[neutron-mc] Integrated Flux - Discrepancies between McStas and MCNP

[Willendrup, Peter Kj=?ISO-8859-1?B?5g==?=r]

Hello everyone,



First of all, thanks to George Apostolopoulos  for the detailed bug-report.

A detailed study of the found discrepancy between McStas and MCNP /
analytics, it turns out that a couple of modifications are needed in the
McStas focusing routines. (Specifically, a solid-angle correction to the
neutron weight does not fully take source geometry into account.)

As also pointed out in George's report on the problem, the effect of the
discrepancy is only severe in situations where source size, focusing area
and focusing distance are all of the same order. (In most practical cases,
the effect is negligible).

Corrections to the McStas runtime code and source components will be
incorporated in the development version of McStas in a few days, and will be
part of the next official release of McStas (available late 2007 / early
2008).


Best regards,

Peter Willendrup



On 10/30/07 5:22 PM, "George Apostolopoulos" <gapost at ipta.demokritos.gr>
wrote:

> Dear all,
> 
> Being a new user of McStas, but with some experience in Monte-Carlo with
> MCNP, 
> one of the first things that I tried to understand was how the
> normalization is handled
> in McStas. After running some test problems the normalization became
> clear but 
> I noticed some discrepancies between McStas and MCNP which I cannot
> understand.
> 
> Specifically, consider the following simple example:
> Particles emitted by a square (d x d) surface source are counted by a
> square 
> monitor, with the same area (d x d), positioned at a distance D.
> 
> I run this problem both in McStas and MCNP and the results I get agree
> very well when 
> D>>d but differ by up to 20% when D~d.
> A plain numerical integration agrees with MCNP, but this requires
> discussion.
> 
> You will find a detailed report in the attached document.
> 
> Best regards
> 
> ******************************************************
> Dr. Georgios Apostolopoulos
> Institute of Nuclear Technology & Radiation Protection
> National Center for Scientific Research "Demokritos"
> 15310 Agia Paraskevi Attikis, Greece
> 
> tel +30-210-650-3731
> fax +30-210-653-3431
> email: gapost at ipta.demokritos.gr
> ******************************************************
> _______________________________________________
> neutron-mc mailing list
> neutron-mc at risoe.dk
> http://mailman.risoe.dk/mailman/listinfo/neutron-mc