Low-background experiments
Experiments searching for rare nuclear events, such as for dark matter searches or neutrino physics, need to have exhibit a radioactive background as low as possible. This background comes from various sources:
- alpha, beta, or gamma-backgrounds from natural radioactive contaminations in the detector construction materials and its surrounding (mainly U and Th decay series, and 40K)
- neutrons from spontaneous fission of 235U, 238U and 232Th, (alpha, n) reactions and muon induced neutrons
- muons or hadronic cosmic rays from the Earth's atmosphere
The lowest level of intrinsic radioactivity is being achieved by placing the detectors deep underground, using a passive or active shielding, applying software cuts and special procedures for selecting and purifying all the detector materials including the purification of the targets.