Radiation detector
A radiation detector is a component used to measure electromagnetic radiation . Depending on the design of the detector, radiation of different wavelengths can be detected. Many radiation detectors can also serve as particle detectors .
If the impinging photons are registered as separate individual events, their number per time unit is called the count rate .
functionality
The functionality of a radiation detector is based on electromagnetic interactions of the photons, i.e. the field quanta of the electromagnetic field , with the electrons or atomic nuclei of the detector material (often noble gases or semiconductors ).
Depending on the type of detector, different interaction mechanisms are used.
Most often, the interaction of the photons with the electrons, thus the photoelectric effect : is the energy of the photon is equal to or greater than the binding energy of the electron, the electron can be obtained by the photon from the atom are dissolved composite. This electron is allowed to drift to the anode by applying an electric field , where it can be detected by measuring the electric current or the electric charge . The light in the visible and near infrared range can knock out the relatively weakly bound valence electrons , the significantly higher - energy X-ray and gamma radiation mainly interacts with the more strongly bound inner electrons.
The energy of the released electron is equal to the difference between the energy of the incident photon and the binding energy of the electron. If the energy of the released electron is high enough, it can ionize further atoms so that numerous electrons are released and can be detected. With X-rays, the number of electrons generated is proportional to the energy of the incident photon.
Examples
- Photo cells for the detection of light ( NIR to UV ) and its quantum energy (out of date)
- Photomultiplier as highly sensitive detectors (up to the detection of single photons) for NIR to UV , coupled with scintillators also for high-energy radiation ( X-ray or gamma radiation )
- Photoresistors , photodiodes ( see also: pin photodiode , avalanche photodiode ) and phototransistors for the detection of visible light, NIR and UV
- CCD sensors for spatially resolved detection of visible light, NIR and UV
- Counter tubes for the detection of most types of ionizing radiation
- Semiconductor detectors made of silicon or germanium for the detection of high-energy ultraviolet radiation ( vacuum UV , extreme UV ), as well as X-ray and gamma radiation
- Bolometers , thermocouples , Golay cells and pyroelectric sensors (e.g. in low-temperature pyrometers ) detect the radiation on the basis of the temperature differences it causes.
- Photographic plates or films in which the radiation causes permanent chemical changes that can be made visible through development .
- IR sensor cards convert infrared radiation into visible light through non-linear effects
- Scintillation counters convert the energy released by the interaction of high-energy quanta or elementary particles in a scintillator into flashes of light and also measure their quantum or particle energy via the amount of light per flash. These can also be used in hodoscopes to track the particle trajectories .