Positronium in a layered-structure material: Montmorillonite

Abstract

Positron-lifetime and Doppler-broadened spectra were measured for ion-exchanged (Na⁺, Zn²⁺, Al³⁺, Cu²⁺ and alkylammonium) montmorillonites (mont). The line-shape parameters of the spectra for alkylammonium-intercalated monts were almost equal to those observed for the corresponding alkylammonium salts used for the intercalation. Upon exchange of diamagnetic ions in the interlayer spaces of mont for paramagnetic Cu²⁺ ions, the longest-lived component ascribed to ortho-positronium (Ps) was shortened from ca 1 to 0.62 ns, and the Doppler-broadened spectrum was narrowed. These results demonstrate that Ps atoms are predominantly distributed in the interlayer spaces of mont, rather than in the aluminosilicate layers.