Cosmic rays of the highest energies: the case for extragalactic heavy nuclei

An analysis has been made of the worldʹs data on very large extensive air showers with the object of deriving a `best-fitʹ primary energy spectrum. reassuring that when the various, independently measured, spectra are standardised, using as a datum the well-known `dipʹ in the spectrum at about 3×1018 eV, and a correction for inferred `noiseʹ, the measurements are all consistent. st-fit spectrum bears out the well-known problem with the lack of observation of a feature (a cut-off) due to interactions of the particles, commonly assumed to be extra-galactic protons, with the cosmic microwave background. However, we contend that a model involving extragalactic nuclei [J. Phys. A 8 (1975) 1518; Astrophys. J. 205 (1976) 638; Astrophys. J. 512 (1999) 521] is satisfactory, although it is premature to be too prescriptive, due to the shortage of astronomical data.