Re: set diffusion coefficient with Cherenkov photon production ON

From: Francesco Cerutti <>
Date: Sun, 13 Jan 2013 15:47:34 +0100

Dear Zhiqiu Li

the diffusion coefficient input through the card [see next thread for the
answer to your question concerning its meaning and value] applies to the
central angular frequency - as indicated in the manual - and is then
scaled over the frequency range by FLUKA assuming proportionality with the
frequency 4th power as expected from theory. Conversely, your dffcff user
routine returns a constant value for every frequency. That's why the two
photon spectra differ.

Kind regards


Francesco Cerutti
CH-1211 Geneva 23
tel. ++41 22 7678962
fax ++41 22 7668854

On Thu, 3 Jan 2013, zhiqiu li wrote:

> Dear group,
> I just came across a strange mistake with OPT-PROP, when I simulated
> Cherenkov photon production by electron beam incident on a water cube.
> I firstly set Diffusion Coefficient = 1.22, and ran the simulation and
> got photon spectrum with USRBDX.
> Then I set Diffusion Coefficient = -100, hoping that FLUKA would call
> function DFFCFF for diffusion coefficient. I have modified DFFCFF.F
> and linked to FLUKA, and this function also return 1.22 for diffusion
> coefficient for all wavelengths. I don't think there is anything
> different, just one is to set through OPT-PROP card, one is to call a
> function and get the same value.
> But the photon spectra of these two methods were totally different (as
> shown in figure spectra comparison.jpg).
> I have tried similar procedure for refraction index, and absorption
> coefficient, and the resulting photon spectra were identical. So I
> really don't know what was wrong with diffusion coefficient setting
> here.
> I have attached all the files, and thanks in advance for any suggestion.
> - Zhiqiu Li
Received on Mon Jan 14 2013 - 17:24:26 CET

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