Dear Anna,
Tank you very much for your answer. I start getting the point. However, I am simulating a 10MeV LINAC and therefore, I am not really interested in neutrons. Nevertheless, I am more interested in the wall layers and exterior air than in the inside of the room. Would it be interesting to apply importance biasing to all particles for this layers to reduce the variance in the regions of interest? Would you recommend me to apply it to any specific particle?
Best regards,
Luis
El Lunes 22 Julio 2019 18:31 CEST, "Anna Ferrari" <a.ferrari_at_hzdr.de> Ha escrito:
> 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
> Institute of Radiation Physics, High Energy Density Division
> Helmholtz-Zentrum Dresden-Rossendorf e.V.
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Received on Wed Jul 24 2019 - 00:23:01 CEST