Cryogenic particle detector

Cryogenic particle detectors operate at very low temperature, typically only a few degrees above absolute zero. These sensors interact with an energetic elementary particle (such as a photon) and deliver a signal that can be related to the type of particle and the nature of the interaction. While many types of particle detectors might be operated with improved performance at cryogenic temperatures, this term generally refers to types that take advantage of special effects or properties occurring only at low temperature. The most commonly cited reason for operating any sensor at low temperature is the reduction in thermal noise, which is proportional to the square root of the absolute temperature. However, at very low temperature, certain material properties become very sensitive to energy deposited by particles in their passage through the sensor, and the gain from these changes may be even more than that from reduction in thermal noise. Two such commonly used properties are heat capacity and electrical resistivity, particularly superconductivity; other designs are based on superconducting tunnel junctions, quasiparticle trapping, rotons in superfluids, magnetic bolometers, and other principles. Originally, astronomy pushed the development of cryogenic detectors for optical and infrared radiation. Later, particle physics and cosmology motivated cryogenic detector development for sensing known and predicted particles such as neutrinos, axions, and weakly interacting massive particles (WIMPs). A calorimeter is a device that measures the amount of heat deposited in a sample of material. A calorimeter differs from a bolometer in that a calorimeter measures energy, while a bolometer measures power. Below the Debye temperature of a crystalline dielectric material (such as silicon), the heat capacity decreases inversely as the cube of the absolute temperature. It becomes very small, so that the sample's increase in temperature for a given heat input may be relatively large.