Abundances of Ultra-Heavy Galactic Cosmic Rays from the SuperTIGER Instrument

The SuperTIGER (Trans-Iron Galactic Element Recorder) experiment was launched on a long-duration balloon flight from Williams Field, Antarctica, on December 8, 2012. The instrument measured the relative elemental abundances of Galactic cosmic rays (GCR) in the charge ($Z$) range $Z>$10 with excellent charge resolution, displaying well resolved individual element peaks for 10$\leq Z \leq$40. During its record-breaking 55-day flight, SuperTIGER collected $\sim$4.73 $\times10^6$ Iron nuclei, $\sim$8 times as many as detected by its predecessor, TIGER, with charge resolution at iron of $<$ 0.18 cu. SuperTIGER measures charge ($Z$) and energy (E) using a combination of three scintillator and two Cherenkov detectors, and employs a scintillating fiber hodoscope for event trajectory determination. The data include more than 600 events in the charge range 30$< Z \leq$40. SuperTIGER is the first experiment to resolve elemental abundances in this charge range with single-element resolution and high statistics. The SuperTIGER measured abundances are generally consistent with previous experimental results from TIGER and ACE-CRIS, with improved statistical precision. Our results confirm the earlier results from TIGER, supporting a model of cosmic-ray origin in OB associations.