19/ writing in the Military Surgeon, has used a factor of 10% per day
recovery for a 20-day period, and according to him this scheme breaks
down beyond this point.
Although some biological recovery certainly takes place, there
is also a degree of permanent residual damage from which an animal
never recovers, or at best, recovers at a rate so slow as to be diffi-
cult to measure.
From a quantitative point of view, 20% of the total
incident gamma radiation received is considered tobe an irreparable
equivalent and 80% to be reparable according to the factors given
above, i.e., 20% per day by E. H. Smith and 10% per day by F. McLean.
A quentitative approach to lethality estimates may be made by
using the following:
(1) ‘Instantaneous lethal curve, such es Figure 12.
(2) Total dose and rate of administration.
(3) Biological recovery rate, using 10% per day and assuming
a first order recovery process.
(4) Irreparable recovery fraction, using 20% of total gamma
dosage.
(5) Fission product decay law, I * 1,078, where
I, = radiation dose rate at time ¢
I,
1
t
= radiation dose rate at wit time
= time
The final equation in a fission product fall-out field then pecomes20/
R_,,(t)
eff
to
0.2
z(t) * *o - (2)
1.2 -Bt
+ 0.8t,""e
e
Bt
[ ra*.
3°
19/ McLean, F.C., et al., Extension to Man of Experimental Whole-Rody
Irradiation Studies.
Some Military and Civil Defense Considera-
tions, Military Surgeon 112, 1953.
20/
Latter, A.L., The RAND Corp., Feb. 1955, Personal communication.
66