Re: pmt glass radiation

From: Josh R Klein (
Date: Tue May 31 2005 - 22:06:34 CDT

> The key to understanding the radiation is that most gammas that hit the
> scint have already scattered away most of their energy. So the energy
> from those gammas is buried in the pedestal noise. So the question,
> which I don't have an answer to, is how often out of that 400 Hz does pmt
> radiation fake a positron? Looking at the energy from the gammas (those
> plots are in my May 13 software talk) I'm guessing it will only be about
> 1% of the time, for a 4 Hz fake e+ rate (almost all from the Tl).

        Oh, this is pretty good then, since at one untagged neutron/day,
that is an accidental rate of 2*4Hz*(1/day)*100us = 1E-8 Hz, or less than one
event/year. Also, it will be no trouble to trigger at that rate.


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