Re: low energy neutron cross section

From: Alberto Fasso' <fasso_at_SLAC.Stanford.EDU>
Date: Mon, 13 Feb 2012 08:31:35 -0800 (PST)

Dear Zhang Weihua,

you are trying to get an energy deposition spectrum in a gas-filled cavity
with a plastic wall. But the energy deposited is largely produced by
particles generated in the wall (mainly protons but also gammas). And these
protons may have lost some energy inside the wall.
It is not a simple situation, and it could well be that the effects you expect
are diluted or washed out by other effects.
If you want to be sure, make a test with a VERY large cavity (perhaps 1 km
radius) without any wall, filled only with a mixture of the elements
you are interested in (C and O).

Anyway, your input is not clear at all, and it is difficult to debug.
Some examples:

- a card LOW-NEUT (which is not needed!) requesting pointwise cross sections,
    while these are not available for any of the materials you use
- a MAT-PROP card with WHAT(4) = Tissue-E and nothing else. What does it mean?
- a lot of stuff not used in the present problem. It can often happen that
    one keeps in in input a number of commands irrelevant for the present
    purpose (in your case: EMF, EMF-BIAS, etc.) but such stuff should be removed
    if you send your input to be checked.
- many STERNHEIMEr parameters and values of ionization potential which
    are not needed, since they don't change the standard values which are
    already in FLUKA


On Fri, 10 Feb 2012, Xu Lijun wrote:

> Dear FLUKA experts,
> Thanks for your return. I checked the C(n,*) cross-section data again.
> The large peaks still couldn't be found below 1MeV neutron.But, there are
> several peaks above 2MeV due to the elastic scattering, not due to the
> inelastic scattering which would happen above 4.8MeV. Now, I attached the
> cross-section library what downloaded from the NNDC website. It's
> And furthermore, the incident mono-energy neutron in my input files is
> 144keV,250keV and 0.5MeV respectively. In the 144keV or 250keV output pulse
> height spectrum, there is a mono-energy peak due to the carbon and oxygen
> material respectively.But for 0.5MeV output spectrum, there is only one
> mono-energy peak due to the carbon material. And, I also simutlated the
> above MeV energy incident neutron, the output spectrum is smooth.So, I
> couldn't understand these phenomenon. Here, I also attached my input file,
> please check it if there are some mistakes so that the output pul use height
> spectrum for keV neutron is not smooth as the experimental spectrum.
> Best regards,
> Zhang Weihua
> P.s. it's me sent the last email from the Xu Lijun email address.
Received on Mon Feb 13 2012 - 18:03:38 CET

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