calibrated Hz203 source was used.
This use of the calibrated
standards allowed a constant check to be made on the stabil-
ity of the equipment (see Appendix I).
ANALYSIS OF DATA
The pulse hetght spectrum of a monoenergetic gamma ray
consists of a total absorption peak and continuous "Compton"
a
distribution.
If the energy of the gamma ray is above 1.02
Mev, pair production begins to take place and one of two
secondary vesks is contributed to, according to whether one
een eee
or both of the annihilation quanta escape from the crystal.
The peaks all have the shape of normal distribution functions
or "Gaussians" because of the statistical nature of the
photoelectric effect and the secondary-emission phenomenon
inherent in the operation of a photomultiplier tube.
If two incident gamma energies are present, the lower
is superimposed additively on the continuous Compton dis-
tribution of the higher.
An example of the idealized
adiition of three different monoenergetic gamma rays is
shown in Fig. 3.
As more gamma energies are added the
resulting confusion becomes progressively worse.
higher energies are above 1.02 Mev,
(If the
the presence of
annihilation radiation escape peaks further complicates
the spectrum and thus
the analysis.)
10