Research and development of scintillation detectors for the study of cosmic ray

At Bose Institute Prof. Debendra Mohan Bose and his co-workers made globally recognised contributions in the field of cosmic rays including the first recording of mu-meson tracks. Prof. D. M. Bose and Dr. Biva Choudhury did their cosmic ray experiments at the Darjeeling campus of Bose Institute (along with Sandakphu and Pharijong). Presently the Darjeeling campus hosts a National facility for Astroparticle Physics and Space Science. In Kolkata also there is a Centre for Astroparticle Physics and Space Science (CAPSS). In these two campuses, we are still working on the R\&D of plastic scintillation detectors for the study of the cosmic rays to preserve the legacy of Prof. D. M. Bose. The only cosmic ray air shower array in the eastern part of India, consisting of seven plastic scintillator detectors is commissioned at an altitude of about 2200~meters above sea level (a.s.l.) in the Eastern Himalayas (Darjeeling) at the end of January 2018. The cosmic ray air shower array has a hexagon shape with six detectors kept at the vertices ofthe hexagon and one at the center of it. The distance between two consecutive detectors is 8 meters. Each detectorelement is made up of four plastic scintillators of dimension 50~cm~$\times$~50~cm~$\times$~1~cm thereby forming a totalactive area of 1~m$^2$. These scintillators are fabricated indigenously in the Cosmic RayLaboratory (CRL), TIFR, Ooty, India. All four scintillators of a detector are coupled with a singlePhoto Multiplier Tube (PMT) using wavelength shifting (WLS) fibers. A custom-built module withseven inputs is used to generate a multi-fold trigger. Measurement of the number of cosmic ray airshower is going on since the end of January 2018. The secondary cosmic ray flux and its variation overtime are also recorded at the laboratory in Darjeeling using a three-fold coincidence technique withplastic scintillators. All the details of the experimental setup, techniques of measurement are reported earlier. The updates in the results are presented in this article. In this review article, the details of the R\&D program of plastic scintillation detectors carried out during the last five years, for the study of cosmic ray is reported.