Characterizing solar proton energy spectra for radiation effects applications

The Weibull distribution for smallest values is shown to be a useful description for solar proton event energy spectra. One advantage is its compact analytic expression, which allows easy conversion between differential and integral spectra. Another is its versatility, which is necessary for describing the highly variable spectra of concern. Furthermore, the Weibull distribution appears to be appropriate for use over broad energy ranges extending out to GeV. Examples are shown and comparisons to previously used distributions are made. An especially useful consequence of this approach for radiation effects applications is that it allows both predictive model spectra and observed spectra to be described by the same distribution. This allows spectra to be systematically ranked by severity of radiation damage caused in microelectronics. It further allows observed spectra to be related to predictive model parameters such as confidence levels. These points are demonstrated by evaluating the ionization dose deposited by various spectra in silicon behind aluminum shielding appropriate for spacecraft.