From: Giuseppe Battistoni (Giuseppe.Battistoni@mi.infn.it)
Date: Thu Nov 15 2007 - 10:43:28 CET
That comment was intended exactly in the way Alberto answered: the
energy of "low-energy" neutrons
is binned in a non-straightforward way. Therefore
1) one has, at minimum, use variable energy bin-width
with limits exactly equal to those of the 72 groups (see the FLUKA
manual at the chapter relevant for low-energy neutrons). If not, plots
are meaningless or wrong!.
You can use ntuples, but you must be very careful and remember that when
you extract plots from them.
2) you can use mgdraw with that caveat, but on top of this question of
histogramming, you have to take into account that even when you are not
using explicitly biasing techniques, low-energy neutrons might have a
weight different from one (Alberto can probably confirm this). In that
case the simple counting of neutrons is again meaningless. Each neutron
has to be accounted for using its weight. Again, this is something
that you must consider in your ntuples.
So, everything can be done, but this is a typical case in which, if you
prepare a scoring of your own, you must be very careful and check twice.
Giuseppe Battistoni
bottai@fi.infn.it wrote:
>
> Dear Alberto ,
>
> my initial idea was to use mgdraw.f and hbook like in the
> example : http://lxmi.mi.infn.it/~battist/fluka_hbk/
> but then I read :
>
> "
> 2) When the user is interested in the multigroup low energy neutron
> transport,
> SIMPLE HISTOGRAMMING, like the standard HBOOK case here described, IS
> MEANIGLESS.
> For the above cases, only the standard FLUKA output, followed, if
> needed, by
> offline post-processing prepared by the user, can avoid the
> introduction of
> technical mistakes."
>
> So I was a little worry about using mgdraw, non undestanding
> well what can be done to avoid problems and why exactly histogramming
> is not possible for such low-energy neutrons (creating an NTUPLE
> directly without having to reprocess output would be easier for me).
>
> Sergio
>
> Quoting Alberto Fasso' <fasso@slac.stanford.edu>:
>
>> On Wed, 14 Nov 2007, bottai@fi.infn.it wrote:
>>>
>>> I'd like to use Fluka but before starting
>>> I've the following question :
>>>
>>> I need to score , event by event , the low energy neutrons
>>> exiting from a calorimeter (or passing through a volume around
>>> it) , recording for each event the multiplicity
>>> and the energies of the neutrons. Is it possible or in some
>>> way this kind of scoring is meaningfull due to multigroup
>>> low-energy neutrons transport ?
>>>
>>> which is the best approach for such scoring , is it possible with
>>> EVENTBIN ?
>>>
>>> best regards Sergio Bottai
>>
>> You can use EVENTBIN, but take into account the following:
>> 1) The energy of the neutrons escaping from the calorimeter is
>> not known exactly, but is known only with a resolution equal to
>> the width of the energy groups
>> 2) EVENTBIN, like USRBIN, does not score the number of neutrons
>> per event, but the neutron tracklength in a specified bin (or
>> in a specified region, if you chose region binning)
>>
>> Remark number 1) is valid in any case, independent of the command
>> you use. The neutron energy is not known better than the group width
>> even inside the program itself.
>>
>> You can avoid the problem described in remark number 2)
>> by using instead USERDUMP and writing a user routine mgdraw.f.
>> In this case you can get the actual number of escaping neutrons,
>> doing some programming after ENTRY BXDRAW (boundary crossing)
>> and after ENTRY EEDRAW (end of event).
>>
>> Alberto
>>
>>
>> -- 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@slac.stanford.edu
>>
>
>
>
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