What is Geiger Counter ? How does it measure Wind Speed?

Geiger Counter

The detection of the creation of a pair of ions cannot be done by the five senses of humans. However, there is an instrument called a Geiger counter which is sensitive enough to detect ionization. These are one of the most inexpensive electronic devices that can detect radiation; however, they cannot give information about the source of the radiation, its type, or how much energy it has. 

What is Geiger Counter?

The Geiger counter is one of the planet’s most renowned radiation detection devices because of its wide applications as a hand-held radiation survey device. 

Do you know what a Geiger counter is? A Geiger counter refers to a device used to detect and quantify particles in ionized gases. It has diverse applications in the fields of radiation dosimetry, radiological protection, and experimental Physics. The device comprises a metallic tube containing gas, and a high range of voltage in the multiples of 100V is applied to this gas to detect beta, alpha, and gamma radiations.

A Geiger counter is also known as a G-M counter or a Geiger-Muller tube. This name was derived from a German physicist who researched radiation detector in the early 1900s. The gas seal was perfected by a graduate Ph.D. student of Geiger named Walter Mueller in the 1920s. Therefore, the name Geiger-Muller was given to the tube to credit his work.

Radiations are mainly of two types— ionizing and non-ionizing. Microwaves are non-ionizing radiation; they have enough energy to shake atoms but cannot change their composition or knock them off. On the other hand, ionizing radiation can strip electrons from the atoms by the process of ionization. Because of this, a pair of ions is formed with a negatively charged electron and a positively charged electron.

Ionizing radiation exposure is detrimental to human health. When it comes in contact with the DNA molecules in living cells, there is a disruption of its energetic nature which alters or damages the DNA. Exposure to some forms of radiation like X-rays for a short period of time for medical examinations does not result in immediate health risks. However, if the exposure is prolonged, it can lead to DNA mutations and cause cancers. Geiger counters are very important tools to evaluate a potential source of radioactivity.

Making sure that the amount of radioactive material administered to humans is as little as possible is very important while using radioactive isotopes in medical research work on humans. For this, a very sensitive device is required to measure the amount of radioactivity of a material. Geiger and Muller developed a ‘particle detector’ to quantify the ionizing radiation of material in 1928. It was named by them a ‘Geiger Muller Counter’ or a ‘GM counter.’

Principle of a Geiger Counter

How does a Geiger counter measure wind speed? The instrument contains the Geiger-Müller tube, which is the element responsible for detecting radiation. The tube contains a gases like neon, helium, or argon at the lowest pressure for the application of a high voltage. Electric charge is conducted by the tube employing ionization when a photon or a particle of incident radiation turns the gas to become conductive. 

Types of Geiger Counter

The type of what is Geiger counter is depends on the tube design. It is generally classified into two types:

1. End Window
2. Windowless

End Window: This type of tube has a small window at one of the ends, which is helpful to ionize the particles that are able to travel easily. 

Windowless: This style of the tube does not have windows, as the name suggests. Additionally, the thickness of this style of the tube is in the range of one to two mm, and it is used to detect radiation that is highly penetrating in nature.

Geiger Counter Units

Different units are used to measure the particles, of which a commonly utilized one is the CPM or Counts Per Minute. Radioactivity is measured in (mR/hr)milli-Roentgens per hour or micro-sieverts per hour.

Working of a Geiger Counter

How does a Geiger counter measure wind speed? A Geiger counter comprises two main parts— a sealed chamber or tube that contains gas and an information display. Radiation goes into the tube, and on collision with the gas, an electron is pushed away from the gas atom to form an ion pair. There is a wire in the center of the tube that attracts electrons, giving rise to ion pairs and initiating an electric current through the wire. This electric current reaches the information display and makes a number display on the screen or moves a needle across a scale. 

These instruments usually give the “counts per minute” or the number of ion pairs formed per minute. The loudspeaker clicks every time a pair of ions is created if it is on. The number of clicks per minute gives a value of how much radiation goes into the chamber of what is Geiger counter. 

A clicking sound is heard as soon as the speaker is turned on as there is always some amount of radiation in the background. This radiation is derived from the natural uranium in the soil, the sun, radon, some rocks like granite, food, plants, or even humans and other animals.

So, how does a Geiger counter measure the wind speed? The clicks from the background per minute vary, so the needle moves or the number changes even when there is no source of radiation in the surroundings. This fluctuation is caused by many factors, including soil moisture, the wind, temperature, precipitation, atmospheric pressure, altitude, and indoor ventilation. Other factors include the size and shape of the detector, geographical location, and how the detector is built.

Based on the type of Geiger counter and the elevation, a typical radiation level for the natural background is around five to sixty counts per minute. Because the radiation in the background randomly varies, you might observe the range standing in one spot. Acknowledging that the best Geiger counter indicates the creation of an ion pair but does not give any information regarding its energy or the type of radiation is important. 

Other types of devices can be used to determine an exposure rate (expressed as mR/hr or milliroentgen per hour). These types of counters need to be calibrated so that a particular type of radiation like alpha, gamma, beta, x-ray, or neutrons is read, and the amount of energy released is determined. The reading is accurate only for that energy level and radiation type. These devices must be calibrated regularly to ensure that they are giving accurate information over time. 

For the reading of more sophisticated environmental radiations, RadNet is used. This equipment is far more efficient than what is Geiger counter and continuously monitors the air. It also samples precipitation, pasteurized milk, and drinking water regularly.

RadNet has been around for around 40 years and has developed a baseline of normal background levels. In March 2011, when this baseline was compared to measurements across the states in the US, the EPA could detect very small fluctuations in radiation in several western states. The radiation from Japan was also detected by the EPA and were found to be 100,000 times below the natural background radiation, which is far lower than any level that could lead to worry. 

If RadNet needed to detect a significant radiation increase above the baseline, an immediate investigation would be carried out by the EPA. With its sophisticated analytical capability and a nationwide system of monitors, RadNet is considered the main source of gathering accurate information on the levels of radiation in the US environment.

Limitations of a Geiger counter

Geiger counter has two main limitations:

1. As the output pulse coming from a Geiger-Muller tube always has the same magnitude regardless of the incident radiation’s energy, differentiation between the different radiation types cannot be made by the tube.
2. At high rates of radiation, the tube is not so accurate because each event of ionization is followed by an intensive period called dead time, during which any further incident radiation does not contribute to a count. Generally, the dead time reduces indicated count rates beyond 104-105 counts per second. This depends on the features of the tube used. Some Geiger counters possess circuitry to compensate for this, but still, ion chamber instruments are preferred for accurate measurements of high radiation rates.

Conclusion

To sum up, the natural process of ionization is exploited by the best Geiger counter to detect and measure radiation. There is a stable gas inside the chamber of the device, which ionizes on exposure to radioactive particles. An electric current is generated as a result that is recorded by the counter over a period of one minute. 

Frequently Asked Questions (FAQ’s)

1. What is ionization?

Ionization refers to the conversion of an atom, molecule, or substance into an ion or a number of ions by eliminating one or a few electrons.

2.What are the two types of Geiger counter?

Based on the design of its tube, the Geiger counter is categorized into two types— an End Window Geiger Counter that has a window at one of its ends and a windowless Geiger counter that lacks a window. 

3.How does the best Geiger counter detect neutrons?

Neutrons can be measured by a variation of the Geiger tube. Helium-3 or boron trifluoride is the most commonly used gas here, and the speed of the neutrons is decreased using a plastic moderator. This leads to the creation of an alpha particle inside the detector. Therefore, we can count the neutrons.