Re: [fluka-discuss]: Clarification on neutron yield

From: <me_at_marychin.org>
Date: Fri, 23 May 2014 21:35:13 -0700 (PDT)

Hello Benjaminas,
On the MCNP(X) side you have at your disposal the output-by-default neutron
creation table, as well as PTRAC bank events differentiating collisions types by
the L, NTER and NTYN, which are related to MT numbers in ENDF6.
:) mary

> On 22 May 2014 at 00:21 Alfredo Ferrari <alfredo.ferrari_at_cern.ch> wrote:
>
>
> Yes
>
> it does not include neutrons generated below 20 MeV, for example
> by (n,2n), (n,3n) reactions.
>
> Perhaps a more physically meaningful check is to compare how many neutrons
> come out of a given target geometry, the number of neutrons generated is
> indeed assumption dependent, for example a non-elastic interaction where
> you have an incident neutron and in the final state one neutron plus
> whatever else will be counted as one "produced" neutron in the counters we
> were looking at (I do not know for MCNP). Indeed only a
> the number of neutrons-escaping-from-target is well defined.
>
> The closest thing to your concept you can score in FLUKA is the "neutron
> balance" estimator which makes the arithmetic balance neutron-out minus
> neutrons-in at each interaction. In the example above it would have
> counted 0, for a (n,2n) it would count +1, for a capture -1 and so
> on... This works also for neutrons below 20 MeV, however you must have
> the same kind of estimator in MCNP if you want to compare...
>
> Alfredo
>
> +----------------------------------------------------------------------+
> | Alfredo Ferrari || Tel.: +41.22.76.76119 |
> | CERN-EN/STI || Fax.: +41.22.76.69474 |
> | 1211 Geneva 23 || e-mail: Alfredo.Ferrari_at_cern.ch |
> | Switzerland || |
> +----------------------------------------------------------------------+
>
> On Thu, 22 May 2014, Benjaminas Marcinkevicius wrote:
>
> > Hello everyone,
> >
> > I have calculated 2 GeV protons impinging on tungsten target and neutron
> > yield in FLUKA 56 neutrons per source particle, while in MCNPX 79 neutrons
> > per source particle.
> > The difference is rather large and I was thinking maybe I do not account all
> > the neutrons in FLUKA.
> >
> > FLUKA defaults were:
> > precision
> > evaporation with heavy fragments is on
> > coalescence is on
> > Low-neut transport is on
> >
> > I took the neutrons from table:
> > Number of secondaries generated in inelastic interactions per beam
> > particle:
> >
> >
> > However low energy neutrons and neutrons are treated separately and maybe
> > this number does not include the neutrons with energy below the 20 MeV ?
> >
> > As I am quite new to FLUKA any insight on the problem would be helpful.
> >
> > See attached summary of the FLUKA run.
> >
> > Thank you for your help in advance.
> >
> > Sincerely,
> > Benjaminas Marcinkevičius
> >
> >
> >
Received on Sat May 24 2014 - 07:52:54 CEST

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