I,
exposure rate at time t
"
Where:
exposure rate at unit time
i
t = time
r = exposure between times t; and t,, where tt 210 seconds
The decay of the residual radiation is expected to vary with device design.
10°
x
103
ho
®
N
NY
——n* (ny)
WN \
108
memew~ Fission Products
x
Ny
\
5 10
Capture -to-Fission Ratio=0.5
SS
”
=i!
oO
107!
uw
(Reference 5)
‘XN
a
x
For ex-
Sy
NQ
N
RO
E
~
=
o 19072
’
o
1073
RN
t
N\
eS
SPA
“~
i074
=
197 §
<
SA
0
'
2
3
4
™
5
Distance from GZ, 10® 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 prescnce of Np?33 would tend to decrease the absolute value of 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 radiation, the variation of intensity with distance is expressed as:
Ip
(1.2)
intensity at distance D
"
a
source intensity
a
ui
Where:
ft
Ip =te _uD
" /4nD?
total linear absorption coefficient (this coefficient generally decreases
with increasing gamma energy)
distance
15