Ion chamber

Dmytry · 2012-04-04T21:16:51+00:00

I've built one: http://dmytry.com/ion_chamber_1.jpg using LMP7721 and 100 TOhm resistor (the thing inside glass tube). The circuit is basically the one from LMP7721 example datasheet, other resistors are for input protection and voltage divider for the positive input, and output protection. I've soldered stuff onto prototype-ish board, which i soldered to flaps bent from the can that used to contain peanuts. The chamber is formed by the can and the wire inside. The other can that used to contain peas is used as shielding. I simply measure the output with digital voltmeter. This thing easily detects 1kg bag of potassium fertilizer (which is the only test source I have here, but i'll go by my granddad and take some old radium clock when i have time). I'm planning to build a better radiation detector with integrator circuitry and reed switches. With the switches i should be able to just leave the chamber disconnected entirely, and do measurements in pulses, measuring the time it takes to recharge, with a micro-controller - that should allow me to use some really cheap common op amp like TL072 . The advantage of ion chamber over Geiger counter is that it works over the entire ionizing radiation range, with the response closely matching that of the body. (Geiger counters are very bad at counting soft x-rays.) Other advantage is that it is just a ton simpler, requires no vacuum, can test for radon directly, etc.