Observation of cosmic-ray particles with Z>35

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Tracks of very heavy cosmic-ray particles have been recorded in nuclear emulsions and several different types of plastic detectors exposed during two high-altitude ballon flights in September 1968. Based on a total of 113 tracks, the following flux values have been derived for kinetic energies >1 GeV/nucleon: J(35≤Z≤40)=(16±4)×10-6 J(41≤Z≤50)=(28±6)×10-6 J(51≤Z≤60)=(9±2)×10-6 J(61≤Z≤70)=(1.8±0.7)×10-6 J(71≤Z≤85)=(3±1)×10-6 J(Z86)=(1.0±0.6)×10-6 The well-established presence of particles with Z86 requires a cosmic-ray source in which the r process of nucleosynthesis has been effective. The relative abundances over the charge region (51≤Z≤85) show agreement with solar-system abundances, but there appear to be significant departures for the two lower-charge groups. Calibration of the detectors and experimental problems are also discussed. © 1973 The American Physical Society.

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Physical Review D

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