[Physics Class Notes] on Geiger Counter Pdf for Exam

A lot of modern applications require working in the presence of high radioactive substances. If adequate safety measures are not taken, then radiation can have a very detrimental effect on the health of people. The horrors of Chernobyl will always be a reminder for humanity that radioactive energy is a force to be reckoned with. 

Therefore, to assess levels of radiation so it does not cause us harm, a device called a Geiger Counter is used. This device is used in the detection and measurement of radiation in ionized substances. This has numerous applications in the field of research and medicine.

History of Geiger Counter

Hans Geiger in 1908, under the supervision of Ernest Rutherford, developed an experimental technique for detecting alpha particles which became the basis for developing the Geiger–Müller tube in 1928. The basic ionization mechanism used was discovered by John Sealy Townsend between 1897 and 1901 and is known as the Townsend discharge.

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Geiger and Walther in 1928 developed the sealed Geiger–Müller tube which they used. It was so small, rugged that not only could it detect alpha-beta radiation both, but also gamma radiation. So radiation-instruments could be produced relatively cheaply, and so the Geiger counter came into existence.

What is the use of Geiger Counter?

A Geiger Counter is an instrument which is used for detecting and measuring ionizing radiation. It is also known as a Geiger–Muller counter; this is widely used in many applications like experimental physics, radiological protection, radiation dosimetry, nuclear industry and nuclear-industry.

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It detects ionizing-radiation such as alpha particles, beta particles and gamma particles using the ionization effect produced in the Geiger Muller tube by which the name of the instrument is known.

What Principle does a Geiger Counter Work on? 

This device consists of a Geiger-Muller tube, which contains a noble gas (usually helium or argon) at a very low pressure, possibly the lowest. Under the application of a relatively high voltage, the electrical change would indicate radiation if the gas becomes conducive. It can be used to detect all kinds of radiation- alpha, beta and gamma. 

The modern type of Geiger Counter uses the halogen tube, and these lightweight instruments offer an improvement. Better range of detection of multiple types of ionizing radiation, i.e. alpha, beta, X-rays, and gamma, all are available even in the same unit. Their features are easy to use, common-interface and compatible with a catalogue of optional accessories for wireless reach back, rechargeable batteries, and extension poles to maintain good ALARA (as low as reasonably achievable) principles.

Types and Applications of Geiger Counter

An intended-detection application of a Geiger Counter explains the tube design being used. Subsequently, there are many designs which may be generally categorized as end-window, or windowless also as thin-walled or thick-walled, and sometimes hybrids of these types.

Historical uses of the Geiger principle was for the alpha and beta particles detection. However, this instrument is still being used for this purpose today. Geiger Counter shares wide applications as they are used as handheld radiation survey instruments and is probably one of the world’s best instruments known for radiation detection.

Some applications of a Geiger Counter are as follows: 

• Detection of radioactive rocks and minerals in mining.

• For first responders such as firemen and hazard management personnel to ensure that the site is clear of radiation.

• Ensuring that levels of radiation are within permissible levels around nuclear power plants. 

• Detection of radiation in scrap metal processing industries.

• Detection of radiation in erstwhile warzones.

• Ensuring that patients undergoing radiation therapy are not overexposed to radiation. 

• Ensuring that uranium mines and surrounding areas do not become overly radioactive.

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The “end-window” type of a GM tube has to be used for alpha particles, and low energy beta particles as the particles show a limited range and are easily stopped by the solid-material. Therefore, this tube requires a window which is thin enough to allow as many as possible of these particles. The window is usually made of mica with1.5 – 2.0 mg/cm2 density.

Alpha particles contain the shortest range, and to detect these the window should ideally be less than 10 mm of the radiation source. Geiger–Müller tube generates a pulse output that is the same magnitude for all radiations detected, hence the Geiger counter with an end window tube is not able to distinguish the alpha or beta particles.

The “pancake” GM tube is a type of end-window probe and designed with a larger detection area for quick checking. However, Atmospheric pressure against fill gas’s low pressure minimizes the window size because of the limited strength of the membrane.

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Some beta-particles can also be detected by thin-walled “windowless” GM tubes that have no end-window, however, allow high energy beta-particles to pass through the tube. The tube walls have more stopping power in comparison to a thin end-window; they even allow these energetic particles to reach the fill gas.

‘End-window’ GM counters are still being used as a portable,  general-purpose, radioactive-contamination measurement and detection-instruments, due to their less cost, robustness and high detection-efficiency especially with energy-rich beta particles.

For differentiation between alpha and beta particles and to know the particle’s energy information, the scintillation counters are used.

Points To Note:

• Detected radiation readout method in Geiger counter are of two types, i.e. Counts and Radiation dose. There is a simple type of display unit which shows the number of ionizing events detected displayed as a count rate, like “counts per minute or seconds” or as the total number of counts over the set period.

• This count readout is usually taken when alpha particles or beta particles are being detected normally. To achieve a display of radiation-dose rate is more complicated. It displays in Sievert, normally used to measure gamma or X-ray dose rates. 

• Presence of radiation can be detected by a GM tube, not its energy, that influences the radiation’s ionizing effect. The electronic processor will apply only known factors to make this conversion, i.e., specific to every instrument and is determined by its design & calibrations.

The readout may be analogue or digital, and the modern instruments provide serial communications with a host network or computer. The option is there to generate audible clicks that repr
esent ionization events. It is the distinctive sound normally seen with handheld or portable Geiger counters.

Advantages of a Geiger Counter

The benefits of using these devices are mentioned as follows: 

• They can prevent nuclear accidents by always giving a reading of radiation levels. Since radiation cannot be seen, it is otherwise impossible to know if the levels at a place have become hazardous. 

• They are used to ensure safety in all operations that require working with radioactive material. 

• They are highly sensitive devices, therefore the readings are usually accurate.

• They can be very useful in expanding the scope of nuclear energy to greater levels in order to fully harness it for the benefit of mankind.

Disadvantages of GM Counter

Below is the list of demerits as discovered by working with Geiger-Muller counter:

• GM counters are less efficient due to its large paralysis time limits and also large dead-time.

• Quenching agents used in GM counters often decompose, which leads to the reduction in a lifetime. 

Thus, GM Counter is primarily used due to its advantages. However, GM counters are not free from disadvantages, its uses make it preferable over other radiation counters.