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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. more...

We report direct evidence of the energy loss of galactic cosmic rays as they diffuse in magnetic irregularities expanding with the solar wind. Using the Cosmic Ray Isotope Spectrometer (CRIS) on the Advanced Composition Explorer (ACE), we report on the energy-dependence of the electron-capture decay of the secondary isotopes ^(49)V and ^(51)Cr. At the highest energies observed by CRIS, where electron attachment is unlikely, ^(49)V and ^(51)Cr are essentially stable; at lower energies the timescale for electron attachment is much shorter and substantial decay does occur. Comparing the energy dependence of the daughter/parent ratios ^(49)Ti/^(49)V and ^(51)V/^(51)Cr during periods of solar minimum and maximum demonstrates that the solar modulation parameter φ is about 400 to 700 MV higher during solar maximum than at minimum. Absolute values of φ inferred from these electron-capture-isotope data agree well with values inferred from comparison of the observed elemental energy spectra with model calculations. more...

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. more...

We report on abundance measurements of ^(10)Be, ^(26)Al, ^(36)Cl, and ^(54)Mn in the Galactic cosmic rays (GCRs) using the Cosmic-Ray Isotope Spectrometer (CRIS) instrument aboard the Advanced Composition Explorer spacecraft at energies from ~70 to ~400 MeV nucleon^(-1). We also report an upper limit on the abundance of GCR ^(14)C. The high statistical significance of these measurements allows the energy dependence of their relative abundances to be studied. A steady-state, leaky-box propagation model, incorporating observations of the local interstellar medium (ISM) composition and density and recent partial fragmentation cross section measurements, is used to interpret these abundances. Using this model, the individual galactic confinement times derived using data for each species are consistent with a unique confinement time value of τ_(esc) = 15.0 ± 1.6 Myr. The CRIS abundance measurements are consistent with propagation through an average ISM hydrogen number density n_H = 0.34 ± 0.04 H atoms cm^(-3). The surviving fractions, f, for each radioactive species have been calculated. From predictions of the diffusion models of Ptuskin & Soutoul, the values of f indicate an interstellar cosmic-ray diffusion coefficient of D = (3.5 ± 2.0) × 10^(28) cm^2 s^(-1). more...

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. more...

Measurements of the abundances of cosmic-ray ^(59)Ni and ^(59)Co are reported from the Cosmic-Ray Isotope Spectrometer (CRIS) on the Advanced Composition Explorer. These nuclides form a parent-daughter pair in a radioactive decay which can occur only by electron capture. This decay cannot occur once the nuclei are accelerated to high energies and stripped of their electrons. The CRIS data indicate that the decay of ^(59)Ni to ^(59)Co has occurred, leading to the conclusion that a time longer than the 7.6 × 10^4 yr half-life of ^(59)Ni elapsed before the particles were accelerated. Such long delays indicate the acceleration of old, stellar or interstellar material rather than fresh supernova ejecta. For cosmic-ray source material to have the composition of supernova ejecta would require that these ejecta not undergo significant mixing with normal interstellar gas before ~10^5 yr has elapsed. more...

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. more...

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. more...

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. more...

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. more...

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. more...

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. more...

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. more...

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. more...

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. more...

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. more...

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. more...

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. more...

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. more...

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. more...

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. more...

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. more...

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. more...