Cosmic-ray Heavy-element Spectra Over an Extended Energy Range from the Advanced Composition Explorer

The Cosmic Ray Isotope Spectrometer (CRIS) on NASA's Advanced Composition Explorer (ACE) spacecraft has been measuring energy spectra and elemental and isotopic composition of galactic cosmic rays (GCRs) since ACE was launched in August 1997. Using measurements of nuclei that stop in thick stacks of silicon detectors, spectra are obtained for all elements from B through Ni. Typical energy coverage extends from 60 to 280 MeV/nuc for oxygen and 115 to 570 MeV/nuc for iron. Energy spectra of GCR nuclei observed near Earth have an intensity peak around several hundred MeV/nuc that is caused by the combined effects of ionization energy loss plus energy-dependent diffusion in the interstellar medium and solar modulation in the heliosphere. While the stopping-particle data provide precise measurements of the spectral roll-off on the low-energy side of the peak, they do not extend to high enough energy to precisely determine the peak shape and location. In addition to the stopping-particle measurements, CRIS routinely collects data on higher energy nuclei that penetrate the entire thickness of the silicon stacks. We have analyzed 18 years of penetrating-particle data using a new technique that achieves clean separation of even individual rare elements such as F and Sc and allows us to extend the CRIS measurements of GCR energy spectra to above the peak. We will discuss this analysis technique and present CRIS elemental energy spectra over a wider energy range than has previously been possible. We will also compare the spectra with predictions of a model calculation of the effects of interstellar and heliospheric transport.