Re: P-32 LSC efficiency

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

I don't have the numbers handy, but the Cerenkov and scintillation
light are both emitted very rapidly.  I don't think an LSC can
time resolve the two.  My first guess as to what is happening,
assuming the P-32 activity is known correctly, is that you are getting
some amount of multiple pulsing.  Photomultipliers will sometimes
have after pulses which have periods characteristic of the particular
tube.  If both PM's are multiple pulsing, and the period permits pulses
after the coincidence gate closes, you will see higher event rates
than you would expect.  If your Beckman has the ability in diagnostic
mode to look at PM singles rates, take a look at those.  You might
also want to take a look at the amplifier outputs on an oscilloscope
to see if you are getting afterpulses.  Some models of LSC's use
after pulses to discriminate between beta and alpha events.

Dale Boyce
dale@radpro.uchicago.edu