100
30
RELATIVE ACTIVITY
4,0 SHOT 6 WATER SAMPLES
COUNTED ON UDR-9 COUNTER
0.05
0.01
10
100
1000
TIME AFTER DETONATION {MIN}
10,000
1oop00
Figure 4.1 Calculated decay (d/m) for Shot 6 fallout.
mined for Shot 6.
The method of calculation is described elsewhere (Reference 3).
Two experimentally determined decay curves covering short time periods fitted
this calculated curve well.
4.2
CALCULATION OF A—GAMMA ACTIVITY RECEIVED
PER UNIT AREA OF THE OCEAN SURFACE
A is determined as follows:
Let C = gamma counts min-!.
Z = depth in cm to which the fallout has become mixed.
If C is assumed to be constant with depth, or at least represents an average value then:
A=CZ
.
(4.5)
No measurements of Z were made for Shot 6. Since it is probable the fallout had
not penetrated to the thermocline at the time most of the surface samples were taken,
an estimate of Z was based upon the following:
1. A mixing function estimated from Shot 5 data (Figure 4.2) which provides Z as
a function of time of mixing tm.
2. An estimated time of arrival t, of fallout as a function of distance, 7 from surface
zero based upon calculated small particle trajectories (Reference 4). and meteorological
data (Figure 4.3).
58