Where:
i = exposure rate at time t
I, = exposure rate at unit time
t = time
r = exposurebetween times t, and t,, where t; 210 seconds
The decay of the residual radiation is expected to vary with device design.
10%
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Distance from GZ, (0° yds
Figure 1.) Graph of gamma exposure versus distance for a one kt surface
burst. This illustration shows the contribution from fission-product gammas.
ample, the presence of Np?38 would tend to decrease the absolute value af the decay
exponent for a period of time.
1.3.3 .Absorption in Air. The absorption of unscattered gamma radiation in air is
exponential with distance. From a point source of mono-~energetic radiztion, the variation of intersity with distance is expressed as:
_yD
Ip = te" /anv?
Where:
(1.2)
Ip = intensity at distance D
ly = source intensity
u = total linear absorption coefficient (this coefficient generally decreases
with increasing gamma energy)
DN = distance
15