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Forum: Biasing and Scoring
Date: 15 Apr, 2014
From: William Donahue <William Donahue>

Hi Everyone,

I am new to the simulation process and am looking for input of experts in it to make efficient and logical code. I apologize for the long winded intro but wanted to provide all the background for my questions.

I am looking at the shielding of polarized low energy photons. I have a simple geometry where a source of these photons in incident on a box made of my shielding material. I have set up a spherical shell to retrieve the scatter information off of the box's surface. I need to score the energy spectrum of each layer in the wall counting only the first time a particle passes through a layer (ignoring backscatter). I also need to use the spherical shell to measure the energy spectrum and fluence. For accuracy I need to have very thin slices in the box to produce accurate fluence curves. On the sphere I need 5x5 degree solid angles.

I have yet to implement this but my current approach would seem to involve having an array of energy region vs depth for my box. This table would then count the number of photons in each region and then add it to the proper row. I would also need to tag the particles with the copy number of the last layer of the box material they passed through. I would then only add the item for the table if the new layer has a larger copy number. This would limit me to only counting the photon if it is the first time it passes through a layer. I expect to use the step information to determine its location in my box but need to know its previous maximum depth.

For the scatter fluence I am looking to make a field of 5x5 degree solid angles. I forsee needing a table of energy versus theta angle for each phi angle. So in my hemisphere I would need something like 36 tables. This just does not seem right or logical but it my best current thought process.

Now for my questions: 1. Is it possible to add a field to my photon tracks that tracks their progression through my box's layers?

2. Can I use arrays in a thread-safe fashion to allow Geant to run in MT mode?

3. Are there any examples out there where this is done? I have read through the general documentation on the examples but, as it appears when reading through the forum, some of the ideal cases are hidden where you least expect them.

4. Would the surface Flux scorer work? I feel like it would count any particles that backscattered and pass back through a plane in the forward direction.

Of course all of these question assume I have the proper thought process and i am not missing useful built in tools for this kind of scoring.

Thanks for your help,

Will

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