The electrical conductivity process in the Earth’s interior is controlled mainly by the diffusion of protons. Therefore, understanding proton diffusivities in hydrous minerals and its response to compression have essential implications in the electromagnetic observation and internal structure of the Earth. The direct observations are crucial for understanding the pressure effects on the proton diffusivities. In this study, we carried out in-situ observation of hydrogen-deuterium (H-D) interdiffusion of brucite [Mg(OH)2/Mg(OD)2] at high pressure and high temperature using neutron radiography measurements.

Neutron radiography measurements were performed at BL11(Hattori et al., 2015) in Materials and Life Science Experimental Facility (MLF), Japan Proton Accelerator Research Complex (J-PARC). High-pressure and high-temperature conditions were generated using a six-axis multi-anvil press, ATSUHIME (Sano-Furukawa et al. 2014), installed on the beamline. Si-pixel camera with LiF neutron converter (Advacam MiniPix) took radiography images of 14 mm × 14 mm size. Polycrystalline Mg(OH)2/Mg(OD)2 powders were pelletized into pellets of 3.5 mm diameter and charged in Pt capsule. Transmission images were collected at 1100 K and 5 GPa for the heating duration of 27 h.

The images show that the change of sample transmittance which indicates the differences in H/D concentration. As for the determination of H-D interdiffusion coefficients, Boltzmann–Matano analysis has been performed on the one-dimensional H-D concentration profiles derived from the measurements. The obtained values are consistent with those of previous work (Guo et al. 2013). The profile determined by the transmission image of the decompression sample shows good agreement with the micro Raman spectroscopy observation. The derivation of these results provides an excellent example of the power of the neutron radiography method.