Development of scintillator detector for detection of cosmic ray shower
We are building an array of active detectors to detect cosmic ray air showers at an altitude of about 2200 meter above sea level in the Himalayas. Each of the elements of this array is a 1m x 1m plastic scintillator coupled with WLS and photomultiplier tube. These scintillators are fabricated indigenously in Cosmic Ray Laboratory (CRL), Tata Institute of Fundamental Research (TIFR), Ooty, India.
All 1m x 1m scintillators are made of four 0.5m x 0.5m blocks. All four scintillator blocks are connected to a single photomultiplier tube (PMT) by using wavelength shifting (WLS) optical fiber. The PMT is mechanically fixed and connected to the base circuit. The negative high voltage (HV) to the PMTs is applied using MHV cable and the signal is collected by BNC cable. Initially all the PMTs are calibrated and their individual efficiencies are measured using other scintillator blocks of same kind.
Three such scintillator detectors are completed and tested. To detect the cosmic ray shower (as a preliminary test) three scintillator detectors are placed on a horizontal plane. The centers of the scintillator detector made a triangle of sides 1.9 m, 3 m and 3.5 m respectively. The three-fold coincidence from this horizontal stack of three detectors, which mimics a cosmic ray shower, is measured for about 1 month period. It is found that the shower rate reaching the detector varies with time between ~ 0.25-0.35 Hz.