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Observations of cosmic-ray helium energy spectra provide important constraints on cosmic ray origin and propagation. However, helium intensities measured at Earth are affected by solar modulation, especially below several GeV/nucleon. Observations of helium intensities over a solar cycle are important for understanding how solar modulation affects galactic cosmic ray intensities and for separating the contributions of anomalous and galactic cosmic rays. The Cosmic Ray Isotope Spectrometer (CRIS) on ACE has been measuring cosmic ray isotopes, including helium, since 1997 with high statistical precision. We present helium elemental intensities between ∼10 to ∼100 MeV/nucleon from the Solar Isotope Spectrometer (SIS) and CRIS observations over a solar cycle and compare these results with the observations from other satellite and balloon-borne instruments, and with GCR transport and solar modulation models.

The abundance of Li, Be, and B isotopes in galactic cosmic rays (GCR) between E=50-200 MeV/nucleon has been observed by the Cosmic Ray Isotope Spectrometer (CRIS) on NASA's ACE mission since 1997 with high statistical accuracy. Precise observations of Li, Be, B can be used to constrain GCR propagation models. \iffalse Precise observations of Li, Be, and B in addition to well-measured production cross-sections are used to further constrain GCR propagation models. \fi We find that a diffusive reacceleration model with parameters that best match CRIS results (e.g. B/C, Li/C, etc) are also consistent with other GCR observations. A $\sim$15--20% overproduction of Li and Be in the model predictions is attributed to uncertainties in the production cross-section data. The latter becomes a significant limitation to the study of rare GCR species that are generated predominantly via spallation., Comment: 9 pages of TeX format with three figures. Accepted for publication to Advances in Space Research (Elsevier)

The abundance of Li, Be, and B isotopes in galactic cosmic rays (GCR) between E=50-200 MeV/nucleon has been observed by the Cosmic Ray Isotope Spectrometer (CRIS) on NASA's ACE mission since 1997 with high statistical accuracy. Precise observations of Li, Be, B can be used to constrain GCR propagation models. \iffalse Precise observations of Li, Be, and B in addition to well-measured production cross-sections are used to further constrain GCR propagation models. \fi We find that a diffusive reacceleration model with parameters that best match CRIS results (e.g. B/C, Li/C, etc) are also consistent with other GCR observations. A $\sim$15--20% overproduction of Li and Be in the model predictions is attributed to uncertainties in the production cross-section data. The latter becomes a significant limitation to the study of rare GCR species that are generated predominantly via spallation., Comment: 9 pages of TeX format with three figures. Accepted for publication to Advances in Space Research (Elsevier)

Precise measurements of predominantly secondary cosmic-ray Li, Be, and B together with current well-measured production cross-sections for these isotopes help to improve our understanding of galactic cosmic ray propagation models. The Cosmic Ray Isotope Spectrometer (CRIS) on ACE has been measuring isotopic composition of cosmic rays since 1997 with high statistical precision. We present the isotopic abundances from CRIS and discuss these observations in the context of cosmic-ray transport models and previous cosmic-ray measurements.

The spectra of galactic cosmic ray (GCR) elements from Beryllium to Nickel in the energy range 40 - 500 MeV/nucleon at 1 AU are being continuously measured by instruments on-board the Advanced Composition Explorer (ACE). The collecting power of these instruments allows statistically precise spectra to be calculated every few months for most elements. Measurements of temporal variations in GCR spectra over the solar cycle are important for understanding solar modulation processes, and also for refining models of the near-earth radiation environment used to perform shielding and dose calculations for manned and unmanned space missions. We report on ACE observations of the evolution of GCR element spectra from solar minimum in 1997 through Spring 2001. We find significant differences between the ACE measurements and the predictions of available models of the near-Earth radiation environment, suggesting that these models need revision. We describe a cosmic ray interstellar propagation and solar modulation model that provides an improved fit to the ACE measurements compared to radiation environment models currently in use.

