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Forum: Processes Involving Optical Photons
Re: Question Optical Photons Spectrum (Dragos Constantin)
Date: 21 Jan, 2011
From: Gumplinger Peter <Gumplinger Peter>

Hello Dragos,

By 'linearly interpolating between bins' I simply mean to say that the strength of the spectrum in a bin is the average of the strenghts you specify at the bin's edges; e.g. half way in between.

You see, the program needs to first decide in which bin the scintillation photon should be sampled. It does that by comparing the average strengths of each of the bins relative to each other. However, and that's confusing you, the photon energy within a bin is sampled random with no weighting as to the strength at the bin's edges and that's why you get a flat distribution of sampled photons within a bin. If that's not satisfactory in your situation you'll need to define your photon spectrum at finer intervals, e.g. at more points. Mind you that many optical properties like the index of refraction or the photo-cathode photon efficiencies aren't seep functions of photon energy.

But you do have a point in that the present code is rather rudimentary and should be replaced by a more clever routine that knows how to sample an empirical spectrum given at finite number of points so that the result is a smooth spectrum, linear or even spline fitted, and succeeds without a great penalty in performance.

There are other places in Geant4 where this is already done and there has been discussion replacing the 'first-hour' Geant4 code (G4MaterialPropertyVector and related classes) with this refined code.

Peter

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1 More: Re: Optical Photons Spectrum   (Gumplinger Peter - 21 Jan, 2011)
(_ More: Re: Optical Photons Spectrum   (Gumplinger Peter - 21 Jan, 2011)
1 Idea: Re: Optical Photons Spectrum   (Benton Pahlka - 21 Jan, 2011)
1 Feedback: Re: Optical Photons Spectrum   (Dragos Constantin - 26 Jan, 2011)
2 Feedback: Re: Optical Photons Spectrum   (Dragos Constantin - 26 Jan, 2011)
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