Renaissance of interest in cosmic rays

Out Earth's atmosphere is continuously bombarded by primary cosmic rays, protons alpha particles and heavier nuclei with energies from 106 eV to 1020 eV. Entering the atmosphere, the cosmic ray particles interact with nitrogen and oxygen nuclei and produce a large number of secondary particles (pions, kaons, strange baryons, etc.) in cascading processes, a phenomenon called extensive air shower (EAS). The characteristic parameters (lateral distributions, intensities, time structure) of the three dominant components of EAS, hadronic, muonic and electromagnetic depend on the energy and mass of the primary, and on the characteristics of the high energy hadronic interaction. The understanding of EAS is crucial for cosmic ray investigations at energies above 1014 eV, (where direct measurements, e.g. balloon borne detectors, are no more possible), looking for information of the nature of interaction as well as of the origin, acceleration and propagation of cosmic rays in the universe. The aim of the KASCADE detector, installed and operated in Forschungszentrum Karlsruhe Germany, is to measure a number of EAS observables like muon multiplicity correlated with total intensity of the shower (size), energy spectra and lateral distribution of both muons and hadrons in the shower core and the muon arrival time distributions, to infer information about the unknown mass composition of high energy primary cosmic rays. Related to the KASCADE experiment an electromagnetic calorimeter WILLI has been set up in IFIN-HH Bucharest with a fine modular structure of thin absorber layers (1 cm Pb), for prototype studies of cosmic rays muon spectroscopy in TeV range and muon charge ratio measurement in the atmospheric muon flux. (authors)