Re: Biasing advice needed...

From: Alberto Fasso' (fasso@SLAC.Stanford.EDU)
Date: Tue Jul 24 2007 - 10:37:20 CEST

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    Hi Frances,

    the recommendations of the FLUKA manual are right in principle,
    but a long experience with electron accelerator shielding has
    shown that you can get very good results with EMF-BIAS alone.
    Apply it EVERYWHERE, and with WHAT(1) = 1022.
    You will not need anything else.

    Alberto

    On Mon, 23 Jul 2007, Burge, F (Frances) wrote:

    > 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
    > slow.
    >
    > 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
    >
    > Frances Burge
    > Health Physicist
    > 01235 778269
    > Diamond Light Source Ltd.
    > Rutherford Appleton Laboratory
    > Chilton
    > Didcot
    > OX11 0DE
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    -- 
    Alberto FassÚ
    SLAC-RP, MS 48, 2575 Sand Hill Road, Menlo Park CA 94025
    Phone: (1 650) 926 4762   Fax: (1 650) 926 3569
    fasso@slac.stanford.edu
    

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