LUDLUM MODEL 3, Technical Manual

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Model 3 Technical Manual
Section 7
Ludlum Measurements, Inc. Page 7-4 April 2016
3. If the input sensitivity is too low, the user could see some
double-pulsing (where the instrument “counts” a single pulse
from the detector multiple times).
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 Mylar window
assembly will usually fix the problem.
Note:
When replacing the window, make sure to use a window
made with the same thickness Mylar 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.