Measurement of the cosmic-ray energy spectrum between 3×1015 and 3×1016 eV using a photon-density spectrum technique

The authors describe a new experiment to measure the cosmic-ray energy spectrum in the astrophysically interesting energy range from 3*1015 eV, to 3*1016 eV, close to the 'knee' in the spectrum. The technique used is a novel variation of the photon-density spectrum technique in which the use of two separated detectors enables the energy spectrum to be investigated independently of any assumptions about the primary mass composition. The results they present are in reasonable agreement with earlier measurements in this energy range and, in conjunction with measurements at lower energies, may indicate the presence of a 'bump' or 'kneecap' in the spectrum. The experiment may also be used to infer gross features of the primary mass composition, and preliminary results indicate the potential of the technique.