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Forum: Biasing and Scoring
Re: None Is there a good way to 'continuously bias' a particle by monkeying with weight? (Peter Mardahl)
Date: 31 Aug, 2011
From: Marc Verderi <Marc Verderi>

Hello Peter,

 What you describe, to my understanding, is the so-called "forced flight" biasing technique. It does not exist yet in Geant4, but this is something considered and under development.
 What is delicate is that if you "force-flight" all the primary particles, you would end-up with only primary particles that cross the shielding, and contribute to the exiting flux. But in reality, this flux is made also of daughter particles created by the primary ones (and recursively, daughters of daughters, etc.). To my understanding, some interactions should still be allowed to generate these secondaries, but this secondaries -or at least the same fraction of them, as for the primaries- should also be "force-flight"'ed to make them traversing the shielding.

 Does is make sense to you ?

 Cheers,
 Marc

On Wed, 31 Aug 2011 13:59:02 GMT, Peter Mardahl wrote:

> Hello,
> 
>   I've been reading the documentation on how to do biasing with interest, and I had a somewhat different idea than is currently implemented, and I am not sure if it is a good one.
> 
>   In particular, I'm looking at X-rays going through shielding.  One can do importance sampling on this, but you have to play with this to get it right.
> 
>   I'm wondering if I can just do this:  NEVER kill an x-ray as it goes through shielding.  Instead, whenever it has an event or process which WOULD kill it, just reduce the weight.
> 
>   The idea is that you can keep a constant number of particles and get good statistics, because one has lots, but still get the right answer because even though everyone survives, they have lost the right amount of weight.
> 
>   Does this make sense?  Can it work?  Has someone already done it successfully?  It seems like this *should* be pretty easy to do, but I am not confident I understand the issues properly.  Or is this already one of the options and I just failed to understand the documentation?  (If so, well, help please?)
> 
> Best,
> 
> --PeterM
> 

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1 None: Re: Is there a good way to 'continuously bias' a particle by monkeying with weight?   (Peter Mardahl - 31 Aug, 2011)
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