Hrm too bad no one has posted on this thread in over a year.[/list]
Actually it's only been 4 months since the last post.
I did some experiments with a circuit like the one on the Hamamatsu site mentioned previously.
It 'worked', but the efficiency was really low. The circuit produced pulses in the 10-20 mV range that were clearly visible on my o-scope. But the pulses were very infrequent.
For example, using an old military glow-in-the-dark switch handle (contains Radium) about 3/8" away from the diode, there was only one pulse every second or two. A standard Geiger counter gets dozens of hits per second with the same radiation source. My scintillation probe gets *hundreds* of hits per second.
I used an ordinary IR photodiode. I tried 3 different types, but all were similar. If you look around on the Hamamatsu page, you'll find diodes that are specialized for radiation detection, but I think they are very expensive, and not carried by the standard electronics parts places.
So, the best 'bang for the buck' is still a Geiger tube.