Characterizing solar proton energy spectra for radiation effects applications

The Weibull distribution for smallest values is shown to be a useful descri ption for solar proton event energy spectra. One advantage is its compact a nalytic expression, which allows easy conversion between differential and i ntegral spectra. Another is its versatility, which is necessary for describ ing the highly variable spectra of concern. Furthermore, the Weibull distri bution appears to be appropriate for use over broad energy ranges extending out to GeV; Examples are shown and comparisons to previously used distribu tions are made. An especially useful consequence of this approach for radia tion effects applications is that it allows both predictive model spectra a nd observed spectra to be described by the same distribution. This allows s pectra to be systematically ranked by severity of radiation damage caused i n microelectronics. It further allows observed spectra to be related to pre dictive model parameters such as confidence levels. These points are demons trated by evaluating the ionization dose deposited by various spectra in si licon behind aluminun shielding appropriate for spacecraft.