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T. G. Guzik (Louisiana State University), ATIC Collaboration
The Advanced Thin Ionization Calorimeter (ATIC), a Long Duration Balloon (LDB) experiment, is designed to measure the charge composition (for Z from 1 to 28) and energy spectra of primary cosmic rays in the region of total energy from 100 GeV to near 100 TeV. The instrument is built around a fully active, Bismuth Germanate (BGO) ionization calorimeter to measure the energy deposited by the cascades formed by particles interacting in a thick carbon target. A highly segmented silicon matrix, located above the target, provides good incident charge resolution plus rejection of the "backscattered" particles from the interaction. Trajectory reconstruction is based on the cascade profile in the BGO calorimeter, plus information from the three scintillator hodoscope layers in the target section above it. The hodoscope planes also provide the primary event trigger to initiate the detector readout, another measure of the incident particle charge and an indicator of the interaction point in the carbon material. The scientific payload weighs ~1,540 kg and consumes ~300 Watts of power supplied by a ~580 Watt solar array system. The instrument was launched from McMurdo, Antarctica on 29 December 2002 and was carried to an altitude of ~37 km above Antarctica by a ~850,000 m3 helium filled balloon for one circumnavigation of the continent yielding about 19 days of data. The subsequent data analysis resulted in element identification up to the Iron peak. Monte Carlo simulations were used to convert energy deposition measurements to primary energy. Here we discuss and interpret the preliminary energy spectra for the abundant cosmic ray elements and compare them with results from other experiments.
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Bulletin of the American Astronomical Society, 36 #3
© 2004. The American Astronomical Soceity.