Source abundances of ultra heavy elements derived from UHCRE measurements

Abstract

A total of 205 tracks have been located, measured, and positively identified as originating from Ultra Heavy (Z ≥ 65) cosmic ray ions with energies over 2 GeV/amu in the 10 UHCRE plastic track detector (mainly Lexan polycarbonate) stacks studied by our Group. About 40 values of reduced etch rate S have been obtained along each of these tracks. A method based on determining the gradient of S, together with calibration in accelerators, is used to determine the charge of each ion resulting in one of such tracks to obtain the charge spectrum of the recorded Ultra Heavy ions. The abundance ratio of ions with 87 ≤ Z ≤ 100, to those with 74 ≤ Z ≤ 86, as well as that of ions with 81 ≤ Z ≤ 86 to those with 74 ≤ Z ≤ 80 are calculated at 0.016 and 0.32, respectively, which agree with the values obtained from measurements in the HEAO-3 and Ariel-6 experiments. The abundance ratio of ions with 70 ≤ Z ≤ 73 to those with 74 ≤ Z ≤ 86 is also calculated, but its value (0.074) did not seem to be significant because of our detectors' low registration efficiency in the charge range 70 ≤ Z ≤ 73. A computer program developed by our Group, based on the Leaky Box cosmic ray propagation model, has been used to determine the source abundances of cosmic ray nuclei with Z ≥ 65 inferred from the abundances measured in the UHCRE. It appeared that r-process synthesized elements were overabundant compared to the Solar System abundances, as predicted by other authors.