Dear Klaus,
it is unique! Simply your values get on the wrong side of the boundary
since they are input with a limited number of digits and in single
precision.
Moreover, note that in the multigroup approach below 20 MeV a neutron is
characterized by the group number (physically corresponding to an energy
range) and not by a specific energy value.
Last, while an energy range has finite length, an energy point has null
length, so its inclusion/exclusion in practice is irrelevant.
Kind regards
Francesco
**************************************************
Francesco Cerutti
CERN-EN/STI
CH-1211 Geneva 23
Switzerland
tel. ++41 22 7678962
fax ++41 22 7668854
On Wed, 14 Dec 2016, Ott, Klaus wrote:
> Dear Francesco,
>
> thanks for explanation. I interpreted the Fluka low energy group values as "upper limits" or written as (A,B];(B,C]; (C,D]. In that case the belonging of the boundary values to a given energy bin would be unique.
> I think it should be unique, because neutrons of just the boundary value energies could occur by many other reasons than sampling.
>
> Best regards
>
> Klaus
>
>
>
> -----Ursprüngliche Nachricht-----
> Von: Francesco Cerutti [mailto:Francesco.Cerutti_at_cern.ch]
> Gesendet: Mittwoch, 14. Dezember 2016 17:53
> An: Ott, Klaus <klaus.ott_at_helmholtz-berlin.de>
> Cc: fluka-discuss_at_fluka.org
> Betreff: Re: AW: AW: [fluka-discuss]: Dips in sampled neutron spectrum
>
>
> Dear Klaus,
>
> actually what happens is that those neutrons get from the beginning a different energy, being moved to neighbouring energy groups and so distorting the spectrum. And the reason is as I previously wrote below.
>
> Let's have three energy groups, from A to B, from B to C, and from C to D, respectively. If you assign as energy value B, C, and D (which is itself a bad idea, since a boundary value makes the group identification ambiguous), and you input for them single precision numbers, it may happen that your B value is interpreted as falling between A and B, your C value as falling between C and D, and your D value as falling between C and D too. So a given spectrum, expected for instance to get N counts in each of the three groups, turns out to be polluted with N, zero, and 2N counts, respectively.
>
> Cheers
>
> Francesco
>
> **************************************************
> Francesco Cerutti
> CERN-EN/STI
> CH-1211 Geneva 23
> Switzerland
> tel. ++41 22 7678962
> fax ++41 22 7668854
>
> On Wed, 14 Dec 2016, Ott, Klaus wrote:
>
>> 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
>>>
>>>> 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
>>>
>>>>
>>>
>>>>
>>>
>>>>
>>>
>>>> --
>>>
>>>>
>>>
>>>> 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
>>
>
> ________________________________
>
> 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 Thu Dec 15 2016 - 02:02:56 CET