Question: How do radiation counters work?

Kate Wright answered on 11 Nov 2015:

Great question, but maybe a little hard for me to explain… “it’s complicated”.

There are two main types of radiation counters, gas counters and semiconductor detectors. You might be thinking of Geiger-Mueller tubes – the ones that click and crackle when there’s radiation around. They’re a type of gas counter.
It’s basically a metal tube filled with a special gas which has a wire running down the middle. You apply a voltage so that the metal tube and the wire are charged – one is negative and one is positive. When radiation comes into the gas it can ionise the gas (not sure if you’re familiar with ions – basically the radiation comes in and knocks an electron off of an atom, which means you now have a negative electron and a positive atom floating around). The electron and the ion go off and create more ions until all of the gas is ionised. The electrons are attracted to the positively charged wire and the ions are attracted to the negative metal tube. When they get to the wire and tube, it registers an electric pulse, so the electronics tell you ‘we’ve detected some radiation!’. Every time you hear a click from a Geiger counter that’s what’s happening – the radiation has ionised the gas and that’s given you an electrical signal.

Like I said, it’s a bit complicated, but they’re really useful!