Re: [fluka-discuss]: Lead neutron library

From: Answers <answers_at_pcfluka.mi.infn.it>
Date: Sun, 26 Apr 2020 12:40:45 +0200 (CEST)

Dear Mitja,
I'm sorry, I cannot reproduce your problem
Please find attached a plot and a tab_lis file, obtained with an input
(also attached)
that has a few minor modifications with respect to yours:
- a larger detector and smaller beam divergency in order to increase
statistics. Together they give a factor 400 on normalization
- Added usrtrack in lead and target
- Added log usrtrack (not really needed)
- Separated collimator hole from vacuum to easily change configuration

As you see from the plot, I get a smooth spectrum in the detector, no
jumps.

You can also check directly in the _tab.lis file, that contains the
numbers to be plotted.

I do not know what could be the problem, maybe you could send one of the
.out files and the _tab.lis you get?

Regards

Paola
On Fri, 17 Apr 2020, Mitja Majerle wrote:

> Dear experts,
>
> updating this issue with this figure:
>
> The lower curve is produced with a minimalistic setup, lead cylindrical
> collimator, isotropic neutron source (gauss distribution, E0=15Mev,
> FWHM=15MeV) at one side, detector on another side (inp file in PS). The
> artefact at 20 MeV is clearly seen.
>
> The upper curve is the same situation, but instead of collimator the lead
> blocks are placed next to the axis from source to detector. What is the
> reason for this artefact ? Is the library below and above 20 MeV consistent ?
>
> Thank you,
>
> Mitja Majerle, NPI CAS
>
> PS -
>
> TITLE
> test
> GLOBAL                                          1. 1.          DEPRBODY
> DEFAULTS NEW-DEFA
> BEAM          -0.015 -0.168558    10000.       0.0       0.0 -1.NEUTRON
> BEAMPOS          0.0       0.0   -122.31       0.0       0.0
> GEOBEGIN COMBNAME
>     0    0
> * air around
> SPH blkbody1   0.0 0.0 0.0 10000.
> SPH void       0.0 0.0 0.0 1000.
> * 1 Li target
> RCC target     0.0 0.0 -122.3 0.0 0.0 0.4 3.5
> RCC ldout      0.0 0.3 -70. 0.0 0.0 70. 20.
> RCC ldin       0.0 0.3 -70. 0.0 0.0 70. 8.
> * 50 det CUP
> RCC detcup     0.0 0.0 75.4 0.0 0.0 5. 2.53
> END
> BLKBODY      5 +blkbody1 -void
> VOID         5 +void -ldout -detcup -target | +ldin
> TARGET       5 +target
> LEAD         5 +ldout -ldin
> DETCUP       5 +detcup
> END
> GEOEND
> ASSIGNMA    BLCKHOLE   BLKBODY
> ASSIGNMA      VACUUM      VOID
> ASSIGNMA      VACUUM    DETCUP
> ASSIGNMA     LITHIUM    TARGET
> ASSIGNMA        LEAD      LEAD
> MATERIAL          3. 0.534                              LITHIUM
> MAT-PROP                             40.   LITHIUM
> MAT-PROP         10. LITHIUM                    DPA-ENER
> STERNHEI      3.1221    0.1304    1.6397   0.95136    2.4993 0.14LITHIUM
> MGNFIELD         20.       0.2      0.10       0.0     0.529 0.0
> USRTRACK          1.   NEUTRON      -25.    DETCUP    100.54 400.detcup
> USRTRACK        0.10 0.0                                      7. &
> RANDOMIZ         1.0        0.
> START           3E+8                                     0.0
> STOP
>
>
>
> On 14.04.2020 21:23, Mitja Majerle wrote:
>
>> Dear FLUKA experts,
>>
>> I observed a strange artefact of the neutron spectrum when using lead in my
>> geometry:
>>
>> It occurs at 20 MeV, at the transition where multigroup transport takes
>> over. Below 20 MeV, there is 10% increase of the neutron flux, which is
>> unphysical. It is very pronounced for lead, barely visible if I change the
>> material to IRON, and dissapears if I replace material LEAD with VACUUM. I
>> am aware of different binning, what is on the Figure are FLAIR plots from
>> _tab.lis files. I am trying to break down the geometry and source to
>> something simpler to demonstrate here, but it takes time and maybe somebody
>> has already seen something similar and can help ?
>>
>> Thank you,
>>
>> Mitja
>>
>>
>


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Received on Sun Apr 26 2020 - 14:16:10 CEST

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