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Forum: Processes Involving Optical Photons
Re: Question How to explain energy spectra of emmited photons from a scintillator, in my code? (Mehdi Abbasian Motlagh)
Date: 01 May, 2012
From: Gumplinger Peter <Gumplinger Peter>

> 1. How translate Geant4 these values in such array? Only one by one, or
> not? I mean, for example, if energy of a photon be 2.035*eV (very close
> to 2.034*eV), do Geant4 accept it as a value of the array? From C++, I
> know the answer in NO.

No.

The user provides the (relataive) strength of the emmission spectrum at a finite number of photon energies. You can pick those out from your continuous spectrum as best and accurate as you can. The program will then numerically integrate this array, normalize it to one, and store it in a new array. When a scintillation photon energy is to be sampled (throwing a number between 0->1) the corresponding photon energy is found by interpolating the integral array. The interpolation used to be linear but is now quadratic. This will result in a photon energy not identical to any of your array input values.

The key word here is 'Inverse Transform Sampling' of an empirical density function at discrete points.

> 2. Perhaps because matter of origin of these photons is a scintillator,
> so only "some energies" will release; Is that correct?

No, the program will produce a continuous spectrum that smoothly approaches your input the more points you provide.

> 3. Please observe attached pic, about NE102A scintillator The emission
> spectra is "continuous". How to explain wavelengths of emitted photons,
> in my code as an array?

As I said, just pick as many points from the spectrum as you feel necessary to describe it in sufficient detail, put the energy and emission strength in an array and feed it to the program. To test how well the program reproduces your spectrum you can histogram the scintillation photon energy the program has sampled. If you are not happy with the representation you will have to increase your number of points or where you choose to pick out the points. Obviously, you'll want points at peaks and valleys of your spectrum

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1 Ok: Re: How to explain energy spectra of emmited photons from a scintillator, in my code?   (Mehdi Abbasian Motlagh - 06 May, 2012)
(_ Question: Re: How to explain energy spectra of emmited photons from a scintillator, in my code?   (Mehdi Abbasian Motlagh - 15 May, 2012)
(_ Feedback: Re: How to explain energy spectra of emmited photons from a scintillator, in my code?   (Gumplinger Peter - 15 May, 2012)
(_ Question: Re: How to explain energy spectra of emmited photons from a scintillator, in my code?   (Mehdi Abbasian Motlagh - 16 May, 2012)
(_ Feedback: Re: How to explain energy spectra of emmited photons from a scintillator, in my code?   (Gumplinger Peter - 16 May, 2012)
(_ Question: Re: How to explain energy spectra of emmited photons from a scintillator, in my code?   (Mehdi Abbasian Motlagh - 21 May, 2012)
(_ Feedback: Re: How to explain energy spectra of emmited photons from a scintillator, in my code?   (Gumplinger Peter - 22 May, 2012)
(_ Ok: Re: How to explain energy spectra of emmited photons from a scintillator, in my code?   (Mehdi Abbasian Motlagh - 23 May, 2012)
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