The cosmic-ray isotopes of lithium, beryllium, and boron (LiBeB) are generally believed to originate from interactions within the interstellar medium, primarily through CNO spallation. Other sources are known to contribute to the abundance of ^7Li and ^(11)B, most notably the production of ^7Li from big bang nucleosynthesis. Thus, identifying the abundances of the galactic cosmic-ray LiBeB places important constraints on the interpretations of early epoch nucleosynthesis. The Cosmic Ray Isotope Spectrometer (CRIS) on ACE has been measuring isotopic composition from helium through zinc in the energy range ˜70-500 MeV/nucleon since 1997 with high statistical accuracy. We present measurements of the isotopic abundances of LiBeB from CRIS and discuss these observations in the context of previous cosmic-ray measurements and predictions from cosmic-ray transport models.

Abundances of the isotopes of the refractory elements Ca, Fe, Co, and Ni in the galactic cosmic-ray source are compared with corresponding abundances in solar-system matter. For the 12 nuclides considered, relative abundances agree to within a factor of 2, and typically within 20–30%. In addition, comparisons of cosmic-ray abundances with model calculations of supernova yields are used to argue that cosmic rays contain contributions from stars with a broad range of masses. Based on these and other results we suggest that cosmic rays probably represent a sample of contemporary interstellar matter, at least for refractory species.

Galactic cosmic-ray (GCR) elemental abundances display a fractionation compared to solar-system values that appears ordered by atomic properties such as the first ionization potential (FIP) or condensation temperature (volatility). Determining which parameter controls the observed fractionation is crucial to distinguish between GCR origin models. The Cosmic-Ray Isotope Spectrometer (CRIS) instrument on board NASA's Advanced Composition Explorer (ACE) spacecraft can measure the abundances of several elements that break the general correlation between FIP and volatility (e.g., Na, P, K, Cu, Zn, Ga, and Ge). Phosphorus is a particularly interesting case as it is a refractory (high condensation temperature) element with a FIP value nearly identical to that of its semi-volatile neighbor, sulfur. Using a leaky-box galactic propagation model we find that the P/S and Na/Mg ratios in the GCR source favor volatility as the controlling parameter.

Cosmic-ray isotope observations from NASA’s Advanced Composition Explorer (ACE) mission have been used to investigate the composition of cosmic-ray source material. Source abundances relative to ⁵⁶Fe are reported for eleven isotopes of Ca, Fe, Co, and Ni, including the very rare isotopes ⁴⁸Ca and ⁶⁴Ni. Although the source abundances range over a factor ~ 10⁴, most of the ratios to ⁵⁶Fe are consistent with solar-system values to within ~ 20%. However, there are some notable differences, the most significant being an excess of ~ (70 ± 30)% relative to the solar system for the cosmic-ray source ratio ⁵⁸Fe/⁵⁶Fe. The possible association of such an excess with a contribution to the cosmic-ray source from Wolf—Rayet star ejecta is discussed.

There are a number of radioactive ‘clocks’ in the cosmic radiation that can be used to measure the time scales for cosmic ray processes in the Galaxy. With high-resolution isotope measurements available from ACE it is now possible to read these clocks with greatly improved accuracy and address key questions about the origin and lifetime of cosmic rays. This paper discusses the status of three such investigations.

In a one-day balloon flight of the Trans-Iron Galactic Element Recorder (TIGER) in 1997, the instrument achieved excellent charge resolution for elements near the Fe peak, permitting a new measurement of the element ratio Co/Ni. The best fit to the data, extrapolated to the top of the atmosphere, gives an upper limit for this ratio of 0.093±0.037 over the energy interval 0.8 to 4.3 GeV/nucleon; because a Co peak is not seen in the data, this result is given as an upper limit. Comparing this upper limit with calculations by Webber & Gupta suggests that at the source of these cosmic rays a substantial amount of the electron-capture isotope 59Ni survived. This conclusion is in conflict with the clear evidence from ACE/CRIS below 0.5 GeV/nucleon that there is negligible 59Ni surviving at the source. Possible explanations for this apparent discrepancy are discussed.

