Characterization of plastic scintillator bars using fast neutrons from D-D and D-T reactions

Abstract

We report results of fast neutron response in plastic scintillator (PS) bars from deuterium-deuterium (D-D) and deuterium-tritium (D-T) reactions using Purnima Neutron Generator Facility, BARC, Mumbai. These measurements are useful in context of Indian Scintillator Matrix for Reactor Anti-Neutrino (ISMRAN) detection, an array of 10×10 PS bars, used to measure reactor anti-neutrinos through inverse beta decay (IBD) signal. ISMRAN detector, an above-ground experiment close to the reactor core (∼13m), deals with an active fast neutron background inside the reactor hall. A good understanding of fast neutron response in PS bars is an essential pre-requisite for suppression and discrimination of fast neutron background from IBD events. A monoenergetic neutron beam from the fusion reaction of D-D at 2.45 MeV and D-T at 14.1 MeV are used to characterize the energy response in these bars. The neutron energy response function has been simulated using the GEANT4 package and are compared with the measured data. A reasonable agreement of deposited energies by fast neutrons in PS bars between data and simulation are obtained for these reactions. The ratio of energy deposition in adjacent bars is used to discriminate between prompt IBD, fast neutron and neutron capture cascade gamma events.

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

“…The measured timing resolution of ∼4 ns leads to a parameterized position resolution of ∼20 cm in a single PSB [29,35] and is almost uniform among the different bars. Due to the segmented geometry of the ISMRAN detector, we can exploit the timing and position information for the localization of an event in the ISMRAN array to differentiate an ν e event from a background event arising due to fast neutron [36,37]. The complex absorption and re-emission processes of optical photons are known to be an important source of the non-linear and non-uniform response of the charge deposition in the PSBs.…”

“…By exploiting the nature of the energy deposition profile in PSBs for the measured fast neutrons from D−D and D−T reactions and simulated prompt event from ν e , a separation of these fast neutron background events are demonstrated in ref [37]. In order to understand and discriminate the non-reactor background, a detailed measurement of the non-reactor background with ISMRAN array has been accomplished at the DIL in BARC, without using any shielding structure.…”

“…A reasonable agreement between data and MC simulated events for the E 1 /E max and E max /E sum distributions are observed with average χ 2 is 0.179. Applying selection criteria on the E 1 /E max and E max /E sum ratios will improve the rejection of fast neutron or accidental background from ν e delayed events [37]. A detailed study of the peak positions and the resolution of the peaks using reconstructed E sum obtained from different radioactive and neutron source are tabulated in table 2.…”

Measurements using a prototype array of plastic scintillator bars for reactor based electron anti-neutrino detection

“…The timing and position resolutions are mostly similar in all the bars and are independent of incident γray energy. Due to a segmented geometry of the ISMRAN detector, we can exploit the timing and position information for the localization of an event in the ISMRAN geometry to differentiate between an ν e and a background event from fast neutron [30,31].…”