Production of $^3$He in Rocks by Reactions Induced by Particles of the Nuclear-Active and Muon Components of Cosmic Rays: Geological and Petrological Implications

TL;DR

This study investigates how cosmic-ray particles produce $^3$He in rocks, analyzing reaction mechanisms, calculating cross sections with simulations, and assessing implications for geological dating methods.

Contribution

It provides new data and models for $^3$He production in rocks, including reaction cross sections and depth-dependent accumulation rates, enhancing geochronological applications.

Findings

Cosmic-ray protons contribute about 10% to $^3$He production.

Muon-induced reactions dominate $^3$He accumulation at depths of 10-50 m.w.e.

Simulations enable calculation of $^3$He accumulation rates for geological dating.

Abstract

The paper presents data on the production of the $^3$He 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 $^3$He and $^3$H are calculated by means of numerical simulations with the GEANT4 simulation toolkit. The production rate of the $^3$He 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 $^3$He in near-surface ground layers by spallation reactions induced by cosmic-ray protons may be approximately 10% of the total production rate of cosmogenic $^3$He. At depths of 10-50 m.w.e., the accumulation of $^3$He is significantly contributed by reactions induced by cosmic-ray muons. Data presented in the paper make it possible to calculate the accumulation rate of $^3$He 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 ($^3$He dating).