Re: Neutron Interaction

From: Stefan Roesler <>
Date: Thu Jun 12 2008 - 19:43:30 CEST


I am not sure you can obtain this information from a multi-group transport

The scattering is not simulated as an exclusive process. Neutrons are
transported between groups (they carry a group number but not a specific
energy) and interactions are described based on matrices of
down-scattering probabilities, i.e. of probabilities for a neutron in
group i to end up in group j after scattering. In addition, only three
discrete polar scattering angle are taken into account. Similarly, gammas
are generated in a multi-group scheme: another down-scattering matrix
tells the probabilities for a neutron in a certain group to emit a photon
with an energy in one of the gamma groups (the gammas, however, are then
followed explicitly as any other electromagnetic cascade).

Energy deposition of a neutron in a certain group is based on kerma
factors averaged over all possible group transfers. Also (n,xn) reactions
are not simulated by explicitly creating x neutrons (except fission) but
by adjusting the weight of the neutron accordingly (becomes larger than
unity). However, *on average* everything is correct (except extreme
cases of very thin material layers) and energy conserved.

Point-wise scattering is available in FLUKA only for a very few elements;
please see the manual for details (input card LOW-NEUT).

Best regards

On Tue, 10 Jun 2008 wrote:

> Dear Fluka Experts,
> I would like to find out for each neutron interaction,the type of material it is interacting in an Alloy, the initial XYZ positions, initial XYZ direction cosines and initial energy as well as final energy and direction cosines. I have attached herewith the input file and modified mgdraw.f. Please let me know whether I am correct in doing that? As fluka treats low energy neutrons by Multigroup cross sections, how far the data generated will be correct in context of initial and final energy determination of neutrons.
> With Regards,
> S. Chatterjee

Stefan Roesler
CH-1211 Geneva 23
Phone:  +41-22-7679891
Fax:    +41-22-7669639
Received on Fri Jun 13 10:35:55 2008

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