Abstract
Decays of 232Th series isotopes such as 212Bi212Po and 208Tl form background events for underground physics experiments. In this study, we performed new delayed coincidence with a day-scale window using data of KamLAND, a 1 kton liquid scintillator detector. We firstly searched for a coincidence of 220Rn–216Po (T1/2 = 0.15 s), prompt coincidence (PC), and then searched for events of 212Bi212Po or 208Tl decays within 2 day from PC. It yields ~80% tagging efficiency with modest, ~10%, deadtime despite the requirement of long time correlation thanks to low accidental coincidence rate of PC. This method will be newly introduced to analyses of solar neutrino measurement at 3 MeV region with KamLAND and neutrinoless double-beta decay search with KamLAND-Zen to reduce the backgrounds.
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