Ludlum Measurements 16, Техническое руководство

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Model 16 Analyzer Technical Manual
Section 7
Ludlum Measurements, Inc. Page 7-4 July 2011
3. If the input sensitivity is too low, the user could see some
double-pulsing.
4. Wires to the tube may be broken or the crimped connector
could have a loose wire.
Troubleshooting Scintillators
1. Alpha or alpha/beta scintillators are prone to light leaks. They
can be tested for this problem in a dark room or with a bright
light. If a light leak is determined, changing the metalized
polyester window assembly will usually fix the problem.
Note:
When replacing the window, make sure to use a window made
with the same thickness metalized polyester and the same
number of layers as the original window.
2. Verify that the
HV
and input sensitivity are correct. Alpha and
gamma scintillators typically operate from 10-35 mV. High
voltage varies with the photomultiplier tubes (PMT) from as
low as 600 Vdc, to as high as 1400 Vdc.
3. On a gamma scintillator, visually inspect the crystal for
breakage or humidity leakage. Water inside the crystal will turn
it yellow and gradually degrade performance.
4. Check the PMT to see if the photocathode still exists. If the
end of the PMT is clear (not brownish), this indicates a loss of
vacuum, which will render the PMT useless.
Troubleshooting Proportional Detectors
1. Check the
HV
and input sensitivity settings. In gross counting of
alpha particles, gas proportional detectors normally operate at
1250 Vdc and 4 mV threshold. In gross counting of beta or
alpha and beta particles, gas proportional detectors normally
operate at 1650 Vdc and 4 mV threshold. In simultaneous
counting of alpha and beta particles, the
HV
is normally about
1600 Vdc, the alpha threshold is normally 120 mV, and the beta
threshold and window are normally 3.5 mV and 30 mV.