2015 Volume 13 Pages 417-421
In order to clarify the chemical states of radioactive cesium sorbed in minerals such as clay, soil, sand and rock, X-ray photoelectron spectra (XPS) have been measured for cesium adsorbed on SiO2 and Al2O3 (sapphire), which are major components of these minerals. Since the number of atoms in radioactive cesium (134Cs or 137Cs) is extremely small, total reflection XPS (TR-XPS) using synchrotron radiation was applied in order to measure trace amount of cesium. For SiO2 surface, it was shown that ultra-trace amount of cesium down to 205 pg·cm−2 can be detected by TR-XPS. This amount corresponds to about 400 Bq of 137Cs (t1/2=30.2 y). Thus it was demonstrated that the ultra-trace amount of cesium corresponding to the radioactive cesium level can be measured by TR-XPS. As to the chemical states of cesium, the binding energy of the Cs 3d5/2 line for cesium adsorbed on SiO2 and Al2O3 ranges from 725.2 eV to 725.5 eV irrespective of the adsorption conditions, suggesting that the cesium is adsorbed through weak Van-der-Waals force. While after rinsing the cesium-adsorbed SiO2 in water, the binding energy of the Cs 3d5/2 line shifted by 0.8 eV to higher energy side. The result indicates that the ultra-trace amount cesium remaining after rinsing is covalently bonded with the SiO2 surface rather than ionically bonded. [DOI: 10.1380/ejssnt.2015.417]
