Re: [fluka-discuss]: Usimbs routine help ?

From: <>
Date: Fri, 28 Feb 2014 16:05:21 -0800 (PST)

Hi Benjaminas,

I didn't find usimbs.f in the link you provided but that's probably not
necessary anyway. A few basic principles:

- the simplest way to do importance biasing is to assign the importance as
WHAT(3) in the BIASING card, without any user routines;

- whether we do importance biasing via BIASING WHAT(3), usimbs.f or ubsset.f, we
always do a dry run first (eg. with START WHAT(1)=10.) to generate a .out so
that we can inspect 2 tables:
"Particle transport thresholds:" and
"Region        Particle   importances"
to verify that our intended importance values have been successfully parsed.

- the following confirm that biasing (importance and other techniques) has
indeed been at work:
1) towards the end of .out:
  "Total number of inelastic interactions (stars)" should be noticeably larger
  "Total weight of the inelastic interactions (stars)"
2) also towards the end of .out:
  "Total number of elastic interactions" should be noticeably larger than
  "Total weight of the elastic interactions:"
3) in mgdraw.f (not necessary to check this under normal circumstances) WTRACK
should sometimes have values <1.

"GeV missing" is no cause for worry. Please refer to:

An extra note: "it seems to work and no errors" is not the recommended way to do
Monte Carlo ;)

:) mary

From: Benjaminas Marcinkevicius <
Date: Tue, 4 Feb 2014 21:36:57 +0200

I am new to FLUKA and FORTRAN so my issue might be trivial but still.

1. I'm trying simplified beam dump geometry. I am using usimbs.f routine to
bias neutrons in radial direction. the routine was taken from example i got
and i modified to my problem. It seems to work and no errors that i noticed
are issued, but the neutrons do not penetrate deeper than R=340 cm. I tried
500 and 5000 particle runs and it seems that neutrons do not go further. I
haven't found any mistakes in geometry or material so thought maybe my
modification of routine was wrong.

This is link to nps=5000 run and usimbs.f routine. includes eps file with
comparison of neutron dose rate with 500 nps and 5000 nps.

2. In total energy balance in run summary it is written that 11.9 % of
energy missing, I was wondering what is the reason of this mismatch.

Any help is appreciated.
Benjaminas Marcinkevičius
Received on Sat Mar 01 2014 - 01:56:32 CET

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