Dear Vladimir
I assume you are using the group neutron cross section for W. If this is
the case, only infinitely diluted (-> no self-shielding) or fully
self-shielded cross sections are available (suitable for thick materials),
and which one is used is left to the user choice through the LOW-MAT card.
Viceversa, using pointwise cross sections (see the LOW-PWXS card), you can
get whichever degree of self-shielding adapted to your problem (at the
price of some extra CPU time). Please try with pointwise cross sections
and let us know if it works as it should for you.
Ciao
Alfredo
> Dear experts,
> I am going to analyse W resonances using flow of neutrons
> after Wnat foil : 0.2 mm width.
> I want to define self-shielding corrections for this foil,
> using FLUKA.
>
> For this I do small experiment:
> I analyze 2 W resonances for E-region : 2-9 eV (see fig-E-3-9-sigma.png)
> -------------------
> I introduce E bins with E-step = 0.010 eV
> and for each Ebin I use rndm points with K= 1000 entries.
> Each neutron starts from X=0,
> Wnat foil is disposed at X=11 m
> N counter is disposed at X= 13 m (to be close to some experiments ...)
>
> Each E-point is translated into T-points according to the expression:
>
> T= 72.29 * L / sqrt(E), (mks, m, eV)
>
> replace air by VACUUM.
> FLUKA suggests 2 variants of Wnat : ordinary and self-shielded, 300 K,
>
> So, I run 2 jobs (2 cases) :
> a) no shield, see W5.inp
> ------
> b) WITH self-shielded W : W5sh.inp
> ---------
> and use 5 cycles.
>
> RESULTS
> ========
>
> 1) FLUKA *.out files does not show any comments about self-shielded mat.
> see fig-FLUKA-T.png ,.... comparing 2 cases ===> no any
> differences
> ---------------
>
> it looks like that FLUKA uses the same input data for both cases
> ..... or I missed something in self-shielding definition ?
>
> 2) I fill also my own array for E, T data using C4 counter
>
> look at the entries for E- T- distributions:
> fig-my-E-entry.png , fig-my-T-entry.png
> ------------------ ------------------
>
> ...there is no any difference for these 2 cases... why ?
>
> 3) Q: is it possible to define self-shielding resonance correction
> using FLUKA ?
>
> 4) Q: ..or I should use the expression for capture flow after the foil:
> ?
>
>
> Ycap = ( 1 -exp(-n*d*SIGtot) ) * SIGcap/ SIGtot
>
> where expression in brackets can be treated as self-shielding
> correction,
>
> SIGtot - total cross section
> SIGcap - capture cross section
> n - atoms density, according to FLUKA it is equal to
> 6.3222E-02 ( at/(cm barn) )
> d = 0.02 cm
>
> ---------------------------------
>
> thank you,
> sorry for the long e-mail
>
> Vladimir
>
>
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Received on Wed Oct 04 2023 - 18:04:23 CEST