Re: [fluka-discuss]: How to set the lower and upper weight limit in ww-factor

From: Santana, Mario <msantana_at_SLAC.Stanford.EDU>
Date: Fri, 11 Oct 2013 08:49:50 -0700

Yuanjie,

Statistical weights are not always 1.0, otherwise WW would not be needed.
Region based BIASING, but also any biased interaction, e.g. biased photo
nuclear reaction, EMF biasing, LAM-BIAS, etc will alter the weight of the
resulting particles and of its descendants. When you use WW you want to
adjust the upper limit to about ~3-4 times the average weight and the
lower limit to about 1/3-1/4 of the average weight in that given region,
so that your window is not too narrow (excessive splitting/russian-rulete)
or too wide (=useless). To obtain what is the ACTUAL average weight you
could either use SCORE (just one card in input file, but somehow cryptic
results), or mgdraw.f (in bxdraw). With the later option you can actually
get the weight/energy distribution and whatever else you want to analyze
how your weight is scattered, but it requires some programming.

On a side note, you could also center your weight window around some
INTENDED average weight (different from the actual one). By doing that you
can spare having the region BIASING card.

To conclude, you will see that you have a couple knobs to tune how the
window acts as a function of energy (one of those is particle-dependant).
Maybe you should not invest so much time getting the best optimized WW,
but some basing filtering can help a lot.

Mario

On 10/11/13 12:04 AM, "±ΟΤΆ½ά" <biyuanjie_at_tsinghua.org.cn> wrote:

>Dear fluka user
>
>
>I want to use weight window to biasing particles. But I am confused by
>the set of the lower and upper weight limit in ww-factor. I think the
>normal paricle weight is 1.0, so the lower weight limit shoule be less
>than 1.0 and the upper limit should be greater than 1.0. But in example 2
>of the manual, the lower and upper weight limit are 13 and 120, which are
>all above 1.0. Could someone explain to me how to set the lower and
>upper weight limit in ww-factor?
>
>
>Many thanks
>Yuanjie
>
>
>
>
Received on Fri Oct 11 2013 - 18:40:18 CEST

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