hand, has a half tion with rigid use restrictions mould be required life of 5.3 years, a.nd it, is therefore necessary to to make the Geiger-hluellcr counting rat,e a inrlude the elapsed time t in days from t,he date quantitative measure of active material. of source calibrat,ion. The radioactive cobalt is Alpha calibrations are done with plutonium or produced artifically in a, rod of ordinary cobalt uranium sources at the center of the plane of the mot a1 t,hrough neutron irradiation in an atbniic external opcninq of the instrument. As a mattw pjlp. A nunibcr of atoms vithin t,he rod will not. of interest, it can be stated that one gram of purc l)clc*omeradioactive; therefore, the weight of t’he natural uranium emits a total of 2.5 x io4 alpha stimple is not necessarily indicative of the radio- particles per second. Considerable effort must be nrtivity. As a result, the source activity A in placed in determining t8hc absolute number of niiIlicurics** giving a numerical quantity of dis- disintegrations for any samplc to correct for self- ‘7‘1~h;df life ofci mdioisotope is the time required to 1o.c lull ofif s actiyity. absorption and geometry. loo0 ciirii!. The rul-ir is acncrnlly accci)trd ~LSthat riuan- Beta calibrations present a more serious prob- 111 5 (if whitancc diidi

12b3431 45 RADIAC

Figure 39. Gamma calibration. Three ionization chamber survey meters are calibrated against a cobalt 60 souree. integrations per second at the time t must he g'riven. rnent and make adjustments in order to minimize Tlie calibration relationships for Cow are: personnel exposure. ' It should be noted that geometrical considerations limit the maximum intensity which can be obtained from a single source. This closest approach of the instrument to the source at which it can be considered that the square law still holds An open area usually is markcd off into con- anti at which the detector is receiving a uniform centric circles with tlie source of radiation placed radiation may be taken as equal to 10 times the at the center as shown in figure 39. Such an maximum dimension of the detector. arrangement can be used for the rapid calibration The gamma calibration of film badges, dosi- of large numbers of medium level dose ratc meters, and other dosage reading is accomplished instruments. Instruments calibrated at extremely in a manner similar to that explained above for high levels, such as 100 to 500 roentgens per hour. iiitcnsitj- meters except that tlie time of exposure require remote control d~vi~csto move the iiistrii- :it n giveu intensity must be measured carefully.

46 12b3438 Chapter 14 OPERATIONAL INSTRUMENTATION

rE 14.01 Available Instruments the explosion occurs closer to the ground, neutrons produced during fission may induce beta and ’ The various instruments and techniques for f gamma activity into the ground materials which r radiation measurement have been covered in a absorb them. Also, as the explosion occurs closer * rather complete but general way. As far as opera- to the ground, there will be certain quantities of L tions are concerned, with the exception of the field unused fissionable alpha producers and beta- laboratory, the following are the instrument types gamma emitting fission products which mill be which are available for military use: deposited on the ground. Alpha, beta, and 1. Geiger-Mueller counters- gamma emitters are possible radiological agents, Low level beta-gamma detectors for- although they will more probably be either beta or a. Field detection. gamma or a combination of beta and gamma (see b. Warning. page 3) ’ c. Decontamination detection. ln the case of an under-water bomb explosion, 2. Ionization chambers- beta-gamma active fission products and unfis- High dose rate gamma survey- sioned alpha-emitting bomb materials will be held, a. Ground. to a large degree, in a cloud which spreads out and b. Ground from the air. rains down on the surrounding landscape. Cer- Direct and indirect reading personnel dosage tain bet a-gamma activity will be produced through recorders. the ncritron irradiation of water contaminants such Group dosage recorder. as the salt in sea mater. The contaminated cloud Alpha detectors in low beta-gamma bacli- may cwntain radiating materials which will give ground. lethal doses with exposures of a fraction of a minute. This cloud material in settling onto the 3. Proportional counters- surfacc of the earth may deposit contamination Alpha detection and survey in medium beta- which \rill produce gamma dosage rates of several gamma background. hundrccl roentgens per hour. Decontamination detection. Atomic bomb explosions in contact with the imize 4. Photographic film badges- grountl or underground will result in contamina- Gamma dosage recorder. tion >omewhat diff erent from that occurring with dera- Indicator of beta exposure. the one under-water shot which has been fired. in be Track plates for laboratory alpha ineasure- Beta-gamma ective fission products and unfis- losest ments. sioned alpha emitting bomb materials may be ivhich A tabulation of use, state of development, etc., held iii a large cloud of dust and earth particles holds for various instruments is given in table 111. which may spread out and settle on the surround- iform In radiological warfare, whether it be atomic ing landscape. In the immediate vicinity of the :s the bombs or a radioactive agent, the chief radiations point of detonation will be a crater depending in are the alpha and beta particles and the gamma size on many different variables such as density dosi- rays. In the case of a high altitude bomb blast and type of soil, strength of bomb, depth of ex- iished virtually all radioactivity is contained in the plos1011. etc. The crater, in addition to the high re for resulting cloud. Some of this material may fall act1110 resulting from the various bomh con- losure out on the earth’s surface many miles from the hrriimiiits, will have neutron-induced activity and lly . blast, but in general the radioactivitj- of the fall-out sliortI\ after the blast may have gamma dosage will be low intensity alpha, beta, and gamma. As ratcs of niariy hundreds of roentgens per hour.

12b3439 41 .

RADIAC

TABLE111.-Use of various radiac instruments

Radiation Instrument Purpose __ USe Remarks tamma -

Pocket dosimeter- -.- Individual ex- X Field or laboratory- - __ . High cost compared to pocket posure chamber. Requires separate charger. Drift meter- _____ - -. Rate of ex- X Secondary standard in posure conjunction with laboratory. Pocket chamber- - - -. Individual ex- x Field or laboratory- - - - - Requires a separate charger- posure reader. Thin window cham- Rate of ex- X In conjunction with lab- Many problems involved with ber posure oratory. thin windows. Chamber survey-_-- Rate of ex- X Field or laboratory- - - -. Use for high dose rate radi- posure ation measurement. Proportional counter. Disintegration In conjunction with lab- Many problems involved with rate oratory. thin aindows. Geiger counter- - -.-. Rate of ex- X Field or laboratory- - -.. Limited to detection and low posure dose rate. Scaling circuit--_. - -. Cumulative X record Count rate meter--_. Rate of ex- X posure Scintillation counter. Rate of ex- X posure Film badge- - Individual ex- X Field or laboratory- - - - - Teriffic problems involved with posure development in any quantity. Gives a permanent record. Track plates Degree of contamination Color crystals and Individual ex- X liquids, chemicals, posure photo conductive crystals, etc. Electrets ------.. . Individual ex- X posure

One of the reasons for the high beta-gamma and not actire in enormous quantities, they may activity immediately following an atomic bomb be overlooked because of the difficulty of detec- explosion is the short half-life elements either tion, and perhaps through their introduction into produced as fission products or as the result of foods, water, ventilating systems, etc., may pre- neutron irradiation. This high activity results in sent a definite hazard to a long term military the rapid decay and rapid removal of the beta- organization. gamma hazard. In the case of an air burst, To give indications of possible military usage, depending on height and many other variables, instruments will be discussed in conjunction with the area beneath the blast may be safe from an each type of radiation. emergency military beta-gamma standpoint, within less than an hour after the burst. This is not 14.02 The Alpha Particle the case if alpha emitters remain after a bomb Because of the very short range and penetrating explosion. These will not show high initial power, alpha particlcs are very difficult to meas- activity and will not decay immediately to a point me. A 5 AIev alpha particle has a range of only of no concern but may rrmain for years to plague 3.5 crntinietcrs in air: therefore, the maximum occupants of a contaminated area. Being alpha distance a detector with an air windon can be 48 IZb3440 RADIAC

Figure 40. Checking meat for alpha contamination with a poppy-type portable proportional counter. ved with y qusn- from such a particle is 3.5 centimeters. A closer face, not to exceed 1,000 disintegrations per rmanent distance is required, since not all particles \\-ill minute per square centimeter for no more than a travel at right angles to the emitting surface. one-day supplv. It must be remembered that Partial shielding by the emitting surface will also the cffrcts of alpha activity, whether from food, reduce the travel distance as will lower particle drink, or brtathing, are cumulative. energies. An ionization chamber such as Radiac Set Detailed alpha measiirements will be made in AN /I’DR-20 will measure the total ionization conjunction with decontamination work and will producd in the chamber and not the number of be specified in alpha disintrgrations per unit of disintrgrations. However, a rough caIibration in time per unit of surface area. terms of number of disintegrations can be made It is difficult to establish general rules for all so that the instrument is not completely useless. ey may types of alpha emitters. Their hazard is internal It niiist be remembered that beta and gamma ’ detec- from inhalation and ingestion, and different ele- activity will rontribute to the reading, although on into ments are deposited in different organs and as x their contribution can be estimated by the use of ay pre- result will produce varying degrers of damage (9). an alpha absorbing shield in front of the window. nilitary As a crude attempt to establish over-all working Portable proportional counters (fig. 40) such values for field use, the following are given: RS J~~diacSet ANIPDK-10 with a large probe usage, (a) food not to exceed one meal- a maximum lcvcl wintlon~ will be the primary alpha detectors. In with of 300 disintegrations per minutp per square Tlicw instruments will be adjusted to respond only centimeter of surface; (b) air containing uniform to Iiighly ionizing cvents and will be useful except dust contamination measured at any surfacc to in vasrs where the bcta-gamma to alpha ratio have a level of not more than thrce disintcgra- esc*c~tIs10’. The instrument is capable of high .trating tions per minute per square centirnetcr for a maxi- coiinting rates. Operation is liniitcd to relatively meas- mum exposur~of eight hours; and (c) drinking tlrv tvc~wtlier,sincc liigli voltage leakage in the of only water, when activity is mcasurt~tlon RII op’n SUI’- cli:ii~ihot. will rcsult in spurious counts. lsimum can be 49 IZb3U I

