National Aeronautics and Space Administration

[VB10.01] The Isotope Magnet Experiment (ISOMAX)

J.W. Mitchell, L.M. Barbier, E.R. Christian, S. Geier, S.K. Gupta, J.F. Krizmanic, J.W. Mitchell, J.F. Ormes, R.E. Streitmatter (NASA/GSFC), H. Goebel, M. Bremerich, T. Hams, M. Hof, W. Menn, M. Simon (U. of Siegen), A.J. Davis, G.A. DeNolfo, R.A. Mewaldt, S.M. Schindler (Caltech)

ISOMAX, a new high-performance cosmic ray instrument and balloon-borne payload system, was flown on August 4-5, 1998, from Lynn Lake, Manitoba, Canada. ISOMAX was developed to measure the isotopic composition of the light elements in the cosmic radiation with a particular focus on obtaining the ratio of radioactive ¹⁰Be to stable ⁹Be over a wide range of energies, and consequently a wide range of time-dilation factors. Excellent isotopic resolution and statistics are achieved using a large superconducting magnet in conjunction with a suite of state-of-the-art tracking, charge, and velocity detectors. The ISOMAX flight returned more than 16 hours of data taken at an altitude of more than 36 km. As configured for this flight, ISOMAX has a geometry factor of 450 cm²sr and can measure Be with a mass resolution of better than 0.25 amu from geomagnetic cutoff to about 1.7 GeV/nucleon. In this paper, an overall description of the instrument and payload and a preliminary evaluation of its performance will be presented. ISOMAX was supported by NASA: RTOP 353-87-02 (GSFC) and grant NAGW-1919 (Caltech), and in Germany by the DFG and the BMFT.