We report the first observation of an energy dependence in the titanium, vanadium, and chromium isotopic abundances in cosmic rays. The observations were made in the 100–500 MeV/nucleon energy interval using data from the Cosmic Ray Isotope Spectrometer on the ACE spacecraft. The ^(51)Cr and ^(49)V isotopes in cosmic rays are produced by fragmentation of heavier cosmic ray nuclides and decay only by electron capture. The observations indicate that electron-capture decay occurred primarily at the lower energies measured, and that there is a resulting energy dependence in the abundances of these isotopes and their decay products.

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.

In a one-day balloon flight of the Trans-Iron Galactic Element Recorder (TIGER) in 1997, the instrument achieved excellent charge resolution for elements near the Fe peak, permitting a new measurement of the element ratio Co/Ni. The best fit to the data, extrapolated to the top of the atmosphere, gives an upper limit for this ratio of 0.093±0.037 over the energy interval 0.8 to 4.3 GeV/nucleon; because a Co peak is not seen in the data, this result is given as an upper limit. Comparing this upper limit with calculations by Webber & Gupta suggests that at the source of these cosmic rays a substantial amount of the electron-capture isotope 59Ni survived. This conclusion is in conflict with the clear evidence from ACE/CRIS below 0.5 GeV/nucleon that there is negligible 59Ni surviving at the source. Possible explanations for this apparent discrepancy are discussed.

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.

Measurements of neon isotopic abundances from the ACE-CRIS experiment are presented. Abundances have been obtained in six energy intervals over the energy range of ~100≤E≤280 MeV/nucleon. These measurements are compared with the ACE-SIS data for lower energies extending down to ~8 MeV/nucleon. We find that the CRIS ^(22)Ne/^(20)Ne abundance ratio at the source is a factor of 5.0±0.3 greater than for the solar wind. The CRIS measured abundances agree well with previous experiments. The CRIS and SIS measurements are in good agreement for the higher SIS energies. However for the lower energy SIS data, where the anomalous cosmic rays (ACR) are being sampled, the ratio decreases and agrees with solar wind abundances. The implications of these results are discussed.

In a one-day balloon flight of the Trans-Iron Galactic Element Recorder (TIGER) in 1997, the instrument achieved excellent charge resolution for elements near the Fe peak, permitting a new measurement of the element ratio Co/Ni. The best fit to the data, extrapolated to the top of the atmosphere, gives an upper limit for this ratio of 0.093±0.037 over the energy interval 0.8 to 4.3 GeV/nucleon; because a Co peak is not seen in the data, this result is given as an upper limit. Comparing this upper limit with calculations by Webber & Gupta suggests that at the source of these cosmic rays a substantial amount of the electron-capture isotope 59Ni survived. This conclusion is in conflict with the clear evidence from ACE/CRIS below 0.5 GeV/nucleon that there is negligible 59Ni surviving at the source. Possible explanations for this apparent discrepancy are discussed.

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.

From the end of 1997 to early 1998, the relatively steady-state solar-minimum conditions provided an ideal period to study the solar modulation of anomalous cosmic rays (ACRs) and galactic cosmic rays (GCRs). Using observations of the energy spectra of the most abundant elements (H, He, C, N, 0, and Ne) from an array of spacecraft and instruments, we calculate the radial gradients for ACRs and GCRs over a wide range of rigidity. The GCR radial gradient is near zero for all rigidities, out to 70 AU. The ACR radial gradient shows a strong rigidity dependence in the middle heliosphere, which is expected, but the rigidity dependence is not present in the outer heliosphere, and is not obvious in the inner heliosphere.

