Differential surface charging of Cs-contained vermiculite as observed by synchrotron radiation X-ray photoemission spectroscopy

Teraoka, Yuden; Iwai, Yutaro*; Okada, Ryuta; Yoshigoe, Akitaka 

The decontamination of Cs is necessary to make volume reduction of radioactive waste. In our research group, chemical bonding states of Cs in clay minerals has been studied by synchrotron X-ray photoemission spectroscopy (SR-XPS). In this presentation, effects of surface charging via an electron flood gun during SR-XPS is discussed. All SR-XPS experiments were conducted at SUREAC2000 of BL23SU in SPring-8. The natural vermiculite produced in Fukushima prefecture, Japan was processed to adsorb Cs by dipping in a non-radioactive CsCl solution. The concentration of Cs was 2.1 wt%. The other Cs compounds, e.g. CsClO, were also used. The synchrotron radiation of 1486.6 eV, identical with the Al-K line for convenience' sake of comparison with experiments in a laboratory, was used. Sample surface charging was changed by an electron flood gun during SR-XPS. It was revealed that the Auger parameter of Cs of CsClO was closest to that of Cs-contained vermiculite, suggesting Cs atoms adsorbed in the vermiculite may also interact with O atoms contained in the vermiculite. Photoemission spectra of Cs-3d core levels were measured to find four components. The component having the highest binding energy is only shifted by the operation of flood gun, suggesting most ionic chemical bonding. Consequently, the shifted component may be originated from Cs hydrated in water of weathered wide crevice between phyllosilicate layers. The other components are corresponding to interaction with O and Si atoms in narrow phyllosilicate interlayers.