SuperTIGER Ultra-Heavy Galactic Cosmic Ray Atmospheric Corrections

The SuperTIGER (Super Trans-Iron Galactic Element Recorder) balloon-borne ultra-heavy Galactic cosmic-ray (UHGCR) detector directly measures UHGCR nuclei. SuperTIGER had successful Antarctic flights in 2012 (55 days) and 2019 (32 days). Stratospheric float altitudes varied between ~120,000 – 130,000 ft, and the observed abundance measurements must be corrected for propagation through the residual ~0.5% of atmosphere using an approach developed for the preceding TIGER instrument. Charge changes due to nuclear interactions are determined starting from assumed top of the atmosphere (TOA) elemental abundances from which instrument abundances are found by iteratively adjusting TOA abundances until the predicted instrument abundances match the flight measurements. TOA abundances are used in a Geant4 simulation for GCR nuclei interacting with the atmosphere to compare with the flight measurements. Differential elemental atmospheric energy losses are corrected for using Geant4 simulations to find TOA minimum energies corresponding to the acrylic Cherenkov detector threshold (~350 MeV/nuc) and scaling TOA abundances corrected for nuclear interactions with the fraction of the integral energy spectrum for its TOA minimum energy, using the scaled iron spectrum for the UHGCRs. Systematic uncertainties are obtained for TOA abundances from a Monte Carlo method by simultaneously and randomly varying the total charge changing cross section of each element over a Gaussian distribution.