1 Neither Geiger-Mueller counters nor film badges activity. However, it is possible to estimate the will be used for alpha detection in military opera- gamma contribution by placing a beta absorbing tions. shield over the chamber or t'iibe window. In the Alpha counting must be performed by well- case of the Geiger-Mueller counters AN/PDR- 1 trained monitors working in conjunction with the T-2 and AN/PDR-7, having thin wall tube ser- ,{ field laboratories in which a large portion of the tions around 30 mg/cni2, beta particles of energy determination of alpha hazard will be made. For less than 160 Kev will be excluded. The very example, none of the inst,ruments we have just t,hin 34mg/cm2 windows associated with Radiac discussed are satisfactory for measuring alpha Sets AN/PDR-8 (series), and AN /PDR-27 mill cut activity in drinking water or in air. A photo- out soft beta activity below 50 Kev. graphic process involving nuclear track plates may Beta measurements with thin wall Geiger- be used in some laboratory alpha investigations (6). Mueller tubes in instruments calibrated in roentgens (the roentgen will be discussed under gamma 14.03 The Beta Particle ray measurements) may cause some trouble, since Faulty measurement of beta particles probably there is no relationship between the roentgen (a presents the greatest hazard of any radiations to measure of electromagnetic radiation) and quan- be encountered in military operations. Very low tities of beta particles. mith the probe shield energy (soft) beta part>icles present virtually the open and the tube directly exposed to beta radia- same measuring problems as do alpha particles. tion, the instrument will in general read sewral As a result, the soft heta particles, which are times the gamma ray reading with the shield dangerous if inhaled or ingested, may be ignored. closed. (See discussion on page 55.) This fea- High energy (hard) beta particles, on the othcr ture adds to the sensitivity of the equipment when hand, may penetrate gamma shields and give used as a detector for decontamination. It must what appears to be enormously high gamma be emphasized that the beta particle reading bears readings. no relation to the roentgen and cannot be con- Beta measurements may be made both in converted into these units. Only for beta particles junction with decontamination and area survey. of one specific energy can a certain roentgen rate Beta particles and gamma rays will always be reRding be stated as equivalent to a certain num- found in some ratio. For example, immediately ber of disintegrations per second. This xi11 not following a bomb blast the ratio will be much be true for beta particles of other energies. This higher than, say, one month later. Beta particlcs, entire problem has led to the recommendation because of their low penetrating power, are as a that beta-gamma sensitive Geiger counters have general rule considered as only an ingestion or an inscription on the dial: mr/hr-hard gamma inhalation hazard. As in the case of alpha only. emitters, the various rlemcnts will lodge in different Proportional counters find little use in beta internal organs; therefore, the beta tolerance measurements, particularly since any counter levels arc primarily a function of the emitting sensitive to hard beta will be sensitive to gamma element. Detailed detrrmination of the specific rays, and the selective advantage of the propor- elements and bet a-gamma ratios will be a function tional counter is lost. of the field laboratory. In many cases, field As previously indicated , personnel film badges laboratory information wiII allow a monitor to utilize a lead shield over a portion of the film so drtermine beta hazard through gamma me~sur~- that the unshielded section of the badge may give ments. a beta plus gamma reading and the shielded por- Specific information is lacking on the tolerance tion a gamma reading only. The beta esposurr range which will be referred to in militwv opera- determined by this method cannot be considered tions. Ionization chamber instruments such as too satisfactory since the waterproof envelope and the AN/PDK-20 Nith thin windows and the light-tight paper container, plus the cloth and othcr AN /PDIZ-8 (series), 37, and T-2 Geiger counters substances in the wearer's pocket, will gire an can be used to indicatc beta particles. Both the unknown degree of beta shielding. If photo- ionization ch am1)rr and thc G eiger-llncller counter graphic film badges are to be used to any cstent (fig.41) \vi11 rend the combined beta plus garima for the measurement of external beta esposurc 50 Ub3442 I 19" If

I Geiger- 1 roent- gamma e, since tgen (a 1 quan- 3 shield a radia- several shield 'his fea- nt when It must ng bears be con- particlrs gen rate tin num- will not s. This endation em have gamma

Pigirre Gezyer counter in iise with beta shield open to increase ddectzon sensitivity in checking for ground contaminntzotl. in beta 41. counter ) gamma during military operations, it mill be necessary to the greatest emphasis must be placed on accurate t propor- prescribe exact methods of attaching the badge gamma-measuring instruments. to the person, This in itself is not a complete The unit of photon absorption, called the n badges solution, since body shielding, equipment, e tc. roentgen, is universally used for measurement of e film so may give degrees of shielding which will give gamma ray dosage. In terms of this unit IT-P state may give false results. that thc permissible amount of gamma radiation lded por- to which the body may be exposed for routhe, exposure 14.04 The Gamma Ray every-day peace time operations is 0.1 roentgen (r) onsid eretl Because of its range and great penetrating or 100 milliroentgen (mr) per day. This is iii the elbpe and ability, the gamma ray presents the least difficulty procc'ss of being reviscd downward to a total of 300 and other of measurement. As stated prwiously, it is fortu- nu' pcr ivcck. For the purpose of performing some 1 give an nate that the greatest military prcoccupatiou will (q(~cinl1yimportant mission in conjunction with [f photo- be with gamma rays. This of course, moans that licltl tests of atomic TVCCL~OIIS,a maxirnnm s111g1c ny extent exposurc 12133443 51 exposure of 3 r is prescribed, provided no further Trained monitors most certainly will be equipped exposure is allowed over a period of 30 days. In with either the pocket dosimeter or with a pocket the event of atomic attack, exposures up to 75 r chamber and chamber reader. In cases where a (perhaps 100 r) will be permitted as one of the record of dosage is required, but where it is not normal hazards of war. Exposures of 75 r or considered advisable for the wearer to know that greater are of considerable interest to commanders dosage, the pock& ’chamber will be used. for the further employment of personnel and to Under some circumstances it is desirable to medical officers for proper treatment of casualties. determine gamma intensities from a remote posi- In 1928 an international committee for radio- tion. It is most probable that the detector ele- logical units defined the roentgen as the quantity ment of any such instruments will utilize ioniza- of x or gamma radiation such that the associated tion chambers. Two possibilities present them- corpuscular emission over 0.001293 gram of air selves for projecting instruments into a contam- produces, in air, ions carrying one electrostatic unit inated area: (a) rocket or gun fired missile, and (b) of quantity of electricity of either sign. It turns an air droppable unit. The latter is under devel- out that one cubic centimeter of dry air under opment as the AN/USQ expendable unit with the standard conditions of temperature and pressure AN/ARR-29 receiver. It has been found that weighs 0.001293 gram, and that 2.083~10~ions of the problems concerned with radiation sensitivity either sign are required to produce one electrostatic are minor in comparison to those of ruggedness and unit. Further examination reveals that the aver- data telernetering. Development work is also age energy of 32.5 electron volts required to pro- under way to evolve airborne radiac equipment duce one ion pair can be converted into 5.24 X 1013 capable of interpreting ground gamma radiations electron volts per gram of air or 83.8 ergs per gram from any altitude. of air. It should be noted that this definition Ionization chamber instruments have been makes the roentgen a unit of dQserate (absprption) designed to perform the function of closing relays rather than a unit of intensity. upon reaching predetermined dose rates of gamma An ionization chamber such as the AN/PDR-20 radiation. Instruments of this type will be of which has discriminating slides for the purpose of use in limited numbers for sounding alarms, clos- additional alpha and beta measurements is useful ing ventilators, etc., as in the case of the AN/ as a survey instrument when the humidity is not ADR-1 for planes flying into a radioactive cloud. at a point which destroys chamber insulation. Chamber instruments can be used to record t,he Chambers with provisions for thin windows are total accumulated dose in certain restricted areas not constructed to withstand rough usage. This such as specific shipboard compartments, the instrument must be used by well-trained monitors pilot compartment of an airplane, or the interior having a close liaison with a field laboratory. Its of a tank. The AN/ADR-2 airborne gamma do- primary usage would be in conjunction with de- simeter is yet to be evaluated, and the AN/PDR-2 contamination activities. group dosimeter requires many improvements to Completely sealed ionization chambers such as make it satisfactory for use outside the laboratory. the radiac meter IM-3/PD and the AN/PDR-T-1 Film badges will continue to record gamma ex- will be standard equipment for reconnaissance and posure of personnel involved with training (fig. scouting parties and for damage control equipment 43) participating in atomic weapon tests, and on board ship (fig. 42). These instruments, which peacetime uses of atomic energy. Because of the in some cases will be designed to read gamma dose many disadvantages associated with film badges, rates which would produce lethal dosages in less they may never be used in extensive military than one hour (500 r/hr), will be used to monitor operations. Pocket chambers or pocket do- unusually hot areas in which urgent work must be simeters will probably replace film badges, so that accomplished. immediate spot readings of dosage can be made. Ionization chambers such as the non-self-read- If a permanent record is required for medical or ing pocket chambers, DT-lG/PD, DT-35/PD, etc., legal reasons, it is relatively simple to make an and the self-reading quartz fibre pocket dosimeters automatically recording reader. (electroscope) , IhI-9/PD, IhI-50/PD, etc.,--will be Geiger-hlueller countei.~such as the ANlPDR- used to record individual gamma ray dosage. T-2, AN/I’DR-8 (series), and AN/YDR-27 are 52 12b34114 L RADIAC

posi- r ele- miza- them- itam- Id (b) level- ,h the that tivity s and also ment "tions

been .clays Figure 42. Ionization chamber being used for gamma surrey work by a shipboard damage ,mma control team. be of clos- AN/ :loud. d the areas , the terior a do- IR-2 Its to "tory. la ex- (fig. and )f the ,dges, Litary do- I that nade. :a1 or ;e an

Figure 43. Indiridirnl do~iiiicrtit. 'DR- 7 are Film badge and dosimeter are collccted upoir Ioaving coritariiiiiated area

53 12b3445 RADIAC

Figure 41. Helicopter grour~dmonitor. The Geiger counter is used for an air check of ground gamma contamination.

