Re: Biasing photons

From: Alberto Fasso' <>
Date: Tue, 19 Feb 2013 08:15:24 -0800 (PST)

Dear Monica,

> After reading the manual, I have found out that biasing should be used in
> order to calculate the generation of photons and the use of the BIASING card
> is recommended.

??? Where did you read that? The BIASING card has nothing to do with
photon generation! BIASING concerns biasing at boundary crossings, or
hadron production in nuclear interactions.

> Therefore, I have set this card for all regions and photon particle.

This card, as you reported it, is meaningless.
WHAT(1) = -1. is a "flag indicating that all region importances shall be
modified by a particle-dependent factor, based on a modifying parameter as
explained in the Note 3 below" (from the manual)
WHAT(2) is the modifying parameter: a number, not a particle. Setting it
= PHOTON is wrong.

> I do not have any experience on biasing and I would be grateful if you could
> advice me if any other card would be needed in order to have accurate
> results.

It depends on what you want to calculate. For shielding design, generally
BIASING is all what is needed by a beginner. But it must be used correctly.

> I read that LAM-BIAS and EMF-BIAS are recommended for electron
> accelerators but not sure about protons.

LAM-BIAS is needed for electron accelerators, together with PHOTONUC,
in order to activate photonuclear reactions, essential for shielding
calculations. EMF-BIAS can be used or not, depending on how you want
to apply biasing (read the manual!) In some special cases (very thin targets,
interactions with residual gas) LAM-BIAS can be used for proton accelerators,
but generally it is not needed.

> I do not really understand why a biasing card is needed in order to obtain
> an accurate photon flux when the neutron flux, of a similar order of
> magnitude, is not necessary to be biased.

Indeed. I have the impression that your ideas are a bit confused. I suggest
that you study the lectures of the last beginner FLUKA Course:
(in particular the lecture on Biasing and the correspondent exercise).

Kind regards,


> Monica Huerta
> --
> Monica Huerta Parajon
> Proton Beam Applications group
> Edificio Cosimet
> Paseo de Landabarri, 2, Planta 1
> 48940 Leioa - Spain
> Tfno.: +34 946 07 66 41
Received on Tue Feb 19 2013 - 18:27:13 CET

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