Relativistic interaction of Ne-22 and Mg-26 in hydrogen and the cosmic-ray implications

The isotopic production cross sections for Ne-22 projectiles at 377,581, and 894 MeV nucleon(-1) and Mg-26 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 O-18 at the cosmic-ray source, which is sensitive to the cross sections for production from Ne-22 and Mg-26 and the uncertainties in cross section prediction formulae, may be explained. There is no evidence for an enhancement of O-18 when these new cross sections are used in a weighted slab propagation calculation.