Radioactive cosmic ray nuclei produced by nuclear interactions during cosmic ray propagation through the galaxy can be used to study the mean interstellar gas density in the propagation volume and the time scales associated with the propagation process. The Cosmic Ray Isotope Spectrometer (CRIS) aboard the Advanced Composition Explorer (ACE) has made high-resolution abundance measurements of the beta-decay secondary isotopes ^(10)Be, ^(26)Al, ^(36)Cl, and ^(54)Mn over the energy range 70-400 MeV/nuc. The large geometrical factor of CRIS (~250 cm^2sr) and the 20 months of data collection at near solar minimum conditions have made it possible since launch in August, 1997 to accumulate data samples considerably larger than previous missions. The isotopic abundances derived from these data are presented and compared with previous measurements.

The Cosmic Ray Isotope Spectrometer (CRIS) instrument on board the Advanced Composition Explorer (ACE) spacecraft is making new measurements of nuclides just beyond the iron-nickel peak in the galactic cosmic rays. Isotopes of copper and zinc have been resolved for the first time. Elemental abundances for nuclei with 29≤Z≤34 are reported with good separation between species. Several of these elements are useful for studying fractionation processes which may depend on the first ionization potential or volatility. Source abundances are estimated using a prior propagation calculation and their potential for distinguishing between source models are discussed.

Cosmic rays that are produced by nuclear interactions during propagation and decay only by electroncapture can be used to determine the level of cosmic ray reacceleration that has occurred. The high resolution, large statistical sample of cosmic rays collected by the Cosmic Ray Isotope Spectrometer (CRIS) aboard the Advanced Composition Explorer (ACE) spacecraft provides a data set that allows precision measurements of these isotopic abundances. We discuss electron capture decay, the signatures of reacceleration, and the sensitivity with which reacceleration models can be tested.

The time dependences of the intensities of low-energy galactic cosmic ray (GCR) nuclei have been investigated using instrumentation carried aboard the Advanced Composition Explorer (ACE). The intensities of these low energy particles near Earth began to decline from solar minimum levels in late-1997 /early-1998, shortly after the launch of ACE, and have been continuously monitored by the Cosmic Ray Isotope Spectrometer (CRIS) instrument since that time. We find that the variations are well correlated with variations of higher energy cosmic rays, as indicated by neutron monitor observations. The relative magnitude of the GCR variations is significantly less than previously reported for anomalous cosmic rays. We also compare the fluctuations observed for different energies and different nuclides.

Supernovae should produce the radioactive nuclide ^(59)Ni, and in the ejecta of the explosions these particles will decay by electron capture with a halflife of 7.6 x 10^5 yr to produce ^(59)Co. However, if the ^(59)Ni nuclei are accelerated to cosmic-ray energies on a time scale short compared to this halflife, they are stripped of their electrons and decay is prevented. Thus the abundances of ^(59)Ni and ^(59)Co can be used to determine whether the time between nucleosynthesis and cosmic-ray acceleration is short or long compared to the 59Ni halflife (Soutoul, Casse, & Juliusson 1978). We have used the Cosmic Ray Isotope Spectrometer (CRIS) on the Advanced Composition Explorer (ACE) to measure the abundances of 59Ni and 59Co in galactic cosmic rays, and find that the data are consistent with complete decay of 59Ni indicating a time delay 2 10^5 yr. We present the observations and discuss their significance for models of cosmic ray origin and acceleration.

Cosmic rays that are produced by nuclear interactions during propagation and decay only by electron capture can be used to determine the level of cosmic ray reacceleration that has occurred. The high resolution, large statistical sample of cosmic rays collected by the Cosmic Ray Isotope Spectrometer (CRIS) aboard the Advanced Composition Explorer (ACE) spacecraft provides a data set that allows precision measurements of these isotopic abundances. We discuss electron capture decay, the signatures of reacceleration, and the sensitivity with which reacceleration models can be tested.

