Cosmic-ray energy spectra between 10 and several hundred GeV per atomic mass unit for elements from _(18)Ar to _(28)Ni - Results from HEAO 3

The Heavy Nuclei Experiment on HEAO 3 included ionization chambers and a Cherenkov detector. For nuclei that arrive at locations and from directions with high geomagnetic cutoff ( > 8 GV) the Cherenkov signal determines the atomic number, Z, while the relativistic rise in ionization provides a measure of the energy. For the secondary cosmic-ray elements, _(19)K, _(21)Sc, _(22)Ti, and _(23)V, the abundances relative to _(26)Fe fall as power laws in energy; combining our results from 10 to ~200 GeV per amu with data between 1 and 25 GeV per amu from another instrument on the same spacecraft gives exponents -0.31 ± 0.01, -0.25 ± 0.02, -0.28 ± 0.01, and -0.23 ± 0.02, respectively. For _(28)Ni, which like _(26)Fe is a primary element, the abundance relative to _(26)Fe is essentially independent of energy over the interval from ~10-500 GeV per amu. The elements _(18)Ar and _(20)Ca, which at a few GeV per amu are mixtures of primary and secondary components, display abundances relative to _(26)Fe which fall with increasing energy up to ~100 GeV per amu and then level off at higher energies; from the energy dependence of these abundance ratios we infer Ar/Fe and Ca/Fe ratios in the source of 2.6 ± 0.7% and 8.8 ± 0.7%, respectively