How Accurate is A Geiger Counter to Measure Ionizing Radiation?

Ionizing radiation belongs to the high energy, short wavelength, and high-frequency portion of the electromagnetic spectrum.

The human body cannot directly detect these radiations and can only be observed or measured using specialized equipment like a Geiger counter.

There are different types of Geiger counters available with the main difference in their sensitivity and ability to measure different types of radiations. With different commercially available Geiger tubes, and you want to buy one of them, a question then arises.

How accurate is actually a Geiger counter to measure the (ionizing) radiation?

Is the Geiger counter accuracy able to detect all the energy levels of the radiation?

Is it worth it to buy as your personal radiation detector? Or perhaps, should you switch to another radiation detector instrument? Let’s find the answer here.

What are the Types of Ionizing Radiations that Geiger Counters Measure?

Before we go further, it’s important to know some basic types of ionizing radiations. These radiations are the objects that the Geiger counters detect and measure.

Ionizing radiations include both natural “Nuclear Radiation” and artificial “Electromagnetic Radiations”.

Natural or nuclear radiation types of ionization radiation are emitted by an unstable naturally occurring radioactive material like uranium. These radiations include Alpha, Beta, Gamma, and X rays.

Artificial or electromagnetic radiation types of ionizing radiations are emitted by metallic materials when excited by high voltage electric current. These radiations only include Gamma rays and X rays.

What is the Energy Level of Alpha, Beta, Gamma, and X Rays?

The ionizing radiations come with a certain energy level. It’s also important to know the energy level of each type of radiation so that you know how accurate your Geiger counter is. Simply, if your Geiger counter is able to detect the radiation from all ranges of energy levels, it should be 100% accurate.

Alpha radiation has the energy level of an average 5 mega electron volt (MeV) but has very small penetration power.

Beta radiation has greater penetration power than alpha radiation. An average energy level of beta radiation is about 0.5 MeV for about the distance of one meter in still air.

X-rays can either be from natural or manmade source and has a moderate to a high energy level that can be in the range of 100 electron volt (eV) to 100000 eV (100 KeV).

Gamma rays are the strongest amount of ionizing. Their starting energy level is between 10 to 100 KeV, to a moderate value of 8 Mega eV and a high value of 1000 Tetra electron volts.

How the Geiger Counter Type Affects the Capability to Detect Radiation

Geiger counter is a simple but efficient radiation measuring instrument.

As we know, in terms of how the Geiger counter tube works, it consists of a metal tube filled with gasses like helium, argon, or neon at very low pressure and high voltage. When this tube is exposed to ionizing radiation, the conduction of electric current of gasses inside the tube changes, this is due to the ionizing effect of radiations. This change conduction of electric current is measured by the electric circuit of the Geiger counter and displayed on the screen.

However, Geiger counters’ metal tube comes in two models. These models affect how the ionizing happens inside the tube.

Based on the design there are two main types of Geiger counter tubes.

  • End Window Geiger tube
  • Windowless Geiger tube

The end window tube has a small window at one end of the tube to facilitate the penetration of ionizing radiation. These are designed for low energy level radiations and are quite sensitive in their operation.

On the other hand, the windowless tube does not have a small window at one end of the tube to facilitate the penetration of ionizing radiation. These are designed for high energy level radiations and are rigid in their operation.

Can A Geiger Counter Be Wrong?

Yes, your Geiger counter can be wrong. It is based on the scenario of how you are using your Geiger counter.

There is a variety of Geiger counters available in the market with each having different specifications. Each counter can measure a specific range and type of radiation based on its specification.

So if you are using a Geiger counter to measure a particular type of radiation that is not recommended as per its specifications then your Geiger counter will give you the wrong reading. For example, if your counters cannot detect alpha particles, then don’t use them for alpha radiation detection.

Another case of your Geiger counter giving a wrong reading is a broken or faulty tube or your Geiger counter is not calibrated to measure the specific radiation type or range which you trying to measure.

