P-32 LSC efficiency -Reply

[Luke.Mccormick@MRD01.usace.army.mil]

The threshold energy of the Cerenkov radiation is a function
of the refractive index of the medium. for n between 1 and 1.8
the threshold energy for the electron to produce cerenkov will
be greater than 100 keV (greater than H-3 18. keV cutoff on
the LSC) .  where n is less than 1.25 the threshold will be
above 300 keV (greater than the C-14 cutoff).  Then number
of photons per electron will be below about 300 for P-32 max.
energy betas. Only about 0.001 of the electrons energy is
turned into photons.  
Counting using an LSC is possible for Cerenkov but there are
some fine tunings that need to be done to use it efficiently.
(wavelength shifters etc.)  I'm not sure why or how you came
up with the 150% but I wouldn't attribute it to Cerenkov.
Having assembled a few P-32 quench curves, I remember
that the curves are not simple functions because of the wide
range of energies involved. The curve had a number of
maxima and minima between 10 and 1760 keV.  (The
quench curve takes into account more than just color and
chemical quenching) .  Knoll had some information on
Cerenkov counting.  Packard also put out some info.