Ludlum Measurements 177, Руководство пользователя

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Model 177
Technical Manual
Section 7
Ludlum Measurements, Inc. Page 7-3 October 2018
2. Check the HV. For most GM tubes, the voltage is normally 900
Vdc, or 460-550 Vdc for “peanut” tubes (Ludlum Model 133
series).
3. If the input sensitivity is too low, the user could see some
double-pulsing. See Page 4-3, “
DISCR
” for further information
on sensitivity/discrimination control.
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 aluminized
polyester window assembly will usually fix the problem.
Note:
When replacing the window, make sure to use a window made
with the same thickness of aluminized 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 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.