How does a Geiger counter detect radiation, and why does it make that clicking noise?
In: 4333
The tube has gas inside it, and a small high voltage capacitor in series with the speaker. Normally, the gas is an insulator, no current flows. If you were to crank up the high voltage a lot higher, it actually could break down the gas in the tube, but that’s not what we want to do.
Radiation will make a track of ionized gas that IS conductive. If the track only covers half the gap, then it will require half the voltage to break down and conduct, and there may be enough voltage present to do that.
Once the gas breaks down and conducts, the capacitor discharges and the current makes a “tick” on the speaker due to a sudden *change* in current. The capacitor will discharge faster that the battery and high voltage inverter will recharge it.
But once the capacitor discharges far enough, it doesn’t have enough voltage to keep the gas ionized, and the gas de-ionizes and becomes an insulator again, current flow stops, which allows the capacitor to recharge and the speaker diaphragm falls back to the rest position.
Here’s a scary fact though- if you hit the tube with an obscene amount of radiation, it may actually STOP ticking! It can keep multiple overlapping conductive tracks present constantly, so the capacitor discharges and makes a tick ONCE, but cannot recover and recharge for another tick because the tube just becomes constantly conducting for an indefinite period of time. So it deceptively stops cycling and goes quiet.
… *too* quiet!
Latest Answers