Re: [fluka-discuss]: ICRES and IBRES not filled for neutron capture on 1H

From: Joshua Albert <joalbert_at_imap.iu.edu>
Date: Wed, 23 Jul 2014 19:42:05 -0400

Dear Anton,

Thank you for the suggestion. I took some time to reply because I was having difficulty understanding why your solution, with the FHEAVY stack was working for me sometimes, but not other times.

I've determined that the residual deuteron gets put into the FHEAVY stack only if the capture occurs on a material with LOW-MAT set to one of the free hydrogen versions of the material. This makes sense, as the molecular version wouldn't really be a free deuteron.

Because my hydrogen is in a compound, I prefer to use the molecular version, and so I'm now resorting to selecting interactions based on icode == 300, the fact that the ICRES and IBRES variables are set to zero, and that the energy of the secondary gamma is predictable. It isn't the most elegant solution, but it seems to work.

This isn't a question, so much as a clarification, in case anyone else runs into a similar problem. I'm including some useful information on identifying 2.22 MeV gammas here.

Cheers,
Josh

*****
The special mono-energetic gamma from capture on 1H only seems to happen if the material name is HYDROGEN. Setting other materials to have the LOW-MAT card for hydrogen seems to default back to the multi-group binned approach. The exact energy of the gamma also depends on they type of LOW-MAT hydrogen used. Here are findings from looking at captures on hydrogen compounds for what the energy of the gamma will be.

     H H2O bound natural Hydrogen 296K ENDF/B-VIIR0 Y HYDROGEN 1 -2 296 Y Only if material name is HYDROGEN, 2.22323090E-03
     H CH2 bound natural Hydrogen 296K ENDF/B-VIIR0 Y HYDROGEN 1 -3 296 Y Only if material name is HYDROGEN, 2.22323090E-03
     H Free gas natural Hydrogen 296K ENDF/B-VIIR0 Y HYDROGEN 1 -5 296 Y Only if material name is HYDROGEN(?), 2.22059712E-03, leaves rxnhvy 3!
     H Free gas natural Hydrogen 87K ENDF/B-VIIR0 Y HYDROGEN 1 -2 87 Y Only if material name is HYDROGEN, 2.22059712E-03, leaves rxnhvy 3!
The exact energy of the gamma may vary outside of these values, but not by very much.

On Jul 3, 2014, at 9:50 AM, Anton Lechner <Anton.Lechner_at_cern.ch> wrote:

> Small correction to my previous Email: IBHEAV =mass number and ICHEAV = charge and not vice versa ...
>
> Cheers, Anton
>
>
>
> ________________________________________
> From: owner-fluka-discuss_at_mi.infn.it [owner-fluka-discuss_at_mi.infn.it] on behalf of Anton Lechner [Anton.Lechner_at_cern.ch]
> Sent: 03 July 2014 15:26
> To: Joshua Albert; fluka-discuss_at_fluka.org
> Subject: RE: [fluka-discuss]: ICRES and IBRES not filled for neutron capture on 1H
>
> Dear Josh,
>
> In your case of neutron capture on 1-H (assuming that point-wise cross sections are applied) you can find the deuteron on the FHEAVY stack. In particular, the deuteron is identified through KHEAVY(xx) being equal to 3. In a similar way as looping over GENSTK entries (e.g. to get the produced photon), you can loop over the fheavy stack to determine the deuteron, e.g.:
> DO IP = 1, NPHEAV
> IF(KHEAVY (IP) .EQ. 3) THEN
> * Write out energy:
> WRITE(79, *) TKHEAV (IP)
> END IF
> END DO
>
> Just for completeness (if you look at other interactions): the other particle codes in KHEAVY are 4 = 3-H, 5 = 3-He, 6 = 4-He,7-12 = "Heavy" fragment specified by IBHEAV (=charge) and ICHEAV (=mass).
>
> Cheers, Anton
>
>
> ________________________________________
> From: owner-fluka-discuss_at_mi.infn.it [owner-fluka-discuss_at_mi.infn.it] on behalf of Joshua Albert [joalbert_at_imap.iu.edu]
> Sent: 03 July 2014 01:12
> To: fluka-discuss_at_fluka.org
> Subject: [fluka-discuss]: ICRES and IBRES not filled for neutron capture on 1H
>
> Dear FLUKA experts,
>
> I am continuing studies on cosmogenic neutron captures, and I have run into a small problem. I am able to get detailed information about most neutron captures by using usdraw and printing events with ICODE = 300 and ICRES and IBRES greater than 1. This is a good way to confirm how many of the residual nuclei (as tracked by usrrnc.f as well as regular resnuclei cards) come from neutron capture, and how many come from other processes.
>
> Unfortunately, this does not work for capture on 1H. For some reason, ICRES and IBRES are both set to zero for this interaction, rather than 1 and 2, as one might expect. I can print out all secondary gammas with energies near 2.22 MeV, but this seems like a very inelegant solution, and may have additional complications. Do you know why ICRES and IBRES are not being properly set for this capture, and if there is a better workaround to positively identify neutron captures on 1H?
>
> Thank you,
> Josh
>
>
Received on Thu Jul 24 2014 - 03:33:56 CEST

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