The portahle Griger-hluellcr detector \rill I)(, :I prinlary iristrumellt for use iri equipment dccoiitanlinatior1.

12b344b I W

RADIAC

Figure 46. Checking hand contamination. The probe beta window is left open to increase sensitivity in checking clothing, hands, feet, etc. Earphones as well as meter indication are used in checking with the Geiger counter. convenient portable instruments for gamnia ray very definite wave lengt,h dependence and the detection (fig. 44). Note that the word detection efficient counting of hard beta particles, it is is used rather than surrey. The counter range unnise to use the Geiger-Mueller counter as a of the equipment is limited to the region from quantitative recorder. background to intensities slightly in excess of The proportional counter is not used as a those which will give daily peace-time tolerance gamma ray measuring instrument, since the dosages (0.1 r) during a normal working day. primary use of the proportional counter is for As such, these instruments will have a primary use discrimination against gamma rays (and beta in conjunction with decontamination work (fig. particles) for the purpose of alpha particle meas- 45). The probe makes them especially convenient urcnicnt . for rapid examination of clothing, hands, feet, etc. (fig. 46). The Geiger-hlueller counter as the 14.05 The Field Laboratory most sensitive gamma detector may have some As can well be seen from an examination of usage as an early stage warning device for air- previous sections, the field laboratory is probablv borne radioactive particles and radioactive gases. as important as any individual instrument. Its Because it counts ionizing events rather than the inst rumentation,. working around the principles ionization produced in air, it is riot possible to we have discussed, must work in conjunction with calibrate the Geiger-hiuellcr counter in terms of chcniical and other analytical methods to give roentgens except for a dcfinite energy spectrum. rapicl, accurate indications of hazards. It, is In many cases calibrations are made in milli- readily apparcnt that ivith a minor amount of roentgens per hour for sources such as R. standard training and supervision a man can take care of radium sample. ,411 otlicr samples of radiations hiriisclf and mtilx satisfactory gamma surveys. within the radium spectrum then can be compared In t Iic case of alpha aid beta particles, high1y in terms of milliroentgens per how. Due to a tr:>iiid mo11ito1 :ire required. A great nniouiit 55 12b3441 RADIAC 8. of decontamination work in connection with alpha a. Variable regulated power supply from and beta emitters will be directly tied into findings approximately 100 to 2,500 volts. f by the laboratory, The present designs of radiac b. Geiger-Mueller and proportional counter iJ equipment used for the detection of alpha and probes. beta radiations do not lend themselves to ruggedi- c. Special ion chambers. 4.06 zation and these instruments may be used most 2. Counting rate meter for beta and gamma It sampling. properly in operations directly tied to a field ,stat a. Variable regulated power supply from laboratory. Some extremely important functions :one approximately 100 to 2,500 volts. such as the examination of drinking water (fig. 47) )asec b. Geiger-Mueller and proportional counter can be handled only with very special laboratory nent techniques. probes. Having located radioactive areas and evaluated c. Variable speed strip recorder. the immediate hazard, the laboratory can be used 3. Gas flow proportional counter for alpha sam- to determine how long the areas will remain pling, IM-I I/UD, with scaler and register. dangerous and what measures, such as covering 4. Miscellaneous accessories such as lead shields, with earth, etc., are required prior to occupation thin window tubes, equipment for sample prepa- or use. The field laboratory can make contribu- ration and determination of weight, sample hold- tions regarding the composition, efficiency, etc., of crs, etc. enemy weapons. 3. Filter type dust collector and electrostatic Only through use and experimentation will all type dusl collector. the components of a field laboratory be established. G. Photographic equipment for alpha track No attempt mill be madc to visualize the various measurements. (Nuclear track plates.) analytical chemical equipments which will be a. hlicroscope. required, but a rough guess as to instrument types 7. Instrument calibration standards. is given below: a. Secondary standard instrument such as 1. Scaler for beta and gamma counting. Scale the radiac meter IM-i’/PD quartz fibre of 1,000, mechanical register, and timing mech- surrey meter. anism. b. Calibration sources.

Fzgure f T. Lahorafory. The field latloratory mill be a tnost important haiard-cvaluating unit during atomis warfare.

56 \

RADIAC

8. Special survey instruments such as: laboratory equipment with such sensitivities and IY from delicateness as to be completely ruled out of the s. a. AN/PDR-20 thin window chamber. field laboratory category. This equipment will counter b. AN/PDR-10 alpha proportional counter. be used to give thorough scientific checks on the results of the field laboratories. 4.06 Other Establishments One very important device which will be used gamma It is anticipated that the various services will at any major decontamination center or at any tablish a number of. organizations within the base doing extensive work on contaminated equip- Y from . zone of the interior, and at perhaps some advance ment is the so-called hand and foot. counter such as the AN/UDR-10 which is used to monitor Counter !bases, in which practically all the radiac instru- pments mentioned herein will be used along with personnel leaving working areas. ha sam-

shields,

8 prepa- le hold- rostatic

track

uch as tz fibre

I S717.48’ -50 --5 57 I Ii 12b3449 1 t 12b3450 Chapter 15 k DESCRIPTION OF ACTUAL INSTRUMENTS 15.01 The Field in General and numbers with the types of instruments we have been discussing. It is desired to give a detailed description of the The writer may not be familiar with all instru- physical properties of commercial and military ments which have been produced and are being instruments which are making their way through- produced; therefore, inchision or omission of a out the Defense Establishment. In addition, specific manufacturer’s equipment is not necessar- some instruments which are perhaps obsolete or of ily to be construed as either condemnation or praise. E no military value have been so widely discussed Indications will be made as to whether an instru- that they will be included to show their relation ment is obsolete, etc. The following code will be ‘ to other such equipments. Laboratory instru- used: “0”-obsolete; “i”-in present military ments are not discussed and personnel interested use; “f“-anticipated for future military use. A I1 , in these equipments are invited to examine Refer- tabulation of instruments of interest is given in : ence (10). For security reasons, a good number of Appendix I. instruments which were developed under the The great majority of the instruments described Manhattan District had code names. Also, some herein are unclassified. Usually there will be no commercial model numbers have come into use. classification on any instruments issued for gen- An effort is made here to correlate these names eral use.

15.09 Pocket Dosimeters and Pocket Chambers

P0ckt.t chambers

Gamma. 100 mr, 200 mr, 100 r, Ionization chamber. 5 cc (less with high range). Separate reader.

1 oz. Size of fountain pen. >$-?$ in. diameter 43/2-5>/2 in. long.

A. Pocket Dosimeters

Distinguishing Manufacturer JBN Number Mf:. model Nunihrr AEC Surnher Full scale reading. color

A. 0. Beckman Company cf) __.______.PIC-10.1 _--- Silver. Black. Cambridge Instrument Corn BXI 17400______PIC-9.1 _____ Grey. PanY (4. Kelley-Koett - Manufactur- IM-S/PD (Set AN/ K-100 ______PIC-7.1 _____ Black. ing Company (i). PDR-3).

K-109 ______~ PIC-7Al_-.. Black. K-110 ______--.PIC-7A2 _.-. Black. IGl 11- - __ -.. . - - - - PIC-7A3-. - -. Black. K-150 (0), 151 (i)-- PIC-7U Blue. K-160 (0), 161 (i)-- PIC-7C- _-- Red. K-170 (0), 171_.__. PIC-7D _____ Purple. Landsverk (0)______IR.I-9( )/PD (Set L200______PIG7A Silver. AK/PDIt-3( )).

‘A number of 100 mr dosimeters have been manufactured for use within htomic Energy Commission laboratories.

871 74 8”-50--0 59 12b3451 L -.,Ftoure LE.. Dosimeters and chargers.

Shown from left to right are: Cambridge 200 mr; Kelley-lioett hlodels, K-110 (200 mr), K-151 (10 r), K-161 (50 r), K-171 (100 r) ; Iielley-Koett charger; Beckman 200 mr and neckman charger.

