Re: Using LOW_BIAS to discard Fissions from low energy (<20 MeV)

Dear Mario and Alberto,

Firstly, thank you for your comments and suggestions.

After some investigating (mainly reading through the relevant sections of
the FLUKA manual), I have learned the following:

LOW-NEUT is turned on in NEW-DEFAULTS and the transport threshold for
neutrons is set to 1E-14 GeV (1E-5 eV). Setting the energy cutoff to 20
MeV in the LOW-BIAS card does not entirely get rid of
the contribution from Neutrons below 20 MeV, confirming what Mario's
point, i.e. Neutrons below 20 MeV energy are deposited at the spot.

To do a comparison check, I set up three sets of runs, Run A, Run B, and
Run C, all with NEW-DEFAULT selected as the DEFUALT.

In all three runs I scored RESNUCLEi in separate LUNs, one with Type set
to "All", one to "Spallation", and one to "Low Energy". I also scored
Neutron Fluence (crossing the Ta container into the Depleted Uranium
target) using the USRBDX estimator.

Run A: No LOW-BIAS and PART-THR cards (so the default E-5 eV threshold cut
for Neutrons)
Run B: Only LOW-BIAS card with energy cutoff set at 20 MeV
Run C: Only PART-THR card with E set at 20 MeV and PART set to Neutron

I am attaching five post script files, showing the results.
1) UO2_Dep_All_Xe-54_ProdRate.ps : residual nuclei yields

2) UO2_Dep_All_NeutronFluence_Ta_to_UO2.ps : Neutron Fluence from Ta to
Dep. UO2 target

Selected information from the output files of each run.
3) UO2_Dep_out.ps - Run A
4) UO2_DP_LB_out.ps - Run B
5) UO2_Dep_PT_out.ps - Run C

The results confirm the behaviour as explained above. However, it seems
that setting the threshold for Neutrons to 20 MeV using PART-THR, does get
rid of Neutrons with energies below 20 MeV without depositing their energy
on the spot (or ranging them out).

The output file for Run C does not have a section on "Number of
secondaries created by low energy neutron per beam particle". This makes
me think that by default, this information is not printed out if the
transport threshold for Neutrons is set to 20 MeV? For the other two
runs, the contributions under this section still do not add up to 100%. I
would have expected this to be the case for Run A (at the very least). Am
I missing something?

Also, can I ask how "stopping particles" are defined? The output file
writes out the Number of stopping particles per beam particle but I don't
know what "stopping particles" designation means.

Thank you very much and best wishes,
Mina

On 11-07-15 04:52 PM, Santana, Mario wrote:
> neutrons
> Sender: owner-fluka-discuss_at_mi.infn.it
>
> Hi Mina,
>
> The cutoff for LE/HE is related to the low-energy neutron definition in
FLUKA,
> so I believe 19.6 MeV. If you test the SCORE command that you already
> defined with different primary proton beam energies above and below that
> limit you will see how the HE-FISSION contribution vanishes when the beam
> is below that energy and slowly appears when you go above it.
>
> Similarly, you can use SCORE to test if the LOW-BIAS command applied from
> low energy group 1 (the highest energy) is enough to suppress all
low-energy
> neutron contribution as defined by FLUKA. You will see that by activating
> that command LE-FISSION does NOT entirely disappear (when neutrons reach
the
> highest low energy group, 1, they are deposited at the spot, not killed).
> However, if you use PART-THRES at 20.0 MeV (kinetic) you completely
suppress
> all low-energy neutron ('low' as defined in FLUKA) and all the fissions =
> are due to 'high-energy' protons, neutrons, etc.
>
> Mario

On 11-07-15 12:16 PM, Alberto Fasso' wrote:
> Dear Mina,
>
>> I am including results from just one run, 1 Million primaries each for
>> two separate runs: Run A: No LOW-BIAS card, Run B: With LOW-BIAS card
>> (ECUT set at 20 MeV). I would have expected the LE-FISS SD to be zero
>> for the run B. But we are getting 6.65228E-04 which is a small number.
>> Should I be accepting this as consistent with zero?
>
> My first answer was easy, but here I confess that I don't know.
> Your questions sound reasonable to me. I hope that you can get answers by
> somebody who knows better than me.
>
>> Also, should we not be getting 0 secondaries created by low energy
>> neutrons per beam particle (as reported in the output file as well) for
>> Run B? [out of curiousity, shouldn't the sum of the particle type
>> contributions add up to 100%?].
>
> Reasonable again... I don't know. Perhaps, if you would send the input
> file, I could look better into your problem.
>
>> The reason we imposed the ECUT in LOW-BIAS card for neutrons is because
>> we are interested in distinguishing low- and high-energy neutron
>> contribution to residual nuclei yield. So, Run B, resnuclei yield
>> results should be in principle lower than those from Run A since we have
>> discarded low energy neutrons. I think we could accomplish this by
>> setting Type (WHAT(1)) to 1 (Spallation) and to 2 (Low Energy) in the
>> RESNUCLEi estimator. Am I right?
>
> Yes, you are right.
>
> Alberto