RE: [fluka-discuss]: less than 20 MeV neutrons

From: Maruyama, Takashi <tvm_at_slac.stanford.edu>
Date: Wed, 30 Jul 2014 10:22:33 -0700

  Thank you all.
  Francesco's statement seems correct. I have tried different defaults/thresholds but I don't see protons at less than 20 MeV.
  Takashi

-----Original Message-----
From: Francesco Cerutti [mailto:Francesco.Cerutti_at_cern.ch]
Sent: Wednesday, July 30, 2014 5:55 AM
To: Fasso, Alberto
Cc: fluka-discuss_at_fluka.org; Maruyama, Takashi
Subject: Re: [fluka-discuss]: less than 20 MeV neutrons


For neutron energy below 20 MeV (differently from higher energy), FLUKA can explicitly produce protons only if you have hydrogen ("recoil
protons") and/or nitrogen (from (n,p)). Therefore, in case of a monochromatic neutron beam < 20 MeV on silicon, you will never see them, no matter which defaults/thresholds you adopt

Francesco

**************************************************
Francesco Cerutti
CERN-EN/STI
CH-1211 Geneva 23
Switzerland
tel. ++41 22 7678962
fax ++41 22 7668854

On Wed, 30 Jul 2014, Alberto Fasso' wrote:

> Dear Takashi,
>
> Francesco's answer is correct, but a little cryptic on an important point.
> It says that the multigroup approach "does not envisage the explicit
> production of charged secondaries but of photons and neutrons only
> (apart from specific exceptions)".
> One of these specific exceptions is rather important for you,
> especially since you noticed that it was missing below 20 MeV: the
> recoil protons. While 4He and heavier nuclei are not produced
> explicitely below 20 MeV (but their contribution to dose is accounted
> for as kerma as stated by Francesco), recoil protons are always
> produced explicitely and transported in detail. If they were missing,
> it was due to the DEFAULTS you used, as pointed out by Mario in a previous answer.
>
> Alberto
>
> On Wed, 30 Jul 2014, Francesco Cerutti wrote:
>
>>
>> Dear Takashi,
>>
>> no surprise. 20 MeV is exactly the threshold below which neutrons
>> are treated through multigroup approach, which does not envisage the
>> explicit production of charged secondaries but of photons and
>> neutrons only (apart from specific exceptions), that's why you cease
>> to see them (and cannot see them), according to what is explicitly
>> said in the manual (10.3.3). At the same time, their contribution to
>> energy deposition is taken into account (in the kerma approximation).
>>
>> Best wishes
>>
>> Francesco
>>
>> **************************************************
>> Francesco Cerutti
>> CERN-EN/STI
>> CH-1211 Geneva 23
>> Switzerland
>> tel. ++41 22 7678962
>> fax ++41 22 7668854
>>
>> On Tue, 29 Jul 2014, Maruyama, Takashi wrote:
>>
>> > I am trying to find energy deposition in a 320 micron-thick
>> > Silicon layer from incident neutrons. The neutron energy is
>> > monochromatic and set by the BEAM card. When I use the energy
>> > density per region in .out file, everything looks good; the energy
>> > deposition varies smoothly at 20 MeV. I wanted to find what
>> > particles are contributing to the energy depositions. So I use
>> > mgdraw to dump these particles. Above 20 MeV neutron incident, I
>> > see many recoil protons, 4He and some e-'s contributing to the
>> > energy deposition. However, as soon as I cross 20 MeV neutron
>> > energy, these recoil protons and 4He disappear, and only e-'s are
>> > present. There must be a switch or threshold for recoil particle tracking, but I cannot figure out what. Please help.
>> >
>> > Takashi Maruyama
>> > SLAC
>
>
Received on Wed Jul 30 2014 - 20:36:32 CEST

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