Energy deposited in a vacuum with USRBIN

From: Jeff Wilkinson (
Date: Fri Feb 15 2008 - 02:59:49 CET

  • Next message: Alberto Fasso': "Re: Energy deposited in a vacuum with USRBIN"

    I think I know what is going on with a simulation I'm running, but I
    wanted to check with the experts, just in case.

    I'm simulating an industrial x-ray source at 400 kV. The electron beam
    is incident on a tungsten target enclosed in vacuum. To speed up the
    calculation I added a very thin sphere of low density material around
    the target to absorb electrons (Thanks Alberto!). The transport cutoff
    for electrons is very high in this thin region and low for photons. That
    stops the secondary electrons ejected from the target quickly before
    they have chance to slow down the calculation by interacting with the
    rest of the regions. It works great and comparing results with and
    without the shell shows no difference other than a 20% decrease in
    calculation time.

    When I looked at the results of USRBIN for ENERGY particles for the
    volume that included the target, sphere and filter structures I was
    surprised to see that Fluka was claiming that the electrons were
    depositing energy in the vacuum region leading up to the absorber shell.
    Turning the absorber back into vacuum (it was hydrogen) gave the
    expected result and no energy was shown as being deposited in the
    vacuum. The photon flux is the same in both cases.

    I'm guessing that Fluka was trying to maintain energy balance when it
    stopped transporting the electrons in the absorber by assigning their
    energy along the track from the target to the shell. Is that correct?
    Thanks for the help,
    Jeff Wilkinson

  • Next message: Alberto Fasso': "Re: Energy deposited in a vacuum with USRBIN"

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