Orthopositronium annihilation and emission in mesostructured thin silica and silicalite-1 films

• Published in: Applied surface science 2008-10, Vol.255 (1), p.187-190
• Main Authors: Liszkay, L., Barthe, M.-F., Corbel, C., Crivelli, P., Desgardin, P., Etienne, M., Ohdaira, T., Perez, P., Suzuki, R., Valtchev, V., Walcarius, A.
• Format: Article
• Language: English
• Subjects: Analytical chemistry; Atomic and molecular physics; Chemical Sciences; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Disordered solids; Exact sciences and technology; Exotic atoms and molecules (containing mesons, muons, and other unusual particles); Gamma-ray energy spectroscopy; Mesoporous silica; Monte-Carlo simulation; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Other interactions of matter with particles and radiation; Physics; Positron annihilation; Positronium; Positronium, muonium, muonic atoms and molecules; Powders, porous materials; Structure of solids and liquids; crystallography; Studies of special atoms, molecules and their ions; clusters; Thermalization; Thin film; Time-of-flight
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2008.05.210

Mesoporous silica films and MFI-type pure silica zeolite films were investigated using slow positrons. Detection of the 3γ annihilation fraction was used as a quick test to estimate the emission of orthopositronium ( o-Ps) into vacuum. Positronium time-of-flight (TOF) spectroscopy, combined with Monte-Carlo simulation of the detection system was used to determine the energy of o-Ps emitted from the films. Evidence for an efficient o-Ps emission was found in both the mesoporous and silicalite-1. A 3γ fraction in the range of 31–36 % was found in the films with the highest o-Ps yield in each type of porous material, indicating that 40–50 % of the implanted positrons form positronium in the pore systems with very different pore sizes. Time-of-flight measurements showed that the energy of the orthopositronium emitted into vacuum is below 100 meV in the film with 2–3 nm pores at 3 keV positron energy, indicating an efficient slowing down but no complete thermalization in the porous films of 300–400 nm thickness.