Off-center geometry in BEAMnrc

[kurtsche]

Hello everyone,

I wanted to ask if it's possible to design an off center geometry in BEAMnrc, as I have only seen (and used) components that are symmetrical around the z axis. For example a square plate with an air filled hole in the center at 3 3 10. Or maybe another way to work around it by broadening the scoring plane and then only analyzing specific positions?
Any help would be really appreciated!

[rtownson]

It depends on exactly what you want to do, but there are a few CMs than can be asymmetrical. If you just want to shift the whole beam, you could use BEAMnrc on-axis as usual and then shift the particles than come out the end of the BEAMnrc simulation when you're using it as a source. If you really require more complex geometry then switch to egs++ instead of BEAMnrc.

[kurtsche]

Thanks for the quick answer, I want to do dose measurements at different positions below a xray tube, so the source origin is defined at z=0 because of the anode material. For now I am using a square below for dose scoring and want to shift that to some other positions on the xy plane. Which CM is most useful to do that?

[rtownson]

I imagine you want to use something like XTUBE in BEAMnrc to model the xray tube. Use the variance reduction technique DBS to increase efficiency. Set it up to score particles on a phase-space plane after the tube. Then use the BEAMnrc simulation as the source for a DOSXYZnrc simulation for dose scoring in a voxel grid, or for an egs++ simulation to model more complex detector geometries.