Experimental-theoretical study of the mechanism of alpha particle ejection from crystalline structure of the zircon mineral

• Grant number: 20/15144-1
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: October 01, 2021
• End date: September 30, 2023
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Geology
• Principal Investigator: Carlos Alberto Tello Sáenz
• Grantee: Luana Rosa Bilac Caetano
• Host Institution: Faculdade de Ciências e Tecnologia (FCT). Universidade Estadual Paulista (UNESP). Campus de Presidente Prudente. Presidente Prudente , SP, Brazil

Abstract

The U-Th/He geochronological dating technique is a method used to determine the age of geological materials. This method is based on the accumulation of alpha particles (helium nuclei) produced by the alpha decay of the U and Th series in minerals such as zircon. Depending on the region of the grain where the alpha decay occurs, this particle can be ejected from the mineral structure or be retained for geological periods. The range of the particle inside the zircon depends on the kinetic energy from the alpha decay (~ 4 - 8 MeV), as well as the grain dimensions. Therefore, the ejection of alpha particles clearly impacts the helium content present in the mineral, which can lead to misinterpretations of geological ages via the U-Th / He method. Thus, this research project aims to understand the alpha decay processes of the 238U, 235U, and 232Th chains that occur in different regions within the zircon, so that the radiogenic He (4He) concentration, ejected from the mineral, is going to qualitatively and quantitatively investigated. This study will be carried out through Monte Carlo simulation with the Geant4 package. This software will be used to simulate the alpha decay of unstable nuclei, belonging to the three natural radioactive series, inside the zircon to understand the range of alpha particles of different energies in the mineral; and, thus, estimate the concentration of alpha particles that are ejected from the mineral structure. The results obtained will be compared with experimental data to be acquired in our research laboratory. The investigation of the alpha decay process inside the zircon and the propagation mechanism of these particles is essential since they significantly influence the diffusion process of 4He in the mineral and the temperature sensitivity of the U-Th / He thermochronometer. (AU)