Background estimation studies for positron double Beta decay

Abstract

Abstract: The study of neutrinoless double beta decay (DBD) has attracted much attention because it can provide valuable information about the mass and the nature of the neutrino. DBD itself is also of interest in nuclear physics. While DBD has been observed in about a dozen nuclei, the positron DBD (β +β +/EC-β +) continues to be elusive. An important signature for β +β + decay is the simultaneous emission of four 511 keV gamma rays, and the coincident detection of these gamma rays can improve the measurement sensitivity. This paper presents an estimation of sensitivity for EC-β+and β +β +, employing coincidence measurement with two high-purity Ge (HPGe) detectors. Simulations for coincident detection efficiency (εc) of 511 keV gamma rays with two HPGe detectors were carried out using GEANT4 for different source geometries to optimize the mass efficiency product (Mεc). A source of size 55 mm × 55 mm × 5 mm (thickness) sandwiched between the front faces of the detectors was found to be optimal for two pairs of 511 keV gamma rays in the present detector setup. The coincident background was estimated at sea level with moderate lead shielding. With this setup, the sensitivity for T1/2 measurement of EC-β+in 112Sn and β +β + in 106Cd was estimated to be ∼1019–1020 years for one year of measurement time.