Wow you got you some markov chains, Monte Carlo, Gamma Radiation, what a fun dissertation. I especially liked the bit about how the NaI detector is not a sphere and sensitivity depends on incident angle. I would never have thought of that. You even did a trip to ORNL, how cool is that!
Walking around with a Giger counter while wearing a hazmat suit seems like fun too, but I suppose it would freak people out. This seems like a much more stealthily way to locate a lost source.