Voyager 1 Measurements Beyond the Heliopause of Galactic Cosmic Ray
Helium, Boron, Carbon, Oxygen, Magnesium, Silicon and Iron Nuclei with
Energies 0.5 to >1.5 GeV/nuc
We have obtained the energy spectra of cosmic ray He, B, C, O, Mg, S and Fe
nuclei in the range 0.5-1.5 GeV/nuc and above using the penetrating particle
mode of the High Energy Telescope, part of the Cosmic Ray Science (CRS)
experiment on Voyagers 1 and 2. The data analysis procedures are the same as
those used to obtain similar spectra from the identical V2 HET telescope while
it was in the heliosphere between about 23 and 54 AU. The time period of
analysis includes 4 years of data beyond the heliopause (HP). These new
interstellar spectra are compared with various earlier experiments at the same
energies at the Earth to determine the solar modulation parameter, phi. These
new spectra are also compared with recent measurements of the spectra of the
same nuclei measured by the same telescope at low energies. It is found that
the ratio of intensities at 100 MeV/nuc to those at 1.0 GeV/nuc are
significantly Z dependent. Some of this Z dependence can be explained by the Z2
dependence of energy loss by ionization in the 7-10 g/cm2 of interstellar H and
He traversed by cosmic rays of these energies in the galaxy; some by the Z
dependent loss due to nuclear interactions in this same material; some by
possible differences in the source spectra of these nuclei and some by the
non-uniformity of the source distribution and propagation conditions. The
observed features of the spectra, also including a Z dependence of the peak
intensities of the various nuclei, pose interesting problems related to the
propagation and source distribution of these cosmic rays.Comment: 35 pages, 5 tables, 14 figure
