electron flow that was directly proportional to the amount of light given off by the phosphor.
The plastic scintillant responded to energies above 130 kev.
While the responses of the two
phosphors overlapped, the additive error was only 3 to 4 percent in the neighborhood of this
dividing line. Figure 2.6 is a schematic of the circuit associated with scintillation probe and
photomultiplier.
In the compressor-oscillator-amplifier unit, the direct currentfrom the scintillation probe
was converted to pulses by the blocking-oscillator tube (V-1 in Figure 2.7), which operated in a
conventional manner.
The compression circuit regulated the oscillator repetition rate by vary-
ing the bias on the tube (V-2 in Figure 2.7), when the tube was conducting, to supply the current
demanded by the photomultiplier. Advantage was taken of the low-voltage characteristics of a
low-mu triode to provide a logarithmic response in the compression circuit. The oscillator
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Figure 2.6 Kaiser dose-rate instrument, gamma Scintillation probe.
output was taken from the plate of V-1 and applied to the grid of the amplifier tube (V-3 in Figure 2.7). The pulse from the oscillator drove the amplifier tube to cutoff and resulted in an
output of 90 volts.
The amplifier output was then applied to the recorder.
The power supply of the instrument furnished 28, 150, and 1,000 volts de to the system.
The
28 volts was. applied through the center tap of a transformer to the plates of six 26A7-GT tubes
in parallel. One of the transformer secondaries supplied 180 volts ac to V-7 (Figure 2.8) for
rectification and to V-8,-9, and -10 for regulation to 150 volts de. The 640~volt output of the
other secondary was rectified and doubled through the action of two sets of seven germanium
rectifiers. Tubes V-9 and V-10 regulated this potential to —1,000 volts.
Several modifications were required in the original instruments to obtain the characteristics
necessary for this application.
to decrease its sensitivity.
Thg plastic scintillant’s size was decreased and its shape changed
This was necessary to obtain the 0.05-to-500-ua output of the orig-
inal design in spite of higher levels of incident gamma flux.
The output-frequency range of the
blocking-oscillator circuit was increased by a factor of forty to 2,000 to 12,000 cps, to provide
a 1-msec response time.
To realize this response time, a quality Ampex magnetic-tape re-
corder was substituted for the wire recorder in the original instrument.
The compressor circuit output was checked for linearity with microampere inputs. The circuit response for inputs corresponding to dose rates up to 40,000 r/hr was linearfor a typical
instrument.
The instruments were also subjected to a burst from the Godiva II assembly at
18