Cryogenic Detectors

Abstract

Most calorimeters used in high energy physics measure the energy loss of a particle in form of ionization (free charges) or scintillation light. However, a large fraction of the deposited energy in form of heat remains undetected. The energy resolution of these devices is therefore mainly driven by the statistical fluctuations of the number of charge carriers or photoelectrons involved in an event. In contrast, cryogenic calorimeters are able to measure the total deposited energy including the heat in form of phonons or quasi-particles in a superconductor. With the appropriate phonon or quasi-particle detection system much higher energy resolutions can be obtained due to the very large number of low energy quanta (meV) involved in the process. This feature makes cryogenic calorimeters very effective in the detection of very small energy deposits (eV) with resolutions more than an order of magnitude better than for example semiconductor devices. During the last two decades cryogenic detectors have been developed to explore new frontiers in physics and astrophysics. Among these are the quest for the dark matter in the universe, the neutrinoless double beta decay and the mass of the neutrino. But other fields of research have also benefited from these developments, such as astrophysics, material and life sciences. The calorimetric measurement of deposited energy in an absorber dates back to 1878, when the American astronomer S.P. Langley invented the bolometer [1]. With this device he was able to measure the energy flow of the sun in the far infrared region of the spectrum and to determine the solar constant. Since then the bolometer has played an important role to measure the energy of electromagnetic radiation

CUORE Opens the Door to Tonne-scale Cryogenics Experiments

“…The historic development of cryogenic detectors was prompted in the 1990's -primarily within the astroparticle physics community -by the need for particle detectors capable of detecting small energy depositions with good energy resolution [1,2,3]. These detectors are basically calorimeters in which the energy deposited by an interacting radiation converts into a temperature rise that is measured by means of a temperature sensor.…”

“…Thus to measure the deposited energy and minimize thermal noise, the detector must be operated at extremely low temperatures. Further, the heat capacity of dielectric materials follows the Debye law which scales as 𝑇 3 and thus is extremely small at low temperatures. Minimizing the heat capacity in turn maximizes the temperature rise for a unit energy deposition in the absorber allowing for improved detection.…”

“…To date the only cryogenic system capable of reaching and maintaining these stable working temperatures over long periods of time is dilution refrigerator (DR). A DR is a cryogenic device whose working principle relies on the properties of a mixture of two isotopes of helium: 3 He and 4 He. The idea was originally proposed by H. London in 1951 [30] and, about ten years later, H. London, G.R.…”

“…To understand the working principle of DRs it is crucial to understand the properties of 3 He/ 4 He mixture. Figure 1 on the left shows the relation between the 3 He molar concentration and temperature for liquid 3 He/ 4 He mixture at saturated vapor pressure. Liquid 4 He acts as a super-fluid -a state of matter in which matter behaves like a fluid with zero viscosityat 𝑇 = 2.177 K, while 3 He does not undergo any phase transition down to few mK.…”

“…Figure 1 on the left shows the relation between the 3 He molar concentration and temperature for liquid 3 He/ 4 He mixture at saturated vapor pressure. Liquid 4 He acts as a super-fluid -a state of matter in which matter behaves like a fluid with zero viscosityat 𝑇 = 2.177 K, while 3 He does not undergo any phase transition down to few mK. However, the temperature of the super-fluid phase transition of the (Bose) liquid 4 He decreases if this is diluted into the (Fermi) liquid 3 He.…”