A Novel Calibration Scheme of Effective Volume in a Large Segmented Liquid Scintillator Antineutrino Detector

The PROSPECT neutrino detector is a contiguous array of 154 15×15×120 cm3 modules, each filled with 6Li-loaded liquid scintillator (LiLS). The LiLS identifies neutrons by detecting the reaction n+6Li→4He+3H using Pulse Shape Discrimination (PSD) to select the α and triton. By dissolving a dilute solution of 227AcCl into the LiLS, we obtain a continuous monitor of relative active volume times efficiency, individually for each module, by observing the “RnPo” α-decays 219Rn→215Po→211Pb. The RnPo rate is 0.5 Bq integrated over the entire detector, providing a 1% calibration of each module over several weeks’ time. This talk will describe the principles of the technique, our prototype tests, and performance in the installed PROSPECT detector.