-4
activity was due to activation of stable elements by neutron capture (for
187
example, Na? or W'').
Using the increased y~activity on the ground as
an index of y3t contamination in exposed forage, pt ingested by cattle
and subsequently appearing in milk can be estimated.
The amount of con-
taminated feed consumed needs to be known unless the correspondence between
y-activity on the ground and yi3l activity in the milk can be established
for a similar incident under the same farming practices.
ments were made by others during the 1962 incident.
Gamma measure-
When (if?) these
data are released it should be possible to estimate the ysl exposure from
previous incidents by this method.
D.
BETA ACTIVITy IN AIR
The Utah State Department of Health began daily measurements of the
gross beta concentration in air at Salt Lake City in 1956.
Winn has made these complete records available to me.
drawn through a filter continuously for about 24 hours.
pads were beta-counted after a suitable wait
Dr. Grant S.
Usually air was
Then the filter
(usually 2-6 hours) to allow
the radon daughters to decay to insignificance relative to the fission
products.
Each peak concentration exceeding 100 picocuries per cubic meter
(pe/m?) was assigned to a preceeding Nevada test.
This arbitrary limit
of 100 pe/m> was low enough to include all important Nevada fallout tra-
jectories at Salt Lake City, but high enough to exclude Pacific and Russian
tests.
Normal background during periods of no testing was about 1-2
pe/m?.
Published meteorological trajectories for 1957 (7) and 1962 SJ were
particularly helpful in assigning air concentrations to particular tests.
Additional air beta measurements have been made in Utah by other