from July 8 meas-
urement.)
t = 27 days (May19June 15)
Ay = 0.0866 day7!
Ao-= 0.0204 day'*
Thus
0.37 = feo fen'0.0868,27 gy itl.107)27
0.0204
Ro = 0.189 pe/gram/day.
Now we determine the infinity [')
dose using Eq. 2.
EXAMPLE: Human Inhalation
On May 19, 1953 the highest concentration of activity in the air due to
fallout that has ever been recorded in the U. S., outside the Nevada Test
Site, occurred at St. George, Utah. It amounted to about 1.3 yue/m?®
averaged over 24 hours. The total radiation dose to the thyroids of the
people at St. George from inhalation of the isotopes of I is estimated to be
0.302 rep as shown in the following tabular calculation.
Estimate of Radiation Doses to Thyroid of Humans From Inhalation
Din = K/XAe + Ap)
where: A = 55 Rofl = 58(0.189)(0.2)
= 2.08
Thus Di. = 224 reps is the infinity [!
dose.
To estimate the dose from shortlived isotopes of I enter Fig. 3 with
these parameters:
start of intake = 3.5 hr
duration of intake = infinity.
The graph indicates 2 ratio of approximately 0.45.
But this is uncorrected for biological
decay, 1.e., it is based on the assump-
tion that the biological decay constant
for the thyroid is significantly less
than the physical decay constant. It
is necessary to correct this ratio by
Time
Average
Fissionproduct
Fraction
after
defanahian
far}
fisstonproduct
activity
(uc; meter?)
activity
originally
retained
(ue)
of fission
product
that tg [131b
w%
F131 aetivity
reaching
thyroid
(malliuc)
Infinity I31
dose to
thyroid
(rep)
2-7
7-10
10-14
14-18
18-30
4.0
2.9
0.62
0.043
0.014
12.4
4.3
1.56
0.104
0.105
0.16
0.35
0.47
0:7
1.1
5.00
O.t7
1.80
0.19
0.29
0.0304
0.0230
0.0110
0.0012
0.0018
Added dose
fram shortlaved I
Total
tsolopest infinity dose
(rep)
(rep)
0.121
0.074
0.030
0.003
0.003
0.155
0.097
0.041
0.004
0.005
Tota 0.302 rep
* Based on 0.83-meter?/hr air intake and assuming that 75% of the activity will be
initially retained either in the lungs or find its way into the gastrointestinal tract.
» Based on assumption that 75% of initial intake of both Te precursors of I?#! will
remain within body until decayed to J™!.
© Assuming 25% of initial retention of I'%! (either in lungs or gastrointestinal traet)
reaches the thyroid.
@ Tnitial dose rate
(53) (0.2) (uc of I'! per gramof tissuc) in reps per day. Infinite
dose = Initial dose rates (A, + Aa).
é From Fig. 1.
Multiply these ratios by (A, -+ An} /Ay for [8! in man.
multiplying by the factort
(A, $ An) Ap = 1.24.
0.45 & 1.24 = 0.557
The infinity cose to the thyroid
from short-lived isotopes of iodine is
this fraction of the [! slose
224 & 0.557 = 125 rep.
Thus the total infinite dose is 22-4 —
125
350 rep.
This is not considered dangerous.
Experimental studies with sheep at
Hanford Atomie Products Operation
suggest that about 16.000 reps are required to produce minimal changes in
the thyroid cellular structure and
about 50,000 reps to produce definite
ceil damage and hypothyroidism.
BIBLIOGRAPHY
1. H. F. Hunter, N. E. Ballou, Necueonics 9,
No. 5, C-2 (1951)
2. J. B. Stanbury, et al. “Endemie Goiter.”
Harvard University Monograph in Medicine
and Public Health No. 12 (Harvard University
Press, 1954}
3. L. Van Middlesworth, NucLeonics 12, No. ©
(1954)
4. H. Kornberg, private communication (1953)
* Biological half-life in sheep thyroids is
about 34 days (4).
{+ See footnote 6 Table 2.
Vol. 14, No. 2 - February, 1956
TABLE 3—Sample Calculations for Figure 3
{
Periods of
antake
(hours after
delonation)
B
Cc
Relatire mean
(7) energy
intake X
Cumulative
haurs tn
pertud’
£13 energy
intake
D
Mean of
ratias of
enerqies
[Short Jisis
E
F
G
Relative
energy
[Short
Cumulative
[Short
Ratio of total energies
fFSeore 7131 for infinite
thyroid dose intake fram
ist hour to end of pervod
BX D)
intake
(Column F + Cy
(Columns
energies
indicated
1-11
11-21
21-31
31-41
41-51
31-61
61-71
160
158
150
146
140
135
130
160
318
168
614
jot
889
1,019
3.6
2.3
1.6
1.3
1.0
0,84
0.70
519
364
240
190
140
115
91
OTe
934
1,179
1,364
1,504
1,624
Lila
3.6
2.93
2.32
2.23
2.0
1.88
1.68
71-8]
125
1,144
0.55
69
1,784
1,56
81-91
“1-101
101-201
120
lla
920
1,264
1,879
2,209
Q.46
0,40
0.20
55
46
184
1,839
1,884
2,000
1,45
1.37
O.400
201-501
301 - 101
650
470
2.049
5,419
0.08
0.042
a2
14
2,121
2,140
O17 1S
0.626
601-801
280)
4,209
0.0005
3
2,155
0.500
401-601
$01 -1,001
600
140
4,019
4.489
0.02
0.005
12
1
2,152
2.13
0.980
0.484
‘ Based on Fig. 2.
>From Fig. 1.
¢ This is uncorrected for biological decay as described in footnote 4 Table 1. For
cases where biological decay in the thyroid is significant for 1°3', multiply last column
G by the factor (A, + A) /Ay.
41