Radiation protection factor: An alternative approach to radiation shield classification

Ionizing radiation exposure is one of the major health concerns for long-duration space exploration. Without the benefit of future technologies that might allow humans to repair biological radiation damage, the requirement exists to find a way to reduce exposure with shielding materials. Present classification of these materials uses complicated calculations to reach exposure estimates that contain a high degree of uncertainty. The Radiation Protection Factor (RPF) is an alternative approach to classifying shielding material that employs summation of Linear Energy Transfer (LET) across different spectra of incident radiation compared with a summation of exiting LET. The resulting fraction is inverted so that an increase in the factor represents an increase in protection. The inverted summation fraction is expressed as the Radiation Protection Factor (RPF). This calculation can be done on actual measurements of the incident and exiting energies or can be derived using transport code energy estimates. The RPF represents an alternative intuitive scale that could help astronauts, managers and engineers make real time decisions regarding the use of radiation shielding material in operational and planning activities.