Production of 3He in rocks by reactions induced by particles of the nuclear-active and muon components of cosmic rays: Geological and petrological implications

The paper presents data on the production of the ³He nuclide in rocks under the effect of cosmicray particles. The origin of the nuclide in the ground in neutronand 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 nearsurface ground layers by spallation reactions induced by cosmic-ray protons may be approximately 20% 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).