| Using data collected by the Cosmic Ray Isotope Spectrometer (CRIS) on the NASA Advanced Composition Explorer (ACE) spacecraft, I report on measurements of Galactic Cosmic Ray isotopes in the energy range from 50 to 550 MeV/nucleon, with emphasis on the electron-capture-decay secondaries, 37Cl, 41Ca, 44Ti, 49V, 51Cr, 55Fe and 57Co. These isotopes, which decay only by electron-capture, are effectively stable in the cosmic rays at high energies where electron attachment is unlikely; at lower energies substantial electron attachment and decay does occur. By comparing the daughter-to-parent abundance ratios 49Ti/ 49V and 51V/51Cr during periods of solar minimum and solar maximum, I report new direct evidence of changes in the amount of energy loss that occurs in cosmic rays between solar minimum and solar maximum. Comparison of the electron-capture-decay abundance ratios with propagation models in the context of reacceleration are also presented. Analysis shows that little or no reacceleration is needed to correctly predict the energy-dependence of the electron-capture abundance ratios. |
