Geoneutrinos in Borexino

Abstract

This paper describes the Borexino detector and the high-radiopurity studies and tests that are integral part of the Borexino technology and development. The application of Borexino to the detection and studies of geoneutrinos is discussed.. The Gran Sasso National LaboratoryThe Gran Sasso National Laboratory (Laboratori Nazionali del Gran Sasso -LNGS), home of the Borexino experiment, is the world's largest underground laboratory. It is located in the center of Italy in the highway tunnel between Teramo and L'Aquila under the "Monte Aquila" (Gran Sasso mountain). The laboratory is financed and operated by the Italian National Institute for Nuclear Physics (Infn). Its total underground volume is about 180,000 m 3 with an area greater than 13500 m 2 . It is composed of three main experimental halls (20 m high, 18 m wide and 100 m long). The overburden rock is on the average about 1,400 m, equivalent to 3,700 meters of water. The muon flux is reduced by about 6 orders of magnitude to a value of approximately 1.1 muons per square meter per hour, whereas the neutron flux is of the order of 3 × 10 −6 neutrons per square centimeter per second with energies greater than 2.5 MeV.The rock of the Gran Sasso mountain has a density of 2.71 ± 0.05 g · cm −3 , and consists mainly of CaCO 3 and M gCO 3 [1]. The primordial radionuclide content of the rock of Hall C is 0.66 ± 0.14 ppm for 238 U, 0.066 ± 0.025 ppm for the 232 Th and 160 ppm for K [2]. The radioactive content of the concrete employed as experimental hall liner is 1.05 ± 0.12 ppm for 238 U and 0.656 ± 0.028 ppm for the 232 Th [3].The LNGS hosts about 15 experiments of astroparticle physiscs such as neutrino research, double beta decay physics, dark matter studies and nuclear astrophysics. Interdisciplinary studies (biology, geology) are also conducted in the LNGS underground location.The Borexino detector is located in one of the big underground experimental halls, hall C. The Borexino detectorBorexino is a real time experiment whose main goal is to study the low energy (sub-MeV) solar neutrinos, and in particular the 862 keV 7 Be solar neutrino line, through the neutrino-electron elastic scattering reaction. The maximum energy of the recoiling electron is 664 keV and the experimental design threshold is set at 250 keV [4].