Biasing advice needed...

From: Burge, F \(Frances\) (
Date: Mon Jul 23 2007 - 12:32:22 CEST

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    Hello Fluka users,

      I'm looking for some advice on using the biasing options in fluka. My
    input file consists of a 3 GeV electron beam striking a target within a
    shielded enclosure, and I need to score dose rates outside the
    shielding, from photons and neutrons. Without biasing, the run is very

    I guess that for the photons, EMF-BIAS is the appropriate option,
    activated for all processes and with SDUM = LPBEMF. I intended to apply
    this in the target region and also the vacuum surrounding it. However
    the fluka manual recommends avoiding biasing in the scoring region and
    adjacent regions, so should I not apply biasing within the shield wall
    regions ? If I wanted to also score dose rates within the shielding,
    would this mean that I should not use EMF-BIAS in this region either ?

    Also, the manual recommends using the weight window biasing to avoid
    large fluctuations in the dose scoring due to heavily weighted low
    energy particles. So it looks like I also need the WW-THRESh and
    WW-FACTOr cards. Can anyone give me any advice on how to choose the
    upper and lower weight limits of the weight window, or is this only
    possible by carrying out repeated runs on a trial-and-error basis ?

    Finally, would it be safer to use neither of the above options and use
    just the BIASING card instead ? In this case, am I correct in thinking
    that the method would be to divide the target and/or shield wall into
    layers (as different regions) and assign each layer an importance which
    increases with distance through the shield ? Presumably I could also use
    this biasing for neutrons.

    All advice gratefully received.


    Frances Burge
    Health Physicist
    01235 778269
    Diamond Light Source Ltd.
    Rutherford Appleton Laboratory
    OX11 0DE
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