for the
finite extension of the source,
it was necessary
to perform tne followings numerical integration:
x
7
a
K= J, ° Krdr
J
Ts
rar
where r, is the radius of tne extended source,
Tne
determination of K is somewhat simplified by the fact
that X is constant over part of the ranse of r,
K = a”/l6(z = b/2)?
~-
i.e.:
(osr <2/2)
~
where a is the collimator diameter, b the collimator
thickness and z the distance from the center of the
collimator to the source.
When r is larger than a/2
and smaller than az/b, K is some function of r determined
grephically by intervolation and derived from Fig. 9 of
Mather's paper.
For values of r equal to or larger than
az/b, K vanishes.
To make the reduction factor X, enersy dependent,
i.e.,to include penetration effects, an approximation?
is used.
Penetration is a function of gamma-ray energy
and the increased averture due to increased energy is
approximately the same as the geometrical aperture of
an opaque collimator two mean-free-patns less tnick.
For the particular geometry involved in the present
experiment, the values of the machine parameters are as
follows:
_
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