Dear Luis,
no, you missed a point in the general concept of biasing.
When you apply a bias you sample from artificial phase-space
distributions, AND you apply a weight to the particles to correct for the
bias! The goal is to have a faster convergence to the same mean quantities
(with a price to pay: you lose correlations and fluctuations in each event,
but for the shielding you are interested only to mean values, with a
variance sufficiently small).
All this means that in your case applying the importance biasing to the
neutrons allowed to have a decent statistics to evaluate the dose equivalent
in the air layer beyond the shielding wall, but normally the resulting
quantities have been correctly re-weighted (remember that if you use biasing
in FLUKA, this is automatically done). If neutrons come from
photo-production processes, biasing only neutrons is a very reasonable
choice.
You can go through these arguments for example here:
https://indico.cern.ch/event/540415/contributions/2194786/attachments/1285753/1912264/12_Biasing_2015.pdf
Hope it helps, kind regards,
Anna
Am Mon, 22 Jul 2019 10:25:36 +0200 schrieb "Luis Eduardo Gonzalez Amoros" :
>Dear Fluka experts,
>
>I am trying to get introduced into the importance biasing and since it is a delicate thing, I want to make sure I am doing the things right. I have seen examples of a hospital LINAC shielding and they used the biasing for the wall and for the first layer of exterior air; they used the importance biasing for neutrons only. However, if you want to calculate the equivalent dose, applying the importance biasing only to neutrons won't give you an unreal equivalent dose distribution (since you are multiplying the number of neutrons reaching the wall and therefore, the equivalent dose deposited by the particles generated from them but not by the rest of the particles)? Wouldn't it be more correct to apply importance biasing for all particles? Am I understanding something wrong?
>
>Best regards,
>
>Luis
>
>
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Dr. Anna Ferrari
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Received on Mon Jul 22 2019 - 20:04:38 CEST