Re: Fluka_neutron_fluence_always_zero

From: Mary Chin <>
Date: Sat, 3 Mar 2012 15:34:44 +0100


In order to see photoneutrons from a 3 GeV electron beam targetting copper
you don't need to play with parameters. You should be able to see them
even without LAM-BIAS. Just insert the PHOTONUC card and run a few more
histories (one single history is not the best bet!)

You can verify the presence of neutrons in .out under the table, "Number
of secondaries generated in inelastic interactions per beam particle".

Next, if you wish to score them, change your USRCOLL to USRTRACK.

Next, if you are not satisfied with the statistics, consider LAM-BIAS.

:) mary

On Thu, 1 Mar 2012, vahan petrosyan wrote:

> Many thanks for attention.
> I tried your suggestion and it didn't give any results. I tried to play with
> parameters but without success . I still get zeroes for neutrons. For
> photons it works and always worked normally.
> If I ask you could you send me my input file with corrections already done
> in it?
>> On Wed, Feb 29, 2012 at 10:35 PM, Alberto Fasso' <>
>> wrote:
>> Dear Vahan,
>> to get neutrons and protons with an incident electron beam, you
>> need to
>> switch on photonuclear reactions in the materials present:
>> And since photonuclear reactions have a very small cross section
>> compared
>> to other photon reactions, you need also to bias the photon
>> hadronic
>> mean free path:
>> LAM-BIAS 0.0 0.02 1.0 PHOTON
>> Look up these two commands in the manual to understand better
>> how they
>> are used.
>> You say also that you cannot get photon fluence. Your input is
>> set for protons,
>> not photons, so the above explanation is valid.
>> To calculate photon fluences, you cannot use USRCOLL: it can be
>> used only for neutrons and hadrons. Use USRTRACK instead.
>> Alberto
>> On Tue, 28 Feb 2012, vahan petrosyan wrote:
>> Hi I am a student and try to use Flair under XP with
>> VirtualBox. I setuped
>> it successfully but I have One problem.
>> My example: Electron beam with 3Gev energy falls on
>> COOPER target.
>> Whatever I do, I changed electrons energy and
>> particle number, I get always
>> ZEROES in output for neutron or photon fluence.Why?
>> Is it a bug or I did
>> something wrong? I followed according flair
>> documentation.
>> I tried both USRCOLL and USRTRACK card without luck.
>> I tried these cards for
>> Photon fluence they worked. Problem with neutrons.
>> I attached my input file. If you have a time could
>> you take a look?
>> If you help me I will be very appreciate.
>> With regards V. Petrosyan
Received on Mon Mar 05 2012 - 09:33:41 CET

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