Not sure how well it would work for Ghost Hunting, but you can find a good geiger counter on e bay for 10-50 bucks.
Some friends of ours have them and many other groups swear by them. I have also thought of picking one for our group. I am not sure if high radioactive readings mean paranormal, but it could explain why people report different events. Again like any other equipment we use none of it is scientifically proven for our uses. So you can't rule it out as a helpful tool.
didn't I see one of those paranormal shows on tv use one? :huh:
geiger counters are nice to have, ive got an old school civil defense model ve used for measuring rads coming off of some of my other equipment.
however, to be honest, a geissometer would probably come more in handy, they allow you to measure electromagnetic fields, and there are a few plans out there online where one can make a unit fairly cheaply.
i miss heathkit.. but ive got a working model in my drawer in the office again for measuring EM and RF interference.
BTW, first post on the board, and im glad im here. hope i can help in the future with any questions.