Ludlum Measurements 2241-3, Руководство пользователя

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Model 2241-3 & 3i Technical Manual
Section 8
Ludlum Measurements, Inc. Page 8-9 January 2016
For most GM detectors, set
DISC
for 30-40 millivolts and adjust
HV
to the
GM detector recommended high voltage. Most GM detectors operate at
900 volts, although some miniature detectors operate at 450-550 volts. If a
recommended setting is unavailable, plot count rate versus HV to produce a
plateau graph. Adjust the
HV
for 25-50 volts above the knee or start of the
plateau. For mixed detector use, both sensitivity and high voltage may be
tailored for other detectors as long as the GM detector is operated within
the recommended voltage range. Caution must be observed in lowering the
input sensitivity to ensure that the counter does not double or multi-pulse.
Alpha Air-Proportional Detectors
: For air proportional alpha detectors, set
the
DISC
for 2 millivolt discrimination. Adjust
HV
until the detector just
breaks down (shown by a rapid increase of count rate without a source
present). Measure the HV output, then decrease the
HV
setting to operate
100 volts below breakdown.
Proportional Detectors
: For proportional detectors, set the
DISC
control for
2-millivolt discrimination (near maximum clockwise). Expose the detector
to a check source and plot count rate versus HV, similar to the one in the
figure below. Refine the
HV
adjustment for optimum source efficiency with
a minimum acceptable background count.
Scintillators
: Set the
DISC
for 10 millivolts. Plot background and
source counts versus HV to produce a plateau graph similar to the
one in the figure. Adjust the
HV
to 25-50 volts above the knee or
start of the plateau. This provides the most stable operating point
for the detector.
C
OUNTS PER MINUTE
(C/
M
) C
ALIBRATION
This procedure will set up the Model 2241-3 for the Counts/minute (C/m)
mode of operation. Refer to Section 8, (Page 8-2 and following) for more
information on setup parameter variables.
A Ludlum Model 500 Pulser or equivalent is required. If the pulser does not
have a high-voltage display, use a high-impedance voltmeter with at least
1000 megohms input resistance to measure the detector high voltage.