B. Pocket Dosimeter- Chargers - - - -_-_-

- Mfp model AEC NO I JAN No number Mariufarturer - -- -~~ ~ ~ ~-P _- P- __ l- - I AV-SA BM-182% AV-7 A P-800 -

K-135- AV-BD

L300. . AV-2B

12b3452 RADIAC

Figure 49. Electrostatic dosimeter charger PP-354AIPD. This small unit is approximately 25 inches wide, 136 inches high, and 132 inches deep (including protuberances). Charging is accomplished by placing the dosimeter in the hole to the left, then turning the friction knob shown on the right. See figure 6.

C. Pocket Chambers K-161 ~- Full scale Manufarturer 1 .JAK Xo dla. modelnunihc~r! AEC So smsitivity' Color

Iielley-Koett Rlfg. Co. (i) DT-35( )/I'D (Set AX/ Ii-700_. PIC-2E Black. PDR-21). :: No Nuclear Instrument and DT-lGA/PD (Set AIS/ 3340- PIC-1B .- Grey. Chemical Co. (i). PDR-4). Victoreen Instrument Co. DT-IG/PD (Set AX/ 352 PIC-SC__ Black. -9A (4. PDR-4). -78 Victoreen Instrument Co. ~_~_~~._~.~__~_.~~__~353 . .- - - .- - (Black with ($1 (magnetic magenta charg i n g color patch). -2D de vice ).

-2B 'A number of 1CO rnr pocket cliambprs have bcen manuiactured for use within the Ato~nirEnergy Commission laboratories. __

61 12b3453 RADIAC

Figure 60. Pocket chambers and charger-reader. Victoreen model 353 100 r (left) and model 352 (DT- 16/PD) 200 mr pocket gamma chamber are shown with the Kelley-Koett model K-425 (PP-43 ( ) /PD) 200 mr charger-reader. Chambers by other manufacturers are of c-omparable size and shape.

D. Pocket Chamber Charger-Reader Figure 51. Vidoreen Minometer type charger-reader. Tungsten fibre electrostatic voltmeter is used for charging and reading the residual charge The chamber is placed in the horizontal tube at the right on pocket chambers. Indication of reading comes of the picture. Readings are made through the vertical from a projected image of the electroscope fibre tube. Charging is accomplished by means of the button on a calibrat

Mfg. model AEC No, Full scale Manufacturrr JAN No number reading

~~ -

Kelley-Koett Mfg. Co. (i) (quartz PP-43 ( ) /PD (Set X S iPDR-2 1) 200 iiir. fibre). (2 lb., I1 oz. battery operated) Victoreen Instrument Co. Mznoinrter PP-3 16/PD (Set AS‘I’DR-4) - -. 200 mr. (i) (tungsten fibre). (6 Ib., 110 v. A. C. operat’ion) Victoreen High range Minometer (j) 392. -. 100 r. (tungsten fibre). (Weight, 6 lb., dimensions, 534 in. wide s 7 in. long x 5 in. high exclu- sive of sight tube: 8 in. high over all. For battery operation. Mag- netic charging device.)

62 12b345U 4 63 RADIAC .a pany (previously by the Landsrerk Electromcter Co.) having the following characteristics: cha mili JAN NO. (f) ______IM-7AIPD. eV0 ' Mfg. model No _____ K-320. con AECNO______SIC-5A. (IN Radiation detected_- Alpha, beta, gamma. AN S c a 1 e r a n g e s 0-100 mr/hr. (gamma). 0-1000 mr/hr. ope turt Detector ______- Ionization chamber-25 in.3 opeJ Indicator------Rate of drift of electroscope fibre Will over a calibrated reticle scale in viewing microscope. Approxi- 36,C mately 6-8 seconds required to in 1 read true indication. An auto- met matic flashing light timer is employed.

Weight. ___.______. 3>/4lbs. Dimensions___ ..__Main case; 6j/,in. long, 4 in. wide, Figure 54. ANIPDR-T-1 gamma survey ionization 6 in. high. hlicroscope tube ex- chamber. tends 231 in. above case. Controls are shown for zero set and range. A push- Window screens. -.Beta-0.001 inch cellulose acetate. button for meter illumination is at the forward end of the Alpha-0.0002 inch nylon. carr! ing handle.

15.04 Ionization Chamber Survey Meter

A. Gamma Ionization Chamber Survey Meter urin

Manufacture _____..-. . -. -. - Iielly-I

MX-6.. ~ ___.._~ ...____. 247A*.

IlI-30/PD ~ ~..- ~ ~ -.. - - - - IM-3/PD.

SIGl5A- -~ __._~ ._..~__. SIC-9B. 0-5, 0-50, 0-500, 0-5000- 0-2.5*, 0-25, (b250, 0-2500.

Ionizatior~chamber-. .~ ~ __ Ionization chamber.

3$2" polyethlene.

Air.

Atmospheric. lleter. 30. 1234. Rectangular with vertical cylindrical ends '3'. \ 5 x 6 101:/3~ 51:/32 x 125?t4.

16 in. cast aluminum. Baked Figui grey enamel. chai Th hand rete COlltl

64 12b345b RAOlAC

p The AN/PDR-T-1 is the first ionization [chamber gamma survey meter to be built to military specifications. These specifications were I evolved from the Sandstone operational tests of commercial instruments (8) such as the 2478 (Ihl-3/PD) and the MX-6 (IM40/PD). The AN/PDR-T-1 is thoroughly ruggedized and will ’ operate under any weather conditions of tempera- .i : ture and humidity in which the batteries will ‘ operate. The chamber is so constructed that it will operate in aircraft to an elevation of at least 36,000 feet. The meter scale changes with changes in the scale range, and a light is provided for I meter illumination during night operations. The Victoreen Instrument Company Model 247 (0) is an obsolete ionization chamber meter used extensively for onizatzon survey work during Operation Cross- roads. This is a large rectangular A pish- box, 12 inches long, 9 inches wide, ~d of the and 10 inches high, weighing 14 Fzpre 56. Victoreen model B47A gamma chamber survey meter (IM-SIPD). pounds. Under the handle are controls for range selection, bat- B. Beta-Gamma Survey Meters tery check, and zero adjustment. A small light-weight, portable, gamma measuring, beta indicating survey instrument with an ionization chamber and a pistol grip was developed Pllt co by the Manhattan Engineering District under the code name of Cutie Pie. Two such commercial instruments are outlined below, and it is known hat at least one other company has produced models having some of these characteristics.

, 0 2500 Manufacturer Sylvania Electric Tracerlab, he. Products Co. (i).

I M-5/PD ------Ih-SjPD. RD-316 ______- SU-ill. SIC-7A- - - - - __ __ - SIC-7B. 50 mr/hr______25 mr/hr. 500 mr/hr_-______250 mr/hr. 5000 mrihr ______- 2500 mr/hr. 3 in. diameter----- 3 in. diameter. 6 in. length .______6 in. length. Paper base, phe- Bakelite tube vertical nolic coated with coated with aquadag. aquadag. 64. Aluminum 0.080 in. Bakelite 5’s in. thick. thick. Babcd Figure 55. Natzonal Technzcal Laboralorzes conzzatzon 1 pounds _.______4f$pounds. chamber gamma survey meter, model ‘$1X-6 (1h-4O/PD). (i’i x 3 x 5 _..____-G)/2 x 3 x 5. The range switch is at the left of the meter eiid of the handle. To the right of the mcter i5 5een thc cap ovcr a recess containing sensiti\ ity adjristinciit control>. A xro control is on the top in thc foreground

65 12b345l J

k’tqtii *’ 68. -Yational Technical Laboratorzes model MX-b beta-gamma surveil meter. The charnber can be seen on the left end of the case. The gamma 5hield has been removed and is showing above Figure 57. Tracerlab (iCutze PZP”(IAf-SlPDl . its holder at the right end of the case. The chamber is the barrel to the upper right. On the The Argonne National Laboratory and its pred- end of the chamber is an adjustable beta window cccssor, the Chicago Metallurgical Laboratory, The National Technical Laboratories liave nianufactured a portable beta gamma nondiscrim- manufactured a medium-sized portable survey in- inating air ionization rate meter type with the do- strument utilizing an ionizatioll chamber u-liicli tcvtor in a probe at the end of a four-foot cable. will measure hard gamma radiation in roentgen This instrument, nom obsolete, was called thc rates and ionization currents due to soft ganiina Btfty Snoop (0). As a matter of identification, and beta radiations. This instrument is 11 itlr1)- tliir instrument was assigned the following num- called the Beckman MetPr. 1l(>lT: JAX Number ANIPDR-9 Mfg. model No ______-MX-2. Mfg. Model Sumber C2M10 AEC No_---_-_._-__ SIC-11A. AEC Number SIC-4A Full scale gamma sen- 20, 50, 200, 500, 2000 nir/hr. sitivity. C. Alpha-Beta-Gamma Chamber Survey chamber- - - - - 50 i11.3 bakelitc coated n.itki graphitc 1Ieter Window ______~- 377/, in.*, 0.010 in. rdliiloid. A number of medium-sized instruments have Beta shield ______$6 in. bakelitc. lwen manufactured utilizing thin windows on one Dimensions (length x 1234 x 754 x G:4. side of tl chamber and, in some cases, discrimi- width x height) inch- n:Lting slides to gh-e indications of alpha-beta- es. gamma radiations in terms of roentgen rates. Case-. -.-. -. - ~ -~.__ - Welded aluminuni n.lth grey hammer t on c finish. ‘I’liese cqiiipments will measure ionization currents 12fk pounds. tliie to soft gamma, beta, and alpha radiations.

