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Everything You Need to Know About Radiation Detectors

Sep 27

Radiation detectors, also known as radiation sensors, are devices that detect and measure the amount of radiation emitted by a source. The types of radiation detectors and how they function will be discussed briefly in this article. Before going through the various types of radiation detectors, we'll go over some basic radiation understanding and the many sorts of radiation emissions.

The fundamentals of radiation

Radiation is defined as energy that is dispersed in the form of rays or high-speed particles. Atoms, according to the traditional model of atomic structure, are made up of a number of particles, including protons and neutrons in the nucleus and electrons in the outer shells. As they seek to transition from an unstable to a more stable state, atoms may decay and release energy in the form of radiation.

Different types of radiation can be found in nature. Radiation can be divided into two categories: electromagnetic and non-electromagnetic.

Electromagnetic radiation can be thought of as a pure energy output. Radio waves, cosmic radiation (sunlight), and X-rays are examples of electromagnetic radiation.

The emission of fast-moving particles having both energy and mass is known as particle radiation. For example, alpha particles, beta particles, and neutrons are all examples of this type of radiation.

Atoms can split in some elements due to the absorption of an extra neutron, a process known as nuclear fission. This process produces both energy and neutron particles, as well as radiation.

Another term for describing radiation is to categorize it as either ionizing or non-ionizing radiation. The difference between ionizing and non-ionizing radiation refers to what the radiation is capable of doing as it passes through matter or strikes a material. Non-ionizing radiation can transfer energy into the substance it passes through, but because of its low energy, it is unable to break molecular bonds or remove electrons from atoms in the material.

Ionizing radiation, on the other hand, can impart enough energy to the material on which it impinges to break molecular bonds and take electrons from the material's atoms. When electrons are taken from an atom, ions are formed, and their presence can be harmful to living cells in plants and animals, including humans.

Because of the dangers of ionizing radiation exposure, most radiation detectors are designed to detect and measure this type of radiation. As a result, the remainder of this paper will concentrate solely on ionizing radiation detectors. Other types of radiation detectors will not be described, such as EMF/EMI detectors, solar radiation detectors, UVA/UVB detectors, and magnetic field radiation detectors.

Both the particle and electromagnetic radiation classes discussed earlier are examples of frequent types of ionizing radiation. The following are examples of ionizing radiation emission types:

  • Particles of alpha
  • Particles of beta
  • Neutrons X-rays
  • Gamma rays are a type of gamma ray

Particles of alpha

Alpha particles are a type of low-energy particle radiation that represents charged particles emitted from a range of materials, both natural and man-made. The capacity of most alpha particle emissions to permeate materials is limited, and they can be effectively prevented by a sheet of paper, a few inches of air gap, or the skin. If alpha particles are consumed or inhaled, however, they can be dangerous.

Particles of beta

Another type of particle radiation that can be emitted by sources like strontium-90 is beta particles. Beta particles can travel a greater distance and enter the skin since they are lighter than alpha particles, but they can be efficiently blocked by shielding with a thin layer of wood, metal, or plastic.


Neutron emissions are a type of particle radiation that consists of high-speed nuclear particles that may easily permeate materials and, through the process of neutron activation, render them radioactive. The majority of neutron radiation is produced in nuclear reactors, which are adequately insulated by concrete walls or barriers containing many feet of water.

X-rays and Gamma rays are two types of radiation

Because of their tremendous energy levels, both X-rays and gamma rays are kinds of electromagnetic radiation that travel at the speed of light and may easily permeate materials. X-rays and gamma rays, which are above ultraviolet light on the electromagnetic spectrum, have the highest frequencies (and shortest wavelengths) of all electromagnetic energy. For this type of radiation, dense materials like lead can be employed to create an efficient shield.

Measurement of radiation

Radiation levels can be measured in a variety of ways, with varying units of measurement depending on the equipment and what is being measured. The following are some of the more common radiation measurements:

  • The radiation's specific energy levels (in kV or MV)
  • The number of counts per minute (minutes or seconds)
  • The number of Roentgens per unit of time in the air (for example, milliRoentgen per hour – nR/hr). The amount of gamma or X-rays necessary to create ions with 1 electrostatic unit of electrical charge in 1 cubic centimeter of dry air is measured in Roentgens.
  • The dosage rate, which is expressed in gray or rad per unit time. One joule per kilogram, or 100 rad, is equal to one gray (Gy).
  • The cumulative dosage, expressed in grays or rads.
  • The biological danger of radiation exposure is quantified in rems or sieverts (Sv)

Radiation detectors come in a variety of shapes and sizes

Radiation detectors can be classified according to the type of radiation they detect or their underlying functioning principles. Counters, spectrometers, and radiation dosimeters are examples of radiation detectors in terms of functionality.

The following are the most prevalent types of radiation detectors:

  • Radiation detectors that are filled with gas
  • Detectors of scintillation radiation
  • Radiation detectors made of solid-state materials

Radiation detectors that are filled with gas

The ionization effect happens when radiation passes through air or a specific gas, and this is how gas-filled radiation detectors work. Ionizing radiation causes the formation of positively charged ions and free electrons that were stripped from the atoms of the gas during the ionization process when a high-voltage potential difference is introduced to a chamber holding air or a specialized gas. Positive ions will gather at the cathode of the detector due to the electrical potential difference in the chamber, whereas free electrons will collect at the anode. The collection of charged particles causes a little current to flow, which the detector can detect and show as an output signal or a "count." The amount of current is determined by the amount of radiation that strikes the detector. Because some radiation may pass through and not produce enough ionization in the chamber to be detected, gas-filled radiation detectors do not detect every particle. Furthermore, most of these detectors do not provide information on the charge, energy level, or type of incident radiation.

Detectors of scintillation radiation

Scintillation radiation detectors determine the level of radiation by measuring the amount of light energy created when radiation interacts with a material. The scintillator light flashes can be short, allowing the device to detect a large number of particles in a short amount of time. Photons are released into a device called a photomultiplier tube when incoming radiation strikes scintillating materials, which can be solids or liquids. The photomultiplier tube is made up of a sequence of plates known as dynodes, each with a higher positive electrical potential than the one before it. As a photon enters the tube, it strikes the initial dynode and, by the photoelectric effect, releases one electron. The freed electron is drawn to the photomultiplier's next plate's higher positive potential, causing more electrons to be released and transferred down the tube to subsequent dynodes. This process is repeated, with the amount of electrons released increasing with each dynode. The photomultiplier tube generates an output pulse proportionate to the amount of light energy entering the tube, which is directly proportional to the amount of radiation energy entering the scintillation radiation detector as a result of this activity.

Radiation detectors made of solid-state materials

Solid-state radiation detectors work on the principle of ionization in a semiconductor device with two types of semiconductor material ­ n-type and p-type. These materials are made up of atoms with charge carriers that are either electrons or holes, which are the lack of electrons. The number of electrons in an N-type material is greater than the number of holes in a p-type material. The movement of electrons from the n-region to the p-region creates a depletion zone when various types of semiconductor materials are combined within a solid-state radiation detector. Incident radiation causes free electrons and holes to form in the semiconductor material, and the number of electron-hole pairs is proportional to the amount of radiation. These charge carriers generate a current pulse as they go through the detector, which can be used to determine the amount of radiation present.