Radiation Exposures from Several Ground Level Enhancements During the 23rd Solar Cycle

Abstract

Solar proton events (SPEs) represent the single-most significant source of acute radiation exposure to humans and space systems during lunar and deep-space missions. In this paper several unique solar particle emissions that occurred during solar cycle 23 were investigated. In particular, there were four (4) events that exhibited both a ground level enhancement (GLE) and an energetic solar particle (ESP) feature. These four SPEs occurred on 1) 6 November 1997, 2) 14-18 July 2000, 3) 4-8 November 2001, and 4) 28-29 October 2003. Each event is discussed in detail. Proton integral and differential energy and corresponding rigidity (momentum) spectra were generated based on GOES MEPAD and GOES HEPAD satellite data and ground-based neutron monitor (NM) data. The differential proton spectra are utilized with the NASA Langley Research Center high energy particle transport/dose code, HZETRN 2005, to compute simulated human exposures behind several shielding materials. We have previously shown that a Band function (double power law in particle rigidity) fit more correctly describes the complete event spectra when compared with an exponential rigidity extrapolation that has been in use by the scientific community for several decades, i.e., the exponential extrapolation method consistently under-estimates the human exposure. Comparisons of simulated human radiation exposures are presented for both the Band function fit and the exponential extrapolation methods.