Question

How does a Geiger Müller tube work to detect nuclear radiation?

Answer 1

This isn’t simple, but I’ll try and then give a diagram and reference ... off we go!

Explanation:

A G.M. tube is a detector of ionising radiation that works on the principle of ‘avalanches’ of electrons accelerated by a high electric field. The field exists between the neutral case and a central ‘spike’ at a p.d. (voltage) of several hundred volts (typically +400-600V.) When an `alpha, beta` particle or a `gamma` ray enters the detector it ionises (liberates a low energy electron from) a particle of the low pressure gas (typically argon at about 0.1 atmospheres) filling the cavity.

The electron accelerates rapidly in the strong electrical field and collides with other atoms, liberating further electrons from them. The effect repeats until a burst of current arrives at the central spike. This is the ‘avalanche’ of electrons.

There is another difficulty in detecting all 3 types of radiation, the `alpha` particles cannot penetrate the metal walls of the detector so a thin mica window is placed at the end of the tube. The difference in ionising power of the 3 types of radiation means that GM tubes aren’t equally sensitive to all of them, but this is a small problem given their sensitivity, range of operation and low cost.

So that the detector can “reset” it is necessary to have a quenching agent present to ‘mop up’ the remaining electrons after a detection (normally a halogen, such as bromine.) This takes up to `100 mus` and during this time no further detection of ionising radiation is possible - hence the term ‘dead time’.

Your diagram should help visualise it all:

And the reference (gives loads more details): https://en.m.wikipedia.org/wiki/Geiger%E2%80%93M%C3%BCller_tube hmmm that didn’t work (Socratic doesn’t like the formatting of Muller!) just stick Geiger Muller tube into Wikipedia!