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

From: Alfredo Ferrari <alfredo.ferrari_at_cern.ch>
Date: Thu, 22 May 2014 09:21:32 +0200

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 Thu May 22 2014 - 10:34:45 CEST