The progress on developing models of the radiation environment since the 1960s is reviewed with emphasis on models that can be applied to predicting the performance of microelectronics used in spacecraft and instruments. Space, atmospheric, and ground environments are included. It is shown that models must be adapted continually to account for increased understanding of the dynamics of the radiation environment and the changes in microelectronics technology. The IEEE Nuclear and Space Radiation Effects Conference is a vital forum to report model progress to the radiation effects research community.

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A predictive model of worst case solar proton event fluences is presented. It allows the expected worst case event fluence to he calculated for a given confidence level and for periods of time corresponding to space missions. The proton energy range is from, > 1 to > 300 MeV, so that the model is useful for a variety of radiation effects applications.For each proton energy threshold, the maximum entropy principle is used to select the initial distribution of solar proton event fluences. This turns out to he a truncated power law, i.e., a power law for smaller event fluences that smoothly approaches zero at a maximum fluence. The strong agreement of the distribution with satellite data for the last three solar cycles indicates this description captures the essential featurcs of a solar proton event fluence distribution.Extreme value theory is then applied to the initial distribution of events to obtain the model of worst case fluences.

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Abstract-A probabilistic model of cumulative solar heavy ion energy and LET spectra is developed for spacecraft design applications. Spectra are given as a function of confidence level, mission time period during solar maximum and shielding thickness. It is shown that long-term solar heavy ion fluxes exceed galactic cosmic ray fluxes during solar maximum for shielding levels of interest. Cumulative solar heavy ion fluences should therefore be accounted for in single event effects rate calculations and in the planning of space missions.Index Terms-Cumulative fluence, solar heavy ion, solar particle event.