Biasing in an air tunnel

Biasing
1

Hello Dear experts,

I’m trying to understand how to apply the Biasing card in the case of an air tunnel, as was shown in the biasing lecture during the last online course (which was great, thanks!)

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As I understand, it’s problematic to apply importance biasing in this case because of the geometry (shielding on the sides) so I’m not sure how to reproduce the picture on the right. Is the source file of this simulation available somewhere?

Many thanks in advance,
Yael

2

Dear @Yael.Fried,

as you pointed out this example is a bit arguable as it applies different importance to adjacent regions (maze regions vs shield region). Moreover, splitting daughters in air are strongly correlated and might not provide sufficient differentiation of their histories.

Nevertheless, the problem is a nice example of how to apply biasing by regions.
It was described in this lecture and the solution was given here.

Best regards, Luigi

3

Hello Luigi, thanks for answering.

I have a follow up question – if my tunnel is in a straight line (for simplicity), can I avoid the geometric problem by assigning the same increasing importance number to the shielding as well? For example:
pic1
Will this help me to get better results and error percentage when scoring the dose at the end of the tunnel compare to the same run without the biasing card?

Thanks,

Yael

4

Hi @Yael.Fried,

this segmentation fixes the first issue, but it is even worse for the second one.

The air interaction length is a few hundred meters, therefore that fine segmentation splits identical tracks with no means of sampling from the full phase space.

In the end, biasing techniques are powerful tools but have to be applied with physical judgement and not as a “black box”.

Cheers, Luigi