Reconstruction of solar activity based on 14C and other isotope profiles in lunar regolith

Abstract

Abstract The Moon might be considered as an integral detector of Galactic Cosmic Rays (GCR) as it contains on its surface cosmogenic isotopes produced by nuclear reactions. Since the retrieval of lunar regolith cores by Apollo missions, there were numerous attempts to measure concentrations and depth profiles of those isotopes and reconstruct the level of cosmic radiation at 1AU at various time scales, ranging from thousands to millions of years. The data also contains encoded levels of solar activity, as the Sun affects the differential flux of GCRs in a well-known manner. All those attempts showed that our nuclear interaction codes, GEANT4 for example, need corrections to describe the lunar data, be it tweaking of cross-sections or any other methods. There are also such archives on Earth: ice cores and trees. Based on terrestrial modulation potential reconstruction we try to calibrate GEANT4 code in a transparent manner, and also present our estimates on the solar activity on time scales of 0.02 and 3 Myrs. The estimates made using our calibration procedure show values consistent with modern understanding of history of solar modulation potential, and demonstrate the necessity to establish an agreed correction method for the analysis of lunar data. We also compare our results and method with another estimation of solar modulation potential during the last 1 Myr.