[en] During solar quiet periods, the Solar Isotope Spectrometer (SIS) on the Advanced Composition Explorer (ACE) measures the composition and energy spectra of anomalous cosmic rays (ACRs) with energies >8 MeV/nucleon in interplanetary space at 1 AU. In particular, the spectra of individual isotopes for the ACR elements N, O, and Ne are studied with SIS. Intensity enhancements are found in low energy ¹⁸O and ²²Ne, with relative abundances of ¹⁸O/¹⁶O∼0.002 and ²²Ne/²⁰Ne∼0.1. The neon abundance ratio appears more similar to that found in the solar wind than in meteorites and is far below that determined for the galactic cosmic ray (GCR) source, indicating that GCRs contain material from sources other than just the local interstellar medium

[en] We have developed a high pressure (3-10 atm) segmented-anode gas ionization chamber and have investigated the capabilities of this type of instrument for identifying energetic heavy nuclei. For individual nuclei which stop in the active volume of the detector, we use one or more measurements of the particle's energy loss (ΔE) and its residual energy (E') to derive its charge and mass. Experiments using accelerator beams have yielded unambiguous charge identification over the range of elements studied (up to Z=26), and mass resolutions from σ_M ≅ 0.08 amu (Z=6) to σ_M ≅ 0.35 amu (Z=26). The energy loss measurements provided by the segmented anode are supplemented by two-dimensional measurements of particle track coordinates made using a combination of drift time and charge division in a set of single-wire proportional counters. These tracking detectors provide a position resolution < or approx.0.6 mm for each coordinate, and make possible the path length corrections needed to study isotropic particle distributions such as those encountered in the cosmic radiation. (orig.)

[en] The abundances of elements from helium to iron have been measured in more than a dozen moderate to large solar energetic particle (SEP) events using the Solar Isotope Spectrometer (SIS) on-board the Advanced Composition Explorer (ACE). Time variations within some of these events and from event to event have been reported previously. This paper presents an analysis of the event of 6 May 1998, for which relatively time-independent abundance ratios are found. This event has been considered to be an example of an impulsive event, a gradual event, and as a hybrid of the two. Difficulties with classifying this event are discussed

[en] Anomalous cosmic rays (ACRs) provide a sensitive probe of the access of energetic particles to the inner heliosphere, varying in intensity by more than two orders of magnitude during the course of the solar cycle. New data which are becoming available from the Advanced Composition Explorer (ACE) can provide a detailed record of ACR intensity and spectral changes on short (∼1 day) time scales during the approach to solar maximum, which will help address issues of ACR modulation and transport. The elemental and isotopic composition of ACRs provides important information on the source or sources of these particles, while their ionic charge state composition and its energy dependence serves as a diagnostic of their acceleration time scale. We review measurements of the ACR elemental, isotopic, and charge state composition and spectra as determined at 1 AU by SAMPEX, ACE, Wind, and other spacecraft. These results are important input to models of the acceleration, modulation, and transport of ACRs

[en] Using the Solar Isotope Spectrometer (SIS) on the Advanced Composition Explorer (ACE), we have studied the properties of a selection of small ³He-rich solar energetic particle (SEP) events with heavy ion enhancements in the energy range ∼11-22 MeV/nucleon. These events contain significantly increased ³He/⁴He ratios over the solar wind value of 0.0004 in the energy range ∼4.5-5.5 MeV/nucleon. In order to characterize the events, the following features have been investigated. First, the heavy element content has been measured and compared to that found in past studies of impulsive SEP events. Next, the simultaneous 38-53 keV electron flux, measured with the Electron, Proton, and Alpha Monitor (EPAM) on ACE, has been examined for possible activity near the ³He-rich event onset times. Finally a list of measured solar X-ray flares, with corresponding H-alpha flares where possible, has been scrutinized for potential correlations with these events. The results show an apparent correlation between event onset and increased electron flux, and a possible association with X-ray flares

