The above counting system had a coincidence loss of about 2 per
cent at 1,000,000 c/m and 7 per cent at 2,000,000 c/m as determined by
the split sample method.
The voltage plateau extended atout 200 v with
a slope around 2 per cent per 100 v.
However, the extent and quality
of the plateau was influenced by tne energy of the incident photon.
The discriminetor and high voltege settings were determined fromda&ta
taken on Cdl09 (80 ke gamma) and Co® (1,1 and 1.3 Mev ganmas) sources
so that both the high and low energy photons were on some part of both
plateaus.
The calculated energy response of the system is shown in Mig.2.1.
The discriminetor and high voltage, when determined as described above,
have little effect on the energy response of the system. The curve ia
a combined effect of aluminum absorber and crystal capture efficiency
showing a virtual cut off at 50 kev due to the adscrber, a fall in
efficiency rbout 200 kev due to the thin crystal, and a maximm efficiency
at about 125 kev.
24364
Gamma Analyzer
A 10-channel alpba energy analyzer (using an alpha ionization
chamter) was sent to the site for planned alpha analysis,
After Shot 1,
when it became evident that the requirements of sample collection and
delivery could not be fulfilled, this analyzer was converted to a gamma
analyzer. To achieve this, certain time constants in the analyzer were
reduced, a scintillation detector-preamplifier was constructed, and an
auxiliary high-voltage suvply was provided. The detector consisted of'
a Dumont 6292 phototube and a sodium iodide crystal 1 in. in diameter
and 1 in. long. The detector was attached directly to the preamplifier
(nominel gain of 100) and the whole mounted within a commercial lead
shield which was covered with 2-in. thick lead bricks to minimize the
background.
The analyzer itself had an interne] gain of 100, followed by o
window amplifier and 10 different discriminetors, each with its ow
scaling xd registering circuits. The discriminetor circuitry was the
Johnstone design.{5,/ The long-term stability and linearity of the system were excellent as long as the ambient tempereture was kept below
80°F; the resolution was about 10 per cent under the usual operating
conditions. An external filter was provided to reduce the ripple in the
high voltage supplied by a Navy Model AN-ZDR/9 acaling unit.
2.3.5
Emigsion Spectrograph
An ARL 2=meter grating spectrograph
was used for exploratory
exemination of samples. A special chamber?/was used to collect the
redicactive debris from the arced samples.
2.326
Speotrophotometerg
A Beckman Model 9200 flame photometer was used for the analysis
of the major constituents in coral and sea water. This photometer was
equipped with a special devicel3/to collect the combustion products from
22