Positron Annihilation Studies of Mesoporous Silica MCM-41

16th International Conference on Positron Annihilation

Williams, J.F.^1 ; Guagliardo, P.^1 ; Sudarshan, K.^1 ; Ranganathaiah, C.^1 ; Koutsantonis, G.^2 ; Hondow, N.^2 ; Samarin, S.^1

Centre for Antimatter-Matter Studies, School of Physics, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia^1

School of Chemistry and Biochemistry, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia^2

关键词: Doppler;    Full energy distribution;    Lifetime data;    Low energy regions;    Measurements of;    Mesoporous silica MCM-41;    Oxygen atmosphere;    Oxygen concentrations;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/443/1/012063/pdf
DOI  :  10.1088/1742-6596/443/1/012063

来源: IOP

【 摘 要 】

Positron annihilation has been used to study the mesoporous silica MCM-41. Lifetime spectra of evacuated MCM-41 indicate a significant contribution from 3γ annihilation events with τ4= 116 ns and I4= 24.5 %. This is supported by measurements of the full energy distribution, where MCM-41 shows enhanced counts in the low energy region (below 511 keV) relative to a pure 2γ sample. MCM-41 was also studied under air and oxygen atmospheres. The presence of atmosphere has a significant effect on both the lifetime and Doppler patterns, with both the lifetime data (τ4and I4) and the 3γ-fraction decreasing with increasing oxygen concentration. This is indicative of paramagnetic quenching of o-Ps by oxygen.