Covering this radiation detector with a piece of aluminum may interfere with the beta reading unless you are intending to focus on reading gamma only.

So to get an accurate reading using the Geiger counter, you should have a complete understanding of the counter specification, and working and the Geiger counter has to be properly calibrated.

So, How Accurate is A Geiger Counter in Measuring the Radiation?

The answer depends.

For each basic type of Geiger tube, there are further different manufacturers and their products, with each product having its capacity, rating and accuracy.

The design, specifications, and performance of some of the basic Geiger tubes are as follow:

1. Glass Geiger Tube

These tubes are usually manufactured with glass walls. Based on the manufacturer these tubes can be 3.5 to 7” in length and 0.433 to 0. 75 in diameter, power rating of 400 Volts, and neon or halogen as gasses filled inside the tube.

These are designed to detect Beta and Gamma radiations with energy levels above 36 KeV only as Alpha radiation cannot penetrate glass. From all other types of tubes, this has the lowest price of about 44 USD as it can only detect a specific range and type of radiation.

2. Pancake Geiger Tube

Pancake tubes were designed with either single or a double window (usually manufacturer choice).

The example of a pancake Geiger tube is GMT-07.

These tubes are circular can have 2 to 3” in diameter with an overall length of 3 to 4” and have to start power rating of 425 Volts with an operating power range of about 475 to 675 volts. These tubes have neon or halogen gas filled inside the pancake-shaped body.

Pancake tubes are designed to detect Alpha, Beta, and Gamma radiations. It has excellent sensitivity with the ability to detect and measure a wide range of most dangerous Gamma radiations (Gamma Sensitivity Co60, (cps/mr/hr) 60). This has the highest price of up to 140 USD as it can detect a wide range and type of radiation.

3. End Window Geiger Tube

These tubes are usually manufactured with stainless steel cylindrical body with a window at one end made mostly from mica (a naturally occurring mineral material).

Based on the manufacturer, these tubes can be 3.75” in length and 0.36 to 1.5” in diameter and can have a power rating of 600 to 1400 Volts and neon or halogen as gasses filled inside the steel tube.

These are designed to detect Alpha, Beta, and Gamma radiations. The sensitivity of this type of tube is different for each type with the ability to detect Alpha radiation of above 3.0 MeV, Beta radiation of above 50 KeV, and Gamma radiation of above 7 KeV. This has a moderate price of about 74 USD.

4. Windowless Geiger Tube

Like Window tubes, these tubes are usually manufactured with stainless steel cylindrical bodies. These tubes are usually very small in size with a length of 0.3” and a diameter of 1”.

The power rating of these tubes is in the range of 450n to 600 volts and neon or halogen as gasses filled inside the steel tube.

These are designed to detect Beta and Gamma radiations only with sensitivity to detect Beta radiation of above 0.25 KeV, and Gamma radiation of above 1100 KeV. This has a moderate price of about 74 USD as it can only detect a specific range and type of radiation.

Last Thought: What is the Recommended Geiger Counter Tube?

Recommending any specific Geiger counter and Geiger tube without knowing the application or use is impossible. Each tube has its range and specification to give a specific output or to be used for a specific case. From the above discussed Geiger tubes End Window Geiger tubes seem to be the most versatile in terms of their ability to detect a wide range of radiations.

There are a lot of Geiger tube models. Surely, they have different performances. For more info about those Geiger tubes, you could read here.

References

  1. https://www.imagesco.com/geiger/geiger-counter-tubes.html
  2. https://www.orau.org/health-physics-museum/collection/geiger-mueller-tubes/20th-century-electronics-gm-tube.html
  3. https://www.orau.org/health-physics-museum/collection/geiger-mueller-tubes/amperex-100nb-200nb-end-window-gm.html
  4. https://www.orau.org/health-physics-museum/collection/geiger-mueller-tubes/anton-pancake-gm-detector.html

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