Determination of Beta Activity in Water 3 Q 3 GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1696-A Determination of Beta Activity in Water By F. B. BARKER and B. P. ROBINSON RADIOCHEMICAL ANALYSIS OF WATER GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1696-A UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1963 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington 25, D.C. CONTENTS Fag* Abstract__--__-______---____________________-_--____--_--____-_ Al Introduction. ______ _______________________________ ___ 1 Sources of radioactivity in water______________________________ 2 Collecting and preserving the sample_________________________ 5 Measurement of radioactivity______________________ 7 Techniques and instruments._____________________________ 8 Statistical considerations___________________________________ 9 Calibration of instruments____________-__-__-_-____-______-_ 13 Control of instrument operation-_-__--_-__-__---_------_-__--_-_ 16 Optimum operation of G-M counters_______________________ 17 Optimum operation of scintillation and proportional counters. __ 18 Background control chart_________________________________ 19 Standard control chart__-______-_____-__________--______-__ 21 Determination of gross beta activity in water.________________________ 22 Principle of determination___________-________.-._______ 23 Apparatus____________________________________________________ 24 Reagents-________-____-_--__-___________________--___-__-_. 24 Procedure-_----__--_-------_--_-___________________________ 25 Calculation of results__________________________________________ 26 Calibration of beta counters. __ ________________ ________________ 27 Preparation of the standard_______________________________ 28 Correction of the standard for radioactive decay__________ 28 Procedure for calibration-___________________-__-__--___ 29 Errors and precision___________________________________________ 30 Literature cited.__________________________________________________ 32 ILLUSTRATIONS Page 1. The uranium series______________________________________ A2 2. The actinium series______________________________________ 3 3. The thorium series_____________________________________ 4 4. Best estimate of "true" counts____________________________ 14 5. Ratio of mean "true" counts to observed counts___________ 15 6. Form for background control chart data_________________ 20 TABLES Page* TABLE 1. Naturally occurring radionuclides. ._____._____________--_._ A4 2. Beta-emitting radionuelides commonly found in nature.-_-_--_ 23t in RADIOCHEMICAL ANALYSIS OF WATER DETERMINATION OF BETA ACTIVITY IN WATER By F. B. BARKER and B. P. ROBINSON ABSTRACT Many elements have one or more naturally radioactive isotopes, and several hundred other radionuclides have been produced artifieally. Radioactive sub­ stances may be present in natural water as a result of geochemical processes or the release of radioactive waste and other nuclear debris to the environment. The Geological Survey has developed methods for measuring certain of these radioactive substances in water. Radioactive substances often are present in water samples in microgram quantities or less. Therefore, precautions must be taken to prevent loss of material and to assure that the sample truly represents its source at the time of collection. Addition of acids, complexing agents, or stable isotopes often aids in preventing loss of radioactivity on container walls, on sediment, or on other solid materials in contact with the sample. The disintegration of radioactive atoms is a random process subject to estab­ lished methods of statistical analysis. Because many water samples contain small amounts of radioactivity, low-level counting techniques must be used. The usual assumption that counting data follow a Gaussian distribution is invalid under these conditions, and statistical analyses must be based on the Poisson distribution. The gross beta activity in water samples is determined from the residue left after evaporation of the sample to dry ness. Evaporation is accomplished first in a teflon dish, then the residue is transferred with distilled water to a count­ ing planchet and again is reduced to dryness. The radioactivity on the planchet is measured with an anticoincidence-shielded, low-background, beta counter and is compared with measurements of a strontium-90-yttrium-90 standard prepared and measured in the same manner. Control charts are used to assure consistent operation of the counting instrument. INTRODUCTION The Geological Survey has adopted analytical methods for certain radioactive species in water. These methods will be described in detail, with complete laboratory instructions, in the present and in succeeding chapters of this Water-Supply Paper. These methods, or modifications of them, are useful in studies of the purity of domestic and industrial water supplies, water pollution, radioactive-waste disposal, and hydrogeochemistry. Al RADIOCHEMICAL ANALYSIS OF WATER Messrs. H. P. Cantelow, of the Lawrence