Cosmogenic-nuclide production rates: Reaction cross section update

Interpretations of cosmic-ray-produced nuclide measurements are dependent on the accuracy of the production-rate estimates. Most production rates are determined using particles fluxes and cross sections for the relevant reactions. The reaction cross sections used for the production of cosmogenic nuclides are discussed. Recently, many experimental cross sections for making cosmogenic nuclides by protons have been compiled, evaluated, and used to study cosmogenic nuclides made by solar energetic protons in lunar samples. Neutrons make most galactic-cosmic-ray-produced nuclides. There are only a few measurements of cross sections for neutrons making cosmogenic nuclides because it is hard to get good fluxes of energetic neutrons, especially with energies >50 MeV. Most neutron cross sections to date have been estimated by using measured proton cross sections, occasionally adjusting them for nuclear systematics or to fit measurements of cosmogenic nuclides in documented samples. The status of spallation cross sections for the main reactions making the six main cosmogenic nuclides (3He, 10Be, 14C, 21Ne, 26Al, and 36Cl) from their major target elements is presented. Some comparisons of production rates calculated with these cross sections with measured rates are presented. The need for additional work to improve these important cross sections is discussed.