Investigation of the Charging State of Radioactive Cs Particles Using Kelvin Probe Force Microscopy

YUKIMI SHINKE, Ayumi Iwata, Keiichi Kurosawa, Makoto Inagaki, Shun Sekimoto, Koichi Takamiya, Yuichi Oki, Tsutomu Ohtsuki, Yasuhito Igarashi, Tomoaki Okuda, Keio University

     Abstract Number: 52
     Working Group: Aerosol Physics

Abstract
The accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) in 2011 resulted in the dispersal of water insoluble glassy radioactive Cs-bearing particles . The dispersed radioactive Cs-bearing particles may accelerate deposition inside the airways due to self-charging by radioactivity of the particles and their deposition may have more adverse effects on the human body than formerly understood. However, a method for measuring the detailed electrostatic properties of individual particles collected from the actual environment has not yet been established. Furthermore, no measurements have been made regarding the charged state of the particles generated by the actual FDNPP accident.

In this study, an attempt was made to elucidate the charging state of individual particles using a technique called Kelvin Probe Force Microscopy (KPFM). Experiments measuring the surface electrostatic potential of particles with known charge numbers have revealed that a linearity is established between the number of charges and the surface potential, and that the equation of the linearity depends on substances that make up the particles.

We also calculated the relationship between the number of charges on the single particle and its surface potential by considering the KPFM measurement system as a capacitor. When the particles are completely dielectric, the slope of the calibration curve is not affected by the physical properties of the particles and only the intercept is expected to depend on the chemical? composition of the particles. In contrast, if some of the particles are conductors due to residual moisture, the slope of the calibration curve would be affected by the physical properties of the particles.

Elucidation of the charge state, or charge number, of the radioactive particles whose charge states are unknown could be achieved by measuring the surface potential by KPFM and fitting it to a calibration curve based on the composition of the particles.