Nuclear Data Needs for GCR Shielding Models

Fundamental nuclear data, such as differential and total cross sections, are critical in the development and improvement of calculational tools used to predict the dose and risk from exposure to galactic cosmic rays (GCR). Those tools include complex Monte Carlo transport codes as well as 3-dimensional analytical codes, all of which rely on an accurate description of the nuclear interactions between the incoming GCR ion and the target nuclei it strikes. As shielding thickness increases, calculations indicate that secondary light ions such as protons, deuterons, tritons, 3-He, 4-He and neutrons become the dominant source of the radiation field behind the shielding. When comparing predictions of doses and particle fluences behind thick shielding between several different codes, differences up to 20 percent or more are observed, mostly due to the prediction of secondary light ions from GCR interactions. The range of GCR ion species and energies along with the range of shielding materials presents creates a potentially large set of differential and total reaction cross sections to consider when improving code predictions. The available data base of measured cross sections will be presented, along with recommendations for additional cross section measurements needed to reduce uncertainties and improve the accuracy of radiation transport models used for GCR shielding.