SuperTIGER Ultra-Heavy Galactic Cosmic Ray Atmospheric Propagation Corrections and Validation

The SuperTIGER (Super Trans-Iron Galactic Element Recorder) balloon-borne ultra-heavy Galactic cosmic-ray (UHGCR) detector had successful Antarctic flights in 2012 (55 days) and 2019 (32 days). Stratospheric float altitudes varied between ∼120,000 – 130,000 ft, and measurements must be corrected for propagation through the residual ∼ 0.5% atmosphere using an approach developed for the preceding TIGER instrument. Changes due to nuclear interactions are determined iteratively starting from assumed top of the atmosphere (TOA) elemental abundances from which instrument abundances are found by solving networks of equations for all elements with partial and total charge-changing cross sections stepping through fine slabs of material and adjusting the TOA abundances after each run until the predicted instrument abundances match 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 iron spectrum for the UHGCRs.