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.