National Aeronautics and Space Administration

[PP01.159] Performance of the ISOMAX Cherenkov Detectors

G.A. de Nolfo, A.J. Davis, R.A. Mewaldt, S.M. Schindler (California Institute of Technology), L.M. Barbier, E.R. Christian, S. Geier, S. Gupta, J.F. Krizmanic, J.W. Mitchell, J.F. Ormes, R.E. Streitmatter (NASA Goddard Space Flight Center), M. Bremerich, H. Goebel, T. Hams, M. Hof, W. Menn, M. Simon (Universität Siegen)

The Isotope Magnet Experiment, ISOMAX, which had it's first flight in August, 1998 is designed with three major detector systems, a magnet spectrometer, a time of flight (TOF) system, and two Cherenkov detectors. The Cherenkov detectors are 80x80x14 cm diffusive light integration boxes, each with two layers of 2 cm thick silica aerogel blocks. Each layer contains four aerogel blocks approximately 38x38 cm in size. Cherenkov light is collected with 16 Hamamatsu R1848 3-inch photomultiplier tubes per box. The aerogel radiators have an index of refraction of n=1.14 corresponding to an energy threshold of 1.08 GeV/n, which compliments and extends the energy range covered by the TOF. Combining the velocity measurement with a measurement of rigidity (momentum/charge) results in a measurement of isotope mass with a resolution of about 0.25 amu. For Z=1 particles, the two Cherenkov detectors measure a total of 24 photoelectrons. The design of the Cherenkov detectors and their performance using ground level muons and in-flight nuclei will be presented. The full ISOMAX instrument and details of the other detector systems are discussed in other papers at this meeting.