Re: Repairing an alpha beta counter

["Dale E. Boyce" <dale@radpro.uchicago.edu>]

Gary,

You have checked most of the obvious things.  Anode wires, especially in
old detectors will grow "whiskers", double ckeck under magnification
for irregularities in the wire.  Check the electronics with a pulser.
Double check your counting gas.  Occassionally, a bad tank with an
impurity will cause problems like you describe.  Bad gas is rare, but
a little air in the gas will mess up the plateau.  The high count
rate and no plateau may indicate multiple pulsing.  Pure argon without
any methane could cause this.  That is another screw up that could
happen when the gas was mixed.  A couple of research groups I used
to work with used pure methane instead of P10 in gas flow counters.
They run at significantly higher voltage than with P10, but gave
really nice plateaus.  Also, we reinstrumented a set of Sharp / Beckman
Low Beta detectors with standard NIM electronics for significantly
less than a new Low Beta system.  We didn't do the sample changer though.
If you would like details let me know.  Hope this helps.

Dale
dale@radpro.uchicago.edu