How Does a Geiger Tube Detect Radiation?

[cragar]

Im trying to understand how a Geiger tube works. So there is a wire in the middle of the tube and then an outer metal shell and the wire and the shell are held at a potential difference. And the tube is filled with a gas like Neon , And when like an x-ray comes in, it ionizes a neon atom and then it gets pushed to one of the metal terminals by the electric field. Now when the neon atom collides with the metal terminal does this cause a small current, Is this how the gieger tube works.

 

[Dadface]

Ions created by the incoming radioactive particles travel to their respective electrodes under the influence of the electric field and this is detected as a momentary pulse of electricity.

 

[sophiecentaur]

It is a bit smarter than that because the pressure, voltage and electrode spacing plus the resistance of the power supply have to be right so that a permanent arc is not struck once some ions start to flow. The discharge has to be as brief as possible so that you can measure high count rates. Also, there is a Mica window at the end so that Alpha particles can get into the detector. They would be absorbed by a glass envelope that was strong enough to maintain the vacuum inside, I believe.

 

[cragar]

Ions created by the incoming radioactive particles travel to their respective electrodes under the influence of the electric field and this is detected as a momentary pulse of electricity.

When the ions reach their electrode do they stay there . And this brief stream of charged particles creates a B field is that what we detect. Or when the ions are created does their own E field change the voltage between the electrodes by the principle of superposition.

 

[nasu]

The main thing in the Geiger counter is the avalanche process. A single ion produced by the incoming radiation is accelerated by the strong field near the wire and it gains so much energy that it ionizes other ions which are accelerated and ionize more atoms. So one single primary ion results in enough secondary ions to produce a current pulse strong enough to be heard in a speaker.
There is no role played by magnetic fields.

 

[cragar]

How is the current pulse detected? And when one ion starts to be accelerated by the voltage why doesn't it hit the other atoms and transfer its momentum to get the electron up to its next orbital, like the Franck hertz experiment. If there are all these atoms in there how does it build up enough kinetic energy to ionizes them.

 

[sophiecentaur]

A current is a current is a current. When it flows out of the anode it can be detected by an amplifier. You were concerned about what happens to the ions. Once they arrive at an electrode they acquire an electron and are neutralised. Likewise, electrons hit the anode and join the others in the sea of conductance electrons. No net charge is produced.

 

[cragar]

Ok that helps a lot , thanks for your response

 

[nasu]

How is the current pulse detected? And when one ion starts to be accelerated by the voltage why doesn't it hit the other atoms and transfer its momentum to get the electron up to its next orbital, like the Franck hertz experiment. If there are all these atoms in there how does it build up enough kinetic energy to ionizes them.

The pulse is detected by hearing the crack in the speaker when the current goes through it.
There is no need for external amplification. The amplification is produced by the ionization in avalanche.

It doe hit other atoms. It does not get the electron on the next orbital but completely out of the atom. This is called ionization. And the new ion and the electron produced are accelerated and so on. This is the avalanche process. What kind of process (excitation or ionization) happens is controlled by the gas pressure and the gradient of the electric field.
If the pressure is low enough, the time between collisions will be enough for the ions to gain enough energy to ionize rather than just excite the other atoms.

 

[cragar]

Bear with me for a moment, so when the ions get accelerated towards the electrodes, when the ions hit the electrode does the E field of the particle cause electrons to flow in the wire and this current is what makes the speaker go off?

 

[sophiecentaur]

Yes. Exactly, except you could possibly say the E field produced by ionising the original atoms (forming ions ). Every ion hitting the cathode has a corresponding electron hitting the anode.

 

[Dadface]

An even more detailed explanation requires a knowledge of the electronics of the ratemeter or scalar or whatever it is that the GM tube is plugged into.The circuitry provides the correct biassing(operating pd),detects and displays the electrical pulses and quenches (clears the tube)after each pulse has been detected.There's a limit on the number of particles per unit time that can be resolved.

 

[nasu]

Bear with me for a moment, so when the ions get accelerated towards the electrodes, when the ions hit the electrode does the E field of the particle cause electrons to flow in the wire and this current is what makes the speaker go off?

The circuit contains a high voltage source. This is what makes the electrons move through the wires. Without ionization the circuit is open, the gas is an insulator. The ionization simply closes the circuit making the gas conductor for a short time.
The ions and electrons in the gas move due to the electric field produced by the high voltage power source and not to the field of the ions in the gas. When the ions reach the electrodes they get neutralized.

Imagine that you have a series circuit with a battery and a speaker but the circuit is open, you cut one of the wires and the two ends are separated. Every time you touch the wires you hear a crack in in the speakers. In the G-M counter the two wires are the two electrodes.

 

[cragar]

ok that makes sense thanks everyone for your replies .