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I am interested in obtaining energy resolution data for organic gamma ray scintillation detectors. It is well known that radiation detectors tend to broaden the energy spectrum, which effects the resolution of the detector. For HPGe detectors this broadening is relatively small, where exactly the opposite is true for scintillation detectors.

The broadening of the spectrum can be expressed as a function of the gamma ray energy

$$ FWHM = a + b \sqrt{E+cE^2}, $$

where $a,b$ and $c$ are fit parameters. Typical values are

$$ (a,b,c)=( 0, 0.0691, -0.0951 ) $$

for NaI and for HPGe

$$ (a,b,c)=( -1.4255E-5 , 2.9001E-1, -7.0761E-6). $$

I need similar data for organic scintillators. For instance, for plastic scintillators such as polyvinyltoluene. I am not sure if such data is available. The resolution of such detector would be very poor, but how exactly is a difficult thing to say. This is why I decided to ask the experts here.

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It depends very heavily on the nature of your light collection system (that's true for $\mathrm{NaI}$ as well, but many implementations use the same PMTs-butted-up-against-opposite-sides geometry which results in predictability).

High coverage liquid organic calorimeters like KamLAND can get $b \approx 0.07 \,\mathrm{MeV}^{1/2}$ similar to germanium detectors,1 while two PMTs pointing into a 55-gallon barrel do much worse than that. Solid organic scintilator geometries like hodoscopes often suffer fram addition uncertainty doe to variations in light path making for worse than nominal energy precision.

1 But recall that KamLAND has 1800+ PMTs covering an appreciable fraction of the inner surface area of the sphere.

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  • $\begingroup$ Thank you for the reply. The detector is part of a free release facility. It is not cooled and the resolution is pretty bad. Actually in this case only integral activity in $4\pi$ geometry is measured. I wanted to get some representative values for the coefficients to use in a computer simulation. Unfortunately, I found values only for NaI and HPGe. $\endgroup$
    – Alexander Cska
    Commented Jun 8, 2017 at 19:36
  • $\begingroup$ I'm not aware of a rule of thumb. You should calibrate the detector with a set of known sources.Perhaps Fe-57, the annihilation gamma from a Na-22, Co-60, and one or two others chosen for lines in the energy range you care about. $\endgroup$
    – dmckee --- ex-moderator kitten
    Commented Jun 8, 2017 at 22:10

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