A ground level measurement of energy spectrum of reactor anti-neutrino using a segmented plastic scintillator detector

Abstract We report on reactor $\bar{\nu _{e}}$ detection using the PANDA detector, a segmented plastic scintillator system operated at ground level. In 2019, the detector was deployed at 45 m from Reactor Unit-4 at the Ohi Nuclear Power Station. Inverse beta decay (IBD) signals were identified through delayed coincidence of positron and neutron capture signals. The stability of energy scale was monitored by natural radioisotopes. By subtracting Reactor-OFF data from Reactor-ON data, the IBD event rate was measured to be 163.6 ± 31.2 /day, excluding the zero-IBD hypothesis at more than 5.2σ. The result agrees with Monte Carlo predictions within uncertainties. Feasibility studies indicate that adding boron-loaded scintillator plates, boron-doped shielding, and time-of-flight discrimination can reduce residual backgrounds from 9000 /day to ∼2400 /day, enabling daily reactor monitoring at 3σ confidence level. These results demonstrate the potential of compact, above-ground detectors for reactor neutrino monitoring and nuclear safeguards.