Probability distributions of high-energy solar-heavy-ion fluxes from IMP-8: 1973-1996

We present probability distributions for the fluxes and event-integrated fluences of solar He, CNO, and Fe ions at high energies relevant to space-system design, based on observations from the University of Chicago´s Cosmic Ray Telescope on IMP-8 in 1973-96. We compare the observed distributions to CREME96, whose new solar models are shown to produce realistic, extreme-worst-case (~99⁺% confidence level) environments. The probability distributions show that a modest reduction in the reliability requirement (from ~99% to ~90-95% confidence level, for example) can significantly reduce the severity of the heavy-ion hazard. This reduction factor is larger for solar heavy ions than for solar protons, and the exact amount of the reduction will depend critically upon other factors, such as device sensitivity, shielding, and orbit. We also show predictions of mission-accumulated solar-heavy-ion fluences as functions of confidence level and mission duration