Radiation Laboratory, 'and W. L. Albrecht, of the Tennessee Valley Authority, reviewed the manuscript of this report. SOURCES OP RADIOACTIVITY IN WATER Many radionuclides (atomic species that undergo radioactive decay) occur in nature. All isotopes of elements of atomic number 83 and higher are radioactive, and several of the elements of lower atomic weight have one or more natural radioisotopes. Most of the radio­ nuclides are members of the three naturally radioactive series: the uranium series, the actinouranium series, and the thorium series. In these series, the parent atoms change successively from element to element by the emission of alpha, beta, and gamma radiation. The major features of these series are illustrated schematically in figures 1, 2, and 3. The other naturally occurring radionuclides, together with u 238 U 234 URANIUM 4.49 xlO 9 2.48 xlO5 years years , Pa»4 ", (99.85 percent) 1.8 minutes PROTACTINIUM '/ Pa 234 I.T.(0.15 / 6.7 hours A percent) Th 234 Th230 THORIUM 24.1 days 8.0 xlO4 years ACTINIUM Ra 226 RADIUM 1,622 years FRANCIUM - Rn 222 RADON 3.825 days At 218 ASTATINE 2 seconds 211 ' d(0-02 Po 2' 4 D/t 218 Po2!0 /° percent) 1.6xlO~ 4 POLONIUM 3.05 minutes 138.4 days seconds f ' 1 a Bi m ' (99.96 percent) Bi 210 BISMUTH (99.98 percei t) M 5.0 days minutes * j 5 Pb 206 Pb 214 0 Pb 210 LEAD ' (5x10 stable 26.8 m nutes (0.04 percer t) 22 years percent) > isotope fi 3 T| zio T! 206 THALLIUM 1 32 m nutes 4.19 minutes FJQUEE 1. The uranium series. DETERMINATION OP BETA ACTIVITY IN WATER A3 u 235 URANIUM 7.13x10" years Pa 231 PROTACTINIUM - 3.43 x 10 4 years Th 231 Th 227 THORIUM a 25.6 hours 18.6 days ft Ac 227 (98.8 percent; a ACTINIUM 22.0 years a Ra 223 RADIUM (1.2 percent) 11.1 days Fr 223 ft a FRANCIUM 21 minutes a (4xl!T 3 Rn 219 RADON 3.92 seconds percent) 9 At 219 (3 At 215 ASTATINE a 0.9 minute percent) 10 4 second * Po 215 (5xlO~4 a 1.8xlO~ 3 Po" 1 POLONIUM (97 percent) percent) a second 0.52 second P ft Bi 215 Bi 211 <° 32 percent) BISMUTH a 8 minutes 2.16 minutes a ft Pb207 Pb" 1 a LEAD stable (99.68 percent) 36.1 minutes isotope X 3 T|207 THALLIUM 4.79 minutes FIGUEE 2. The actinium series. their half-lives and mode of decay, are listed in table 1. Some addi­ tional radionuclides are produced from the interaction of cosmic rays with stable atoms and from the spontaneous fission of uranium atoms; however, only two of these nuclides are of much importance: hydrogen-3 (tritium) and carbon-14. A4 RADIOCHEMICAL ANALYSIS OP WATEB Th 232 Th 228 THORIUM 1.39 xKT 10 1.90 years years / 0 Ac 228 ACTINIUM a a 6.13 hours X / & Ra 228 Ra 224 RADIUM 6.7 years 3 64 days FRANCIUM a 220 RADON Rn 54.5 seconds At 216 1 3x10 " 4 ASTATINE a second 0 Po 216 Po 212 (0.013 percent) POLONIUM 3.0xW" 7 0.158 second (?) a second 0 a Bi [66.3 percent) BISMUTH (*100 60.5 minutes a percent) 4 (3 Pb 212 Pb 208 a LEAD stable 10.6 hours (33.7 percent) isotope * ^ (3 Tl 208 THALLIUM 3.1 minutes FIGURE 3. The thorium series. TABLE 1. Naturally occurring radionuclides, other than members of the natural radioactive series [From Friedlander and Kennedy, 1955] Relative isotopic Mode of Radionuclide abundance decay i Half-life (years) (percent) 0.012 ft K 1.2X10" Rubidium-87.-.,- _ __ .___ __ _ __ __ _ 27.8 0 6.2X101° Inditim-115_ _______ _________ __ __ _ 95.8 0 6X10" Lanthanum-138- __ __ _______ __ __ __ .089 K, j8 »2X10" Neodymium-144___ _____ _____________ 23.9 a «5X1015 Samarium-147 __ _____________________ 15. 1 a 1.3X10" Lutecium-176_ _ _ __ ___ ___ _ _ _ __ _ 2.60 fi 4.6 X1010 Rhenium-187__ _ _ _ _ _ _ ___ _ __ __ 62.9 0 «5X1010 Platinum-190 _ ___ _ _ _ _ __ _____ __ . 012 «10'2 i The mode of decay is indicated by the type of particle emitted (a, 0). If decay also occurs by electron capture, this is indicated by K; the predominant mode is indicated first. DETERMINATION OF BETA ACTIVITY IN WATER A5 Within recent years, several hundred artificial radionuclides have been produced. The most important of these are the fission products those nuclides produced in the course of the fission of uranium-235, plutonium-239, or uranium-233 atoms. Other radionuclides have been produced by various nuclear-bombardment reactions. A com­ plete list of nuclides, with their half-lives and modes of decay, is given by Friedlander and Kennedy (1955, p. 413). All natural water contains some radioactivity, if only that due to the ubiquitous element potassium. Before the development of atomic energy and nuclear devices, the radioactivity in water came primarily from radionuclide-bearing rocks and minerals with which the water came in contact, with lesser contributions from the cosmic- ray-produced radionuclides picked-up mainly by meteoric water. Since the advent of the atomic age, however, measurable amounts of other radioactive substances have found their way into the Nation's water resources as a result of fallout from nuclear explosions and dis­ charge of radioactive waste from nuclear reactors, uranium mills, research laboratories, and other producers and users of radioactive materials.