Analysis of GCR Spectra and Composition Using Penetrating Particle Data from the CRIS Instrument on ACE

Abstract

The Cosmic Ray Isotope Spectrometer (CRIS) on NASA’s Advanced Composition Explorer (ACE) spacecraft has been making precise measurements of cosmic-ray elemental and isotopic composition and energy spectra for nearly 18 years. This instrument uses the dE/dx versus total energy technique to identify nuclei that stop in thick stacks of silicon solid-state detectors and to measure their energy. The energy range covered for these stopping particles extends up to ∼280 MeV/nuc for O and ∼570 MeV/nuc for Fe. We have developed a new technique for identifying particles that penetrate the entire detector stack that relies on a combination of the total energy deposited in the stack and the change of dE/dx from the front to the back of the stack. This technique allows us to extend energy spectra for cosmic-ray elements to higher energies and can be used for bridging the energy gap between the CRIS stopping-particle spectra and measurements made in low-Earth orbit by instruments such as HEAO-C2, PAMELA, and AMS-02. We describe the technique for assigning atomic number and energy to penetrating particle events and discuss the corrections needed for deriving energy spectra from these data.