t 10:23 AM 6/6/03 -0700, Tim May wrote:

I certainly never implied in any way that a simple G-M tube would be useful for this. Implicit in my radioistope mapping comment was that a gamma ray spectrometer would be used.

And note that this is just what can be easily bought on the open market...N.E.S.T. (Nuclear Emergency Search Team) and similar LEO people almost certainly have more miniaturized detector setups.

Indeed, there is a group of GeigerCounterEnthusiasts on Yahoo whose members have/make this kind of thing. You use scintillation plastic & photomultiplier tubes; you can get these on eBay. Sometimes they mount their detectors in cars and find that some sections of roads are hotter than background, or a hot railroad car.

For this I used a pair of large sodium iodide crystals

which also show up on eBay

mode that resulted in a pair of gammas sent out in opposite directions.

Also the principle behind PET scans. Mr. positron meets Ms. electron, and bang, two little Gammas carry the momentum away... GM tubes use avalanche to amplify; the scintillators, NaI, semiconductor junctions measure analogue energy, so you get an energy spectrum. Add a few comparators and a logic gate and you get a channel. ... Pierre Curie didn't die from radiation poisoning, he was hit by a horse drawn cart