Production of 3He in Rocks by Reactions Induced by Particles of the Nuclear-Active and Muon Components of Cosmic Rays: Geological and Petrological Implications
Abstract
The paper presents data on the production of the 3He nuclide in rocks under the effect of cosmic-ray particles. The origin of the nuclide in the ground in neutron- and proton-induced spallation reactions, reactions induced by high-energy muons, and negative muon capture reactions is analyzed. The cross sections of reactions producing 3He and 3H are calculated by means of numerical simulations with the GEANT4 simulation toolkit. The production rate of the 3He nuclide in the ground is evaluated for the average level of solar activity at high geomagnetic latitudes and at sea level. It is proved that the production of 3He in near-surface ground layers by spallation reactions induced by cosmic-ray protons may be approximately 10% of the total production rate of cosmogenic 3He. At depths of 10-50 m.w.e., the accumulation of 3He is significantly contributed by reactions induced by cosmic-ray muons. Data presented in the paper make it possible to calculate the accumulation rate of 3He in a rock depending on depth that is necessary for the evaluation of the exposure time of the magmatic or metamorphic complex on the Earth's surface (3He dating).