superimposition of the suitable Gaussian on the pulse height
spectrum with the aid of a frosted~glass light table, the
area of each total absorption peak was determined without
tedious measuring with @ planimeter.
For errors incurred
by this measuring system see the section on errors.
.
The ratio of absolute photon intensity to total absorption peak area 2s some function of the energy of the gamma
ray, I/A = T{E). For the determination of the graphical
relationship between I/A and E, it was first necessary to
-
a@scertain further machine parameters and other energydependent factors...
;
(zp)
These were:
Crystal
interaction probability, v.
This
~~
is simply the fraction of incident photons of a par-
ticular energy which interacts in the crystal and is
pees
given by:.
v= 1 -exp(-n,X)
where HW, is the total linear absorption coefficient
for gamna raya in sodium 1odide® and X is the crystal
length.
For a@ crystal 20.16 cm (4 inches) in length,
‘vy versus E is shown plotted in Fig. §.
(2).
Peak-to-total ratio, w.
This
factor iis deter-
Mined experimentally byrecording the spectra of several
sources of known gamma energy and measuring areas of the
total absorption peaks and the areas under the total spectrum,
The rretios of these areas plotted against energy
14