Diffusion

Starting a month ago or so, I started writing up some notes on diffusion (specifically, its application in simplified form to the qualifying exam). The idea was that if I didn't pass, I would have a handy reference to help with re-learning diffusion. Anyway, I did pass, but I decided to finish it somewhat and make it available. It's meant for someone already familiar with reactor physics and diffusion, but it emphasizes some points that aren't that common, and it presents a good simplified summary of the one-speed homogeneous method. The content is all correct to the best of my knowledge, but caveat emptor.