Re: Problems with LOW-BIAS card

From: Mina Nozar <>
Date: Fri, 22 Jul 2011 10:56:07 -0700

Dear Paola and Danny,

This is indeed the case for us. The depleted Uranium Oxide (d_UO2) target
is enclosed by a Tallium container and the proton beam passes through the
thin Ta container window (0.38 mm in thickness) before impinging on the
d_UO2 target. In the Fluka input setup, I did not have the LOW_BIAS
cutoff applied to both regions and only to the d_UO2 region. So, the
neutron flux distribution crossing the boundary (from Ta to d_UO2) are
secondary neutrons produced in the Ta container. The neutron flux in the
target scored via the USRTRACK estimator shows a similar distribution.

Paolo, from your explanation, it seems that I would not have seen the
behaviour had I applied the LOW-BIAS energy cutoff to both regions. Is
this true? I can run a quick test to check.

Thank you very much for investigating this,

On 11-07-22 12:45 AM, Paola Sala wrote:
> Dear Danny,
> thank you for your mail,
> indeed there is a small bug in the code:
> the check on the LOW-BIAS cut-off is not
> applied at the first step after a boundary crossing.
> This could also be the source of the problems experienced
> by Mina Nozar : neutrons are killed only *after* the first interaction or
> scattering in a new region.
> Note that neutrons that are generated INSIDE the region to which LAM-BIAS
> is applied, either by source or by interactions, are IMMEDIATELY checked.
> The problem is there ONLY for neutrons coming from a non-cut region and
> entering into a cut region, and only for the first step.
> The bug has been solved, the patched version will be available with the
> next respin.
> Ciao
> Paola
> ************************
> Dear FLUKA users,
> Hi,everyone.I have some trouble when I am using LOW-BIAS card.I have
> defined a neutron source and 2 regions stuffed with Cobalt.The radium of
> the source is big enough to cover the regions.I want to emit the
> neutrons entering the region called "target",while neutrons entering
> another region called "t" can just go through.The cut-off energy set in
> the LOW-BIAS card is higher than the source energy set in the BEAM
> card.However,neutrons can be detected in both regions.There must be some
> problems in it.The input and output files are attached to this letter.
> Any ideas would be helpful.
> Yours,
> Danny
> ***********************
> Paola Sala
> INFN Milano
> tel. Milano +39-0250317374
> tel. CERN +41-227679148
Received on Sun Jul 24 2011 - 15:50:50 CEST

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