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.

The Trans-Iron Galactic Element Recorder (TIGER) for the Ultra-Long Duration Balloon project Demo2000 (TD2K) is designed to measure the abundances of all elements in the Galactic Cosmic Rays (GCRs) with 26 ≤ Z ≤ 40 and energies above 300 MeV/nucleon. TD2K's flight is expected to approach 100 days in length. Launch will be from New Zealand in 2001. TD2K will have sufficiently good resolution to measure the individual abundances of the odd-Z elements between Z=26 and Z=40 for the first time. Measurements of odd-Z nuclei are important for distinguishing between the effects of first ionization potential and volatility in the injection process for ultraheavy GCRs, for models of nucleosynthesis, and constraining models of cosmic-ray propagation at short pathlengths. TD2K uses a combination of Cherenkov and scintillation counters to determine the atomic number and energy of incident cosmic rays, and a coded cintillating-fiber hodoscope for trajectory corrections. TD2K is an improved version of the TIGER instrument flown in 1997, results from which are reported at this conference (Sposato et al., 1999). We will present the status of the TD2K instrument and of the ULDB program as it affects the Demo 2000 flight.

We present measurements of the nickel and cobalt isotopes from the Cosmic Ray Isotope Spectrometer (CRJS) which was launched in August, 1997 aboard the NASA Advanced Composition Explorer (ACE). The objectives of CRJS are to measure the isotopic abundances and energy spectra of galactic cosmic rays ~GCRs) with 3 ≤ Z ≤ 30. We find that for these nuclei the measured ^5Ni/^(60)Ni and ^(59)Co/^(60)Ni ratios imply a time delay between nucleosynthesis and acceleration to cosmic ray energies of > 10^5 y.

TIGER is a balloon-borne cosmic-ray experiment designed to measure the elemental abundances of Galactic Cosmic Rays (GCRs) in the charge range 26

We report the results of an accelerator calibration of detectors planned for use in the ZIM experiment for ACCESS. The experiment utilizes silicon detectors to measure dE/dx, and aerogel and acrylic Cherenkov counters for velocity measurements. For a 79Au beam with energy 10.6 GeV/nucleon, we obtain resolution in charge for the silicon, acrylic Cherenkov, and aerogel Cherenkov of 0.20, 0.22, and 0.45 cu respectively.

The High Energy X-ray Timing Experiment (HEXTE) is one of three scientific instruments aboard the Rossi X-ray Timing Explorer (RXTE), which was launched on December 30, 1995. RXTE performs timing and spectral studies of bright x-ray sources to determine the physical parameters of these systems. The HEXTE consists of two independent clusters of detectors, each cluster containing four NaI(Tl)/CsI(Na) phoswich scintillation counters sharing a common 1 degree FWHM field of view. The field of view of each cluster is switched on- and off-source to provide near real-time background measurements. The net open area of the eight detectors is 1600 cm2, and each detector covers the energy range 15-250 keV with an average energy resolution of 15.4% at 60 keV. The in-flight performance of the HEXTE is described, the light curve and spectrum of the Crab Nebula/Pulsar is given, and the 15-240 keV spectrum of the weak source, active galaxy MCG 8-11-11 is presented to demonstrate the weak source spectral capabilities of HEXTE., Comment: 30 pages, 14 figures, 4 tables, accepted by Ap. J., to be published in vol 496, March 20, 1998

Our previous studies showed that the fragmentation cross sections of gold nuclei interacting in hydrogen have large variations between the values measured at 0.9 and 10.6 GeV/n, which has very significant implications on calculations of the propagation of the heaviest UH cosmic ray nuclei, such as Pb and Pt We have now completed a series of runs at the Brookhaven AGS using beams of gold nuclei of intermediate energy. The data from these runs will allow us to establish the excitation functions for these cross sections in a wide range of targets and hence model propagation more accurately than hitherto. In addition we will be able to study the energy dependence of nuclear charge pickup, electromagnetic dissociation and fission. Beams of gold nuclei with seven energies between 4.0 and 0.9 Ge V /n were studied interacting in targets ranging in mass from hydrogen to lead. We will present data on the cross sections derived from several of these beams and discuss some of the implications.

