‘for the finite extension of the source, it was necessary
to perform the followings numerical intesration:
f*
Fe Krdr
[*
o
rar
LC
where Yr, is the radius of the extended source,
Tne
determination of K is somewhat simplified by the fact
that K is constant over part of the ranse of r, 1.e.:
K = e2/l6(z = b/2)®
———
(or <2/2).
where @ 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
graphically 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 XK, enersy dependent,
i.e.,to include penetration effects, an approximation?
is used.
Penetration is a function of gamma-ray energy
and the increased aperture due to increased energy is
‘approximately the same as the geometrical aperture of
an opaque collimator two mean-freeepatns less tnick.
For the particular geometry involved in the present
experiment, the values of the machine parameters are as
follows:
_
13