Hey, thanks for indirectly reminding me to see if my Ludlum 2221 digital counter will gate envelopes with just the power of the audio output. Works great.
I've been planning to use it as a random trigger source. You can buy a little piece of radioactive uranium ore off eBay (far from any kind of dangerous level) and move it closer or farther away from the detector for a different random trigger rate, lol.
Here's a WAV with it gating my Macbeth M5 if anyone's curious as to what it might sound like (using a sample of pitchblende that gives 90kcpm at the surface with a pancake probe). I'm just randomly moving the probe at different distances from my radioactive source:
http://petmeats.com/radioactivem5.wav
But yeah, something like that would be fun in a module, You'd probably get 20 or so "triggers" per minute just off background radiation with a regular GM tube.