Direct Measurement of the Internal Pressure of Ultrafine Bubbles Using Radioactive Nuclei

Abstract

The internal Xe gas pressure of ultrafine bubbles has been directly measured for the first time by using the γ-γ angular correlation technique, a well-known measurement technique in nuclear physics. Radioactive 125Xe (T1/2 = 16.9 h) was induced inside natural Xe-ultrafine bubbles in water, having an average diameter of 200 nm, by thermal-neutron irradiation. The asymmetry factor for the 55–188 keV γ-γ cascade in 125I, followed by the β decay of 125Xe, was used as a probe for the gas pressure in ultrafine bubbles. The internal pressure of the ultrafine bubbles was determined to be (Figure presented.) × 105 Pa, lower than those for ultrafine bubbles of N2, CH4, and Ar by Ohgaki (6 × 106 Pa) or that from the Young-Laplace equation (1.6 × 106 Pa).