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The isotopic composition of galactic cosmic-ray Ca has been measured over the energy range ˜ 150 to 400 MeV/nuc on the Advanced Composition Explorer (ACE) mission. Using the measured abundances of the dominantly-secondary Ca isotopes with A = 41-46 as constraints, in combination with measured cross sections for the production of Ca isotopes by fragmentation of ^(56)Fe on hydrogen, we show that the two doubly-magic isotopes ^(40)Ca and ^(48)Ca consist mainly of primary material. We find that their relative abundances in the cosmic-ray source are very similar to those found in solar-system material, in spite of the fact that different types of stars are thought to be responsible for producing these two isotopes. This observation is consistent with the view that cosmic rays are derived from a mixed sample of interstellar matter.

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.

The secondary isotopes ^(37)Ar, ^(44)Ti, ^(49)V, ^(51)Cr, ^(55)Fe, and ^(57)Co decay only by electron capture, which occurs preferentially at the lower cosmic-ray energies, where electron attachment is more likely. Measurements of the abundances of these isotopes may reveal the interstellar energies of cosmic rays during propagation and whether reacceleration occurred. Stable secondary isotopes may also be used to examine energy dependence and reacceleration. The Cosmic Ray Isotope Spectrometer has detected large numbers of these nuclei at 100 - 500 MeV/nucleon during a time spanning solar minimum and solar maximum, allowing an additional study of solar modulation. This paper will discuss several subiron abundance ratios and the implications for reacceleration and solar modulation.

The ECCO instrument is one of two instruments which comprise the HNX mission. The principal goal of ECCO (the Extremely-heavy Cosmic-ray Composition Observer) is to measure the age of galactic cosmic ray nuclei using the actinides (Th, U, Pu, Cm) as clocks. As a bonus, ECCO will search with unprecedented sensitivity for longlived elements in the superheavy island of stability. ECCO is an enormous array (23 m2 ) of BP-1 glass track-etch detectors, and is based on the successful flight heritage of the Trek detector which was deployed externally on Mir. We present a description of the instrument, estimates of expected performance, and recent calibrations which demonstrate that the actinides can be resolved from each other with good charge resolution.

The primary scientific objectives of HNX, which was recently selected by NASA for a Small Explorer (SMEX) Mission Concept Study, are to measure the age of the galactic cosmic rays (GCR) since nucleosynthesis, determine the injection mechanism for the GCR accelerator (Volatility or FIP), and study the mix of nucleosynthetic processes that contribute to the source of GCRs. The experimental goal of HNX is to measure the elemental abundances of all individual stable nuclei from neon through the actinides and possibly beyond. HNX is composed of two instruments: ECCO, which measures elemental abundances of nuclei with Z≥72, and ENTICE, which measures elemental abundances of nuclei with 10≤Z≤82. We describe the mission and the science that can be addressed by HNX. 1. Introduction The Heavy Nuclei eXplorer (HNX) mission that is currently being studied as a possible Small Explorer Mission (SMEX) has the primary objective of determining the origin of the galactic cosmic rays. The abundance patterns of the elements and isotopes in the GCRs provide the key because they are the fingerprints of GCR origin. HNX will, for the first time, measure with high precision the abundance of every individual element in the periodic table from neon through the actinides (thorium, uranium, plutonium, curium, and perhaps beyond). The HNX spacecraft will carry two high-precision instruments, the Extremely-heavy Cosmic-ray Composition Observer (ECCO) and the ENergetic Trans-Iron Composition Experiment (ENTICE), which cover overlapping ranges of the periodic table (Figure 1).

The HNX mission is composed of the ENTICE and ECCO experiments. The experimental goal of ENTICE is to measure with high precision the elemental abundances of all nuclei with 10≤Z≤82. This will enable us to determine if the injection mechanism for the cosmic ray accelerator is controlled by FIP or Volatility and to study the mix of nucleosynthetic processes that contribute to the galactic cosmic ray source. The ENTICE experiment utilizes the dE/dx-C method of charge determination and consists of silicon dE/dx detectors, Cherenkov detectors with two different refractive indices, and a fiber hodoscope. We will describe the instrument and its performance based on beam tests of a prototype instrument.