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Hyper-Kamiokande is a next-generation neutrino experiment built in Japan and is scheduled to become operational in 2027. It will be the world's largest underground water Cherenkov detector instrumented with three kinds of photomultipliers (PMTs): 20- and 3- inch PMTs, supplemented with multi-PMTs. The physics program of the Hyper-Kamiokande experiment will address the most important, unsolved questions in physics, including CP violation in neutrino oscillations and nucleon decay. An overview of the experiment is presented, emphasizing photo-sensors and electronics. [ABSTRACT FROM AUTHOR]

In operating mines, as well as in deep locations for planned scientific activities, it is essential to recognize the natural background radiation from the point of view of both occupational hazard and experimental background. Callio Lab, located in the Pyhäsalmi Mine, Finland, is one of the underground laboratories participating in the Baltic Sea Underground Innovation Network (BSUIN). The characterization of the natural background radiation was done at the Lab 2, which is the deepest located in Callio Lab. It involved in-situ gamma spectrometry, thermal neutron flux measurements, radon concentration determination, and α ∕ β laboratory spectrometry of water and rock samples. At a depth of 1436 m (∼ 4000 m w.e.) within the felsic volcanic bedrock occurs a volcanogenic massive sulphide deposit, wherein a thermal neutron flux of (1.73 ± 0.10) × 10−5 cm−2s−1, a gamma-ray flux of 12.7 ± 1.5 cm−2s−1, a gamma-ray dose of 0.158 ± 0.029 μ Sv/h and a radon concentration of 213.3 Bq/m3 ± 11% were determined. • Gamma ray dose of 158 ± 29 pSv/h was observed at the depth of 1436 m in felsic volcanic bedrock with sulphide deposit. • Deep underground location in pyrite mine has neutron flux of (1.73 ± 0.10) × 10−5 cm−2s−1. • Disequilibrium between 238U and 226Ra indicates the content of industrial wastes in wall coverage materials. • Increased intensity of gamma rays gives high-energy summation peaks on the spectrum. • Metal component susceptible on neutron activation are 24Na, 28Al, 46Sc, 56Mn, 59Fe. [ABSTRACT FROM AUTHOR]

The detailed characterization of ionizing radiation is essential for understanding occupational hazards as well as for planning scientific and industrial activities requiring well-defined conditions. The characterization of natural background radiation in the TU Bergakademie mine of Freiberg, Germany, which is one of the underground laboratories participating in the Baltic Sea Region's Underground Innovation Network (BSUIN), involves in-situ gamma spectrometry, neutron flux measurements, radon concentration, and alpha/beta laboratory spectrometry of water and rock samples. At a depth of 150 m within the gneiss formation (410 m w.e.), a neutron flux of (3.12 ± 0.10) × 10−6 [cm−2 s−1] and a gamma ray dose of 0.036 ± 0.008 μ Sv/h were determined. • Gamma ray dose of 36 ± 5 pSv/h was observed at the depth of 150 m in orthogneiss deck. • Shallow underground location in orthogneiss has neutron flux of about 2.6 ± 0.1 n/h. • 238 U series γ -rays with low contribution in the environmental spectrum are observed. • Increased intensity of gamma rays gives high-energy summation peaks on the spectrum. • Metal component susceptible on neutron activation are 110 Ag, 76 As, 56 Mn, 60 Co, 24 Na. [ABSTRACT FROM AUTHOR]