R: Re: [fluka-discuss]: Neutrons on carbon still

From: <francesca.belloni_at_libero.it>
Date: Wed, 5 Aug 2015 19:53:01 +0200 (CEST)

Hi,

   thanks a lot!!!

I was so sure I was shooting 18 MeV neutrons that I did not checked that at
all...
Thanks also for all the explanations.
The final goal of the simulations would be to reconstruct the response of the
detector to
an incident neutron beam.
About the last point you mentioned, does it mean that since the charged
particles
by low energy neutrons are not generated I can not score the energy they
deposit in the diamond,please?


Thanks really a lot!

Regards,
Francesca




>----Messaggio originale----
>Da: Francesco.Cerutti_at_cern.ch
>Data: 05/08/2015 18.58
>A: "francesca.belloni_at_libero.it"<francesca.belloni_at_libero.it>
>Cc: "FLUKA discussion"<fluka-discuss_at_fluka.org>
>Ogg: Re: [fluka-discuss]: Neutrons on carbon still
>
>
>Hi Francesca,
>
>you believe to shoot a 18 MeV (kinetic energy) neutron, whereas you are
>shooting a 18 MeV/c (momentum) neutron, which - as written in the
>quite useful Beam properties section of the output - has a kinetic energy
>of 170 keV. So we are in a region (group #144) where one just expects
>capture (apart from elastic), indeed yielding 13C (on 12C) and 14C (on the
>small fraction of 13C).
>
>Note also the following:
>
>- your interpretation of the residual nuclei probabilities is wrong, see
>http://www.fluka.org/web_archive/earchive/new-fluka-discuss/6203.html
>
>- you are in the world apart of low energy neutrons (also at 18 MeV
>kinetic energy), based on library data and not on models. This means that
>EVAPORAT and COALESCE are totally pointless. And also LAM-BIAS does not
>apply (pointless too), as you can realize looking at the (missing) effect
>on number (vs weight) of performed low-energy neutron interactions and CPU
>time.
>
>- additionally, as a continuation of the above point, remember that -
>apart from very few exceptions - charged particles (including residual
>nuclei) by low energy neutrons are not generated explicitly and so cannot
>be transported (IONTRANS pointless). You can ask FLUKA to evaluate the
>production rates of low energy neutron reaction residues, but these do not
>exist as particles in the simulation. The adopted group-wise treatment
>prevents from simulating exclusive reaction channels.
>
>Ciao
>
>Francesco
>
>**************************************************
>Francesco Cerutti
>CERN-EN/STI
>CH-1211 Geneva 23
>Switzerland
>tel. ++41 22 7678962
>fax ++41 22 7668854
>
>On Wed, 5 Aug 2015, francesca.belloni_at_libero.it wrote:
>
>> Dear all,
>>
>>        I am still trying to get alphas out of n+diamond_material
interaction, but with no
>> success.
>> So I switched to another code and for a 5 m thick diamond, I get alphas
(and other heavy
>> ions).
>> Then I went back to FLUKA and reduced the input at the minimum: only a
diamond 500 cm
>> thick and neutrons striking it.
>> I asked RESNUCLEI in the diamond region, but I only get C13 and C14, as
product of n+natC.
>> Could anyone give a look, please?
>>
>> If I look at the output file everything seems to have been activated
>> In my *.inp LOW-NEUT, WHAT(4)=4 asks for a printout of  the information
about the residual
>> nuclei. This is dumped on the *.out file.
>>
>> If I look at my *.out file I see that the neutrons I am shooting belong to
the Neutron
>> (low energy)
>> Xsec group number 5:
>>
>>
>> Neutron group n.:    5  upper limit 1.8221E-02 GeV,  average energy 1.7995E-
02 GeV,
>>                                   velocity 5.7846E+09 cm/s,  momentum 1.8477
E-01 GeV/c
>>
>>  
>> Later on, on the same *.out file, there is written that the FLUKA medium
number 26
>> corresponds to the Xsec medium number 1.
>>
>>
>>    Fluka medium     Name     Xsec medium  atomic density          Id.
1        Id.
>> 2        Id. 3
>>      number                   number     ( at/(cm barn) )
>>
>>          1        BLCKHOLE         0         0.0000
E+00               0           
>> 0            0
>>
>>          2        VACUUM        1000         0.0000
E+00               0           
>> 0            0
>>
>>         26        DIAMOND          1         1.7649E-
01               6          
>> -2          296
>>
>>
>> Going down again in the *.out file there is written:
>>
>>  Residual nuclei informations for medium    1
>>
>>   Group:    1   A     Z    Prob
>>
>>               12     6    7.54E-01
>>               11     5    9.09E-01
>>               13     6    9.09E-01
>>               12     5    9.36E-01
>>                9     4    1.00E+00
>>               14     6    1.00E+00
>>                1     1    7.44E-02
>>                2     1    1.07E-01
>>                4     2    6.44E-02
>> [..]
>>
>>  Group:    5   A     Z    Prob
>>               12     6    7.87E-01
>>               11     5    9.11E-01
>>               13     6    9.12E-01
>>               12     5    9.48E-01
>>                9     4    1.00E+00
>>               14     6    1.00E+00
>>                1     1    4.18E-02
>>                2     1    1.18E-01
>>                4     2    5.25E-02
>>
>>
>> Therefore it means that in FLUKA the neutrons I am shooting have a certain
probability
>> (different from 0.0)  to interact with the diamond and give alphas,  Be-
9,  B-11 and B-12.
>>
>> I thought it could have been a problem of statistics (I shoot 9E+7 neutrons
on a material
>> where lam-bias=-0.001) . But looking at those probabilities, it seems it's
more likely to
>> get B-12 than C-13  (IF i am understanding the table correctly...which is
not sure).
>>
>> But I get C-13 and C-14 only.
>>
>>
>> What am I missing,please?
>>
>> Thanks,
>>
>> regards,
>>
>> Francesca
>>
>>
>>


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Received on Wed Aug 05 2015 - 21:11:48 CEST