A set of particle detectors has been exposed to beams of _(79)Au nuclei at ~ 11 Ge V /nucleon from the Alternating Gradient Synchrotron (AGS) at Brookhaven National Laboratory (BNL). We report preliminary results on the responses obtained from silicon solid state detectors and from Cerenkov counters utilizing total internal reflection with waveshifter bars for readout.

The Cosmic Ray Isotope Spectrometer instrument on the Advanced Composition Explorer (ACE) spacecraft has been built and tested and will be launched into space in a few months. This paper briefly describes the overall instrument and expected performance.

Measurements of the elemental abundances of galactic cosmic ray nuclei with charge 26≤z≤92 can provide important information that should help to resolve the question of cosmic-ray origin; i.e. whether cosmic rays originate from the acceleration of interstellar grain material or from preferential selection and acceleration of nuclei from stellar photosphere-chromosphere regions with T-10^4 based on first ionization potential. They will also refine tests of whether freshly synthesized rprocess material is a significant component in cosmic rays. The detector concept described utilizes an array of silicon detectors for dF/dx measurements, two Cherenkov counters with radiators of different refractive index for velocity determination (one using aerogel and one using a novel waveshifter readout approach), and scintillating fibers for a hodoscope/time-of-flight detector. The numbers of particles which can be collected with this approach and the expected charge resolution are discussed.

The Scintillating Optical Fiber Trajectory (SOFT) detector, the hodoscope for the Cosmic Ray Isotope Spectrometer (CRIS) on the NASA Advanced Composition Explorer, was calibrated using 155 MeV/n He, Li, C, N, 0, and Ar at the Michigan State University National Superconducting Cyclotron Laboratory (NSCL), and 200 - 700 MeV/n C, Si, and Fe at the GSI facility in Darrnstadt. Germany. The flight instrument consists of three hodoscope fiber planes and one trigger plane. read out by an image intensified CCD camera system and by intensified photodiodes respectively. The spatial and angular resolution of the hodoscope is described, along with the detection efficiency of both the hodoscope and trigger plane as a function of charge.

The High Energy X-ray Timing Experiment (HEXTE) is one of three scientific instruments aboard the Rossi X-ray Timing Explorer (RXTE), which was launched on December 30, 1995. RXTE performs timing and spectral studies of bright x-ray sources to determine the physical parameters of these systems. The HEXTE consists of two independent clusters of detectors, each cluster containing four NaI(Tl)/CsI(Na) phoswich scintillation counters sharing a common 1 degree FWHM field of view. The field of view of each cluster is switched on- and off-source to provide near real-time background measurements. The net open area of the eight detectors is 1600 cm2, and each detector covers the energy range 15-250 keV with an average energy resolution of 15.4% at 60 keV. The in-flight performance of the HEXTE is described, the light curve and spectrum of the Crab Nebula/Pulsar is given, and the 15-240 keV spectrum of the weak source, active galaxy MCG 8-11-11 is presented to demonstrate the weak source spectral capabilities of HEXTE., Comment: 30 pages, 14 figures, 4 tables, accepted by Ap. J., to be published in vol 496, March 20, 1998

We describe a mission concept which has as its primary objective the measurement of the elemental abundances of galactic and solar energetic nuclei over the charge range of 14 less than or equal to Z less than or equal to 92. The instruments would have sufficient collecting power to improve the number of particles collected over that of previous measurements by more than an order of magnitude and, more important, will have the capability to clearly distinguish individual elements. These measurements are of fundamental importance to an understanding of the origin, nucleosynthesis, and acceleration of energetic galactic and solar particles.