Résumé du preprint DAPNIA-07-125

Orthopositronium annihilation and emission in mesostructured thin silica and silicalite-I films
L. Liszkay, , C. Corbel, M. Etienne, V. Valtchev, P. Desgardin, M.-F. Barthe, T. Ohdaira, R. Suzuki, P. Crivelli,g, A. Walcarius, P Perez
Mesoporous silica layers and silicalite-I 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 (oPs) into vacuum. Positronium time-of-flight (TOF) spectrocopy, combined with 
Monte-Carlo simulation of the detection system was used to determine the energy of oPs emitted 
from the layers. Evidence for an efficient oPs emission was found in both the silicalite-I layer and 
in mesoporous films. A 3γ fraction in the range of 31-36 % was found in the layers with the 
highest oPs 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 approximately 2 nm pores at 3 keV positron energy, indicating an efficient slowing down but 
no complete thermalization in the porous layer.


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