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Structural analysis of latent tracks in epidote

Grant number: 15/12679-3
Support type:Scholarships abroad - Research Internship - Post-doctor
Effective date (Start): August 15, 2015
Effective date (End): August 14, 2016
Field of knowledge:Physical Sciences and Mathematics - Geosciences
Principal Investigator:Julio Cesar Hadler Neto
Grantee:Wagner Massayuki Nakasuga
Supervisor abroad: Rodney C Ewing
Home Institution: Instituto de Física Gleb Wataghin (IFGW). Universidade Estadual de Campinas (UNICAMP). Campinas , SP, Brazil
Local de pesquisa : Stanford University, United States  
Associated to the scholarship:14/16683-2 - Improvement using epidote in thermocronology by fission track and Pernambuco Lineament dating, Northeast, Brazil, BP.PD

Abstract

Fission Track Dating firstly and after the middle of the 1980 decade Fission Track Thermochronology are methodologies based on the spontaneous fission of 238U, over the geological time scales commonly applied to minerals that contain trace amounts of uranium. When the fission occurs, two nuclear fragments dissipate energy and slow down in the mineral forming a narrow cylinder with a few nanometers in diameter and several micrometers in length. This is known as latent track, that can be enlarged by chemical etching to become visible under optical microscope. In decade of 1960, studies demonstrated that fission tracks are sensitive to thermal treatments, decreasing in size when subjected to thermal treatment. This reduction is due to the thermal instability of the modified mineral structure, and is called annealing. Etching completely erases the initial damaged structure and, much because of this, the annealing models are essentially empirical. However models with greater physical meaning, necessary to capture the essential features of the annealing process, demand knowledge of the processes taking place in the latent track. This kind of information is beginning to appear for tracks in apatite and zircon. Experiments simulating latent fission tracks using swift heavy ions in several materials were carried out. Recently, un-etched apatite and zircon latent tracks were studied using transmission electron microscopy, TEM, and small angle x-ray scattering, SAXS. Latent tracks in epidote have not been studied yet. Together with the Chronology group of UNICAMP we made systematic studies on etched tracks in epidote. Now, to continue these studies, the next step is to analyze the annealing in un-etched tracks. With this purpose, we contacted Dr. Weixing Li and Prof. Rodney C. Ewing of Stanford University about a possibility of carrying out a joint project on this subject, once they pioneered the studies on un-etched apatite and zircon latent tracks. They readily accepted the proposal because of the possibility of working with a mineral that has not been studied with this purpose before. For this, epidote samples were sent to Dr. Li for irradiation with heavy ions. The analysis will be made using TEM and SAXS in order to study the structure and annealing of epidote latent tracks.