Data Analysis of Cosmic-ray Nuclei Observed by The Antarctic Balloon Flight

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The aim of this study is the understanding of the acceleration and the propagation mechanisms of galactic cosmic-rays with observing the cosmic-ray nuclei by means of long duration balloon flights. For this purpose, we are working on the TRACER project which is mainly performed by the University of Chicago, and the various kinds of cosmic-ray nuclei have been observed by the long duration balloon flight in Antarctica. Finally we obtained the absolute flux and the energy spectra for many elements of the cosmic-ray heavy nucleus.The instrument for the TRACER experiment consists of plastic scintillators for measurement of ionization energy loss, a Cherenkov counter for Cherenkov lights, proportional tube arrays for the measurement of the ionization and the coordinates for particles and the transition radiation detectors. The procedure of data analysis is as follows. First, the tracks of incident particles are reconstructed with use of the signals from 1,600 of proportional tubes. Next, th … More e charges for each particle are identified by the combination of the signals of scintillator and Cherenkov counter. On the other hand, the energies are measured 1)by Cherenkov signal for the energy region around 1GeV, 2)by relativistic rising of the ionization loss for the energy region from several times 10 GeV to several times 100 GeV, 3)by transition radiation signal for the energies more than 400GeV. As results, the energy spectra for heavy cosmic-ray nuclei are obtained with high statistics for the region from 10^<14>eV〜 10^<15>eV. Comparing these results to some models for the acceleration and the propagation of Galactic cosmic-rays, they are consistent with the conventional diffusive shock acceleration model at supernovae remnants for all species we observed. For the propagation mechanisms, we got some model parameters, -2.3 of power index of the energy spectrum at the source and 0.1 g/cm^2 of the residual path length around source region, for example.The TRACER group performed another balloon flight for observation of cosmic-rays during four and half days with use of improved instrument from Sweden to Canada in July 2006. We made a preliminary data analysis for this observation and confirmed that boron nuclei, which were not observed in previous observation, have been detected without any biases. This is an accomplishment of the improvement of the dynamic range of the detector. It made us possible to obtaine the relative abundance of boron to carbon which is very important data for understanding the propagation mechanisms of the Galactic cosmic-rays. One more long duration balloon flight with this instrument is scheduled in near future. Less