nMTy. dk. ALFRED W. eLrMea No. 50—isotope Calculations Activity and Thyroid Dose from Radioiodines by RONALD L. KATHREN, Lawrence Radiation Laboratory, Livermore, Calif. RaDIOIODINES ARE PRODUCED bothdirectly from fission and as daughters of other fission nuclides. Thus the fraction of total iodine activity contributed by a given iodine nuclide will change with time. Since the total energy release and specific activity differ for each fission radioiodine, it is important to know the proportions of these nuclides so that biologica] hazards can be assessed more accurately. The figure provides the means of determining the relative activity of the various fission radioiodines as a function of time after fission. The curves are based on thermalfission of U**5 and are plotted from data given by Bolles and Ballou (1). Several individual points on each curve were confirmed by calculations based on the fission-product yield data of Katcoff (2). Because of the short half-lives of I/3*-I!# and their precursors, they are not included in the figure. Similarly I}28-I?*° are excluded becauseof their low fission yields. The relative dose contribution can be determined by multiplying the relative activity by the dose constant for the nuclide under consideration. This dose constant R, expressed in terms of the total integrated thyroid dose in rads/uc uptake, is determined by the expression derived below and based on the body-burden equations of the International Commission on Radiation Protection (3, 4): This data can be used to determine maximum permissible R= [ KikoH e—™dt 0 R _= concentrations for mixtures of gaseous-fission iodines and thyroid doses following inhalation or ingestion. The method can also be used to determine the isotopic proportions of the various radioiodines from fallout in milk and other foods. 37rt kiukok kama ( 1 ~ e™ ° kiko or, asti— , = —— yma REFERENCES in which / is a constant equal to 1.33 X 10° disintegrations/ hr/ye, ke is a constant equal to 1.6 X 10~% ergs/ Mev,kz is a constant equal to 100 ergs/gm/rad, EF is the effective absorbed energy per disintegration in Mev, m is the mass of the critical organ in gm, d is the effective decay constant in reciprocal hours and is the time in hours after deposition. This equation simplifies to R = 0.15 #7, in which is the half-life in hours. RELATIVE ACTIVITY from radiciodines following fission of U235 Values for #, m and T are given by the It. N.C. Bolles, N. E. Ballou, USNRDL-456 (1956) 2. S. Katcoff, nucLEontcs 16, No. 4, 78 (1958) 3. International Commission on Radiation Protection, Committee IIT Report, Heaithh Phs. 3, 1 (1960) 4. R. L. Kathren et al., UCRL-7456 (Appendix) (1963}; Health Phys. 10 (1964) * * * Work done under the auspices of the U. 8. Atomic Energy Commission. International Commission on Radiation Protection (3). The total integrated thyroid doses in rad/ue of uptake can be calculated and are: T31: 1132: T33; T'34: J135: 6.3 rads 0,23 rad 1.8 rads 0.11 rad 0.54 rad Ronald L. Kathren, who holds degrees from UCLA and the University of Pittsburgh, has been associated with the Radiation Safety Section of the Lawrence Radiation Laboratory for the past two years. His major interests and activities are in the areas of personnel dosimetry and healthphysics instrumentation. November, 1964- Vol. 22, No. T1 60 reprinted ronNUCLEONICS - Copyright 1964, McGraw-Hill, Inc.