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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.

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.

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.

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.

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 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.

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.

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.

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.

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.

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.