Measurement of the Relative Abundances of the Ultra-Heavy Galactic Cosmic Rays (30 ≤ Z ≤ 40) with TIGER

Observations of ultra-heavy (Z≥30) galactic cosmic rays (GCR) help to distinguish possible origins of GCR. The Trans-Iron Galactic Element Recorder (TIGER) measures the charge (Z) and energy of GCR using a combination of scintillators, Cherenkov detectors, and a scintillating fiber hodoscope. The two Cherenkov radiators, one acrylic and one aerogel, provide TIGER with an energy sensitivity between 0.3 and 10 GeV/nucleon in the instrument. The threshold at the top of the atmosphere is close to 0.8 GeV/nucleon for Fe. TIGER has accumulated data on two successful flights from McMurdo, Antarctica launched in D ecember 2001 and December 2003 with a total flight duration of 50 days. The combined dataset resolves ~140 nuclei with Z > 30, and provides the best measurements to date for 30Zn, 31Ga, 32Ge, and 34Se. The results for Ga and Ge taken together are inconsistent with a GCR source with Solar-System abundances modified either by preferential acceleration of elements of low first ionization potential or by preferential acceleration of refractory elements, suggesting that elemental composition of the GCR source is different from that of the Solar Syste