Micro-crystalline inclusions analysis by PIXE and RBS

TL;DR

This paper explores the combined use of PIXE and RBS techniques to analyze micro-crystalline inclusions in minerals, improving elemental analysis accuracy and enabling precise dating of mineral inclusions.

Contribution

It introduces a combined PIXE-RBS method for detailed geometrical and chemical analysis of mineral inclusions, enhancing accuracy over traditional optical methods.

Findings

Combined PIXE-RBS improves elemental analysis accuracy.

Geometrical parameters significantly affect concentration measurements.

Enhanced precision in micro-inclusion dating, exemplified with monazite.

Abstract

A characteristic feature of the nuclear microprobe using a 3 MeV proton beam is the long range of particles (around 70 \mu m in light matrices). The PIXE method, with EDS analysis and using the multilayer approach for treating the X-ray spectrum allows the chemistry of an intra-crystalline inclusion to be measured, provided the inclusion roof and thickness at the impact point of the beam (Z and e, respectively) are known (the depth of the inclusion floor is Z + e). The parameter Z of an inclusion in a mineral can be measured with a precision of around 1 \mu m using a motorized microscope. However, this value may significantly depart from Z if the analyzed inclusion has a complex shape. The parameter e can hardly be measured optically. By using combined RBS and PIXE measurements, it is possible to obtain the geometrical information needed for quantitative elemental analysis. This paper will present measurements on synthetic samples to investigate the advantages of the technique, and also on natural solid and fluid inclusions in quartz. The influence of the geometrical parameters will be discussed with regard to the concentration determination by PIXE. In particular, accuracy of monazite micro-inclusion dating by coupled PIXE-RBS will be presented.