Abstract
We use energy spectra of anomalous cosmic rays (ACRs) measured with the Cosmic Ray instrument on the Voyager 1 and 2 spacecraft during the period 1994/157-313 to determine several parameters of interest to heliospheric studies. We estimate that the strength of the solar wind termination shock is 2.42 (−0.08, +0.04). We determine the composition of ACRs by estimating their differential energy spectra at the shock and find the following abundance ratios: H/He = 5.6 (−0.5, +0.6), C/He = 0.00048 ± 0.00011, N/He = 0.011 ± 0.001, O/He = 0.075 ± 0.006, and Ne/He = 0.0050 ± 0.0004. We correlate our observations with those of pickup ions to deduce that the long-term ionization rate of neutral nitrogen at 1 AU is ∼ 8.3 × 10−7 s−1 and that the charge-exchange cross section for neutral N and solar wind protons is ∼ 1.0 × 10−15 cm2 at 1.1 keV. We estimate that the neutral C/He ratio in the outer heliosphere is 1.8(−0.7, +0.9) × 10−5. We also find that heavy ions are preferentially injected into the acceleration process at the termination shock.
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Cummings, A.C., Stone, E.C. Composition of anomalous cosmic rays and implications for the heliosphere. Space Sci Rev 78, 117–128 (1996). https://doi.org/10.1007/BF00170798
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DOI: https://doi.org/10.1007/BF00170798