Lat40,
Accordingly, a chemical separation of Bal40 way made froma -
fallout sample.
Nine days after the separation, Ral40 had come to
transient equilibrium and a scintillation spectrometer pulse-height
distribution was obtained. This distribution was used in the analysis
of all the fallout spectra.
,
Upon eubtractJog of bhe Rat40 and 1al40, a peak at about 750
kev was founde Since Zr?5~
vielded only one major photo~-peak at
about 750 kev with only an insignificant peak at 235 kev, a standard
curve for Zr95-Nb95 was obtained and a subtraction procedure similar
to that for Bal40-12140 wes used. Similarly, a peak at 500 kev was
found after the subtraction of Bal4[-pal40
and Z2r95-Nb95, This peak
was assigned to Rul03, A standard curve was also obtained for Rul03,
Two standard spectrometer curves
at the two amplifier gains used for
the fallout spectra were obtained for each of the isotopes mentioned.
At gamma-ray erergies of a few hundred kilovolts or mre, two
pulse-height distributions per gamma ray are obtained, a bell=shaped
distribution called a photo-peak and a broad, nearly flat, distribution due to Compton effect. At lower erergies the amount of Compton
effect becomes increasingly small compared to photo-effect,so that at
about 100 kev the Compton effect is negligible. In addition, there
are secondary scattering effects which throw counts normally in the
Compton distribution into the photo-peak which for low gamma-ray
energies results in a great reduction in the theoretical Compton dis~
tribution. This effect is illustrated in Fig. 3626 by the theoretical
and experimental curves of the ratio of the photo~peak to total area.
At the low gamma-ray energies the procedure was to work first
with the highest energy photo=peak left from the subtraction of known
isotopes.
The photo-peak was fitted with a Gaussian curve and its
area determined. The Compton effect is found from the experimental
curve of ratio of photo=peak to total peak. The Compton distribution
was then subtracted from the peaks of lower energy and the procedure
repeated.
At energies below about 200 kev the photo-neak of the various
gamma rays overlapped. As an aid in the subtraction procedure it was
assumed that the width of the peaks at one=half maximum followed the
ES law, 18/ where E is the energy of the gamm2 ray procucing the
photo-peak. Thus, three conditions were imposed upon the photo-peaks,
(1) all available counts were used, (2) the peaks were Gaussian in
shape, and (3) the width of the peak followed the Ed law.
3083
Detection Efficiency of the Scintillation Spectrometer
Assume that the gamm-ray souwce emits gamm rays of one
energy only.
crystal are
The number, Ny, of these gamma rays detected by the
,
Nh 2 HoeBa . oo nar ia) b.
where
= gource strangth
79
(3222)