Study of cosmic-ray H and He isotopes at 23 AU

Abstract

view Abstract Citations (34) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Study of Cosmic-Ray H and He Isotopes at 23 AU Seo, E. S. ; McDonald, F. B. ; Lal, N. ; Webber, W. R. Abstract We have measured the spectra of H and He isotopes during the 1987 solar minimum with the cosmic-ray detector system (CRS) on the Voyager 2 spacecraft. By carrying out the measurement near solar minimum and at large heliospheric distances, the effects of solar modulations were reduced. In particular, the adiabatic energy losses were smaller, and these results from 23 AU over the solar minimum period of cycle 21 represent observations at energies not accessible from previous measurements near 1 AU. The modulated spectra with the diffusion coefficient constant k0 = 3.15 x 1022 sq cm/s (which corresponds to a solar modulation parameter of 360 MV at 23 AU and 500 MV at 1 AU) agree well with both our data at 23 AU and the previous solar minimum measurements at 1 AU. The measured H-1 and H-2 spectra are both consistent with the calculated spectra, using standard Galactic and heliospheric propagation models without invoking an anomalous hydrogen component. With the fixed modulation parameter of 360 MV, the mean pathlengths, source spectra, and cross sections were varied to study the effects of different input parameters on the spectra and relative abundances. At this stage of our work, we have not found any strong evidence from the low-energy H-2 and He-3 data that H-1 and He-4 should have a different propagation history, or different types of source spectra from the heavier cosmic-ray nuclei. Publication: The Astrophysical Journal Pub Date: September 1994 DOI: 10.1086/174604 Bibcode: 1994ApJ...432..656S Keywords: Cosmic Rays; Energy Spectra; Helium Isotopes; Hydrogen Isotopes; Interplanetary Medium; Nuclear Interactions; Abundance; Kinetic Energy; Radiation Detectors; Solar Spectra; Voyager 2 Spacecraft; Astrophysics; ISM: COSMIC RAYS; INTERPLANETARY MEDIUM; ISM: ABUNDANCES full text sources ADS |