Re: Ni-63 portable detector -Reply

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

Paul's comment about voltage sensitivity is accurate in my experience.
I haven't used plastic scintillators for low energy betas, but have
used them for higher energy beta coincidence.  The stuff I was using
did not plateau very well.  There are several things operating that
prevent good plateaus and therefore stable efficiency determination.
One the very large change in gain of PMT's for small voltage changes.
Two with a gas flow the beta doesn't necessarily need to make many
ionization to be counted, but with a scintillator you have a strong
dependence on the number of photons made in the scintillator on
the probability of a photon or photons reaching the PMT.  This is
magnified by the gain sensitivity.  These two factors combine to
actually make the angular acceptance change as a function of gain/energy
in scintillators.

Dale Boyce
dale@radpro.uchicago.edu