Lead, platinum, and other heavy elements in the primary cosmic radiation - HEAO 3 results

From an analysis of 580 days of exposure of the Heavy Nuclei Experiment on the HEAO 3 spacecraft, we have selected 322 nuclei with reasonable charge resolution, E ≥ 1.3 GeV n^(-1) and Z ≥ 50. These data show a defined abundance peak in the "platinum" (74 ≤ Z ≤ 80) region, a small abundance of "lead" (81 ≤ Z ≤ 83), and a significant number of "secondary" nuclei in the 62 ≤ Z ≤ 73 range. The deduced ratio in space of 0.25 ± 0.09 for "Pb/Pt" is distinctly lower than that predicted by any of the standard models for cosmic-ray sources and propagation effects. Although this low ratio suggests an enrichment in the cosmic-ray source of products of r-process nucleosynthesis, it may rather be an indication that the Pb abundance is suppressed by a source fractionation effect, or that there is less Pb in the solar system than is assumed in the standard compilations.