Dear Katja
Thanks for contacting us. The issue you see, that is the higher dose rate
at 0 deg with 2023.3 when compared with 2021.2, has nothing to do with
physics, but it is rather due to the fluence-to-dose conversion
coefficients.
Until 2021.2 included, since no conversion coefficient were available for
ions, their contribution to dose (in that case H*(1)) was zero as reported
in the manual of the time.
With 2023.3, the conversion coefficient for ions are still missing in the
ICRP/ICRU publications (those for alpha are now available up to a few
hundreds GeV), but Fluka now does attempt to make a very rough estimate of
how much they could be. This estimate can easily be a factor of a few in
error wrt the (unknown) "correct" conversion coefficient, however it was
felt that having something, even though inaccurate, was somewhat better
than scoring zero. From the current Fluka manual (AUXSCORE description):
4) Dose conversion coefficients exist only for some particle types:
protons, neutrons, muons, photons, electrons/positrons, and charged
pions. 4-He conversion coefficients are also available for AMBDS,
EAP116, EPA116, EIS116. For elementary hadrons a tentative, albeit
approximate, association is made with one of the proton, neutron,
charged pion conversion coefficient set. For all other particle
types, in the past zero factor was returned. Starting with
FLUKA2023, a very crude attempt is made to return a non-zero
conversion coefficient, rescaling from available ones. This is
anyway highly inaccurate, and therefore it should never be relied
upon, particularly when heavy ions are an important contributor
to the scored quantity (see Note 5).
5) For particles such as heavy ions, for which fluence conversion
factors are not available, it is possible to score with USRBIN the
generalised particle DOSEQLET, i.e. dose equivalent as defined by
ICRU: H = D x Q(L), where L is the unrestricted Linear Energy
Transfer in water.
Indeed the "old" manual version of note 4) was:
4) Dose conversion coefficients exist only for some particle types:
hadrons, muons, photons, electrons/positrons. For all other
particle types, zero factor will be returned. This is particularly
important for heavy ions where zero factor will be scored (see
Note 5)
So, the increase in dose at zero deg you observe is due to use of some
(possibly inaccurate) conversion coefficients for ions heavier than
alphas, where in the past zero was used (-> no dose). Of course if a non
negligible fraction of ions survive the target the effect is highly
visible, particularly for the heavier ions. Indeed the scaling factor used
is proportional to the stopping power of the particle, hence the
approximate conversion coefficients for ions roughly scale with Z^2 wrt
those of a proton at the same speed (energy/nucleon).
Perhaps more emphasis should have been put on this change by mentioning it
explicitly in the release notes. I would like to draw your attention to
note 5) as an alternative method of obtaining a dose equivalent estimation
for ions, very likely more accurate than the simple rescaling. A possible
way out would be to recompute the dose map excluding the ion contribution
(eg with a suitable fluscw routine), and computing a second map with
DOSEQLET restricted to the heavy ion contribution only (again with fluscw)
and ideally putting the two maps together.
Lety me know if the explanation is clear (I am not sure...)
Alfredo
> Dear Alfredo,
>
> Thank you very much for the fast reply. After installing new FLUKA
> 2023.3.3 I ran again my input file with a carbon target and
> uranium-238/nickel-58 beam. The results are better now, not a such big
> difference for the uranium beam (Anna Senger reported you), but I see
> still the difference if you compare the dose rates a specially after the
> target at zero degree.
>
> I did additionally very simple calculation with carbon targets and
> uranium/nickel beam with/without iron beam dump. I attached input file.
> The differences between FLUKA 2023.3.3 and FLUKA 2021.9.2 is visible for
> uranium-238 and for nickel-58. Are such differences for the dose rates
> correct?
>
> Best regards
> Katja
>
> P.S.: The comparisons between two FLUKA versions are presented in PP
> Presentation.
>
> -----Ursprüngliche Nachricht-----
> Von: alfredo.ferrari_at_mi.infn.it <alfredo.ferrari_at_mi.infn.it>
> Gesendet: Mittwoch, 31. Januar 2024 17:35
> An: Senger, Anna Dr. <A.Senger_at_gsi.de>
> Cc: 'fluka-discuss_at_fluka.org' <fluka-discuss_at_fluka.org>; Kozlova,
> Ekaterina Dr. <E.Kozlova_at_gsi.de>
> Betreff: Re: [fluka-discuss]: Heavy ions passing through thick target
> almost without interaction
>
> Dear Anna
>
> Thanks for your report. Indeed there was a problem when AA collisions were
> performed in inverse kinematics (like 238U on C) setting a threshold for
> the interaction model much higher than what it should have been.
>
> In your example this has no consequence for 58Ni but it spoils 238U.
>
> A fix is already ready and it will be released in a respin tomorrow at
> most, together with a few other fixes/improvements.
>
> Thanks again
> Alfredo
>
> P.S. The Flair default for heavy ion should be changed, the DPMJET card is
> useless, and the default should be better be PRECISIO, we will change it
>
>> Dear FLUKA experts.
>> My colleague repeated her calculations with new FLUKA release
>> September 2023. She found some inconsistency with previous results
>> (see first page of the pdf file). I tried to investigate this issue,
>> and found, that heavy ions passing through thick target almost without
>> interaction (second page). I put the input, which I used for this
>> study. I used November 2023 FLUKA version.
>>
>> Could you please check, that this is valid issue, and correct it?
>>
>> Best regards
>> Anna
>>
>>
>> PS.
>> Input was generated as FLAIR default input for heavy ion beams.
>> ______________________________________
>>
>> Dr. Anna Senger
>>
>> Office KBW 2.01
>> Tel. +49(0)615971 1844
>> E-Mail A.Senger_at_gsi.de
>>
>> FAIR - Facility for Antiproton and Ion Research in Europe GmbH �
>> Planckstr. 1
>> 64291 Darmstadt
>> DEUTSCHLAND
>>
>>
>
>
>
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Received on Tue Feb 06 2024 - 18:51:06 CET