Observations of the Abundances of Secondary Galactic Cosmic Rays from Z equals 5 to 28 Between 10 and 200 MeV/nuc Beyond the Heliopause by Voyager, Some Unexpected Anomalies and Their Interpretation Using a LBM for Galactic Propagation

TL;DR

Voyager's low-energy cosmic ray observations reveal unexpected secondary nuclei abundances, challenging existing models and suggesting complex propagation and source interactions in the galaxy.

Contribution

This paper presents new Voyager data on low-energy secondary cosmic rays and evaluates their implications using a Leaky Box Model, highlighting discrepancies and proposing alternative interpretations.

Findings

Large B abundance at low energies exceeds model predictions.

Zero counts of certain heavier secondaries challenge nested LBM assumptions.

Galactic matter traversal likely dominates B production at these energies.

Abstract

Voyager observations for over 3 years beyond the heliopause have started to define features of the low energy, less than 100 MeV per nuc, cosmic ray secondary nuclei that have a zero or negligibly small source component. As an example, the abundance of B between about 7 and 15 MeV per nuc is unexpectedly large, greater than the prediction of a LBM by 2 or 3 in the measurement and cross section error. On the other hand, for several other heavier secondary nuclei with a low source abundance such as F and Z equal 17 to 19 and 21 to 23 nuclei, in the corresponding energy channels between about 10-20 MeV/nuc, zero nuclei have been observed. The same LBM calculations would predict about 6 to 7 events for the sum of these three groups of nuclei. The B observed intensities could be more closely matched by considering a nested LBM with 0.3-1.0 g/cm2 of matter near the cosmic ray sources, essentially a source component of B. This nested LBM calculation, if extended to the production of the above groups of secondaries, would however predict a total 8 to 12 events thus leading to an even larger discrepancy with the zero events that are observed. The measurements of heavier secondaries at low energies therefore make it very problematical that a nested LBM with more than a few 0.1 g/cm2 or more of matter near the sources could be the source of the large B abundance seen by Voyager. The large abundance of B at the lowest energies is best understood, so far, as the result of production mostly from a matter traversal of 10 g/cm2 in the galaxy, possibly in combination with uncertainties in the data and cross sections at these low energies.