66 12b3458 /

RADlAC

Zeus* (0). Rauland. 4 2-100. i Mfg. model No______.______-4 JAN No______------AEC NO____-___-______SIC-l7A__ - Function--. ______D i s c r i m i- Discriminat- nating ing. Full scale gamma______50 mr/hr____ PTimarily used for Sensitivity: 5,000, 25 mr/hr. 500 mr/hr. alpha u~thindica- 50,000, and 500,- 100 mr/hr. 5000 mr/hr. tion a function of 000 per minute. 500 mr/hr. calibration. 2500 mr/hr. Indication ______Meter ____--- Meter___- - - -.- - .. . Meter. 1 Weight (pounds) ______5- _...8----.--- .___-. 10% Dimensions (length x width 9 x 55’4 x 4.. - 1034 x 55 x 35h-.- - 13 x 1076 x x height) in inches. 576. *In the Model Z-IOOA (01, the Rauland Manufacturing Cornyany has left off the thin window and has produced a gamma-onlg chamber which may, in some cases, be referred to as the 7e7u. two such instruments under the trade name of Protezimeter which have the following charwter- is t,ias: ICE 111 Y-2 .JAN No ______ANIPDR-2 (i)--- llfg. model No__. 300 ___.____..-~- 392 (i). the case. AEC No _.__._._MIC4A _._____. ring above Frill scale reading- 200 nir--. - 50 r.

Chamber ~ ~ ~. - )/le in. polythylene Magenta colored. its pred- wall 3 in. high x )oratory, 3 in. diameter. Battery life. ~.~. 300 hr. continuous idiscrim- reading. h the de- Case._- ~...__ ._ Cast aluminum Scale colofed ma- lot cable. with grey genta. Illfd the crackle finish. ifica t ion, 1) i ni e 11 s i o n s Case 9 x 4 x 434 ex- 9 x 4 x 4)/2exclu- , _--- - (length x width clusive of cham- sive of cham- ing num- Figure 59. Raitland “Ze~rs”. s height) in ber, 7 in. over ber, 7 in. over- inches. all. all height. The chamber occupies a space under the meter with the t,hin window on the bottom of the instrument case. if‘eight______. .__ 5 pounds- _____-- 5)/4 pounds. A gravity switch in the top of the AN/PDR-2 The General Electric. Company has manufac- is designed to discharge the chamber when the tured a Zeus-type radiac. set to military spccifica- sur\.ey instrument is inverted. A manual switch has been tions which is still t,o he fully evaluat,ed: placed in the Model 392 to prevent accidental dis- ents have JAN NO__-______.__._._- ~ _-.__~.AK/PDIt-20 (j). charge as the result of inversion, vibration, or Full scale gamma (r/hr) - - -.- - - - -.- 500, 2.5, .25, ,025. NS on one shock. The chamber may be detached for use Weight _._____-.-. -. - __ .. . - ~ ~ -.- 10 pounds. away from the instrument base (see fig. 12). discrimi- Dimensions (length x width x height)_ 9% x 6 x 656. pha-beta- Beta shield- ___~__.__ ~ ._____.~_. ._$6 in. bakelite. E. Ionization Chamber Instrunients for Air-

:en rates. Alpha shield- -. -. -. ~ - - - . 0.003 in. aluminum. craft Use n currents Window area-. .- __ __ - - ______- - ~ - - 65% of 17 in2. a. Gamma Intensity Meter Volunie of chamber- ______.______88 in3 ia t ionr . Instruments which may be used to indicate D. Ionization Chamber Group Dosimeter dose rate and dosage within aircraft are now reaching the prot,otype evaluation stage. Such an Several instruments have been devisd to instrument, is the ANIADR-1. The A4N/L4DR-1 make integratrd gamma dosagc records. Thr (XN--2) as it now esists consists of four units of Victoreen Instrumcnt Company niailufacturcs upprosiiiiatelg the following types and sizes:

67 12b3459 Fzgure 60. The ilN/PDIZ-dO( Xh’-l) on erpf“!mf,//td model mzlatariy “Zeii\” Beta and gamma shields are moved h> mean\ of tllc coli- troIs on either side of the handle. (1) An indicator of the smallest sta~~tlartl size intended for panel installation. having the following dimensioris 2 jix 234 x 43i inches, with a 1 %-inch scale (2) Flight control box of diiiic.nsions Flyitre 61. Victoreen high-range “Protexzrrieter”. roughly 4 x 6 x 4 inches. The chamber is shown above the meter. A total of 50 (3) Power amplifier of tlimensioiis 10 s roentgen gamma may be recorded. 8 x 15 inches. (4) Receiver of dimensions roughly 10 s Controls are provided to actuate external 7 x 5 inches. vircuits to close ventilators, open oxygen valves, The total weight is presently I)ctwrcn 38 and 40 insert filters, etc., at predetermined levels of pounds. i adiation intensity. The indicator includes tlic follon iiig char- 1). Gamma Telemetering System acteristics: Two scales; one 0-20 mrilir, and thc Equipmcnts capable of being dropped or other 0-2000 mr/hr. On one side of the scale a projected into contaminated areas to relay infor- yellow light indicates close ratcs of 4 mr/hr. On mation on dose rate and rate of decay are well the other side of the scale a red light indicates 20 advanced in development. One such unit which mr/hr. At the 20 mrhr dose rates thc meter may be dropped from aircraft is tlie AK/USQ-l. scale automatically changes, and other rclng con- P. Seutrori Chamber tacts are actuated. In ordcr to make a complete presentation of The receiver compartment contains two ion- nomcnclature, mention is made of the Chang and ization chambers of noncoated stainless steel and Eng portable survey instrument designed to filled with about 10 ml of argon gas at 50 atmos- measure fast neutrons in the presence of gamma pheres pressure. One chamber actuates the 0-20 ~ticliatiori. The Chang and Eng consists of two mr/hr meter scale,while tlie other chambci actuates ioiiization chambers, connected in parallel, with the 0-2000 mr/hr meter scale. A radium c:rliImt- ii quartz fibre electrometer to measure the differ- tion source actuatcd by thc flight coirtrol box ( lit~1,~ cti(*t’of tlie ionization current in the two chambers. instrument operation on tlie 0-20 inr’lir scnlc. ()tu, of the chambrrs indicates neutrons PIUS 68 12b34b0 Figure 62. ANIADR-1 (XN-2) ai7borne radzation detection system. 1 ! From left to right; (a) Detector Unit, (b) Power Supply, Amplifier Unit, (e) Control Console, and (d) Panel Meter with automatic changeable scale and indicator lights.

gamma rays, the other cliamber indicates only gamma rays. As a result the gamma ionization currents can be made to cancel so that the only indication is the ionization current indicat,ion of fast neutron exposure.

Portable Alpha Proportional Counter T”. 15.05 a1 of 50 The Manhattan Engineering District developed two portable alpha proportional counters for laboratory survey work. These instruments have xtcrnnl virtually no usage within the military estnblish- valves, ment and only minor commercial usage. iels of Poppy (Wulkze Pee Wee (i). POPPY). Argonncb Na- Los Alainox Scien- #ped or tional Labora- tific Lalioratory. ,- infor- tory. hrgonne Na- Nuclear Iriatru- re well tional Lahora- meiit aiid Cheini- which tory. cal Co. USQ-1. SI’C-l.\_._ - SPC-IC. Ftqicit 6 !. Origmal “Poppy” type portable alpha propor- CLlL-41-.- - 2111. tional counter. Ltion of Greg anodized aluniiiiuin. ,I fiat prol)e niay he seen in the foreground ad mg Shape __...._~. - Rectangular. ned to Dimensions_- .~ 1176 x 536 x 8. gamma Weight_-_-~ ~ ~ __~~~16 poiiiids. Both instruments are important, since they are of two Scale readings 0-30,000 0-2,000, (r20,OOO. tlic forerunners of modern equipment being de- 31, with (counts pcr 0- 3,000. minute). vcilopcd by tlic Atomic Energy Commission and 2 differ- Indication. - - .~ - 0 ut 11 ut met e r 0 11 t 1) II t 111 c t e r tlic Dcqmrtincnt of Defensc. ambers. crystal head- I1eadplioiies. ns plus plioiies. 69 IZb34bi

Y a. Top ?leu ofthe ANIPDP-10 shou)rng mrter and coutrols. Earphonrs nre also used lor indication

Figure 64. Nuclear Znstrume?at and Chemcnl Co. “Pea Wee” proportional alpha counter model 21 11.

A pencil type probe is shown to the right of the, inctru- ment case.

An improved Poppy known as the AN/PDR-lO (j)is in the latter stage of dcvelopment. A proto- type form is shown in figure 65. 11 Ifottom mew of the AA7PDR-10 nhowang holes an the bottom of the CaSL corenug the tktn II Indow. Sefrrnl parallel uzrrs are used for elertton rolltitton. Fagure 65. ANIPDR-10 “Poppy” type proportzonal alpha Full Scale Meter Readiilgs detector. (counts per minute) _____ 1,000, 10,000.

