  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.
