Relativistic Interaction of 22Ne and 26Mg in Hydrogen and the Cosmic-Ray Implications

The isotopic production cross sections for ²²Ne projectiles at 377,581, and 894 MeV nucleon^-1 and ²⁶Mg projectiles at 371 and 576 MeV nucleon^-1 interacting in a liquid hydrogen target have been measured by the Transport Collaboration at the Lawrence Berkeley Laboratory Heavy-Ion Spectrometer System (LBL HISS) facility. These cross sections are compared with those predicted by semi-empirical formulae. The systematics are studied to develop suitable inputs for calculations of galactic cosmic-ray interstellar transport. These calculations are used to unfold the transport effects from available observations of cosmic-ray CNO isotopes to extract the underlying source composition. With these new cross section measurements, the previously reported enhancement of ¹⁸O at the cosmic-ray source, which is sensitive to the cross sections for production from ²²Ne and ²⁶Mg and the uncertainties in cross section prediction formulae, may be explained. There is no evidence for an enhancement of ¹⁸O when these new cross sections are used in a weighted slab propagation calculation.