(1). Overlapping Fallout Patterns.
The average n can be used to compute nuclear data in areas of nonstandard decay created by a single
nuclear burst. When dealing with overlapping contaminated areas caused by more than one nuclear
burst using an average n value for the overall pattern could lead to serious error. Fallout produced by
more than one explosion will normally have different decay exponents at different locations within the
area.
The following methods are applicable to two or more overlapping fallout patterns. The choice of
method is dependent upon whether enough is known about each burst to separate the dose rates
contributed by each.
(2). Sufficient Information Known to Permit Separation of Different Contributing Dose
Rates.
Separate the contributing dose rates. This requires that H-hour of each burst be known and that two or
more dose rate readings be available for the location of interest after the fallout peaks and prior to the
arrival of new fallout. Normal procedures for calculating the decay exponent n for each contributor at
the location of interest are used. Calculate the total dose rate for a specific location at any time in the
future by calculating the dose rate at the desired future time for each contributor separately and adding
the results. Repeat this process for each location of interest within the overlapping fallout patterns.
EXAMPLE PROBLEM. At a location where fallout has been received from two detonations, one at
0800 hours and one at 1100 hours, the following dose rate readings were recorded:
Time
Dose rate cGyph
0830
160
0900
100
0930
61
1000
44
1100
27
1130
462
1200
219
1300
108
Predict the dose rates at this location for 0800 hours in 24 and 48 hours (H + 24 and H + 48 hours) after
the first burst.
Solution: Sufficient data are available to separate the two contributors.
6-15
CM2308
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