Ultra-Heavy Galactic Cosmic Ray Propagation and Atmospheric Corrections for SuperTIGER.

SuperTIGER (Super Trans-Iron Galactic Element Recorder) is a balloon-borne instrument designed to directly measure ultra-heavy galactic cosmic-ray (UHGCR) nuclei. SuperTIGER had two successful Antarctic flights: one in 2012 for 55 days and one in 2019 for 32 days. Stratospheric float altitudes varied between ~36-40 km for both flights. SuperTIGER measured abundances must be corrected for the atmosphere and the mylar, aluminum, and melamine layers above the active detector, totaling to $\sim$5.65 g/cm$^2$ of material. To obtain top-of-atmosphere (TOA) abundances of UHGCR nuclei, the observed measurements are corrected for using results of Geant4 simulations to understand the nuclear interactions and energy losses cosmic-ray nuclei experience propagating through the atmosphere. Matrices are created to describe charge-changing losses or gains of nuclear species, with a cut for the energy threshold to trigger the acrylic Cherenkov detector (320 MeV/n). Galactic cosmic-ray source (GCRS) abundances are found from TOA abundances by propagating assumed GCRS abundances through the interstellar medium via the leaky-box model with a Fisk-model correction for solar modulation and comparing the results with SuperTIGER TOA abundances. The assumed GCRS abundances are modified based on the results. This process is performed iteratively until the GCRS abundances produce TOA abundances that match SuperTIGER’s.