RE: [fluka-discuss]: Neutron cross section

From: Alberto Fasso <>
Date: Thu, 20 Feb 2014 15:24:17 +0100

Hi Jonathan,

reading your first email, I wasn't sure where you had found PNP and PNA.
Now that you say you refer to the cross sections printed by LOW-NEUT, I
can assure you that neither is there with such names. The only ones that
more or less look similar are the following (I am quoting from the Manual,
Chapter 9):

PNUP = upscatter probability (can be different from zero only if
          there are several thermal groups)
PNABS = probability of Non-ABSorption (= scattering).
          It is = SIGST/SIGT, and can sometimes be > 1 because of
          (n,xn) reactions
PNEL, PXN, PFISS, PNGAM = partial cross sections, expressed as
          probabilities (i.e. ratios to SIGT). In the order:
          non-elastic, (n,xn), fission, (n,gamma)

Group cross sections are mainly for neutron transport, not for activation.
The only exceptions are PNGAM and the 14-N(n,p)14-C cross section. The
situation is different for the few cases where pointwise cross sections
can be used (6-Li and 10-B(n,alpha)7-Li). In FLUKA, activation by
low-energy neutrons is obtained by a separate table of residual
nuclei, where the values are group dependent and uncorrelated with the
actual sampled reaction.


On Thu, 20 Feb 2014, Jonathan Derrien wrote:

> Hello Vittorio,
> Thank you to trying to answer my question. Well, for neutron with energies
> below 20 MeV, cross-section libraries are used. These cross-sections can be
> seen by using the command LOW-NEUT.  Have you any idea about how compute the
> activation cross-section thanks to the data given by LOW-NEUT?
> Best,
> Jonathan
> --
> []
> ____________________________________________________________________________
> Date: Thu, 20 Feb 2014 14:26:53 +0100
> Subject: Re: [fluka-discuss]: Neutron cross section
> From:
> To:
> CC:
> Dear Jonathan, 
> What do you exactly mean with "data used by Fluka,  I'm not sure if I'm
> mislead by the name but I had some memories that those could be the
> probabilities of emission of a neutron and a proton (Pnp) and the one for
> the emission of a neutron and an alpha (Pna). 
> best, 
> V.
> On Thu, Feb 13, 2014 at 10:55 AM, Jonathan Derrien <>
> wrote:
> Hello dear Fluka Users,
> I'm using the data used by Fluka for the low neutron and  I found
> among the cross section and different probabilities two probabilities:
> PNP and PNA. I do not see what it is, so what is their meaning?
> Moreover, does anyone know how from these data to determine the
> activation cross section? 
> Sincerely, 
> Jonathan Derrien
> --
> []
Received on Thu Feb 20 2014 - 16:22:22 CET

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