Abstract
The OSIRIS detector is a subsystem of the liquid scintillator filling chain of the JUNO reactor neutrino experiment. Its purpose is to validate the radiopurity of the scintillator to assure that all components of the JUNO scintillator system work to specifications and only neutrino-grade scintillator is filled into the JUNO Central Detector. The aspired sensitivity level of 10^{-16}hbox { g/g} of ^{238}hbox {U} and ^{232}hbox {Th} requires a large (sim 20,hbox {m}^3) detection volume and ultralow background levels. The present paper reports on the design and major components of the OSIRIS detector, the detector simulation as well as the measuring strategies foreseen and the sensitivity levels to U/Th that can be reached in this setup.
Highlights
The Jiangmen Underground Neutrino Observatory (JUNO) [1] is a dedicated experiment to measure the neutrino mass hierarchy
The Online Scintillator Internal Radioactivity Investigation System (OSIRIS) facility serves as the last stage in the purification chain of JUNO, measuring the residual radioactivity of the liquid scintillator (LS) before being injected into the JUNO Central Detector
OSIRIS will provide valuable information on the efficiency of the purification chain and issue a timely alert in case problems occur with the radiopurity of the LS
Summary
The Jiangmen Underground Neutrino Observatory (JUNO) [1] is a dedicated experiment to measure the neutrino mass hierarchy. JUNO will observe electron antineutrinos emitted by several nuclear reactor cores at a distance of ∼ 53 km with a 20 kiloton liquid scintillator (LS) detector In such a measurement shielding against external radiation and careful selection of radiopure detector materials play a crucial role. Simulations have helped to determine the required size of the water buffer surrounding the LS volume, the distance of the inner PMT array from the AV and to set radiopurity limits for all internal components of the OSIRIS detector External background We find that gamma rays emitted in the decays of natural radioactivity in the outer detector materials and surrounding rock are dominating the single-event spectrum. Despite 3 m of water shielding, the dominant background source are isotopes of the 232Th chain (especially 208Tl) in the surrounding rock, followed by the contribution of decays in the PMT glass
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