The Science of SuperTIGER

SuperTIGER (Trans-Iron Galactic Element Recorder) is a large-area, balloon-borne cosmic-ray experiment designed to measure the Galactic cosmic-ray (GCR) abundances of elements from 10Ne to 56Ba at energies from ~0.8 GeV/nuc to ~10 GeV/nuc, with the primary goal of measuring relative abundances of ultra-heavy elements above Z=30 (Zn). SuperTIGER has had two successful Antarctica campaigns, flying a record 55 days in 2012-2013 and 32 days in 2019-2020. In the first stratospheric flight SuperTIGER was able to measure the relative abundances of GCR nuclei with good statistical precision and well resolved individual element peaks from 10Ne to 40Zr, with further measurements with lower statistics out to 56Ba. (N. E. Walsh et. al, 2022 Adv. in Space Research) Our SuperTIGER measurements through 40Zr support a cosmic-ray source model with a significant contribution from OB associations that have supernovae accelerate the nucleosynthetic products of preceding massive stars (R. P. Murphy et. al 2016 ApJ). This model includes the preferential acceleration of refractory elements that more readily condense onto the interstellar dust grains than volatiles with a charge dependence that is consistent with grain sputtering cross sections. However, the measurements of Z>40 are inconsistent with that model and suggest an additional GCR source and/or different acceleration model for those elements. Here we report on work that has been carried out to improve the atmospheric propagation calculations to correct for the residual ∼0.5% of atmosphere overburden encountered at float (to be submitted to Adv. in Space Research), the progress obtaining energy spectra for elements Z<30, and our effort to use a nested-leaky box model for determining source abundances.