Constraints on cosmic-ray acceleration and transport from isotope observations

Observations from the Cosmic Ray Isotope Spectrometer (CRIS) on ACE have been used to derive constraints on the locations, physical conditions, and time scales for cosmic-ray acceleration and transport. The isotopic composition of Fe, Co, and Ni is very similar to that of solar system material, indicating that cosmic rays contain contributions from supernovae of both Type II and Type Ia. The electron-capture primary ^(59)Ni produced in supernovae has decayed, demonstrating that a time ≳10^5 yr elapses before acceleration of the bulk of the cosmic rays and showing that most of the accelerated material is derived from old stellar or interstellar material rather than from fresh supernova ejecta

Extended Energy Spectrum Measurement of Elements With the Cosmic Ray Isotope Spectrometer (CRIS)

We describe a multiple dE/dx technique used to identify particles that penetrate through the bottom of the CRIS instrument, significantly extending the measured energy ranges for major elements beyond that for stopping particles. In preliminary analysis, the upper energy limit for oxygen has been extended from ∼240 MeV/nuc for stopping particles to ∼410 MeV/nuc for penetrating particles, and the upper energy limit for iron has been extended from ∼470 MeV/nuc to ∼670 MeV/nuc. We report new element intensities in these extended energy ranges, and compare them with previously reported intensities and with spectra derived using cosmic ray transport and solar modulation models

Implications for Cosmic Ray Propagation from ACE Measurements of Radioactive Clock Isotope Abundances

Galactic cosmic rays (GCR) interact to produce secondary fragments as they pass through the interstellar medium (ISM). Abundances of the long-lived radioactive secondaries ^(10)Be, ^(26)Al, ^(36)Cl, and ^(54)Mn can be used to a derive the confinement time of cosmic rays in the galaxy. Abundances for these species have been measured recently using the Cosmic Ray Isotope Spectrometer (CRIS) aboard the Advanced Composition Explorer (ACE) spacecraft. To interpret this data we have modeled the production and propagation of the radioactive secondaries, taking into account recently published isotopic production cross-sections. Abundances for all species are consistent with a confinement time of π_(esc) ~22 x 10^6 years

Time Variations of the Modulation of Anomalous and Galactic Cosmic Rays

Between the launch of the Advanced Composition Explorer (ACE) in 1997 and the end of 1999, the intensities of galactic cosmic rays at 1 AU have dropped almost a factor of 2, and the anomalous cosmic rays have decreased by an even larger amount. The large collecting power of the Cosmic Ray Isotope Spectrometer (CRIS) and the Solar Isotope Spectrometer (SIS) instruments on ACE allow us to investigate the changing modulation on short time scales and at different rigidities. Using anomalous cosmic ray (ACR) and galactic cosmic ray (OCR) intensities of He, C, O, Ne, Si, S, and Fe, and energies from ~ 6 MeV/nucleon to ~ 460 MeV/nucleon, we examine the differences between the short term and long term effects. We observe the expected correlation of these intensities with neutron monitor data, but see little correlation of OCR and ACR intensities with the locally measured magnetic field

Cosmic Ray Source Abundances and the Acceleration of Cosmic Rays

The galactic cosmic ray elemental source abundances display a fractionation that is possibly based on first ionization potential (FIP) or volatility. A few elements break the general correlation of FIP and volatility and the abundances of these may help to distinguish between models for the origin of the cosmic ray source material. Data from the Cosmic Ray Isotope Spectrometer instrument on NASA’s Advanced Composition Explorer spacecraft were used to derive source abundances for several of these elements (Na, Cu, Zn, Ga, Ge). Three (Na, Cu, Ge) show depletions which could be consistent with a volatility-based source fractionation model

Balloon observations of galactic cosmic ray helium before and during a Forbush decrease

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95497/1/grl6996.pd

Measurements of the Elemental Composition of Galactic Cosmic Ray Nuclei with 6≤Z≤28 from the Cosmic Ray Isotope Spectrometer on ACE

The elemental abundances of galactic cosmic rays (GCR) observed near Earth provide information about the composition of the cosmic ray sources as well as their propagation history. The Cosmic Ray Isotope Spectrometer (CRIS) onboard the Advanced Composition Explorer (ACE) spacecraft measures the elemental and isotopic composition of GCRs with energies '"" 50 - 500 Me V /nucleon with high statistical accuracy ('"" 5000 stopping nuclei heavier than helium per day) due to its large geometrical factor. The CRIS data are used to derive cosmic ray abundances at the lowest level of solar activity during the last solar minimum. We present elemental abundances measured by CRIS, compare them with previous measurements, and discuss the plausible origins of the disagreement