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Two questions about biasing 

Forum: Biasing and Scoring
Date: 14 Feb, 2017
From: Huagang Yan <Huagang Yan>

What I want to simulate is the dose deposit of a small volume in a large volume 50000 times bigger in each dimension. I adapted ExampleB01, and used several concentric shells each assigned with different importance(innermost volume has the biggest importance). These shells all have the world as their mother volume. The whole volume is irradiated with X-ray photons.

Water is the only material used.

Q1: is it possible to kill the secondary electrons using Russian Roulette? When I attempted to increase the importance and the number of irradiating photons, the program can get killed. I think the reason might be too many electrons need to be tracked.

Q2: The dose deposit for the inner volumes sometimes is zero, when no photons get there. This is understandable. However, for those volume(shells) that do have dose deposit, the dose values are very strange, basically follow this pattern of magnitude(in terms of approximate ratio) from outer to inner: 1, ..., 1, 3~5, 0.1~0.3, 0,.... This pattern repeats itself when I use another seed of random number engine, so I think it is not due to fluctuation.

I wonder what's wrong with my program.

Any help is greatly appreciated.

Huagang.

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