Measuring excitation functions needed to interpret cosmogenic nuclide production in lunar rocks

摘要

Radionuclides produced in lunar rocks by cosmic ray interactions are measured using Accelerator Mass Spectrometry or gamma-ray spectroscopy. From these measurements, estimates of the solar proton flux over time periods characterized by the half-life of the isotope under study can be made, if all the cross sections for all the reactions of all cosmic ray particles with all elements found in lunar rocks are known. Proton production cross sections are very important because (approximately) 98% of solar cosmic rays and (approximately) 87% of galactic cosmic rays are protons in the lunar environment. Many of the needed cross sections have never been measured. Targets of C, Al, Si, SiO(sub 2), mg, K, Ca, Fe and Ni have been irradiated using three accelerators to cover a proton energy range of 25--500 MeV. Excitation functions for (sup 7)Be, (sup 10)Be, (sup 22)Na, and (sup 26)Al production from Mg and Al will be reported, and the consequences of using these new cross section values to estimate solar proton fluxes discussed.