Isotope effects in electron exchange reactions of lanthanide and actinide elements including chemical uranium enrichment

Full text: Isotope separation by chemical exchange is very popular for light elements, such as hydrogen, lithium, boron, carbon, nitrogen and oxygen. Due to the mass dependence of the isotope effects, the chemical exchange was considered not to be applicable to uranium enrichment. However uranium enrichment processes by ion exchange and solvent extraction have been developed in Japan and France, respectively. The principle of the chemical uranium enrichment was not known for many years. It was clarified 10 yeas ago that the origin of the uranium isotope effects was not in the molecular vibration but in the electron-nucleus interaction. Since then, attention has been placed on the similarities between the isotope effects in chemical exchange reactions and the isotope shifts in atomic emission spectra. Study on the temperature dependence of the isotope separation factor was a key to separate the 'electron effects' and 'molecular effects'. In the present paper, experimental work on gadolinium isotope effects in amalgamation is presented and isotope effects of lanthanide elements and actinide elements are reviewed. Discussion is extended to the role and effects of 'f' electrons of these elements. Non-proliferation is the most serious problem in nuclear technology development. The chemical exchange uranium enrichment has been regarded as the proliferation resistant technologies. Chemical enrichment, of which development has been abandoned in Japan and France, could be reconsidered again among international nuclear technology communities. (author)