In experimental and appliedparticle physics,nuclear physics, andnuclear engineering, aparticle detector, also known as aradiation detector, is a device used to detect, track, and/or identify ionizingparticles, such as those produced bynuclear decay,cosmic radiation, or reactions in aparticle accelerator. Detectors can measure the particle energy and other attributes such as momentum, spin, charge, particle type, in addition to merely registering the presence of the particle.
The operating principle of a nuclear radiation detector can be summarized as follows:
The detector identifies high-energy particles or photons—such asalpha,beta,gamma radiation, orneutrons—through their interactions with the atoms of the detector material. These interactions generate a primary signal, which may involve ionization of gas, the creation of electron-hole pairs in semiconductors, or the emission of light in scintillating materials. The primary signal is then amplified and processed by electronic systems. Finally, the resulting electrical pulse is analyzed to determine characteristics of the radiation, such as its energy, count rate, or spectral distribution.[1]
Many of the detectors invented and used so far are ionization detectors (of whichgaseous ionization detectors andsemiconductor detectors are most typical) andscintillation detectors; but other, completely different principles have also been applied, likeČerenkov light and transition radiation.
Historical examples
The following types of particle detector are widely used for radiation protection, and are commercially produced in large quantities for general use within the nuclear, medical, and environmental fields.
Electroscope (when used as a portable dosimeter)
Commonly used detectors for particle and nuclear physics
Modern detectors in particle physics combine several of the above elements in layers much like anonion.
Detectors designed for modern accelerators are huge, both in size and in cost. The termcounter is often used instead ofdetector when the detector counts the particles but does not resolve its energy or ionization. Particle detectors can also usually track ionizing radiation (high energyphotons or even visiblelight). If their main purpose is radiation measurement, they are calledradiation detectors, but as photons are also (massless) particles, the termparticle detector is still correct.
Beyond their experimental implementations, theoretical models of particle detectors are also of great importance to theoretical physics. These models consider localized non-relativistic quantum systems coupled to a quantum field.[2] They receive the name of particle detectors because when the non-relativistic quantum system is measured in an excited state, one can claim to have detected a particle.[3][4] The first instance of particle detector models in the literature dates from the 80's, where a particle in a box was introduced byW. G. Unruh in order to probe a quantum field around a black hole.[3] Shortly after,Bryce DeWitt proposed a simplification of the model,[5] giving rise to theUnruh-DeWitt detector model.
Beyond their applications to theoretical physics, particle detector models are related to experimental fields such asquantum optics, where atoms can be used as detectors for the quantum electromagnetic field via the light–matter interaction. From a conceptual side, particle detectors also allow one to formally define the concept of particles without relying on asymptotic states, or representations of a quantum field theory. AsM. Scully puts it, from an operational viewpoint one can state that "a particle is what a particle detector detects",[6] which in essence defines a particle as the detection of excitations of a quantum field.
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