Taking the actinide dioxide AnO₂ system as an example, we present an investigation of electronic property at low temperatures by means of NMR spectroscopy. It is a key feature that NMR of both An and O nuclei can be observed in the AnO₂ system. This system is typified by UO₂, which is a standard nuclear fuel. In this context, the property of AnO₂ at high temperatures has been studied intensively so far. Recently, however, it is noticed that the ground state AnO₂ system is also an exotic electronic state called multipole ordering. Interesting physical properties of actinide compounds at low temperature are introduced.

Actinide compounds are interesting systems, because a variety of condensed matter physics, such as heavy fermion superconductivity, ferromagnetic superconductivity and “hidden order” is known. In order to study these systems, the high quality single crystal growth is quite important to open up the frontiers of research. Here we present the technique of single crystal growth, such as Czochralski method, flux method, Bridgeman method, chemical transport method and the related technique, as case studies.

Research on the Mössbauer spectroscopic study of actinide elements in the United States and European countries started soon after the discovery of the Mössbauer effect in 1958. Although several Mössbauer isotopes were discovered in actinide elements, application of the actinide Mössbauer spectroscopy to material science has been limited. In this paper, the history and utility of actinide Mössbauer spectroscopy, especially, ²³⁸U and ²³⁷Np, are reviewed.