Re: neutron transport threshold

Dear Christoph,

thanks for your iteration and your input.

In fact, for historical reasons [in the past, PART-THR applying to neutron
was used to set the boundary with the low energy group treatment], a
neutron transport threshold between 20 and 58 MeV turns out to be
forbidden, implying the forced stop you reported. This will be fixed.

>From the physical point of view, when setting a neutron cutoff so waiving
their transport down to thermal energies, one has to keep in mind that, as
the neutron kinetic energy reaches the input value, it is dumped on the
spot. For many purposes (evidently for energy deposition and activation
calculations) this just makes no sense.

All the best

Francesco

**************************************************
Francesco Cerutti
CERN-EN/STI
CH-1211 Geneva 23
Switzerland
tel. ++41 22 7678962
fax ++41 22 7668854

On Mon, 8 Feb 2010, Christoph Bobeth wrote:

>
> Dear Francesco,
>
> thank you for your clarification concerning the neutron transport
> threshold.
>
> I was writing about "conflicts" because when I raise the transport
> threshold over 20 MeV FLUKA stops running with the following message
> in the *.err-file and *.out files:
>
> Abort called from KASKAD reason ??? WHY HERE ??? Run stopped!
> STOP ??? WHY HERE ???
>
> I have attached the input file and if I change the line
>
> PART-THR -.021 NEUTRON ANEUTRON 1.0 0.0
>
> to
>
> PART-THR -.019 NEUTRON ANEUTRON 1.0 0.0
>
> everything runs as expected. Thats why I was wondering about the
> exact interplay of PART-THR and LOW-NEUT and the 20 MeV threshold
> below which the low energy neutron transport sets in.
>
> I have attached also all my user-routines in case you want to
> have a closer look - I am sorry, perhaps it is a bit messy, but
> I did not try to reduce the input-file/user-routines to a minimal
> configuration which still would have still the same problem.
> I can try to do so if you like.
>
> The reason I am trying to raise transport thresholds is, that
> I would like to optimise my geometry for pion production with
> momenta larger then 400 - 500 MeV and I hoped to gain running
> time this way, since I would expect that particles with momenta
> around 20-50 MeV will not contribute much. Once I have found the
> optimal setup I wanted to lower the thresholds to their defaults
> and study energy deposition and other things.
>
> Cheers,
> Christoph.
>
> Francesco Cerutti wrote:
>>
>> Dear Christoph,
>>
>> since quite some time ago, the neutron transport threshold can be fully
>> controlled with PART-THR. If you input a value <20MeV, this is translated
>> into the respective group (which will become the cutoff group); moreover,
>> one can *raise* locally the threshold on a region basis with LOW-BIAS
>> (obviously not above 20MeV). If instead you give in PART-THR a value
>>> 20MeV, the low energy neutron transport is not activated at all,
>> regardless of the implicit request from the DEFAULTS settings and of the
>> explicit presence of LOW-NEUT in the input (which by the way in this case
>> is clearly contradictory). Why do you talk about conflict?
>>
>> Cheers
>>
>> Francesco
>>
>> **************************************************
>> Francesco Cerutti
>> CERN-EN/STI
>> CH-1211 Geneva 23
>> Switzerland
>> tel. ++41 22 7678962
>> fax ++41 22 7668854
>>
>> On Tue, 26 Jan 2010, Christoph Bobeth wrote:
>>
>>> Dear FLUKA users,
>>>
>>> I would like to raise the neutron transport cutoff threshold above 20 MeV
>>> using PART-THR, but this seems to conflict with LOW-NEUT. How can
>>> I deactivate the LOW-NEUT card?
>>>
>>> With best regards,
>>> Christoph Bobeth.
>>>
>>>
>
>
Received on Thu Feb 11 2010 - 00:36:41 CET