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 - 11:33:43 CEST