Window-_- ______Plyofilrn window- 011 bottom 15.06 Geiger-Mueller Counters of case. A. Commercial Portable Detectors. Indication-. - - - - - Metcr and earphones. Portable Geiger-Mueller counters have reached Dimensions (length x width the commercial market in a great number of x height in inches) __.-. 12)$ x 4)/2 x 2)$ (approxirnate). different shapes and sizes. Among the bettrr Weight- __-- known surrey instruments are thcse:

70 12b34b2 P RADIAC Manufacturer__------El Tronics (i)------National Technical Nuclear Instrument Victoreen Instrument Labs. (i). and Chem Co. (k) (0). Co. (i) (0). iJ JAN number- - - ______AN/PDR-26 __-______IM-39/PD------IM-8( )/pD (Set AN/ IM-lA/PD (Set AN/ I PDR-7). PDR-5). I Mfg. modelNo ______SM3- ______MX-5 .___-______2610 ______263A. i AEC NO______SGM-18A _-______SGM-15A ______SGM-4B ______SGM-2B. Radiations ______Beta-gamma ______Beta-gamma ______Beta-gamma ______Beta-gamma. GM tube __.______RCL MK-1 MDL 20- RCL h4K-1 hlDL 20- NICC D-12 ______Victoreen VG13. Wall thickness (mg/ Glass 30 plastic 15 ____ Glass 30, plastic 17- Glass 35 ______Glass 30. cme) . Probe opening (inches) - (4) % x (1) x 1W--- 60% of 3 x circurn- 66% of 2% x circum- 80% of 2 x 2% ference. ference. Dimensions (length x 7%~%______8 x 1 ______9% x 1 ______-_--_-9 X 1% diameter, inches). Probe cable length (in- 30______-___ 30 ______36 -______24. ’ ches).

Beta shield ______2mm brass______y32“ brass-- _._.--_52” brass ______-_ y3z” brass. Indicator ______Meter, earphone Meter, earphone Meter, earphone Meter, earphone (magnetic). (magnetic). (crystal). (crystal). Scale ranges (mr/hr)--- 0-0.2,0-2.0,0-20 _____ 0-0.2,0-2.0,0-20_-- 0-0.2,0-2.0,0-20 _____ 0-0.2, 0-2.0, 0-20. Useful operating life 200_----_----_----- 400_------.---- 200__---_-----__---- 150. (hrs.).

Weight (lbs.) ______831 ____.______9.6 _____-._-_._.__11.6 ____-______-___ 13.4.

Shape .___-______-__-_Rectangular ______Rectangular __..__.Rectangular _____-_-_ Rectangular. Case dimensions (length 974 x 5 x 6 ______934 x 5 x 6 ____..___11 x 6 x 4_-______12% x 3% x 8%. x width x height in inches). Case material- - - Welded aluminum- - - Welded aluminum Welded steel grey en- Grey enamel. grey hammrrtorre amel. finish . i High voltage supply - - - 3-300 v batteries. - - - - 3-300 v battcricx - - 3-300 1 batteries-- __ - 3-300 v batteries (one 900 v battery in some). of the cast I collec/ron I a1 alpha

seached iber of bettcr

71 12b34b3 Victoreen Instrument Company Mode] x- 263, IM-2( )/PD (Set AN/PDR-q‘ (0). This instrument is a small light- v weight, low voltage (300 v) Geiger- Mueller survey meter without a probe and is now obsolete because of unsatis- factory performance. The Victoreen Instrument Company Model 263, IM-l( )/PD (Set AN/PDR-5) (o), the predecessor to the Slodel263A (IM-lA/PD). This instrument has nearly the same physical characteristics but is not as fully refined as the 2638. A Model 263B, which involves further improvements, has recently been issued. A great number of light-weight beta-gamma sensitive Geiger-JIueller counters have been manufactured as prospector instruments. In many cases these instruments do not have count rate circuits and output meters and utilize earphones for their means of indication. Typical instruments are the Midwest Electronic Laboratories RD-1’; Radia- Figure 66. El-Tronics model SM-3 Geiger couilier tion Counter Laboratories Mark 11, (ANIPDR-$6). Model 21, and the National Technical Laboratories hfs-8. The probe is in the well along the side of the top. One of the original Manhattan project portable, beta-gamma detecting survey instruments, utilizing a Geigcr- The IhI-39/PD, IM-8( )/PD, and IJl-lA/ Xlueller tube probe supplied with high PD received field tests during Operation Sand- voltage from a vacuum tube, oscillator stone (8) which resulted in the specifications and rectifier circuit received the codr for the ANIPDR-”-2. This instrument will bc name walkie talkie (0). The walkir described in the paragraph on military Geigcr- sgzlawkie (0) was the same type of in- Mueller counters. Other commercial instrunicnts strument. The difference being the which have had some military usc and \diirli talkie used headphones while tllc should be noted are: squawkie utilized a loud-speaker.

79 12b34b4 RADIAC

involves recently t-gamma ,ers have xtor in- bese in- rate cir- d utilize haillrlle. dication. Midwest The ’; Radia- The phc dark 11, eclinical

1 project tirig sur- L Geiger- with liigh oscillator the code he walkie ype of in- being the vSde the aker.

n. 73 RADIAC

Maxi

Radi Scale

Dete

Beta cm Winc

Figure 69. Victoreen Instrument C'ritLpany ?i~odc1 263A IndEc Geiger counter (ALV/PDIC-.i). Probl The probe (foreground) is carried in the bracket> at one end of the instrument case. The suitch and pl~o~rt,jack Len) are located mid-case under the Iiantll(~. cal Forn: Dime wic ine Weig

Powc

Fagure 70. Recent commerczal zm~rot~iw~~iszri por/ablc Gizgei-.~lnellersurrey meters. e r\-uclear Instrument and Chemical Company Modrl 2blO.A uith tlie probe held in a recess in 1:he handle. Right; the V ictoreen Instrument Company Model 2633 which III\ 011 ('5 >o~ncinnl)ro\ ements or er Models 263 and 263A.

2b34bb -

RADIAC 1 Military Portable Geiger-Mueller Detectors

mber- _____ a. AN/PDR-8 (f) ___.____AN/PDR-15 (j) __..__ AN/PDR-27 (23 ______ANIPDR-T-2 (i). b. AN/PDR-8A (f) c. AN/PDR-8B (f) d. AN/PDR-8C (f) \

cturer______a. Hoffman ______-______._____~.~__General Electric ______El-Tronics (mc b. R. C. A. PR-2). c. Hoffman d. Admiral

oh-. ~ -. Beta-gamma. - -.- - Beta-gamma.. -. .. . ~ - Beta-gamma-- - - -.- - - Beta-gamma. nges(mr/hr)_ a. Calibrated in r/24 hr. b, 0-0.5, 0-5.0, 0-50, 0- 0-0.5, 0-5.0, 0-50, 0- 0-0.5, 0-5.0, c, d. 0-0.5, 0-5.0, 0-50, 500 (beta indicat.ion 500 (beta indication 0-50. 0-500 (beta indication on first two scales). on first t,wo scales). on first two scales). r-..-- - - - BS-1; halogen-filled mica BS-1; halogen-filled mica RS-1; halogen-filled mica RCL MK-1 MdI end window (first two end window (first two end window (first two 21. scales). BS-2, low sensi- scales). RS2,low sen- scales). BS-2, low sen- tivitg halogen tube (3rd sitivity halogen tube sit,irity halogen tube and 4th scale). (3rd and 4th scale). (3rd and 4th scale).

a window (mg/ 3-4--___- ___~____.__ 3-4.-. ~.~.~_~_ .~.3-4_. ... . _._._ ~ .____ 30.

m’) . ,~

Idow area (in.Z)-- 0.44- ______.~ .______._0.44- -.. - ._._.~ .~~ 0.44_. -.__.______8 openings $$ in. x 13i~in. ~

jCator----.----- Meter plus headphows.___ Meter plus head- Meter plus head- Meter plus head- ,. phones. phones. phones. P I pbe dimensions-__ 8 x 136 x 196 in ...- .... _... 73/4 x 156 x in. dia- ~.. 8 x 1% x 136 in ______836 x H in. dia.

Ybngth of probe 6Oin ___.~ ~ ._._._.. ~- 60in_-_-~.---- ~.-FOin-..- ._.______36ik I ‘.cable. form factor-. - ~ - ~ Kidney-shape- ~ - -... Rectangular “flat iron”_ Rectangular. ------Rectangular. jimensioiis (length x 10 x 6% x 7___..______llji x 4j6 x 3% ~ .._ 9K x 5!46 ~‘455______10 x 6 x 7. I vidth x height in nchcs).

b. 11.5 t;. t;. c. 12.8 d. 11.5 1

Supply- ~ - ~- - a. Electronic vibrator-_~ ~ . Electronic lribrator ~_.R’eon oscillator (plug 3-300 17 batteries. r, in electronic unit). 8 b. Vi brator (si1h-mil iiatii re tubes). t. c. Neon oscillator i d. Vibrat.or (sub-miniatllre d.. tubcs).

75 a. Kidney-shaped radiac set ANIPDR-8. The tube is vertically held in a box on the right of the inst,rument. The extension pole is collapsed in a box 011

from the body of the iristrutnellt.

