地球核の水素―高温高圧下中性子回折による鉄中の水素の観察

抄録

Large amounts of hydrous components can be stored in the deep Earth. The Earth’s core is thought to contain light elements because of its lower density compared to pure iron. Among several candidates for light elements in the core, hydrogen is the most promising light element because of its high solar abundance and siderophile nature; the Earth’s core can be an important hydrogen reservoir. To understand the density deficit induced by the incorporation of hydrogen into iron, the unit cell volume of iron and the concentration of hydrogen must be determined. Neutron diffraction experiments under high pressure and high temperature solve this problem. In Japan, the PLANET beamline at MLF, J-PARC, which enables neutron diffraction measurements at high pressure, is open to users worldwide. A unique feature of the PLANET beamline is the six-axis multi-anvil press, ATSUHIME. The press can generate high pressure around 10 GPa and high temperature using a 6-6 type cell assembly, with an available sample volume of approximately 50 mm³. By use of a 6-8 type cell assembly, the generated pressure is higher than 20 GPa, which corresponds to the pressure in the mantle transition zone. This paper reviews recent progress in the study of iron hydrides under high pressure and high temperature in relation to hydrogen in the Earth’s core.