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From: Francesco Cerutti <Francesco.Cerutti_at_cern.ch>

Date: Thu, 15 Dec 2016 00:15:33 +0100

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

Date: Thu, 15 Dec 2016 00:15:33 +0100

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:

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Received on Thu Dec 15 2016 - 02:02:56 CET

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