76 12b34b8 RADIAC

he is a The prohe case uith tkirc end wtndol~Qezger tube ZY shown inforeground b. Side i'fexof case irdh probe tartical in holder at the &Mend ofznst~um~nt. Figure 73. Radiac set :I .\'jPIIR-97. This instruinerit was originally knon.~~as t,he AN/PDlt-8E. These radiac equipments have automatic scale causw an alarm to sound intermittently at gamma number-changing devices with changes in scale int,ciisities of about 0.1 r with the frequency in- ranges. The AN/PDR-T-2 has an illuminated creasing to continuous alarm at 0.14 r. dial for night operation. The AN/PDR-8 series b. Probably the most important of the is supplied with a fish-pole type of extension (36 pre,sently available monitoring instruments are inches) for probe examinations at a distance from tlw hand .foot monitors (i) such as the com- the instrument (SW fig. 29). The probe of the m(v~ia1equipment manufactured by the Kelky- AN/PDR-15, and also of the AN/PDR-27, is Koct t Jlnnufact8uringCompany: carried in a vertical hole through the instrument case, so that when the instrument is being held J AS number ____ - -.-AN/UDR-3. by the handle, the beta window is exposed to tlic >If%. model number._K-240.

ground to facilitate ground beta survey work. AXC number- ~ _._-_CGM-l7B. The ANjPDR-T-2 is intcnded as an interim Iliiiierisions _____.___67 in. high, 3656 in. n-ide, 22 in. deep.

training instrument and is the combined result \\'c~ighf;___.~ - - ~ - - -.-600 pounds.

of the Sandstom. ex-aluations (8). Power ____ ~ __ __ - ~ - - -115 v 60 cycle A. C. C. Monitors ITtilizing Geiger Detection a. A number of instruments are manufactured There are five scaling systems uith rcgist,ers as commercially as monitors for detecting gamma follows: 2 GM tubes for palm and back of each radiation. The majority givc an audible signal, hand (4 systems with a total of 8 tubes) and 4 GM either as amplified Gcigcr clicks or as a buzz. trilm for the feet. An over-all total of 12 GM when a prdetermincd lcvcl of radiation is reached, tnlm. The t'uhes are sensitive to beta particles .tairce and as a result some have bcen called squawkers, having energies greater than 160 Kev. The etc. The Geopliysical Instrument Company :il)l)roximatewarning level is 15 count,s (including Model 600 is a good example. This instrument Ixicsligrouiid) in 24 seconds for the feet.

77 RADlAC

Fzgure 74. The ANIPDR-T-2 Grrc/cr-A$f~~elli~slrlz~y meter. A push-button for scale illumination is on the meter end of the handle. The shleld on the tube probe is open, and the Geiger tube may be seen. Scale range-battery check switch and zero adju-tmerlt are partially obscured by the handle.

A haul and foot monitor, manufactured to military specifications, has reached an advanced stat(>of derelopment:

Rlaiiufacturer- .. . Radio Corporatioll of America.

J.4Y iiuinbcr .__._.AXjUDR-10 (f).

1If: iiiodel iiriuibcr . EM4-2B. AF.C iirimber. . CCM-T4A. Diiireiisiolls (inchc,) (approsinlate\:

1’etlcstaL. ~ ~ ~ ~ ~ 60 high, 48 Tyide, 30 deep (at base).

Figure 75. Grophysacal Instrument Coinpany model 6‘00 monitor. E The Geiger tube caae is rhown at thc lower right. 78 12b3410 RADIAC .~ The AN/UDR-10 is designed to operate automatically and indicate the degree of contamination of five selected areas. as follows:

right hand-back right hand-palm left hand-back left hand-palm soles of both right and left shoes

Counts for each of the selected areas are separately channeled into five counting and recording systcms. This unit has been designed for the convenience of both organization and personnel. Several pedestals may be placed in exit gates, etc., at any distance from the control cabinet which can be located; for example, in a guard house. Indication is by means of signal lights on both the pedestal and control cabinet.

15.07 Photomultiplier Survey Meters J.4X number----- AN/PDR-ll (n--AN/PDR-18 (f;). Radiation detect- Alpha .______Gamma. ed.

Scale range.. _.~ ~ Up to 10,000 d/ 500 r/hr. d the 0.5,5,50, min. mdle. Detector.-.-.--- Phosphor and Phosphor and .d to photomultipli- photomultiplier. ers in probe. iiced Indication- ~ ~ ~ ~ - Output meter or Output meter. headphone.

JVeight (pounds) - 12_. ~ ~ ~ ~ -. - - - S:/2 (maximum). Case tliinensiorls 6 x 3 x 12- __.___6 x 4 F; 10 (ap- (length x width prox.).

I height in inches;).

13ot8hiiistrume,nts are involved with later stage me). clc~vclopmentand production engineering under

Figure 76. Kelley-Koett ntodrl K-2.40 hurrd and foot Colillt (li~c.tionof Bureau of Ships and should be ready (AA'/ UD12-5) . for field test in 1950.

79 I Zb3Ll-l I RADIAC .

Figure 77. AN/UDR-IO jive-channel counter for detecting beta-gamma contamination of the hands and jcct. Plastic envelopes in the hand holes may be changed aft,er contamiiiation. At the lower left is a box containing a roll of paper which replaces the paper covering the area used to inonitor t,he .~lesof shoes. 80 12b3412 RADIAC

- i5.08 . Badge ... :.p Film Dental film size packets, 1%x lyi inches not including waterproof coverings. Uaeful sensitivity range-Roellloena* Ernubion

Ansco non-screen- .. . ------

DuPorit 502. - - - ~ ~..-. - ~ -.. . Eastman Type I<._-. -.. ~~.. . AIISCOSuper Ray- ~~~~._.__

DriPont 552b.. ~ ~ ~ ~ .~. .. . ~ ~

DriPorit 552a- - ~ -.~ ~. ~ - ~.-~ ~ Eastman type A _._-.._.--~-. Eastman Cine Pos. 5301_----- DuPont 605- - _~.~.._~._~-__ East,man Cine Pos. fine grain 5302. Eastrnan Kodalith 6567. - - - -. Eastman Kodabromide G-3-. - East man 548-0 double coat - - - East man 548-0 single coat- - -. Figure ‘78. AN/PDR-ll(XN- ) alpha survey inefer. The scnsitivity ranpe of these film emulsions depends upon the choice of developer. Some nominal values are given which may be altered by as much The sensitive window is to the rear left of the probc in as a factor of 100 through the use of different developing solutions. Densi- the picture foreground. tometers (see page 35) having a top density reading of 3 have been in general photopraphic use for a number of years. The Weston Electrical Instrument Corporation manufactures such an instrument having a model number 6. Thc Anxo Division of the General Aniline and Film Corp. have recently ni:o.kctcd 3 Model 12 color densitometer which can measure a density of 6.

aiiiing a

81 12b3413 RADIAC

E Pagure 79. ANIPDR-18 yamma photom1titzplzer surrey meters. t shon 11. Two models are shown wit11 experimental form factors. The final instrrltllents ma! have no resetnblallce to those I I

12b3414 i ., -. . I. . -2

REFERENCES*

(1) Radiological Defense, Volume I. Joint Cross- (7) Pollard, Ernest and Davidson, W. L. Applied roads Committee, 1948. Nuclear Physics. Wiley, 1942. (2) Lapp,/?. E. and Andrews, H. L. Nuclear Radiation (8) Andrews, H. L. and Campbel!, D. C. Evaluation Physics. Prentice-Hall, 1948. of Radiological Survey Instruments used for (3) Sfrong,John. Procedures in Experimental Physics. Health Protection during Operation Sandstone. Prentice-Hall, 1941. Restricted. Sandstone Scientific Director's (4) Ross;, 6. and Staub, H. H. Ionization Chambers Report 31, Annex 10, 1 April 1949. and Counters: Experimental Techniques. Me- (9) Radiological Defense, Volume 111. Armed Graw-Hill, 1949. Forces Special Weapons Project, 1949. (5) Korff, S. A. Electron and Nuclear Counters: Theory and Use. D. Van Nostrand, 1946. (10) Radiation Instrument Catalog. U. S. Atomic (6) Yagoda, H. Radiation Measurements with Energy Commission, Technical Infor- Nuclear Emulsions. Wiley, 1949. mation Branch, 1949.

'A more complete bibliography will t~elonnd in iSucleonics I, 68 (December 1947). Other hihliography and references which may be of interest to the reader can be found appended to Rcfcrcncr ('31.

83 12b3415

._ 'yF'r .e-- I Appendix I

A-N NOMENCLATURE LIST

The following table lists A-N numbers for equipments now in field use or anticipated for use in the near future. It should be noted that this is far from a complete listing. - Nomenclature Instrument Manufarturer

Airborne gamma dose rate. Airborne dosimeter. Ion chamber group dosimeter. AN/PDR-3:

~ _._. IM-S/PD- __ __ Pocket dosimeter_-~ - ~.~ Kelley Xoett _____

IM-SA/PD_--. Poc.ket dosimeter__- - -.. Iielley Koett ___..- ~ - ~. Iielley Iioett -.- - - PP-31 lA/PD- - Charger. ~.~.~ ~. - ~. .. ~. ______.___.~.~. PP-354BiPD- - Charger- - ~ -.~ ~.- -. .~ ~ ~ Iielley Koett AN/PDR-4:

DT-lG/PD--_- Pocket chamber-. -.. . -~ Victoreen ____.-.-. . . ~ ~ DT-lGA/PD_ - Pocket chamber- -.. . . - - Nuclear Instrument and Chemical Co. PP-316/PD- - - Charger-reader- - - -.- - -. Victoreen - - - - .- - - .- - .. AN/PDR-5: (IM-1A/PD) - - Portable G-R.Z detector- - ANIPDR-7: (IN-S( )/PD) Portable G-M detector-. Nuclear Instrument and Chemical Co.

Portable G-M detector.. Hoffrnaii. - - - ~ ~.~ ~ ~. - ~

Kidney shaped G-&I- ~ ~. Radio Corporation of America.

