- 33 Span
To the best of our knowledge, except for high level radiation to
vital organs, the life shortening effect of ionizing radiation is the
reault of total body exposure or it may manifest itself in succeeding
generations as a result of genetic damge. There is considerable ex~
perimental data in small mammals on the effecta of fairly large single
event whole body exposure, 1.e., one to two hundred r and more given
either once or repeated.
There ia considerably less information at
smaller dose increments.
In general, it can be said that with large
inerements (100 r or more) there is a curtailment of life expectancy
from the time of exposure of approximately 25% per 1D/50. Thus, a
single dose of 200 r would be expected to reduce an individual's life
expectancy from that point on by roughly 12.5%. (28)
With smaller inore-.__
ments, several] r to upwards of 100 r, the effect in experimental animis
ig less marked.
Probably this can be explained on the basis of a partially
effective reparative process so that the curtailment of life expectancy is
a little less than 14 per 100 r. (4)
If this holds for humans a group
of persons who had accumulated at the age of 45 years approximately 100 r
in increments of several roentgens at a time and who would normally be
expected to live another 25 years would lose an average of 2-3 months
of their life span,