Radiation is the emission of energy from matter in the form of rays or high-speed particles. Broadly, it can be thought of as either electromagnetic radiation (like radio waves or visible light) or particle radiation (like alpha particles or beta particles).
Radiation Sensors or Radiation Detectors are devices that can sense and measure radiation. The radiation sensors discussed here are mostly based on the photoelectric effect. The phenomenon of emission of electrons from a material when electromagnetic radiation, such as a photon of visible light, falls on them is called the photoelectric effect.
Common Types of Radiation Sensors are
- Gas-filled radiation detectors.
- Scintillation radiation detectors.
- Solid-state radiation detector.
Gas-filled radiation sensors
A chamber filled with air or special gas is given a high voltage potential difference which causes ionization and as a result, positive ions gets collected to the cathode and free electrons to the anode which in turn causes a small current flow. The level of current indicates the level of radiation. A common type of gas-filled radiation detector is Geiger-Muller Detector, filled with helium, neon, or argon.
Scintillation radiation sensors
Solid or liquid material is hit with radiation which releases photons into a photomultiplier tube. The tube consists of multiple dynodes each one having higher electrical potential than the previous one. The released photon strikes the first dynode and an electron is emitted as a result of the photoelectric effect. The electron freed hits the next higher potential dynode and more electrons are emitted and are repeated forward. Hence, the output pulse from the tube is proportional to the light entering the tube.
Solid-state radiation sensors
A semiconductor device that contains two materials, n-type and p-type, are used in this detector. The n-type semiconductor material has electrons as majority carriers and the p-type has holes(positively charged) as majority carriers. When these two are joined, electrons from the n-region migrate to the p-region creating a depletion region between them. When radiation hits the depletion region, free electron-hole pairs are created. These charge carriers travel within the detector and the current pulse they cause is proportional to the level of radiation.