[Gate-users] Simulating Beta Particles - Problems

[Amy Meldrum]

Hello all,

I am trying to simulate a beta source with plastic scintillators and
counting the photons that make it to a PMT. However, there are some aspects
of my initial results that do not make sense to me, and do not seem correct.

The beta sources I have tried to simulate include C-14, Cl-36, and
Sr-90/Y-90. For all of these isotopes, my 'pulse height spectrum' I get at
my PMT is very highly skewed to the left - many, many instances of
detecting only a handful of optical photons that were produced, and very
few 'counts' of higher energy pulses. Related to this issue is that the max
number of photons I seem to collect at my PMT per parent particle is
extremely low compared to what is likely generated by the beta particle.
For example, the maximum photons I collect from Cl-36 is about 2% of the
maximum number of photons that are generated from the scintillator. I feel
like There should be at least SOME instances where more than 2% of the
originally generated photons from a parent particle are collected at the
PMT.

And lastly, my simulated data for C-14 compares fairly well against my
experimental data despite some of these issues. Yet my simulated data for
Cl-36 and Sr-90/Y-90 are vastly different from my experimental data. I
suspect it might have something to do with how my beta source is being
defined. Has anyone simulated Cl-36 or Sr-90/Y-90?

I have tried so many things to try and correct my simulations to be more
like my experimental data, but I am running out of ideas. Any help or
advice for these problems I'm having would be greatly appreciated. I am
trying to use these simulations for my graduate research.

-Amy M
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