Cosmic Ray Isotope Measurements using the Cherenkov-Rigidity Technique in ISOMAX

Abstract

The Isotope Magnet Experiment, ISOMAX, which had its first flight in August 1998, is designed to measure the isotopic composition of the light elements using a complement of three major detector systems: a magnetic spectrometer, a time-of-flight (TOF) system, and two Cherenkov detectors. ISOMAX measures mass by combining the velocity measurement with charge and magnetic rigidity (momentum/charge) measurements. In the energy range from 1.1 to 1.7 GeV/nucleon, the velocity measurements are provided by two aerogel Cherenkov counters. The aerogel radiators have a nominal index-of-refraction n = 1.14 corresponding to an energy threshold of 1.08 Ge V /nucleon, which complements and extends the energy range covered by the TOF. Combining the velocity measurement with a measurement of rigidity results in a determination of isotope mass with an expected resolution of ::;: 0.25 amu. We present preliminary isotope data.