What Is a Geiger Counter?
A Geiger counter is one of the radiation measuring instruments used to determine the amount of radiation present on the surface of a material or in a space.
It is also referred to as a Geiger-Muller counter tube or GM counter tube, named after its creators, Geiger and Muller. A Geiger counter is a type of survey meter that contains a metal, gas-filled cylinder called a GM tube.
Due to its simple structure, it is available at a relatively low price. They are widely used from public facilities such as electronic power generation facilities, police stations, and hospitals to individuals.
Uses of Geiger Counters
Geiger counters are used to measure radiation levels in space and materials. Radiation is used not only in the medical and industrial fields, but also in the agricultural field.
The simple measurement of radiation levels makes it possible to check food surfaces for contamination and to measure a wide variety of samples, including soil, water, and air doses. Although the Geiger counter is a very simple device, it is not a panacea for radiation measurement. Thus, it is necessary to understand the object to be measured and to measure it correctly.
Principle of a Geiger Counter
A Geiger counter is a cylindrical electrode called a GM tube filled with inert gases such as argon and helium. It measures the radiation dose by detecting the discharge (pulse) that occurs when radiation passes through the tube.
The measurement results are displayed in units of microsieverts per hour (μSv/h). A microsievert per hour is the amount of radiation you would receive if you were in a certain location for one hour. Radiation is the electromagnetic waves or particle rays produced when radioactive materials decay. Some radiation can penetrate the human body.
A particularly large number of gamma rays, which have a high penetrating power, affect the human body when their energy is high. The unit for this effect is the sievert (Sv). A sievert is defined as the number of gamma rays absorbed by the human body x energy. A Geiger counter measures the number of radiation rays present inside the device. The measured radiation counts per unit of time (cpm: counts per minute) are multiplied by a constant and converted to microsieverts per hour.
Types of Geiger Counters
There are two main types of Geiger counters:
1. A type in which the Counting Gas is inserted into a Cylindrical Container
This type of Geiger counter is a cylindrical container made of glass or metal with a counting gas sealed inside. This type of Geiger counter is used to measure gamma radiation doses.
2. Type with a Mica Window
One end of the Geiger-Mueller counter is made of a thin film, and there is a window made of mica, an ore called mica window, through which radiation reaches the boundary surface. It measures the number of beta rays entering through the mica window and is used to investigate contamination by radioactive materials.
A Geiger counter is properly a radiation measuring instrument using a Geiger-Mueller counter. However, radiation measuring instruments with different measuring principles, called scintillation type or semiconductor type, are also sometimes called Geiger counters.
Characteristics of Geiger Counters
Geiger counters are simple in construction and easy to handle, but care must be taken in handling the measurement results. It is important to understand that the measurement results of a Geiger counter are highly variable.
Radiation is randomly emitted from a radioactive material, so the measurement results can vary. Due to the randomness of the radiation emitted, even a change in the direction of the Geiger counter in the same location can change the measurement results. When measuring radiation levels with a Geiger counter, it is important to orient the Geiger counter and repeat the measurement multiple times before taking an average reading.
Also, if the Geiger counter is contaminated with radioactive materials, it will not give correct results. It is important to handle the Geiger counter in such a way that it does not get dirty.