Re: AW: [fluka-discuss]: Dips in sampled neutron spectrum

From: Ott, Klaus <klaus.ott_at_helmholtz-berlin.de>
Date: Tue, 13 Dec 2016 18:07:50 +0000

Dear Francesco,



I send you the source file.

Side note: It should be d2Phi/dOmega/dE



Best regards



Klaus







----Ursprüngliche Nachricht-----
Von: Francesco Cerutti [mailto:Francesco.Cerutti_at_cern.ch]
Gesendet: Dienstag, 13. Dezember 2016 15:22
An: Ott, Klaus <klaus.ott_at_helmholtz-berlin.de>
Cc: fluka-discuss_at_fluka.org
Betreff: Re: AW: [fluka-discuss]: Dips in sampled neutron spectrum





Dear Klaus,



my first guess would be indeed related to the group structure. The actual group assignment resulting from the energy sampling in your source.f may be responsible for the dips. This would mean that the sampled energy value falls in the wrong group range. -

Considering that your original spectrum already follows the group structure, this hypothesis looks surprising, but a final word cannot be said without looking into your source.f.



On a side note, I understand that with dPhi you actually mean dE.



Kind regards



Francesco



**************************************************

Francesco Cerutti

CERN-EN/STI

CH-1211 Geneva 23

Switzerland

tel. ++41 22 7678962

fax ++41 22 7668854



On Mon, 12 Dec 2016, Ott, Klaus wrote:



>

> Dear Leonel,

>

>

>

> I used of course the low energy groups for sampling (the original

> spectrum has been calculated by Fluka). The Fluka output is

> d2/dPhi/dOmega and if you plot this, you see that this curve decreases

> by orders of magnitude. If these values are multiplied

>

> by the energy interval of the respective bin, the effect of the small

> low energy bins

>

> is (roughly) compensated. For neutron sampling I used the group

> fluence

> (d2/dPhi/dOmega*2pi*deltaEi) which I integrated (summarized) and

> normalized

>

> and the energy values of the Fluka groups below 20 MeV (255) and

> further 12 high energy bin values up to 0.5 GeV.

>

>

>

> Best regards

>

>

>

> Klaus

>

>

>

> Von: Leonel Morejon [mailto:leonel.morejon_at_eli-beams.eu]

> Gesendet: Montag, 12. Dezember 2016 17:06

> An: Ott, Klaus <klaus.ott_at_helmholtz-berlin.de<mailto:klaus.ott_at_helmholtz-berlin.de>>;

> fluka-discuss_at_fluka.org<mailto:fluka-discuss_at_fluka.org>

> Betreff: Re: [fluka-discuss]: Dips in sampled neutron spectrum

>

>

>

> Dear Klaus Ott,

>

> It is probably is related to the way you scored and/or sampled.

>

> Did you take into account that in Fluka usually by default the

> group approach is used for neutrons below 20 MeV?

>

> Is difficult to guess without your sampling routine, but if you

> sampled linearly from all energies then the lower bins are extremely unlikely.

>

> Indeed if you sample linearly with energy, even with 10E10 sampled

> particles, the particle density per energy in the low range (20MeV to

> 1e-5eV) is less than 1E3 part/eV, and this might be ok for bins

> spawning 100-10meV but not for those thinner. Is not enough statistics

> especially because the groups are not linearly spaced, and some spawn 1e-2meV.

>

> To have them populated equally, you need to sample according to

> the characteristics of the spectrum, Maxwell+1/v.

>

> But this are just conjectures, is hard to answer w/o seeing your

> routine.

>

> Regards,

>

> Leonel

>

> On 12.12.2016 15:23, Ott, Klaus wrote:

>

> Dear Fluka team,

>

>

>

> I calculated a neutron spectrum outside the shielding of an

> electron accelerator (1.7 GeV) and used that spectrum for

> sampling in a simple geometry:

>

> an isotropic irradiating neutron source in the center of the

> coordinate system, surrounded by vacuum and a sphere just used

> for USRBDX

>

> counting. It is just a test to see, if the sampled spectrum is

> the same as the original one.

>

>

>

> What I found is a similar spectrum, but it has several zero bins

> in the low energy region < 20 MeV. (This behaviour is not a

> statistic effect, it occurs also

>

> when 7E9 neutrons are sampled and it is not an effect of a wrong

> integrated and normalized spectrum function used in source.f,

> using source.f outside Fluka, an almost identical spectrum is

> returned).

>

> It seems to be an artefact of the neutron transportation similar

> to the one described in chapter 10 of the manual, which is in

> that case a result of the interaction of neutrons with matter.

>

>

>

> Could you recommend optimized transport/threshold parameters to

> reduce/avoid this problem?

>

>

>

> Best regards

>

>

>

> Klaus Ott

>

>

>

> HZB/BESSYII Berlin Germany

>

>

>

>

>

>

>

>

>

>

>

>

>

>

>

>

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> Helmholtz-Zentrum Berlin für Materialien und Energie GmbH

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> --

>

> Leonel Morejon

>

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> Helmholtz-Zentrum Berlin für Materialien und Energie GmbH

>

> Mitglied der Hermann von Helmholtz-Gemeinschaft Deutscher

> Forschungszentren e.V.

>

> Aufsichtsrat: Vorsitzender Dr. Karl Eugen Huthmacher, stv. Vorsitzende Dr.

> Jutta Koch-Unterseher

> Geschäftsführung: Prof. Dr. Anke Rita Kaysser-Pyzalla, Thomas

> Frederking

>

> Sitz Berlin, AG Charlottenburg, 89 HRB 5583

>

> Postadresse:

> Hahn-Meitner-Platz 1

> D-14109 Berlin

>

> http://www.helmholtz-berlin.de

>

>


________________________________

Helmholtz-Zentrum Berlin für Materialien und Energie GmbH

Mitglied der Hermann von Helmholtz-Gemeinschaft Deutscher Forschungszentren e.V.

Aufsichtsrat: Vorsitzender Dr. Karl Eugen Huthmacher, stv. Vorsitzende Dr. Jutta Koch-Unterseher
Geschäftsführung: Prof. Dr. Anke Rita Kaysser-Pyzalla, Thomas Frederking

Sitz Berlin, AG Charlottenburg, 89 HRB 5583

Postadresse:
Hahn-Meitner-Platz 1
D-14109 Berlin

http://www.helmholtz-berlin.de




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Received on Tue Dec 13 2016 - 20:59:23 CET

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