Chemical states of ultra-trace alkali metals sorbed in laminar oxides

Baba, Yuji  ; Shimoyama, Iwao   ; Hirao, Norie

In order to clarify chemical states of radioactive cesium in clay and soil, X-ray photoelectron spectra (XPS) have been measured for cesium sorbed in laminar oxides such as mica. Since the number of atoms in radionuclides such as Cs is extremely small, we have measured XPS spectra under total reflection condition of incident X-rays. This method enabled us to measure XPS spectra for ultra-trace level alkali metals down to 1/1000 monolayer. For rubidium and cesium, the XPS core levels shifted to lower energy side with the decrease in the number of layer. While for sodium, the direction of the energy shift was reverse to those of rubidium and cesium. On the basis of point charge model, it was clarified that the lower the number of layer is, the stronger the iconicity of the chemical bond becomes for rubidium and cesium.