I have a setup where I'm detecting neutrons from an AmBe and Cf-252 source using a scintillation detector optically glued to a PMT at 1.5KV HV. The PMT feeds to a amplifier. Now, when I'm using a gamma source, and an amplifier gain of 100x times, the dead time is about 1-2%, no more than 3%. But when I use the AmBe and Cf-252 source on the same gain, the dead time is 80%. What is the relation between gain and dead time? Is it because the gain causes voltage spike which causes dead time, especially because the neutrons cause a greater energy deposition in the scintillator and therefore a greater light output per particle? Any help is appreciated!

  • $\begingroup$ 1/ Look at the osciloscope. 2/ check the gamm spectra for 100x gain - are they meaningful? $\endgroup$
    – jaromrax
    May 30, 2017 at 7:20
  • $\begingroup$ What is the count rate in each case? Compare that with the specs... $\endgroup$
    – Jon Custer
    May 30, 2017 at 13:08
  • $\begingroup$ Previously: physics.stackexchange.com/q/334281/44126 $\endgroup$
    – rob
    May 30, 2017 at 15:37
  • $\begingroup$ how did you determine deadtime? $\endgroup$
    – Natsfan
    Jun 3, 2017 at 19:15
  • $\begingroup$ Are you sure the neutrons have a larger energy deposition? I don't recall the neutron energy of the sources you are using nor the gamma ray energies since source was unnamed. The gamma rays could be much higher energies. $\endgroup$
    – Natsfan
    Jun 5, 2017 at 20:05

1 Answer 1


The flux of the neutron sources is probably much greater than that of the gamma source. The detector is getting more signals than it can handle. You should try increasing distance from neutron sources to detector and seeing how that effects your dead time. How did you determine deadtime?


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