Biasing neutrons

From: Jing Hantao <>
Date: Tue, 11 Nov 2008 11:00:12 +0800

Hello, everyone,
    Recently, I calculate the back-scattering neutron spectra from targets
    by using fluka. I find that I just score few neutrons
at the place of 2500 centimeters away from the target at backward
    direction. These results are useless due to too few events. I know that
    it is because of too few primaries, but at this time I have used
    1000000 primaries(protons in my simulation). So I consider using the
    biasing card to obtain more neutrons, for example,
* bias: set 1 everywhere
BIASING 1.0 1.0 1.0 1.0 35.0 PRINT
* now bias in steps of 2
BIASING 1.0 1.0 3.0 DE4 DE4
BIASING 1.0 1.0 9.0 DE5 DE5
BIASING 1.0 1.0 27.0 DE6 DE6
BIASING 1.0 1.0 81.0 DE7 DE7
BIASING 1.0 1.0 243.0 DE8 DE8
BIASING 1.0 1.0 729.0 DE9 DE9

        The biasing card is working, but I still score the few neutrons. In
        fact I want to place a moderator for back-scattering fast neutrons
        at 2500 centimeters away from the the target at backward
        direction. Maybe there are three reasons for my problem, the first
        is too few primaries, the second is too small area for the
        detector, the last one is too far distant from the target to the
        detector. If I increase the primaries, it will need more cpu
        time. Now the 1000000 primaries simulation will spend half of a
        day. Someone can given me some experiences for dealing with this
        embarrassing situation. Thank you very much!

Jing Hantao
Received on Tue Nov 11 2008 - 09:48:02 CET

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