Dear Vladimir
You have to use the pointwise cross sections as you were doing. The
self-shielding correction will then be computed automatically.
The misunderstanding is that
W natural and W natural SelfShielded
are for GROUPWISE cross sections, there are no separate materials,
self-shielded and not self-shielded for pointwise, because the "correct"
self-shielding will automatically come out runtime using them, for both
resolved resonances and unresolved ones.
So forget the existence of two different W for the groupwise corss
sections, they are not used if you select pointwise and the correct
selfshielding will come out.
Ciao
Alfredo
> Dear Alfredo,
> thank you for the answer.... BUT I cannot fully understand it.
>
> Let me explain my understanding for now about self-shielding problem:
>
> 1) in the input cards : W5.inp and W5sh.inp
> I use LOW-PWXS cards, and in both cases
> in the FLUKA output I see lines :
> ............
> *** Pointwise cross sections activated for Xsec mat. # 7 TUNGSTEN
> ***
> *** corresponding to the Fluka mat. # 23 TUNGSTEN ***
> *** decomposed into # 5 isotopes as following***
>
> Isotope # 1 id # 17 fraction: 0.3064
> activated from 1.00000E-14 GeV to 2.00000E-02 GeV, T = 296.00 K
> read from file: 741840-endfb8r0-296.pwx
>
> Isotope # 2 id # 18 fraction: 0.2843
> activated from 1.00000E-14 GeV to 2.00000E-02 GeV, T = 296.00 K
> read from file: 741860-endfb8r0-296.pwx
>
> Isotope # 3 id # 19 fraction: 0.2650
> activated from 1.00000E-14 GeV to 2.00000E-02 GeV, T = 296.00 K
> read from file: 741820-endfb8r0-296.pwx
>
> Isotope # 4 id # 20 fraction: 0.1431
> activated from 1.00000E-14 GeV to 2.00000E-02 GeV, T = 296.00 K
> read from file: 741830-endfb8r0-296.pwx
>
> Isotope # 5 id # 21 fraction: 0.0012
> activated from 1.00000E-14 GeV to 2.00000E-02 GeV, T = 296.00 K
> read from file: 741800-endfb8r0-296.pwx
> -------------------
>
> i.e. why I got the same results for both cases.
> and it means that FLUKA uses point-wise cross sections ...
>
> 2) now in the manual I see lines :
> .....
> 10.5.1 Resonances and self-shielding with pointwise cross sections
>
> Resolved resonances are obviously fully described in the pointwise
> cross sections, properly broadened at the given temperature.
> In the resolved resonance energy range self-shielding is
> automatically accounted for.
> ...........................
>
> so, I see, that using LOW-PWXS library all resonances in
> my E-region will be self-shielded corrected
> i.e why I got the same results for 2 input cards
>
>
> 3) my understanding was:
> a) I see 2 W74 materials in the manual : p.360
> W natural and W natural SelfShielded
> and my thought was - compare these 2 materials
> and I get self-shielding correction...
>
> b) now, if I got your answer
> I have to compare 2 variants :
> - with LOW-PWXS card
> - and with commented this card, i.e with group method, no
> point-wise
> and remove MAT definition for self-shielded material
>
> then I will get self-shielding correction
>
> ... otherwise it means that FLUKA cannot give this correction ?
>
> is it correct ?
>
> -------------------------
>
> thank you
> Vladimir
>
>
>
> On 04.10.2023 16:53, alfredo.ferrari_at_mi.infn.it wrote:
>> 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 Thu Oct 05 2023 - 17:34:00 CEST