Measurements of Relativistic Ultraheavy Galactic Cosmic Rays

To date we have collected ~1400 relativistic ultraheavy cosmic rays with Z > 45 by scanning a portion of sheets near the top of 7 modules. (For comparison, the HEAO dataset contained ~370 nuclei in this charge range.) The figure shows a Monte Carlo simulation of HIIS measurements of UHGCR elemental abundances, compared to the HEAO observations. Below and above Z=65, HIIS will primarily use CR-39 and Lexan detectors, respectively.

The HIIS simulation took into account

• A total of 1120 tracks at Z > 45
• Geomagnetic Modulation of the GCR flux and spectrum to the LDEF orbit
• Ultraheavy Relative Abundances, as previously reported (Binns et al. 1989, Ap.J. 346, 997)
• Fragmentation in the ~2 g/cm^2 of material above the measured sheets
• Z-dependent Geometry Factor implied by the detector response and track etch
• The Detector Calibration
• Kinetic Smearing due to the cosmic ray spectrum
• The Registration Temperature Effect, based on our reconstruction of the thermal history
• Measurement Error

If HIIS attains the resolution which this simulation suggests, HIIS will clearly offer a substantial improvement over HEAO. At Z<65, HIIS will make more accurate measurements of the even-Z elements and, in some cases, the first abundance measurements of odd-Z elements. Above Z=65, HIIS cannot resolve elements, but the Pt (Z=78) and Pb (Z=82) peaks are clearly separated.