Indian Scintillator Matrix for Reactor Anti-Neutrinos (ISMRAN), a plastic scintillator array (10×10), is being constructed for the purpose of electron anti-neutrino (ν e ) detection for reactor monitoring applications. A prototype detector called mini-ISMRAN, which consists of 16% of ISMRAN, has been setup for studying the detector response, background rates and event characterization in the reactor and non-reactor environment. The data acquisition system based on waveform digitizers is being used for pulse processing and event triggering. Monte-Carlo based simulations using GEANT4 are performed to optimize lead (Pb) and borated polyethylene (BP) shielding for background reduction and to study the positron, neutron and γ-ray response in the ISMRAN detector. Characterization of plastic scintillator detectors with known radioactive sources is performed for energy, timing and position measurements.Using the energy summation and bar multiplicity selection, coincident events from 60 Co decay are reconstructed in non-reactor environment. Results from background measurements using various detectors are quantified in reactor ON and OFF condition. The shielding of 10 cm Pb and 10 cm BP along with the requirement of hits in multiple bars, reduces the uncorrelated background in reactor ON condition. been shown to be sensitive to the reactor ON and OFF cycles. Also, since the ν e rate and energy spectrum changes as the uranium in the core is consumed and plutonium is produced, it is possible to calculate the burn up and estimate the isotopic content of the core [3]. Several groups across different countries are already pursuing this activity [4,5,6].This technique of monitoring reactors remotely may be useful for the International Atomic Energy Agency's (IAEA) 'Reactor Safeguards Regime' aimed towards ensuring implementation of safeguards for reactor facilities [7].Apart from relatively small volume of the detector, factors such as mobility of the setup, safety and convenience of use, especially, from the point of view of long-term operation are crucial for the goal of reactor monitoring. Due to their chemical composition, LS are toxic, flammable and face issues of compatibility with the container material, as they are good solvents. Plastic scintillators (PS) on the other hand are 98% Polyvinyl chloride (PVC), Polyvinyl Toluene (PVT) or polystyrene i.e. similar to normal plastic with no toxic or radioactive component and non-flammable. Therefore, for long-term near reactor operation use of PS is preferable. However, PS suffers from issues such as reduced light output due to attenuation and radiation damage. These aspects have been extensively studied and addressed to a reasonable extent in modern commercially available PS detectors [8]. Also, majority of PS can not use pulse shape discrimination (PSD) technique for discrimination between neutron and γ-ray signals.However, a segmented geometry of many plastic scintillator bars, employing a thermal neutron capture agent, can make use of the hit patterns and energy deposition ...
A: The Indian Scintillator Matrix for Reactor Anti-Neutrino detection -ISMRAN experiment aims to detect electron anti-neutrinos (ν e ) emitted from a reactor via inverse beta decay reaction (IBD). The setup, consisting of 1 ton segmented Gadolinium foil wrapped plastic scintillator array, is planned for remote reactor monitoring and sterile neutrino search. The detection of prompt positron and delayed neutron from IBD will provide the signature of ν e event in ISMRAN. The number of segments with energy deposit (N bars ) and sum total of these deposited energies are used as discriminants for identifying prompt positron event and delayed neutron capture event. However, a simple cut based selection of above variables leads to a low ν e signal detection efficiency due to overlapping region of N bars and sum energy for the prompt and delayed events. Multivariate analysis (MVA) tools, employing variables suitably tuned for discrimination, can be useful in such scenarios. In this work we report the results from artificial neural network classifierthe multilayer perceptron (MLP), particularly the Bayesian extension -MLPBNN, to achieve better signal detection efficiencies with reasonable background rejection. The neural network response is used to distinguish prompt positron events from delayed neutron capture events on Hydrogen, Gadolinium nucleus, and from a typical reactor γ-ray background. A prompt signal efficiency of ∼91% with a reasonable background rejection of ∼73% is achievable with the MLPBNN classifier for the ISMRAN experiment.
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.
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