Primary cosmic ray energy spectrum above 1 PeV as measured by the PRISMA-YBJ array

Abstract

Primary cosmic ray energy spectrum above 1 PeV has been measured with PRISMA-YBJ being a prototype of PRISMA array at altitude of 4300 m a.s.l. It realized a novel type of EAS recording method measuring hadronic EAS component over the total array area through thermal neutron detection with a specially developed so-called en-detectors sensitive to electron and thermal neutron EAS components. Primary c. r. spectrum was recovered in 2 ways: through usual Ne procedure as well as through measurements of EAS size spectrum in thermal neutrons. Monte-Carlo simulations of the experiments allowed us recover the primary spectrum above 1 PeV. The both obtained spectra follow power law function with index close that measured by direct measurements below 1 PeV.