Re: Scint Counting

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

Bruce,

We use LSC for wipe tests of sealed sources.  We calibrated with
Np-237.  Our efficiency was 100 % within our knowledge of the 
standard.  One would expect the efficiency for Uranium to be
much greater than 100% for the reasons you state.  I don't
have a good explanation for why Am-241 would be much above
100% (you might get a little Np-237 growing in, but not much).
My only guess would be that the standard was intended as a gamma
and x-ray standard and has other alpha-beta contaminants.  You
could try to calibrate the Am-241 with a gamma spectroscopy system,
or look at the LSC spectrum if you can get access to a LSC with
spectroscopy capability.  We have an LSC that does have spectroscopy
capability.  It is interesting that the apparent energy of alphas
is shifted down by a factor of 6 to 8.  This is why you can
count alphas even though most LSCs have Upper level discriminators
set to about 2 MeV.

Dale Boyce
dale@radpro.uchicago.edu