Detecting radiation - Looking for ideas
Digital camera sensors would be a promising lead.

From that same publication, a picture that shows shot noise induced by ionizing radiation hitting the sensor.



Note that of course larger sensors simply have a higher chance of getting hit; and better sensors lower-noise amplification and digitization, but for a start: A not-too-cheap webcam would probably do.

Note that webcams, especially the really cheap ones, often connect the sensor to an all-included digital IC that does an overboarding lot of noise reduction (exactly the opposite of what you want) and JPEG compression and whatnot, just to compensate using the cheapest image sensor available.

So, spending 50€ on a HD cam does sound like a good idea. The publication uses a small NTSC/PAL camera module, but honestly, I'd probably try to avoid the additional Digital-to-analog conversion to get an analog TV signal.

Here's a Finnish Guy doing a test with a rather large-sensor'ed DSLR, and he concludes it works well. Note that he says "Camera took no damage" – don't know how he can assess that at the point, seeing that flash memory is pretty much an excellent radiation sensor, too (ask the folks who need to build satellite electronics), and firmware memory corruption might not be the first thing to notice. I wouldn't try to use consumer flash memory as sensor, though, as it has copious amounts of self-repair / error correction mechanisms that will hide radiation from you.