Use Of The Geiger-Mueller Detector Tube

Oct 4

Radiation may be detected with special tubes called Geiger-Mueller Tubes.

This introductory piece describes and explains the fundamentals of how Geiger-Mueller tubes work.

Products & Equipment

Scaler holders are necessary for use with GM tubes
Narrow opening General Motors (GM) tube
Extremely pure gamma sources are Co-60 with a stop filter or Ra-226 with a thick filter
Pure beta radiation (Strontium 90)
A safe place to store radioactive substances
Matches' box if a gamma GM tube is available

Guide To Health & Safety Procedures & Other Technical Notes

To function properly, Geiger-Mueller tubes must be operated at a voltage inside its "plateau." In closed loop systems, this is adjusted routinely.

To prevent a loud spark from occurring when an energetic particle enters a Geiger-Mueller tube, the voltage across the tube is often maintained low.

In the case of alpha particle analysis, Geiger-Mueller tubes are particularly vulnerable. The thin mica glass might allow alpha particles to enter the chamber. In order to avoid damage from accidental handling, a protective covering is necessary. A capable alpha detecting Geiger-Mueller tube can be used to count photons. Light a match in front of it and you'll see some UV light.

The First Steps In The Process

This will depend on the specific type of Geiger-Mueller tube you're using. If you have a completely standalone setup, all that has to be done is to power it up. In the case of an earlier type Geiger-Mueller tube that plugs into a separate ratemeter or scaler, the voltage will need to be adjusted on the scaler. To accomplish so, just stick to following steps.

Put a radioactive source in its holder. You can clamp this onto a retort stand.

Put the Geiger-Müller tube in a display case. Set it up so that it is pointing directly at the source from a distance of 5 centimeters.

Activate the scaler (counter) with the Geiger-Müller tube inserted.

Set the voltage at roughly 200 volts to start. To do this, you may keep track of how many times a clock ticks in a given time period, like 15 seconds.

Power up with a 25-volt boost.

As the voltage increases, the numbers will rise and fall until they stabilize. You don't need to draw the graph, but it would look like this:

After a certain voltage threshold is crossed, the counting rate will level out. It maintains its constant value over a broad range of voltages. You should increase the voltage by 50 volts to 100 volts over the threshold.

If you hear the clicking increase in volume when the voltage is increased, you have overcome the plateau. Turn the power down another notch.

Put the source away safely until the presentation is over.

Steps To Carry Out The Experiment Activate The Geiger-Mueller Tube Counting System

It's important to call attention to the fact that there's a silent tally in the background.

Bring a radioactive source close to the Geiger-Mueller tube to get people's attention with the rising counts.

It's possible to measure both the total number in the background and the number near the source. Repeat for intervals of 30 seconds. Be sure to emphasize the distinction.

Advice For Educators

Discuss the state of affairs in the Geiger-Mueller tube. It should be emphasized that it outperforms the spark counter in terms of sensitivity and stability.

Focus on the numeric discrepancies between the Geiger-Mueller tube and the spark counter. All ionization processes inside the Geiger-Mueller tube are continuously recorded. No one is left to join up now.

Discuss the Geiger-Mueller tube, which evolved from the spark counter. This is how you may say it: "The high voltage source is integrated into the scaler, and the spark counter wire is protected by a metal shield that also functions as the second electrode. Scalers are responsible for keeping track of the number of charge pulses sent to the central wire by the torrents of electrons. The right mixture of gases within the tube keeps the sparks from burning too long. After the spark has died down, the tube and scaler are prepared to tally the 'bullets' from another radioactive atom's 'explosion. As can be seen and heard, the tube has a lightning-fast response time to each avalanche."

Similar to the spark counter, the Geiger-Mueller tube generates a current pulse (an avalanche of charge) when ionization occurs between two high-voltage electrodes. In contrast, a Geiger-Müller tube is hermetically sealed, filled with low-pressure gas (often argon with a tiny quantity of bromine), and typically integrated into a circuit with a scaler counter.

The scaler's counter keeps track of and records the number of charge pulses.

The actual events within a tube are far more complex than the simplistic scenario of ionization leading to an avalanche of electrons. There's a good chance that ultra violet photons and crashing electrons and ions play a part within the tube, and the full picture is quite convoluted.

The charge pulse produced by an ionizing particle is rather consistent in magnitude. The magnitude of the pulse is independent of the ionizing particle's kinetic energy or ionization yield.

The greater the number of pulses, the greater the flux of ionizing particles into the tube.

If a particle enters a Geiger-Mueller tube but does not immediately exit, the tube cannot tell the difference between particles of various types or energies (as most gamma rays do).