I have a fast-neutron scintillator which also is sensitive to gammas (much less so, though). When I connect it to a SiPM instead of a PMT, the gamma pulses (obtained from performing pulse shape discirmination) are almost negligible compared to neutron pulses. Under what circumstances could it be possible that a SiPM responds differently to scintillation light from neutrons vs gammas?

  • $\begingroup$ What kind of scintillator is more efficient in detecting fast neutrons than gamma-rays? $\endgroup$ – jmh Sep 26 '19 at 0:51
  • $\begingroup$ Where are the neutrons you detect coming from? Do you make them during a reaction? Maybe the reason for so few gamma rays is due to a small number produced. Most scintillators are much more efficient in detecting gamma rays than fast neutrons. Do you have shielding around your detector? $\endgroup$ – jmh Sep 26 '19 at 1:02

One possible reason is the time it takes the particle to dump energy in the scintillator. This will affect the rise time of the pulse. The neutrons must scatter off a nucleus to be detected while a gamma-ray interacts with the atoms in the scintillator which are much larger than nuclei of course.

  • $\begingroup$ Thank you for this bit. It's an interesting bit to think about. However, the crystal in both cases remains the same, just differs in how the light is read out (PMT vs. SiPM). That is where I'm left wondering, why is the SiPM acting far differently from a PMT towards gammas as compared to neutrons? To answer your previous comment, I am using a fast neutron scitnillator that by itself has a lower sensitivity towrads gammas. The neutrons have an (n,p) reaction in my crystal which then gets converted to light. $\endgroup$ – Betsy Sep 30 '19 at 18:18
  • $\begingroup$ That's a good question I'm afraid I can't answer unless its something simple like SiPMs are not sensitive to rise time of the pulse. $\endgroup$ – jmh Sep 30 '19 at 19:30

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