Influence of Aircraft Self-Shielding on World-Wide Calculations of Effective Dose Rates to Occupants

It is commonplace when calculating ionizing radiation exposures of aircraft occupants to neglect the influence of the aircraft’s presence on the dose rate, which greatly simplifies calculations of dose rate. FAA technical report DOT/FAA/AM-17/8 describes a method of revising CARI-7 calculations to approximately account for aircraft structure when calculating effective dose rates based on the NASA Langley Research Center OLTARIS toolset, which yields results consistent with findings of earlier researchers, but without the need for detailed aircraft structure and loading models. The method is applied here to investigate the reasonableness of the common simplification on a global scale at typical flight levels from 30,000 to 40,000 feet, using effective vertical cutoff rigidity world-grids calculated by Smart and Shea. Shielded occupant dose rate is consistently reduced relative to the unshielded case, but the reduction in dose rate at cruise altitude is typically only a few percent at the levels of shielding considered (up to 1.27 cm Al-2024). Results thus indicate that the practice of ignoring this source of occupant shielding does not lead to large errors in effective dose rate calculations for flights in the altitude range examined. Effective doses for both solar minimum and solar maximum are discussed for a number of flight paths (routes) including several polar routes.