Hayden Hollenbeck

> I went ahead and updated with the rejection sampler to speed this up (and take a little work off your sholders!): @hhollenb the reduced rejection rate here looks correct...

> Does this supersede #1162 ? Yes, I'll close that one. I reused any relevant code but had to make enough major changes I thought it was worthwhile to start...

> Sorry it's taken some time to go through this: this looks really solid; I think you've got basically all the skeleton there! I've got a thought or two about...

Made a PR for absorption and Rayleigh interactors here: #1317

I made a rough draft of an idea I had for splitting out some of the builder functionality: https://github.com/hhollenb/celeritas/pull/1 I'm not fully happy with it, but there might be something...

Ack sorry I clicked merge before I read you comment. I'll setup the Rayleigh scattering PR which will be mostly the same and can be used for some further review.

After reviewing some of the content of `G4OpBoundaryProcess.cc`, there seems to be a rough pattern between most of the models: ``` while dot(newMomentum, globalNormal)

Going through the code a bit more, I think the looping is meant to simulate the chance of multiple reflections / refractions at a single surface crossing. If there's a...

Reference for the UNIFIED surface model in Geant4: A. Levin and C. Moisan, "A more physical approach to model the surface treatment of scintillation counters and its implementation into DETECT,"...

Here's my current notes on how the optical surface physics can be separated out. There's quite a few branching points for model choices, so I'm not sure if it'd be...