アイテム詳細

要旨

The LENS project aims at the real-time spectroscopy of low energy solar neutrinos. Detection would proceed via inverse-EC to an isomeric state. The coincidence of prompt electron and delayed nuclear de-excitation gives a specific signature for background suppression. The most promising targets are Yb-176 and In-115. In both cases the detector would be modular and the target dissolved in liquid scintillators. The Yb-176 tag is difficult, because of the short delay (lifetime=50 ns) and low energy (E=72 keV) of the coincident event. The background due to statistical self-correlations of single events was investigated. This included the measurement of the fluorescence time of metal-loaded scintillators, the study of reflections from photomultipliers and the development of photon-tracing simulations. In a indium detector the background suppression requires high granularity and good energy resolution. Through measurements and simulations it was shown that the detector optical performances would not be dominated by the segmentation. As a result of these investigations, the project advanced to the pilot phase, with the construction of prototype detectors. The optical performances of prototype cells were measured, including attenuation length, energy and spatial resolution. First background results of the final LENS prototype are presented. The implications of these investigations for the feasibility of both proposed approaches is discussed.