From: Lindley Anne Winslow (LAWinslow@lbl.gov)
Date: Fri Mar 23 2007 - 01:23:14 CET
Alberto,
1) In response to the below:
"Everything is clear now. Counting gammas or neutrons or events has no
meaning. You should always count the corresponding weights."
This means that running 10,000 lowEnergy neutrons has no meaning. I have actually run the sum of the weights of those 10,000 neutrons? Is the number of neutrons made be n,2n reactions sum of parent weights - sum of daughter weights?
2) Thank you for noticing the DEFAULTS. I will change that.
3) As per COMPOUND issue.
In a previous post Alfredo told me compound works like this for atomic composition.
C9H12 would be 9/21=+0.428... 12/21=+0.571... My liquid scintillator is actually a mixture of several things but for the previous discussion I thought talking about C9H12 would be easier to talk about.
Alfredo's post:
http://www.fluka.org/web_archive/earchive/new-fluka-discuss/0654.html
4) Thank you for the warning about FLUSCW I did not realize it was also calling FLDSCP. I only wanted FLUSCW.
Once again thank you for spotting the errors,
Lindley
----- Original Message -----
From: Alberto Fasso' <fasso@slac.stanford.edu>
Date: Friday, March 23, 2007 8:14 am
Subject: Re: Thermal Neutron Capture Gammas
To: Fluka Discussion <fluka-discuss@fluka.org>, Lindley Anne Winslow <LAWinslow@lbl.gov>
> Everything is clear now. Counting gammas or neutrons or events has no
> meaning. You should always count the corresponding weights.
>
> I have looked at your input and I have found some errors.
>
> The card DEFAULTS should be placed at the beginning of input. See
> the manual:
> 2) IMPORTANT! Option DEFAULTS must be issued at the very
> beginning of
> input. It can be preceded only by a GLOBAL card and by
> commands such as COMMENT or TITLE. This is one of the
> rare cases, like GLOBAL,
> MAT-PROP and PLOTGEOM, where sequential order of input cards
> is of
> importance in FLUKA (see 7}).
>
> In the COMPOUND definitions, if both WHAT(1) and WHAT(2) have a
> positive sign,
> WHAT(1) is the number of atoms in the molecule. Same for WHAT(3)
> and WHAT(5)
> etc.
> So, since yout LIQUIDS compound is made of 9 atoms of C and 12 of
> H, it is
> not correct to write
> COMPOUND +0.3381203 6.0+0.6618797 3.0 0.0
> 0.LIQUIDSbut you should have:
> COMPOUND +9.0 6.0 +12.0 3.0 0.0
> 0.LIQUIDS
> But if you prefer instead to use mass fractions, you should put
> WHAT(1) and
> WHAT(3) with a negative sign:
> COMPOUND -0.9 6.0 -0.1 3.0 0.0
> 0.LIQUIDSIn fact, 9 atoms of C with mass 12 plus 12 atoms of H of
> mass 1 make a total
> of 120. And 9*12/120 = 0.9, 12*1/120 = 0.1. I don't understand
> where you got
> those numbers 0.3381203 and 0.6618797.
>
> Finally, I am surprised by seeing
> *Custom Weighting.
> USERWEIG 0.0 0.0 4.0
>
> According to the manual, WHAT(3) = 4.0 means that you multiply your
> fluence of
> yield scores by a function FLUSCW (and that is quite normal) but
> also that
> "The routine FLDSCP is also called, applying a shift to the current
> binnedtrack"
>
> FLDSCP is normally used to simulate a drift. Is that what you
> intend to do?
> Why?
>
> Alberto
>
>
> On Fri, 23 Mar 2007, Lindley Anne Winslow wrote:
>
> > Thank you Alberto.
> >
> > I am sorry I forgot the material. I have attached my setup this
> time.>
> > It is Liquid Scintillator C9H12. I couldn't find a reference for
> (n,alpha) on carbon12 quickly but my understanding is (n,gamma) on
> hydrogen should be the dominant process. Gammas should be generated
> for both these materials and some are.
> >
> > The number quoted below is just the counted number of events with
> gammas.> The sum of the weights of these particles is ~2100 which
> is the same as the weights of the incoming neutrons.
> >
> > I also see very little deuterium or carbon13 produced. When I run
> thermal neutrons in this environment I would expect no fewer
> capture gammas than neutrons entering the volume (and not escaping).
> >
> >
> > Lindley
> >
> >
> > ----- Original Message -----
> > From: Alberto Fasso' <fasso@slac.stanford.edu>
> > Date: Friday, March 23, 2007 6:26 am
> > Subject: Re: Thermal Neutron Capture Gammas
> > To: Fluka Discussion <fluka-discuss@fluka.org>, Lindley Winslow
> <LAWinslow@lbl.gov>>
> > > Dear Lindley,
> > >
> > > your question is too vague to give it an answer.
> > > Which material(s) are you using? Have you made sure that
> > > the cross sections of all of them include gamma production?
> > > (See Chap. 10 of the Manual).
> > > Are you aware that not all neutron captures produce gammas?
> > > For instance you can have a (n,alpha) reaction without gamma.
> > > Are you aware that in a (n,gamma) reaction you may have
> > > more than one gamma?
> > > Have you just "counted" the neutrons and gammas, or have
> > > you calculated the sum of their weights?
> > >
> > > Alberto
> > >
> > >
> > >
> > > On Thu, 15 Mar 2007, Lindley Winslow wrote:
> > >
> > > > Hello all,
> > > >
> > > > To try to understand FLUKA's treatment of low energy
> neutrons, I
> > > > simulated 10,000 thermal neutrons (group 72)
> > > >
> > > > I found 5575 scatter and leave the detector.
> > > > This leaves 4425 that stay in the detector.
> > > > I only see 951 capture gammas from the neutrons that stay in the
> > > > detector.
> > > >
> > > > I would expect that all neutrons that stay in the detector
> should> > > capture. Is there another way to lose neutrons from the
> last group?
> > > >
> > > > Thank you,
> > > > Lindley
> > >
> >
>
> --
> Alberto Fassò
> SLAC-RP, MS 48, 2575 Sand Hill Road, Menlo Park CA 94025
> Phone: (1 650) 926 4762 Fax: (1 650) 926 3569
> fasso@slac.stanford.edu
>
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