the Project 2.2 instruments. The Conrad detectors were calibrated with the 200-curie
Co® source and the 250-kv X-ray generator. The initial-gamma instruments, the
Gustaves and the photomultiplier feedback-circuit detectors, were calibrated with the
250-kv X-ray and the 2.5-Mev Van de Graaff generator.
The 250-kv X-ray machine was operated at an applied potential of 250 kv, and 10-ma
current.
The X-ray beam was hardened with 1 mm of cadmiumfiltration to give an
effective energy of 190 kev.
The instrument response to this beam was the same as
for Co® since the instrument response was flat to below 125 kev.
The maximum
=—
a
(OM
TT
iM
TT
iM
TT
1M
ns
45V
1M
1M
IM
82K
IM
IM
22M
Phosphor
Figure 2.5 Schematic diagram showing the photomultiplier feedback
circuit of the initial-gamma detector system.
usable-exposure rate attainable with this X-ray generator (consistent with good geometry) was 6,400 r/hr.
The Van de Graaff generator was operated at 1.0, 1.5, and 2.0 Mev, resulting ina
maximum rate of 10° r/hr.
The 200-curie field calibrator was specifically designed for operation under EPG
weather conditions. The main components were the source container and the control
trailer. The source container was made of stainless steel and the plug-and-rise-tube
assembly of Monel metal. The source, inclosed in a double-walled Monel capsule, was
raised and lowered pneumatically and was supported by three spring-loaded pins, one
of which actuated a microswitch to indicate when the source was up.
The Co® was in pellet form and filled a space 0.39 inch in diameter and 1.58 inches
in length. The Monel metal shielding (capsules and rise tube) was 0.33 inch. The
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