Re: particles in beam interacting with each other

From: Alberto Fasso' (fasso@SLAC.Stanford.EDU)
Date: Tue Jan 09 2007 - 21:18:52 CET

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    Dear Mary,

    there is no "specific principle / theory": it is just that in nearly
    all applications one can think about, these effects are so small that
    they can be safely neglected. The density of particles from most sources
    is many many orders of magnitude smaller than the density of the most
    rarefied gases. Taking into account the interactions between different
    histories would spoil the linearity of normal Monte Carlo (results would
    not be just proportional to number of histories, but would be dependent on the
    source intensity). A similar lack of linearity can arise if we want to account
    for the changes in material composition due to the irradiation (e.g. plutonium
    production in a reactor). It is not impossible to do it in principle: some
    specialized codes do it, but one has recourse to this kind of increased
    complexity only if there is an actual necessity.

    Are you just interested in this problem for theoretical reasons, or do
    you have an application in mind? Probably there could be an interest
    in some astrophysical problems, but I would not recommend using FLUKA
    to to track particles in the center of the Sun :-)

    Kind regards,


    On Tue, 9 Jan 2007, wrote:

    > Hi.
    > Could someone help me explain:
    > 1. Presumably particles from a source don't interact with each other -
    > otherwise serial and independent computation of each radiation history,
    > as practiced in Monte Carlo simulations, wouldn't be valid. Why?
    > 2. Presumably radiation histories do not perturb each other - otherwise,
    > as above, the way we do Monte Carlo simulations won't make sense. Why?
    > What specific principle / theory can I use to support statements such as
    > these?
    > Many thanks,
    > mary

    Alberto Fasso`
    SLAC-RP, MS 48, 2575 Sand Hill Road, Menlo Park CA 94025
    Phone: (1 650) 926 4762   Fax: (1 650) 926 3569

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