Speaker
Description
1. Introduction
The Earth’s interior is one of the forefronts of Earth science, and the inner core, the center part of the Earth, has been a long-term research topic. The Earth’s inner core, which is approximately three-quarters the size of the Moon, is considered to be mostly iron. However, laboratory experiments and theoretical studies have shown that the density and sound velocities of the inner core, based on the seismic models, Preliminary Reference Earth Model (PREM) [1], cannot be explained by pure iron [2,3,4]. Therefore, it is estimated that the inner core contains some light elements. To determine the type and quantity of light elements present in the inner core, it is important to accurately measure the compression properties and sound velocities of iron and iron-light element alloys under high-pressure and temperature conditions. Many high-pressure compression experiments under the core conditions have been conducted using a diamond anvil cell with a synchrotron light source. On the other hand, sound velocity measurements under these conditions have not been well studied due to technical difficulties.
2. Results
We have been working to improve the method of measuring the sound velocity of metals under high-pressure conditions by inelastic x-ray scattering (IXS). To obtain weak IXS contributions from small, thin samples at multi-megabar pressures, we developed a newly designed Soller screen system at BL43LXU beamline of SPring-8, a third-generation synchrotron radiation facility in Japan. This system allows us to reduce noise as much as possible [5]. We also improved the shape of the diamond anvil to maintain stable pressure during long-term IXS measurements [3]. These improvements enabled us to successfully perform high-pressure sound velocity measurements of pure iron and other metals at pressures above 3 megabars and at ambient temperatures [3,4]. Additionally, we developed a portable laser heating system (COMPAT) [6] to conduct sound velocity measurements at high temperatures. We have also conducted sound velocity measurements of iron-light element alloy under high-temperature conditions. Here, we present our recent advances in IXS sound velocity measurements at high pressure and temperature.
This abstract is one of the contributions from Commission of Physics of Minerals (CPM), International Mineralogical Association (IMA).
3. References
[1] A. M. Dziewonski and D. L. Anderson. Phys. Earth Planet. Inter. 25 (1981) 297-356.
[2] D. Ikuta, E. Ohtani, and N. Hirao. Commun. Earth Environ. 2 (2021) 225.
[3] D. Ikuta, E. Ohtani, H. Fukui, T. Sakai, D. Ishikawa, and A. Q. R. Baron. Nat. Commun. 13 (2022) 7211.
[4] D. Ikuta, E. Ohtani, H. Fukui, T. Sakamaki, R. Heid, D. Ishikawa, and A. Q. R. Baron. Sci. Adv. 9 (2023) eadh8706.
[5] A. Q. R. Baron, D. Ishikawa, H. Fukui, and Y. Nakajima. AIP Conf. Proc. 2054 (2019) 020002.
[6] H. Fukui, T. Sakai, T. Sakamaki, S. Kamada, S. Takahashi, E. Ohtani, and A. Q. R. Baron. Rev. Sci. Instrum. 84 (2013) 113902.
