Abundances and Energy Spectra of Galactic Cosmic-Ray Nuclei above 20 Mev Per Nucleon in the Nuclear Charge Range 2 ≤ Z ≤ 26

Abstract

view Abstract Citations (73) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Abundances and Energy Spectra of Galactic Cosmic-Ray Nuclei above 20 Mev Per Nucleon in the Nuclear Charge Range 2 <= Z <= 26 Comstock, G. M. ; Fan, C. Y. ; Simpson, J. A. Abstract The individual abundances of the elements helium through silicon, as well as the nuclear-charge group 15 <Z < 25 and the Fe-Ni group, have been measured using a telescope composed of solid-state detectors on the OGO-I satellite in the period October, 1964, to June, 1965. Also measured were the differential energy spectra for He, B, C, and 0 over the energy range 201000 MeV per nucleon, with some integral measurements above 1000 MeV per nucleon. The spectra for Ne, Mg, and the Fe-Ni group were obtained over a narrower energy range. The experimental results are divided into two time intervals approximately 6 months apart in order to investigate the dependence of abundances and energy spectra upon changes in solar modulation. The abundances of the elements in the kinetic energy range 20 to 330 MeV per nucleon are normalized to oxygen with a flux of 5.4 X 10- nuclei ster (MeV/nucleon)-1. The ratio of abundances of nuclei with even-to-odd nuclear charge number Z, especially in the range 6 < Z < 14 is approximately 8:1. The elements Li, Be, and B are present down to the lowest observed energies in the approximate ratio 2:0.7:2.5. The ratio (Li, Be, B): (C, N, 0) = 0 26 + 004. The abundance of the Fe-Ni group relative to C and 0 is nearly equal to its abundance at high energies. For nuclei 5 <Z < 14 the differential energy spectra are remarkably independent of energy below 300 MeV/nucleon. It is shown that the spectra for these nuclei, when extrapolated to the nearby interstellar medium, must be continuously rising toward the lowest observed energies ( 20 MeV/nucleon) with greater negative slopes than for the He spectrum. Experimental evidence for the galactic origin of these nuclei is presented. The bearing of this experiment on the origin and propagation of cosmic-ray nuclei is discussed, and it is pointed out that some assumptions commonly accepted are no longer tenable. Two specific alternatives are considered. It appears that energy degradation by ionization loss alone may not account for the results It is suggested that the rate of particle acceleration for a wide range of Z competes effectively with the rate of ionization loss at these low energies. Alternatively, a discrete, and possibly nearby, source in the Galaxy could account for these low-energy measurements. Since the technique of using solid-state devices for measuring multiply charged nuclei is novel, a description of the instrument and the methods for analyzing the data are given. Publication: The Astrophysical Journal Pub Date: October 1966 DOI: 10.1086/148859 Bibcode: 1966ApJ...146...51C full text sources ADS |