Abundances of the sub-Fe group of nuclei and their implications

Abstract

Recently evidences have been presented for a large flux of antiprotons in low energy cosmic rays. It is found that this implies a large amount of matter traversal by low energy cosmic rays. There is already evidence for the large amount of matter traversal in the form of a large ratio of Fe secondaries to Fe nuclei at energies below 100 MeV/nucleon. A calculation of the expected ratios at the earth based on the realistic propagation models yield the result that indeed the amount of matter traversed by the Fe group nuclei is nearly five times larger than the ones by the high energy particles. At the same time the evidence from the antiproton is for substantial grammage as well as a large deceleration in energy since the production. These two facts are combined into a new model of acceleration and propagation of cosmic rays. Here the cosmic rays traverse substantial amount of matter during the first phase of acceleration. Subsequently, when the particles are confined in source region, which undergoes an expansion in volume, the particles would lose a lot of energy due to adiabatic deceleration. This can explain the apparently anomalous abundances of antiprotons and iron secondaries. It is shown that this model is in good accord with the experimental observations.