[en] Observations of a number of relatively large solar energetic particle (SEP) events that have occurred since the launch of ACE in August 1997 have shown that the ratio of ³He/⁴He can be enhanced over the solar wind value (∼4x10^-4) by more than an order of magnitude in such events. Since particle acceleration in these 'gradual' SEP events is thought to be caused by CME-driven shocks traveling through the solar corona and interplanetary medium, a source of ³He in addition to the solar wind appears required to provide the seed material. Using data from the Solar Isotope Spectrometer on ACE, we have carried out a more detailed investigation of the characteristics of the ³He enhancements at energies >5 MeV/nucleon in three large SEP events (4 Nov 1997, 6 May 1998, and 14 Nov 1998). We find that the ³He/⁴He ratios are essentially time-independent during the events, that the ³He energy spectra are markedly harder than those commonly observed in impulsive events, and that the spectra of ³He may be harder than those of ⁴He

[en] The average composition of solar energetic particles (SEPs), like the solar corona, is known to be depleted in elements with first ionization potential (FIP) more than ∼10 eV by a factor of approximately four. We examine evidence for event to event variations in the FIP-related fractionation of SEPs, following up a 1994 study by Garrard and Stone. In a survey of 46 SEP events from 1974 to 1999 the deduced FIP-fractionation varies by a factor of ∼2 from event to event, with no apparent relation to charge-to-mass dependent fractionation patterns in these same events. These results are compared to similar variations observed in the solar wind

[en] Since the launch of ACE in August 1997, the Solar Isotope Spectrometer (SIS) has observed 11 large solar particle events in which elemental and isotopic composition was determined over a large energy range. The composition of these events has raised many issues and challenged generally accepted characterizations of solar energetic particle (SEP) events. In particular, ³He/⁴He enhancements have been observed in several large events as well as enhancements of heavy ions typically associated with smaller impulsive events. The isotopic composition varies substantially from event to event (a factor of 3 for ²²Ne/²⁰Ne) with enhancements and depletions that are generally correlated with elemental composition. This correlation suggests that the isotopic enhancements may be related to the Q/M fractionation typically evident in the elemental composition of SEP events. However, there are also significant deviations from this pattern, which may imply that wave-particle resonances or other mass fractionation processes may be involved. We review the recent isotopic observations made with ACE and discuss their implications for particle acceleration and transport

[en] Solar energetic particles (SEPs), like the solar wind, provide a direct sample of the Sun. Although SEP abundances show a variable amount of mass fractionation, it is possible to develop methods of correcting for it in order to deduce the composition of the corona. Using high-resolution measurements from the Solar Isotope Spectrometer on the Advanced Composition Explorer, we have studied the isotopic composition of 10 abundant elements from C to Ni in 32 large SEP events from late 1997 to the end of 2001 at energies >15 MeV/nucleon. We show that various isotopic and elemental enhancements are correlated with each other, discuss the first order corrections used to account for the variability, and obtain estimated coronal abundances. We compare the coronal values and their uncertainties inferred from SEPs with those that are available from solar wind and meteoritic measurements and find generally good agreement. We include C and Ni isotopic abundances, for which no solar wind measurements have yet been reported

[en] Galactic cosmic rays (GCRs) pass through the interstellar medium (ISM) and undergo nuclear interactions that produce secondary fragments. The abundances of radioactive secondary species can be used to derive a galactic confinement time for cosmic rays using the amount of ISM material traversed by the cosmic rays inferred from stable GCR secondary abundances. Abundance measurements of long-lived species such as ¹⁰Be, ²⁶Al, ³⁶Cl, and ⁵⁴Mn allow a comparison of propagation histories for different parent nuclei. Abundances for these species, measured in the energy range ∼50-500 MeV/nuc using the Cosmic Ray Isotope Spectrometer (CRIS) aboard the Advanced Composition Explorer (ACE) spacecraft, indicate a confinement time τ_esc=16.2±0.8 Myr. We have modeled the production and propagation of the radioactive secondaries and discuss the implications for GCR transport