Hiroshi Hidaka

Biography

Hiroshi Hidaka is a professor of the Geochemistry and Cosmochemistry Laboratory of the Department of Earth and Planetary Sciences at Nagoya University, Japan. During his USIAS fellowship, he will be hosted by Professor Benoît Gall at the Hubert Curien Pluridisciplinary Institute (IPHC) of the University of Strasbourg.

His research interest is understanding the mechanisms of nuclear reactions occurring in nature through the isotopic variations of elements found in natural substances. As an isotope analyst, he studies the origin, formation and evolution of planetary materials and their circumstances by analysing the isotopic variations of several elements caused by natural nuclear reactions. He is highly experienced and has conducted several successful studies analysing the isotopic data of rare natural materials such as meteorites, lunar rocks, and the Oklo natural reactor materials.

Professor Hidaka received his undergraduate degree (1984), master degree (1986), and PhD (1992) from the University of Tokyo. He was an assistant professor at Kumamoto University (1988-1989), the University of Tokyo (1989-1992), and Tokyo Metropolitan University (1992-1995). He then moved to Hiroshima University as an associate professor (1995-2001) and, subsequently, became full professor (2002-2016). He has occupied his present position of professor at Nagoya University since 2016. During this period, he was a visiting professor at the Australian National University (1994), Curtin University (2000), and the University of Strasbourg (1998, 2001, 2003, 2005, 2007, 2010, 2019). He was also an associate member of the Commission on Isotopic Abundances and Atomic Weights organized by International Union of Pure and Applied Chemistry (IUPAC) from 1999 to 2008, which is charged with the critical evaluation and dissemination of the isotopic abundances and atomic weights of the elements.

Fellowship 2026

Dates - 01/12/2026-31/08/2028

Project summary

A COMPREHENSIVE UNDERSTANDING OF THE OKLO PHENOMENON FROM SYSTEMATIC ISOTOPIC ANALYSES AND NUMERICAL SIMULATIONS

The ‘Oklo phenomenon’ in the title of this project refers to the natural process of self-sustaining fission reactions that occurred in several areas of the Oklo uranium ore deposit in the southeastern region of the Republic of Gabon, central Africa. It is known that 16 separate areas in the uranium deposits (14 at Oklo, one at Okelobondo adjacent to Oklo, and one at Bangombé located 30 km southeast from Oklo) functioned as natural fission reactors around two billion years ago. Individual reactor parts are called reactor zones (RZs). Since the discovery of the first RZ at Oklo in 1972, three major international consortium studies have been conducted to clarify the Oklo phenomenon from the perspectives of several research fields, including physics (particularly reactor physics and nuclear physics), chemistry (particularly isotope geochemistry and radiochemistry), geology, mineralogy, hydrology, radioactive waste management, and so on.

In Professor Hidaka’s research field, isotopic analyses of multi-elements in the Oklo natural reactors have helped to understand the mechanisms of several nuclear reactions that occurred in the reactors. Most of the isotopic data on the Oklo RZ materials was provided over a quarter of a century ago. Significant progress has recently been made in the instrumental developments of mass spectrometry for isotopic analyses. If we can obtain more precise and accurate isotopic data from the RZ materials, we can expect new insights into understanding the Oklo phenomenon. This simple idea underlies the current USIAS project, in which Professor Hidaka proposes the isotopic measurements of several key elements like rare earth elements (REEs) and hafnium (Hf) in the Oklo RZs using state-of-the-art analytical techniques. The resulting isotopic dataset can be used to characterize individual RZs and improve our understanding of the Oklo phenomenon.