Microbeam recoil detection for the study of hydration of minerals

The elastic recoil detection technique in the glancing angle geometry is ideally suited for hydrogen content determination of thick geological samples, obviating the need for elaborate sample preparation such as that required for the transmission mode. With an appropriate scheme for locating the sample, the technique can be applied generally with a microbeam. Combined with simultaneous PIXE measurements, problems arising from uncertainties in beam charge collection are eliminated. The method is applied to the investigation of the hydration characteristics of silicates, in experimental petrological samples produced at high pressure and temperature, simulating lower crust and upper mantle conditions. Preliminary results show that the technique can be applied readily on a microscopic ( < 100 μm) scale for determination of H at a fraction of atomic percent level, at beam current levels that avoid radiation and thermal damage to the specimen.