-~2-~
somewhat larger due to the short-lived iodine isotopes 1) and the y31
from Pacific and Russian tests.
ysl is a fission product formed in nuclear explosions.
It and
other products are carried in the air downwind from the point of detonation.
When this fallout settles on pastures, the exposed forage becomes
contaminated.
feed.
yi3i appears in the milk of cattle ingesting ysl in their
If man drinks this radioactive milk, pst concentrates in and
irradiates his thyroid gland.
These processes suggest 5 ways for estima-
ting thyroid exposure from yi31
They are listed in decreasing order of
validity in Table 1 and will be discussed separately.
Table 1
WAYS OF ESTIMATING THYROID EXPOSURE
A.
B.
C.
D.
E.
31 in thyroid gland
I
in milk
Gamma activity in pastures
Beta activity in air
Fission yield and fallout trajectory
a. 12°! in THyROD GLAND
The most direct way to evaluate 731 dose to the thyroid is to
measure its I
131
during the Utah I
content by y-ray counting.
131
We measured I
131
in 24 people
incident of 1962, but unfortunately failed to include
infants among this sampling (3) ,
Children 0-2 years old are regarded as
most susceptible to ysl radiation damage because of (a) the small size of
a child's thyroid,
(b) its presumed greater sensitivity to irradiation and
(c} the long post-irradiation life span during which delayed effects could
appear.
A drawback to thyroid counting is that specialized equipment is
required and only a limited number of people can be evaluated.
B.
I
131
IN MILK
Fresh milk is by far the major source of fallout yt for our