In order to untangle these overlapping distributions
and arrive at the basic gamma lines, a method of graphical
unfolding is used.
One starts at the highest-energy peak
present (assuming that it is not superimposed on the Compton
distribution of a still higher energy) and measures the area
under the total absorption peak.
Then knowing the peak-to-
total ratio (the method of ascertaining this ratio is described later) for each energy, one can calculate the area
of the Compton distribution.
After drawing in the Compton
distribution of the highest energy, the process is repeated
for the next highest-energy peak using the Compton of the “«
highest energy as a base line.
The process is continued
until all the energies present are analyzed.
Knowing the
resolution of the instrument for each energy,
one can tell
whether there is only one enerrsy contributing to a particular peak, or two or more unresolved energies present, by
the width of the peak.
The resolution (width of a peak in
kev at half-maximum height) was determined by measuring the
resolution for several total absorption peaks of known energy
and plotting the results (Fig. 4).
In order to facilitate the measuring of the photopeak
areas and to aid in estimating the relative size of two
unresolved peaks,a series of Gaussian curves of predetermined
widths, various heights and,thus, known areas, were drawn by
means of a Gaussian curve generator
12
(see Appendix II).
By