Evaluation of the response of plastic scintillator bars and measurement of neutron capture time in non-reactor environment for the ISMRAN experiment

TL;DR

This paper evaluates the response of plastic scintillator bars and measures neutron capture time in a non-reactor environment to support the ISMRAN experiment's goal of detecting reactor anti-neutrinos and understanding background signals.

Contribution

It provides a detailed experimental and simulation analysis of detector response, background characterization, and neutron capture time measurement for the ISMRAN setup in a non-reactor environment.

Findings

Neutron capture time measured as 68.29 ± 9.48 μs, consistent with MC simulation.

Validated detector response to gamma and neutron sources using experimental data and simulations.

Developed analysis techniques to discriminate background events from true inverse beta decay signals.

Abstract

We present a detailed study on detector response to different radioactive sources and the measurements of non-reactor environmental backgrounds with the Indian Scintillator Matrix for Reactor Anti-Neutrinos (ISMRAN) detector setup consisting of 9$\times$10 Plastic Scintillator Bars (PSBs) array at BARC, Mumbai. These measurements are useful in the context of the ISMRAN detector setup, which will be used to detect the reactor anti-neutrinos (${\bar{\ensuremath{\nu}}}_{e}$) and measure its energy spectra, through the inverse beta decay (IBD) process. A GEANT4 based Monte Carlo (MC) simulation is used to understand the optical transmission, energy resolution and energy non-linearity of the ISMRAN detector. A detailed analysis procedure has been developed to understand the natural radioactive, cosmogenic and cosmic muon-induced backgrounds with the ISMRAN detector setup in a non-reactor environment, based on their energy deposition, number of bars hit as well as topological event selection criteria in position and time for triggered events. Data and MC simulated distributions of reconstructed sum energy and number of bars hit has been compared for the radioactive $\gamma$ + positron source such as $\mathrm{{}^{22}Na}$ placed at the center of the ISMRAN array. Fast neutron energy response and capture time distribution in ISMRAN array has been studied using a novel technique involving Time of Flight (TOF) of the measured fast neutrons. The observed characteristic neutron capture time ( $\tau$ ) of 68.29 $\pm$ 9.48 $\mu$s is in good agreement with $\sim$65 $\mu$s obtained from MC simulation. These experimentally measured results will be useful for discriminating the correlated and uncorrelated background events from the true IBD events in reactor ON and OFF conditions inside the reactor hall.