Re: [fluka-discuss]: Area of a complicated surface

From: Alessandro Calamida <alex.calamida2_at_tiscalinet.it>
Date: Wed, 18 Mar 2020 18:15:31 +0100

After your correction I obtained a good results. The theorical Area was
312.59 cm^2 and the real one 314.16 cm^2.

I run 10^6 particle for the simulation. An increase in statistics maybe
could decrease the difference between the two valus. But the methods
could be a good alternative to measure tha area of complicated surface.

Best regards and thank you for your time, Alessandro Calamida.

Il 18/03/2020 15:34, Answers ha scritto:
> Hello
> the USRBDX scoring should be FLUENCE, not current (what(1)=111 , not 11)
> ( in an isotropic field, there is a factor two between fluence and
> current, that is exactly what you find)
> Regards
>
> On Wed, 18 Mar 2020, Alessandro Calamida wrote:
>
>> Dear FLUKA experts,
>>
>> I tried with differents bodys and test surface. Unfortunately the
>> method that you suggested seems to not work for me.
>>
>> The last attempt was with a sphere and it leads the results of
>> At=624.86 cm^2 instead of an Ar=314.16 cm^2 as it should be. The
>> sphere has a radius of 5 cm.
>>
>> Maybe I made some mistakes. What is the correct value given by the
>> usrbdx scoring that I have to use?
>>
>> I attach on the email the input and the scoring file.
>>
>> Best regards and thank you for your time, Alessandro Calamida.
>>
>> Il 16/03/2020 10:27, Answers ha scritto:
>>> Dear Alessandro
>>>
>>> there is no obvious way for computing the surface of a complicated
>>> region.
>>>
>>> However there could be a possibility (never tested... ) using the FLOOD
>>> option in the BEAMPOS card.
>>>
>>> This possibility works perfcetly when computing volumes for
>>> complicated regions, on paper it could work for surfaces as well (no
>>> guarantee).
>>>
>>> Let me explain the logic (see also the manual for the BEAMPOS card):
>>>
>>> a) your problem should have for this purpose all regions (apart
>>> blackhole)
>>>    filled with vacuum;
>>> b) you define a beam (whichever particle, say PHOTON's) and put a
>>>    BEAMPOS card with SDUM=FLOOD;
>>> c) this will generate an isotropic and uniform fluence inside the
>>> sphere
>>>    with radius = WHAT(1) of the BEAMPOS card, be sure such radius
>>>    contains wholly your region;
>>> d) the fluence so generated will be equal to 1/(pi R^2), this is an
>>>    exact analytical result;
>>> e) you define a USRBDX, fluence-like, two-ways, estimator between the
>>>    region you want to know the surface of and the surrounding, with
>>>    normalization surface=1. It would be highly preferable/simple if the
>>>    surrounding is made of a single region (you could make an ad hoc
>>>    run/geometry for this purpose);
>>> f) you run Fluka for sufficient primaries/cycles in order to get
>>>    a negligible statistical error on the USRBDX result (let's call
>>>    its result F);
>>> g) since you know that F/Area should be equal to 1/(pi R^2) you
>>>    can easily derive Area
>>>
>>> Normally this method is used in order to compute volumes using
>>> a tracklength estimator instead of a USRBDX, and using the
>>> equation F_track_length/Volume = 1/(pi R^2). This works perfectly
>>> and it is sure to give the exact answer within the statistical
>>> errors. On paper I do not see an obvious reason why it should not
>>> work for computing an area as well, there will be numerical precision
>>> issues since for grazing incidence a fluence boundary crossing
>>> estimator would result into an infinite (or better a division by
>>> zero). This
>>> is protected in the code and the influence of the necessarily
>>> approximate protection should be small, however as I said before we
>>> never tried this method.
>>>
>>>                 Let us know if it works!
>>>
>>> On Fri, 13 Mar 2020, Alessandro Calamida wrote:
>>>
>>>> Dear FLUKA experts,
>>>>
>>>> In my geometry I have a regione that is the union of different bodies.
>>>> Calculating the surface of it is quite complicated and so I cannot put
>>>> the normalization factor in the USRBDX scoring.
>>>>
>>>> There is a FLUKA or Flair tool that allows to evaluate surfaces.
>>>>
>>>> I attach in the email the input of the file. The region from wich I
>>>> need
>>>> the surface is the SUPP_TRG.
>>>>
>>>> Best regards and thank you for your time, Alessandro Calamida.
>>>>
>>>>
>>>>
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>>
>>
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Received on Wed Mar 18 2020 - 19:59:59 CET

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