Formation of Quasi-Free and Bubble Positronium States in Water and Aqueous Solutions

Abstract

It is shown that in aqueous solutions a positronium atom is first formed in the quasi-free state, and, after 50-100 ps, becomes localized in a nanobubble. Analysis of the annihilation spectra of NaNO3 aqueous solutions shows that the hydrated electron is not involved in the positronium (Ps) formation. PACS: 71.60.+z Positron states (electronic structure of bulk materials); 34.80.Lx Recombination, attachment, and positronium formation; 82.30.Gg Positronium chemistry Most usually, the positron annihilation lifetime (LT) spectra in liquids (below we consider aqueous solutions) are well described in terms of three exponentials (3-E analysis). It is believed that this fact indicates that 1) Ps formation is a fast process, its duration not exceeding 10 ps, the typical width of one channel of the time analyzer, and 2) the Ps atom is not involved in the non-homogeneous diffusion-controlled intratrack chemical reactions with radiolytic products. However, several facts plead against this conventional analysis, in particular: 1) The ratio of I3 to I1 (intensities of the ortho-Ps and para-Ps components) is not 3:1, as theoretically expected, but rather close to 2:1, Fig. 1 [1]; 0 20 40 60 80 100 temperature, oC 10 15 20 25 30 in te ns it ie s, % I3