Chemical state analysis of trace-level alkali metals sorbed in micaceous oxide by total reflection X-ray photoelectron spectroscopy

• Published in: Applied surface science Vol. 384; pp. 511 - 516
• Main Authors: Baba, Y., Shimoyama, I., Hirao, N.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.10.2016
• Subjects: Adsorption; Alkali metal; Alkali metals; Cesium; Micaceous oxide; Oxides; Photoelectron spectroscopy; Reflection; Sodium; Total reflection; X-ray photoelectron spectroscopy; X-rays; Cesium; Alkali metal; Total reflection; Adsorption; Micaceous oxide; X-ray photoelectron spectroscopy
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2016.05.067

[Display omitted] •Total-reflection XPS for Na, Rb, and Cs on micaceous oxide were measured.•Detection limit of 100pgcm−2 was achieved in Cs, corresponding to 200Bq of 137Cs (t1/2=30.2 y).•Cs sorbed in micaceous oxides is found ionically bonded with oxygen atoms. In order to determine the chemical states of radioactive cesium (137Cs or 134Cs) sorbed in clay minerals, chemical states of cesium as well as the other alkali metals (sodium and rubidium) sorbed in micaceous oxides have been investigated by X-ray photoelectron spectroscopy (XPS). Since the number of atoms in radioactive cesium is extremely small, we specially focused on chemical states of trace-level alkali metals. For this purpose, we have measured XPS under X-ray total reflection (TR) condition. For cesium, it was shown that ultra-trace amount of cesium down to about 100pgcm−2 can be detected by TR-XPS. This amount corresponds to about 200Bq of 137Cs (t1/2=30.2 y). It was demonstrated that ultra-trace amount of cesium corresponding to radioactive cesium level can be measured by TR-XPS. As to the chemical states, it was found that core-level binding energy in TR-XPS for trace-level cesium shifted to lower-energy side compared with that for thicker layer. A reverse tendency is observed in sodium. Based on charge transfer within a simple point-charge model, it is concluded that chemical bond between alkali metal and micaceous oxide for ultra-thin layer is more polarized that for thick layer.