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The HEAO-3 Heavy Nuclei Experiment has measured elemental abundances of ultraheavy cosmic rays near earth. The elements with atomic number (Z) in the intervals 44≤Z≤48 and 62≤Z≤74 arriving at earth are expected to have significant secondary components. However, their source abundances are unlikely to be low enough to warrant treating them as pure secondaries. Our results are consistent with solar system abundances modified for first ionization potential with possibly some enhancement of tho r to s ratio.

As part of a recent calibration at the LBL Bevalac for the Heavy Nuclei Experiment on HEAO-3, we have compared the response of a set of laboratory ionization chambers to beams of _(26)Fe, _(36)Kr, _(54)Xe, _(67)Ho, and _(79)Au nuclei at maximum energies ranging from 1666 MeV/amu for Fe to 1049 MeV /amu for Au. The response of these chambers shows a significant deviation from the expected energy dependence, but only a slight deviation from Z^2 scaling.

The HEAO-3 Heavy Nuclei Experiment (Binns, et al., 1981) is composed of ionization chambers above and below a plastic Cherenkov counter. We have measured the energy dependence of the abundances of elements with atomic number, Z, between 18 and 28 at very high energies where they are rare and thus need the large area x time of this experiment. We extend the measurements of the Danish French HEAO-3 experiment (Englemann, et al., 19S3) to higher energies, using the relativistic rise of ionization signal as a measure of energy, and determine source abundances for Ar and Ca.

Over the past few years, we have been analyzing the HEAO-3 measurements of the abundances of ultra-heavy cosmic ray nuclei (Z>26) at earth. In order to interpret these abundances in terms of a source composition, allowance must be made for the propagation of the nuclei in the interstellar medium. Vital to any calculation of the propagation is a knowledge of the total and partial interaction cross sections for these heavy nuclei on hydrogen. Until recently, data on such reactions have been scarce, and we have relied on the semiempirical formalism of Silberberg and Tsao to predict the partial cross sections. However, now that relativistic heavy ion beams are available at the LBL Bevalac, some of the cross sections of interest can be measured at energies close to those of the cosmic ray nuclei being observed.

The Heavy Nuclei Experiment on (HEAO-3) high energy astronomy observatory 3 uses a combination of ion chambers and a Cerenkov counter. During analysis, each particle is assigned two parameters, Zc and Zi, proportional to the square roots of the Cerenkov and mean ionization signals respectively. Because the ionization signal is double valued, a unique assignment of particle charge, Z, is not possible in general. Previous work was limited to particles of either high rigidity or low energy, for which a unique charge assignment was possible, although those subsets contain less than 50% of the total number of particles observed. The maximum likelihood technique was used to determine abundances for the complete data set from approx. 1.5 to approx. 80 GeV/amu.

This paper reports an observation of the abundances of cosmic-ray lead and platinum-group nuclei using data from the HEAO-3 Heavy Nuclei Experiment (HNE) which consisted of ion chambers mounted on both sides of a plastic Cherenkov counter (Binns et al., 1981). Previously we have reported on a search for actinide nuclei, Z > 88 (Binns, et al. 1982a). Further analysis with more stringent selections, inclusion of additional data, and a calibration at the LBL Bevalac, have allowed us to obtain the abundance ratio of lead and the platinum group of elements for particles that had a cutoff rigidity R_c > 5 GV.

The ratio of cosmic ray source abundance to solar-system abundance was examined for individual elements. Correlations of these ratios with first-ionization potential (FIP) and the expected mass-to-charge ratio (A/Q) of the elements in a million-degree plasma are analyzed. The FIP correlation was examined and it is shown that the correlation is affected by the choice of C2 or C1 chondritic meteorites as the solar-system standard for comparison. An A/Q correlation is suggested as a consequence of the shock acceleration model in the hot interstellar medium. The correlations are presented.