The charge distribution of the energetic very heavy nuclei in the primary cosmic radiation

Abstract

A fully digitized, semiautomated photodensitometer has been employed to study the detailed charge composition of primary cosmic-ray nuclei having [Formula: see text] detected in a stack of nuclear emulsions flown from Hyderabad, India under approximately 4 g/cm² of residual atmosphere. One hundred and twenty nuclei heavier than phosphorus have been analyzed. These nuclei all had energies exceeding 7.1 GeV per nucleon and have had their charges measured with an accuracy estimated to be ± 0.4 of a unit charge. It has consequently been possible to resolve the individual charges and to determine the elemental abundances. The observed charge distribution has been corrected to the top of the atmosphere and compared with various cosmological abundance compilations. After deriving values for the fragmentation parameters in hydrogen, it is concluded that the data are consistent with the charge distribution predicted if an initially pure sample of iron nuclei had traversed some 4 g/cm² of matter since the initial acceleration. The cosmologically abundant elements sulphur, argon, and calcium appear to be relatively absent from the source, while nickel is only present with the predicted abundance.