From: Buthaina Abdalla Suleiman Adam (buthaina@aims.ac.za)
Date: Mon Feb 25 2008 - 09:49:36 CET
---------------------------- Original Message ----------------------------
Subject: Re: Flux
From: "Buthaina Abdalla Suleiman Adam" <buthaina@aims.ac.za>
Date: Mon, February 25, 2008 10:01 am
To: "Alberto Fasso'" <fasso@slac.stanford.edu>
--------------------------------------------------------------------------
Dear Alberto Fasso,
Thank you alot,
I have changed the momentum of the beam from 0.2 to -0.2, but still there
is no flux (see output file).
Kind Regards,
buthaina
> Dear Buthaina,
>
> you have an incident beam of protons with a momentum of 0.2 GeV,
> which means about 21 MeV kinetic energy. Protons of 21 MeV energy
> have a very short range: about 2.8 mm in beryllium.
> And your energy cutoff for protons is the default, equal to 10 MeV.
> So, as soon as each proton has lost half of its energy, it is ranged
> out without any nuclear interaction. At 10 MeV, the residual range
> is about 0.8 mm, so each of your protons has only a short distance
> available (2.8 - 0.8 = 2 mm) to have a nuclear interaction.
> The proton nuclear cross section between 10 and 21 MeV is anyway
> very small. And I must add that this energy range is
> at the limit of the FLUKA preequilibrium model, so any result must
> be taken with some caution.
> (If your intention was to simulate 200 MeV protons, then you should
> have input -0.2 and not 0.2).
> If you look at the end of your .out output, you will see that:
> - on average, 99% of the proton energy is dissipated as dE/dx
> - there are only very few inelastic interactions (stars): about 1600
> for 1.E5 protons
> - only a very few neutrons are produced: about 1100 for 1.E5 protons
>
> I would like to add another comment about your input: from a test I
> did, it seems to work, but it would be better to avoid building
> contiguous regions by means of bodies having a common surface (in
> your case, regions regBE4 and regST5 have a common face at z=1.96
> and regST5 and regFe6 at z=201.96).
> You can obtain that by making some of the bodies a little longer
> and cutting them out. Instead of:
> ............
> RPP body3 -1.0 +1.0 -1.0 +1.0 0.0
> +1.96
> RCC body5 0.0 0.0 +1.96 0.0 0.0
> 200.0
> 1.5
> RPP body6 -2.375.0 +2.375 -2.375 +2.375 +201.96
> +401.96
> .............
>
> * Be target 2nd half
> regBE4 5 +body3 -body4
> * beam tube
> regST5 5 +body5
> * Iron Collimator
> regFe6 5 +body6
>
> you could have
> ............ make body3 0.04 cm longer, and body5 1 cm longer
> RPP body3 -1.0 +1.0 -1.0 +1.0 0.0
> +2.00
> RCC body5 0.0 0.0 +1.96 0.0 0.0
> 201.0
> 1.5
> RPP body6 -2.375.0 +2.375 -2.375 +2.375 +201.96
> +401.96
> ...................
>
> * Be target 2nd half -- subtract body5 to make it end at z=1.96
> regBE4 5 +body3 -body4 -body5
> * beam tube -- subtract body6 to make it end at z=201.96
> regST5 5 +body5 -body6
> * Iron Collimator
> regFe6 5 +body6
>
> This latter definition is more likely to work without problems.
>
> Best regards,
>
> Alberto
>
> On Sun, 24 Feb 2008, Buthaina Abdalla Suleiman Adam wrote:
>
>> Hi
>> I want to get the flux of neutron at 400cm away from the target outside
>> Steel tube 200cm (regST5) and iron tube200cm (regFe6). My problem is the
>> flux value is zero, even when I made the iron tube shorter than 200cm
>> (10cm, 100cm). Also I made regFe6 just as vacuum to see if I can get any
>> flux but still the same. I don't is this problem due to the number of
>> regions (there is a flux outside regST5)? Please any help, I attached
>> the
>> input file
>>
>> Thank You in Advance,
>> Buthaina Adam
>>
>
> --
> Alberto Fasso`
> 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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