Dear Francesco,
now it works fine, the sampled spectrum looks like the original one. Thanks a lot!
One last question: Why are neutrons of some energies not transported, if the source routine returns
energy values from table 10.4.1.1 (energy group structure of the 260- neutron data set)?
(these are the energy values in my EBIN array)
Best regards
Klaus
-----Ursprüngliche Nachricht-----
Von: Francesco Cerutti [mailto:Francesco.Cerutti_at_cern.ch]
Gesendet: Mittwoch, 14. Dezember 2016 12:17
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,
thanks. Now the picture is clear: you are sampling an energy value just at the boundary between two groups, which is not a good idea (since by definition a boundary value challenges the identification of the range it belongs to), and you are doing so with single precision numbers (as stored in your arrays, where the D specifier is missing). Apart from using double precision energy values, a robust solution - assuring your spectrum reproduction - is rather to take an energy value in the middle of the respective group
ENERGY=(EBIN(K)+EBIN(K-1))/TWOTWO
(To avoid the undesired case K=1, set SYCUM(1)=-ONEONE, i.e. to a negative value instead of zero, since FLRNDM(DUMMY) may return 0, never 1).
Also for E>20 MeV, if the energy array is meant to store the histogram bin limits, it makes anyway more sense to sample a value in between.
Kind regards
Francesco
**************************************************
Francesco Cerutti
CERN-EN/STI
CH-1211 Geneva 23
Switzerland
tel. ++41 22 7678962
fax ++41 22 7668854
On Tue, 13 Dec 2016, Ott, Klaus wrote:
>
> 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>;
>
> > 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
>
> >
>
> >
>
> >
>
> >
>
> >
>
> >
>
> >
>
> >
>
> >
>
> >
>
> >
>
> >
>
> >
>
> >
>
> >
>
> >
>
> > ____________________________________________________________________
> > __
>
> > ______
>
> >
>
> >
>
> >
>
> > 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
>
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>
> > Frederking
>
> >
>
> > Sitz Berlin, AG Charlottenburg, 89 HRB 5583
>
> >
>
> > Postadresse:
>
> > Hahn-Meitner-Platz 1
>
> > D-14109 Berlin
>
> >
>
> > http://www.helmholtz-berlin.de
>
> >
>
> >
>
> >
>
> > --
>
> >
>
> > Leonel Morejon
>
> >
>
> > --------------------------------------
>
> >
>
> > ELI Beamlines
>
> >
>
> > Address:
>
> >
>
> > Za Radnicí 835
>
> >
>
> > 25241 Dolní Bøe¾any
>
> >
>
> > Czech Republic
>
> >
>
> >
>
> >
>
> > Office: +420 266 051 406
>
> >
>
> > Mobile: +420 773 666 453
>
> >
>
> > --------------------------------------
>
> >
>
> > ____________________________________________________________________
> > __
>
> > ______
>
> >
>
> > 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
>
>
________________________________
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 Wed Dec 14 2016 - 18:49:51 CET