An extensive study for correcting the nonlinear particle density measured by GRAPES-3 scintillator detectors

The GRAPES-3 extensive air shower (EAS) array located at Ooty is equipped with 400 plastic scintillator detectors spread over an area of 25,000 m2 and a muon telescope of area 560 m2 built with 3,712 proportional counters. One of its principal objectives is to measure the primary cosmic ray energy spectrum in the TeV-PeV energy region. The response of the photo-multiplier tubes (PMTs) used in the plastic scintillator detectors becomes nonlinear at densities > 50 particles-m−2 in large EAS. We describe a technique to correct for the nonlinearity of these PMTs, thereby extending the dynamic range of the detectors for observed particle densities up to ∼5000 particles-m−2. The details of the technique will be presented.