# RE: A neutron problem

From: Joachim Vollaire <joachim.vollaire_at_cern.ch>
Date: Wed, 16 Dec 2009 00:01:50 +0100

Hi Ali
It may be that you are plotting a lethargy plot with gnuplot (I guess
you are using flair ?). If you want to generate a similar plot with
excel take the tab_lis file value, multiply by the energy bin width and
then divide by ln (Emax) - ln (Emin), using a log scale in x in excel
then the plots should be similar... Send me the output (tab lis) and the
excel if this not the case.

value * (Emax-Emin)/(ln Emax- ln Emin) for each bin

cheers
Joachim
________________________________

From: owner-fluka-discuss_at_mi.infn.it on behalf of ali taheri
Sent: Tue 12/1/2009 10:20 AM
To: fasso_at_slac.stanford.edu
Cc: fluka-discuss_at_fluka.org; Francesco Cerutti
Subject: Re: A neutron problem

Dear Mr Fasso

Thank you for guidance, it's absolutely helpful.

But there is another question about USRTRACK output: when I use
GNUPLOT to plot the neutron spectrum from ***_tab.lis there is a
normalized graph, but when I enter the same data in Excel and
normalize them by multiplying in "energy bin width * 2pi" , there is
another spectrum shape with different values!

So I don't know which of them is my real neutron spectrum, and which
integration is
neutron fluence.

I will be thankfull if there is any help

Regards
Ali

On 12/1/09, Alberto Fasso' <fasso_at_slac.stanford.edu> wrote:
> There is a very simple way to get the neutron fluence in any
> energy range. The result file from USRTRACK and USRBDX gives you, in
> addition to the differential spectrum, also the cumulative spectrum at =
the
> end of each energy interval (or each of the 260 energy groups below 20 =
MeV).
> The integral fluence between any pair of energies (therefore in any =
energy
> range) can be obtained as the difference between the corresponding =
values
> of the cumulative spectrum.
> As Francesco says, the energies can perhaps be approximated (3.927864 =
eV
> instead of 4 eV and 10.33298 keV instead of 10 keV). Although the =
error is
> small, you can make it even smaller by interpolation (linear, or even =
better
>
> Alberto
>
> On Sun, 29 Nov 2009, Francesco Cerutti wrote:
>
>>
>> Dear Ali,
>>
>> if you wish to get 3D maps of neutron fluence in the cavity =
corresponding
>> to different neutron energy ranges, you can clone a USRBIN detector =
in
>> your input and link a fluscw routine (to be activated by USERWEIG =
with
>> WHAT(3)=3D3.0) where, according to the USRBIN index value (JSCRNG, =
for
>> ISCRNG =3D 2), you prevent from scoring (setting LSCZER=3D.TRUE.) =
unless the
>> neutron energy (PLA, check the sign according to the routine header) =
falls
>>
>> in the respective range. Of course the latter will be approximated by =
the
>> group structure (your 4 eV limit becomes 3.927864 eV and the 10keV =
one
>> 10.33298 keV).
>> [If instead you look at the neutron spectrum averaged over the cavity =
as
>> produced by USRTRACK, neutron fluences corresponding to the indicate
>> ranges are obviously immediately given by the integration of the =
spectrum
>> over these energy ranges].
>>
>> Hope this helps
>>
>> Francesco
>>
>> **************************************************
>> Francesco Cerutti
>> CERN-EN/STI
>> CH-1211 Geneva 23
>> Switzerland
>> tel. ++41 22 7678962
>> fax ++41 22 7668854
>>
>> On Sun, 29 Nov 2009, ali taheri wrote:
>>
>>> Dear Francesco,
>>>
>>> In fact my problem is to determine the neutron flux in these 3
>>> ranges: 0 to 4 eV , 4eV to 10 keV and 10 keV to 10 MeV .
>>> Of course I've used the pre-defined bins to plot neutron spectrum,
>>> but in BNCT (is a kind of neutron therapy) it's needed also that we
>>> know these fluxes separately!
>>>
>>> Thank you for your attention
>>> Ali
>>>
>>> On 11/29/09, Francesco Cerutti <Francesco.Cerutti_at_cern.ch> wrote:
>>>>
>>>> Dear Ali,
>>>>
>>>> I miss the problem. The 260 pre-defined bins (from 20 MeV down to =
1e-5
>>>> eV)
>>>> are indicated in the manual and are printed in the neutron scoring
>>>> files.
>>>> The transport of neutrons below 20 MeV cannot prescind from this
>>>> binning
>>>>
>>>> Ciao
>>>>
>>>> Francesco
>>>>
>>>> **************************************************
>>>> Francesco Cerutti
>>>> CERN-EN/STI
>>>> CH-1211 Geneva 23
>>>> Switzerland
>>>> tel. ++41 22 7678962
>>>> fax ++41 22 7668854
>>>>
>>>> On Sun, 29 Nov 2009, ali taheri wrote:
>>>>
>>>>> Dear Fluka Users
>>>>>
>>>>> Hi
>>>>> I am working on a simple Neutron source,there is a vacuum cavity
>>>>> and I need to know the neutron fluence in thermal,epithermal and
>>>>> fast ranges separately in the cavity.
>>>>>
>>>>> As I knew,in Fluka we can't specify energy bins for neutrons! =
>>>>> help me to solve this problem.
>>>>>
>>>>> I'd be thankful to you for help
>>>>>
>>>>> Best Regards
>>>>> Ali Taheri
>>>>>
>>>>>
>>>>
>>>
>>
>>
>
> --
> Alberto Fasso`
> SLAC-RP, MS 48, 2575 Sand Hill Road, Menlo Park CA 94025
> Phone: (1 650) 926 4762 Fax: (1 650) 926 3569
> fasso_at_slac.stanford.edu
>
Received on Wed Dec 16 2009 - 09:33:53 CET

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