O'BRIEN, LOWDER, AND SOLON
1000)
©
GOLDSTEIN
AND WILKINS
(REF 4)
APPROXIMATE CALCULATIONS
o.5mev
100-—-
Oo
~
0
MS
zmev
v
Oo
10-—
© io mev
L- MEAN- FREE PATHS
ft
2
|
4
ft
6
[
98
|
0
ft
12
ft
4
ft
6
|
18
|
20
|
22
ft
24
ft
26
Fic. 1. Buildup factors for HO
the medium corresponding to the source energy in em‘, p is the density of the
medium in g/cm, / the distance to a differential emitter dV in units of mean free
path (= y.v, where x is this distance in cm). The system is in spherical coordinates, and @ and @ are the azimuthal and altitudinal angles respectively.
According to Fano (7) the asymptotic form of the buildup function value of
the attenuation coefficient is given by 2". We propose to modify this and write
(2)
b(t) = (1 + at)?
If the use of a single form for the buildup function is to be justified it must be