Re: "low energy neutrons not found" error in the new FLUKA version

From: Florian Sommerer <>
Date: Wed, 25 Mar 2009 12:30:40 +0100

Dear Vitaly,

your 5000 primaries are not enough to get a reasonable number of
neutrons into your detector, you will need an orders of magnitude
higher number of primaries. I fear that this would lead to
unacceptable long execution times. I would suggest you to improve your
simulation by using importance biasing. If you are not familiar with
importance biasing you can have a look at the FLUKA course website (
) where you can find an example (Exercise 7).

By the way: your primaries are deuterons which you create by making
heavy ions with Z=1 and A=2. You should use the particle DEUTERON
(sdum of the BEAM card) instead. However, FLUKA corrected that mistake
as you can see in the test001.out file. But check carefully if you got
what you wanted: for heavy ions you have to give the total energy per
nucleon and for deuterons just the total energy.

Cheers, Florian

On Mar 24, 2009, at 12:53 PM, Vitaly Pronskikh wrote:

> Dear Guiseppe,
> many thanks for the suggestion about correction
> for the new neutron group properties in FLUKA.
> However, after all corrections, I get the new
> 260 group low energy part of the neutron spectrum
> empty. Is it possible to suggest what the reason is ?
> Vitaly Pronskikh
> <test.inp>
Received on Wed Mar 25 2009 - 17:58:33 CET

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