He didn't mention which satellites they were, I think he was under the impression they were Russian military satellites. Unfortunately this was all during my lower division courses so I didn't get a chance to work with him. When I was doing my senior project with a different professor we used different types of detectors for gamma ray spectroscopy. The two we had were these little sodium iodide detectors and a larger liquid nitrogen cooled gallium arsenide based detector. Pretty much just chunks of metal or salt that caused Compton scattering and were detected by photon multipliers or single photon counting modules. They often had multiple channels and were not very sensitive.

It's been six years so my memory is kinda fuzzy. >_<