[Fwd: Re: AW: [fluka-discuss]: COMPOUND card error]

From: <alfredo.ferrari_at_mi.infn.it>
Date: Fri, 16 Jul 2021 15:31:17 +0200

---------------------------- Original Message ----------------------------
Subject: Re: AW: [fluka-discuss]: COMPOUND card error
From: alfredo.ferrari_at_mi.infn.it
Date: Fri, July 16, 2021 3:30 pm
To: "Ophoven, Niklas" <n.ophoven_at_fz-juelich.de>
--------------------------------------------------------------------------

Dear Niklas

the atomic weight used by Fluka is indeed "atomic", that is is the average
weight of all atoms, in your case:

Pa_fluka = [ 1 Psm + 3 Pcl + 7 Po + 14 Ph ] / 25

your one is the molecular weight:

Pa_niklas = 1 Psm + 3 Pcl + 7 Po + 14 Ph

there is no problem ! The important things is to be consistent, Fluka
knows that the number of atoms (note *atoms*) per unit volume is given by

rho Navog / Pa_fluka

and that each atom can be Sm, Cl, O, or H in the proportions 1:3:7:14,
and everything is computed correctly.

The densities you gave in input are those of Samarium and Chlorine
*alone*, they do not matter at all in the compound: they would matter if
you were using somewhere Samarium or Chlorine as such. Those that you
quote from the output are the partial densities *in the compound*, eg for
Samarium:

rho_Sm = rho_tot Psm / [ 1 Psm + 3 Pcl + 7 Po + 14 Ph ]

where rho_tot = 2.383 as per your input.

Ciao
Alfredo

> Dear Alfredo,
>
>
> thank you very much for your detailed answer and time. I have run your
> attached input, however, the problem remains. As I have already written, I
> already tried exactly what you did, to define water with hydrogen and
> oxygen rather than using pre-defined water. I have attached the output
> file generated with your input. Again, the atomic weight and atomic number
> of the compound are completely incorrect (see line 1605). I have checked
> the relative atom content, that is now correct. Also, the partial
> densities of samarium and chlorine as defined in the input (7.356 g/cm^3
> and 3.21E-03 g/cm^3) are not correctly listed in the ouput (the output
> gives densities of 0.93598 and 0.66204 g/cm^3, respectively) . As long as
> FLUKA does not use the correct atomic weight (it should be 382.82 g/mol
> instead of 15.31 g/mol, as indicated in the output file), the results will
> be not correct, right? Why does FLUKA not calculate the atomic weight of
> the compound properly?
>
>
> Kind regards,
>
>
> Niklas
>
> ________________________________
> Von: alfredo.ferrari_at_mi.infn.it <alfredo.ferrari_at_mi.infn.it>
> Gesendet: Freitag, 16. Juli 2021 08:36:31
> An: Ophoven, Niklas
> Cc: fluka-discuss_at_fluka.org
> Betreff: Re: [fluka-discuss]: COMPOUND card error
>
> Dear Niklas
>
> your problem derives from the fact that Fluka assumes compositions "per
> atom" and not "per molecule" when making a compound of a compound. So in
> Water "one atom" is 1/3 H2O and hence the result you get.
> This behaviour could appear counter-intuitive, however for complex
> molecules, or for materials with a non standard isotopic composition there
> is no obvious way for the code to behave otherwise, It is important for
> all users to be well aware of this behaviour, we shall stress it better
> in the manual in a future respin.
>
> You can easily define your compound as in the example attached. I checked
> and it works as expected.
>
> I also corrected the PART-THR card where you were asking 10^-5 eV as
> threshold for all particles, while it makes sense for neutrons only, for
> the other particles typically it is 1 keV the minimum energy (100 eV
> for photons). It was immaterial because the code was anyway raising
> those thresholds to the minimum allowed.
>
> Ciao
> Alfredo
>
>> Dear FLUKA experts,
>>
>>
>> I want to obtain the gamma self-absorption factors for different primary
>> photon energies. Therefore, I use a quite simple geometry with the
>> sample
>> surrounded by a spherical surface detector (USRBDX). The sample is made
>> of
>> samarium(III) chloride heptahydrate (SmCl37H2O). I have defined chlorine
>> and samarium with a MATERIAL card and linked them together with
>> pre-defined water by means of a COMPOUND card. The results are wrong,
>> and
>> the output file (see attachment, line 1603) shows that the compound is
>> made wrong, i.e. the atomic number and weight are incorrect as well as
>> the
>> atom content of samarium in the compound is wrong in the output. I have
>> also tried to define the compound by means of mass fractions instead of
>> relative atom contents as well as with hydrogen and oxygen instead of
>> pre-defined water, but unfortunately this did not solve the problem. I
>> have attached my input file as well as the output file.
>>
>>
>> It would be very helpful, if you could give me some hints what might be
>> the problem. Thanks in advance.
>>
>>
>> Kind regards,
>>
>>
>> Niklas Ophoven
>>
>>
>> ------------------------------------------------------------------------------------------------
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>> Vorsitzender des Aufsichtsrats: MinDir Volker Rieke
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>>
>>
>



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Received on Fri Jul 16 2021 - 17:37:23 CEST

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