3
_~” “Fig:.1. Calculatedcumulative strontium-90 fallout in millicuries per square mile as of June 1957.
debris. However,a method of ‘compuia- .
tion has been devised by which the latter
“difficulty can be minimized. _
‘months, and these sums were added for
the desired period of accumulatien.
The assignment of activity on a given
day tothe most recent ‘test was a reason-
able approximation during the period of
tropospheric fallout. The deviations between -gummed-film estimates and radiochemical analyses became larger as the
contribution from stratospheric fallout
increased. To improve the estimation of
Methods of Computation
The adhesive-coated films, which have
been exposed for 24 hours, are shipped
to the U.S. Atomic Energy Commission’s Health and Safety Laboratory in | strontium-90, a system was devised which
New York. The total beta activity of the _ takes stratospheric debris into account,
Tests of this simplified model yielded
ashed samples is measured and corrected
values that are in good agreement with
by the 63 percent efficiency factor. The
computations from more complex modstrontium-90 component of the fallout
is calculated from modified Hunter and
Ballon (3) ratios. In addition, an estimate of the infinity external gamma dose
an air is made from the beta activity (4).
The original calculations of strontium90 deposition from measurements of
‘total beta activity on ashed gummed:film samples were performed as follows:
1) The activity measured on a given
sampling day was attributed to the test
immediately preceding that sampling
: els...This method, “whic
plied to data subsequent to-May 1956,
is as follows,
1) Estimates of the yields of total
fission products and of strontium-90 are
obtained fot.each weapon test.
2) The total fission-productyield for
each test is added to the calculated fis-’
sion-product residue from previoustests.’
(The ¢-2-? law is used for decaying total
fission product activity.)
” 3) The strontium-90 activity <from
each test is added to the accumulated
strontium-90 activity from previous tests,
4) For each sampling day, the stron-
Table 2, Comparison of strontium-90 estimates from gummed-film with radiochemical
analysis of monthly pot collections,
~ _
-day. -
2) The measured activity on the
counting day was extrapolated to a fixed
day hy the formula
A=Ai.
3) The strontium-90 fraction of the
total beta activity on this day was taken
from modified Hunter and Ballou curves.
4) The strontium-90 activity values
for the individual days were summed by
BEE KRBE
-
Period of
,
observation
Total Sr
(me/mi*)
Ratio
Low
0.90
0.32
2.2
11
Pittsburgh
10.6
1.14
Chicago
0.62
2.5
1.2
1.0
1.9
14
il
3.3
iB
0.78
24
14
0.82
3.7
"7
0.64
5.5
1.6
Pots
12.3
13.7
5/56-6/57
12.1
12/56-6/57
6.3
5/36-6/57
12/56-6/57
- 15.4
12/56-6/57
3.5
10/56-6/57
5.6
8/56~6/57
6.7
tra/pot
,
High
Film
film/pot
i
Monthly ratios
New York City
4.6
1.37
Salt Lake City
91
1.66
Los Angeles
3.1
1.13
Hiroshima
3.7
1.51
Nagasaki
5.5
1.22
mean
.