Portable G-M detector.- Hoffman. - __~__.~.~.~ Portable G-PI1 detector.. Admiral- _~.~.._.~-~ Beta-gainma ion cham. Argon ne ?i at i o n a 1 her. Laboratory.

Portable alpha propor General Electric__~. ~.~ tional counter. AI p ha s ci n t i 11 at i 01, Itadio Corp. of America coiintcr. Portable G-AI detector-- G ariiina sci n ti11 at i o 11 cou liter Bct,a-ganima descrimi. General Electric-_-- nat i 11 g e ti amber.

Pocket chamtm------. IC-700. . K-425.- - Charger-reac!er__~ .~ - - Portable G-M detector- 8M3- - - - - Portable G-hI detector- Ion chamber 5urvey- - __ SIC-18A K-350 ___-1 Portal)le G-ill detector- PR-2. I Haiid and foot monitor___ CGAI-17B IC-240- _. IIaiicl nncl foot iiioiiitor--.l CGRI-T4.L EPvl,1-2B-- *The AN/PDR-27 was once known as the AX/I’I’K4E. 85 12b34lb . . . , I. -

RADIAC

Nomenclature Inst rumen t AEC No. Manufacturer Modcl. name - ___ ~ ___..

Gamma telemetenug- - ~.. - ~... ~ ~ ~ ~ ~ ~.~. ~.. . . - ~ ~..- - - __ ~- -.. . -. .. . . 3 Ion chamber survey-. ___ SIC-SB-.-.- Victoreen ____.______.24712 . Alpha-beta-gamnia ion SIC-2A- .. . . Victoreen ____ ------356- -.-. . Zeuto. chamber. Beta-gamma ion chamber. SIC-7A_. .~. Sylvania.. - - ___ - - ___ - __ RD-316__. Cutie pie. SIC-7B- -.. . Tracer Lab. ___ - __ __ ._- STJ-lA-. ~ ~ Cutie pie. 1 Drift meter-. -.-~. - ~-... SIC-SA- . . ~ ~ Kelley Koett ______.- -.. K-320- -.

Port.able G-M detector- ~ ~ SGM-15.1. ~ ~ Sational Technical Lab- MX-5- oratories.

Ion chamber survey- - - - - SIC-15A. .~ ~ Sational Technical'Lab- MX-6- oratories.

Pocket dosimeter__-~. ~.~ PIC-108- ~ -. A. 0. Beckrnan Co- - -.- -.~ ~ ~.~. ~ ~.

Pocket dosimet,er_-~ ~.~. PIC-9.k Cambridge Instriirnent BM 17400 co .

Dosimeter charger___.. __ ~.. ~ ~ ~ ~ ~ ~ Chatham Electronics- - - ~ ~ ~... -. ~ ~

Dosiiriet,cr cliargcr- ~ ~ ~ ~ ~ AT'7A ~ ~ ~ Cain1)ridge In~trunient -.. . ~ ~... , ' co. i

86 12b3411 1 APPENDIX II GLOSSARY OF TERMS CONCERNED WITH RADIAC INSTRUMENTS

- - pie. Avalanche- - - - The action within proportional and Dead time.. - The time interval between individ- pie. Geiger counters in which one ion ual counts in which a counter is (electron) produces another ion insensitive. by collision, these two ions (elec- Densitometer- - Electronic-Optical device used to trons) producing still further determinethe density (blacken- ionization. ing) of film badges. Dosimeter-- - An individual dosage indicating The ' background count is that Background--- device-more specifically, a which is caused by any agency direct reading quartz fibre elec- whatever other than the radia- troscope sensitive to gamma tion which it is desired to detect. radiation and about the size of a. For health prot,ection, it usually fountain pen. Otherwise known includes the radiations produced as a pocket dosimeter, a pocket by naturally occurring radio- electroscope, or a quartz fibre activity and cosmic rays. dosimeter. Calibration--- The process of checking and ad- Electrometer A specially constructed vacuum ' justing instrument operation tube. tube used for the amplification against known sources of radio- of minute currents such as those activity. obtained from ionization Chamber- - - - - A container in which ionization is chambers. allowed to take place and in Film badge---- A small packet containing photo- which all the original ions arc graphic film which is used to collected-otherwise known as obtain individual radiation dos- an ion chamber. age readings. Readings are Count------A terminated discharge produced primarily of gamma radiation. by an ionizing event in a counter (Teiger counter - A low dose rate, high sensitivity tube. detector of beta and gamma radiations. It may be either a Counter-- - A device, such as a proportional ___ light-weight portable detector or counter or a Geiger-Mueller a laboratory instrument. Also counter, which responds to or known as Geiger-hlueller counts individual ionizing a events. counter. Geiger region- - The part of the characteristic Count rate The instrument used to indicate curve of pulse size as a function meter. the rate of counts indicated by a of voltage in which the size of counting chamber or a propor- the pulse is independent of the tional or Geiger counter. It magnitude and type of radiation may be used with hot11 portable producing the initial ionizing and laboratory equipment. event. Curie------The curie is a standard measure of Half l;;fe------The time required for the disinte- the rate of radioactive decay gration of a radio-isotope to equal to 3.7 s 10" disintegra- one-half of it,s initial rate of tions per second. activity.

87 12b3418 Ionization- - - - The process by which a neutral cules-the opposite of ioniza- atom or molecule loses an elec- tion. tron with the remaining ion Recovery time- The time interval after recording becoming positively charged and a count before the pulses pro- the electron and positive ion duced by the next ionizing event, forming an ion pair. in the counter are of substan- Ionization A high dose rate, low sensitivity tially full size. chamber instrument for the measure- -1 Region of con- The part of the characteristic 1 survey ment of gamma radiation- tinous dis- curve of pulse size as a funct,ion 1 meter. also known as a gamma survey charge. of voltage in voltages higher meter or an ion chamber. than those of the Geiger region. Photographic The entire operation required to In this regign the tube goes into dosimetry. obtain individual dosage records a state of continuous discharge. by the use of film badges. This Region of lim- The part of the characteristic includes calibration, film devel- i t e d propor- curve of pulse size as a function opment, densitometry, etc. tionability. of voltage in which the gas The roughly horizontal part of the amplification depends both up- counting rate as n function of on the numbers of ions produced voltagc curve in which there is in the initial event and upon the very littlc change in count rate voltage (very little use). with change in voltage. Roentgen- - - - For military purposes, this is a Pocket cham- A non-self-reading individual gam- unit of dosage for the measure- ber. ma dosage indicating device ment of gamma radiation. This about the size of a fountain pen. is the quantity of radiation Proportional An instrument which counts alpha which, under standard condi- coun,ter. particles and descriminates tions, produces 2.08 x log ion against counts produc~dby beta pairs per cc of air. and gamma radiations. It mag be either a portable or a labora- A laboratory electronic device tory instrument. used to record the number of Proportional The portion of the characteristic pulses from R counter. An elec- region,. curvo of pulse size as a function tronic circuit capable of divid- of voltage in which the size of ing the incoming pulse rate by a the pulse is proportional to the constant factor so that mechani- number of ions formed by thci cal methods of recording the initial ionizing event. pulse may be used. Quenching- - - - The process of extinguishing the> Threshold- - - - In the Geiger counter character- action within a Geiger countvr istic curve there are two thresh- tuhc. External quenching uti- olds: (a) The voltage below lizes an electronic circuit. A which no pulses are recorded is self-quench is produced by ac- the characteristic curve thresh- tion within the counter tube. old, and (b) the voltage at Recombina- The process of union between which the plateau starts is tion. electrons and positive ions to known as the threshold of the foim neutral atoms or mol(,- Geiger region.

88 12b3419

I ioniza- SUBJECT INDEX ording 's pro- 39 ;event 67 ibstan- 49 67 teristic 47 mction 47 45 higher 3, 11 region. 48 )es into 47 charge. 28 47 teris tic 21,87 inction he gas )th UP- oduced Don the is is a leasure- 1. This tdiation condi- iog ion

device nber of An clec- f divid- ate by a iechani- ing the

laracter- thresh- , below :orded is 38 1 thresh- 3 tage at 13 tarts is 3 d of the 41 41 41 41 42 42 43 89 RADIAC

Page Instrument characteristics, pressure and temperature effects- - - ______.____...~- .. ._~_...____ 43 Instrument characteristics, saturation effects--. - - - 43

Instrument characteristics, strap- - - ~ ~.- __. - ~ - -- - 41 Instrument characteristics, switch knobs-. .-. .__ - 42

Instrument characteristics, weight- - ~ -.. . . . ~ ~- __ - 41 Instrument use _____------....-.~~...... --.--47 Insulation .______--.--.----.--...-~~---..-13,49 Ion ..pair ______..------..---~.-...--.~- 4 Ionization ______.____..___~~.__.. . 4,87

Ionization of air.__ -. ~.- - - - -.. - - ~ ~... -. . . -. 4

Ionization chamber-. .-. . . . ~ ~ ~ ~ ~ ~... ~ ~ ~ ~ ~... . 5,7, 87

Ionization chamber characteristics- ~ ~ -.. . ~ ~ ~ - -.. 10 Ionization chamber characteristics, circuit...... - 13

Ionization chamber characteristics, gas.. .. . ~ - - - 12

13 51,88 67 56,88 27 32 32 31 12,43 77 45 39 39

11,66 21 47 47 45 10 13 32 39 69 72 72 49,5F 11 10 3 43 67 67 0 90 12b3481 i

fZb3482