Abstract
Positron annihilation lifetime spectra of MCM-41 and zeolite Y were measuredat different vacuum levels. When the experiments were carried out in air, avery long lifetime component (τ4 = 35-45 ns, I4 = 15-20%) was observed for MCM-41,while the longest lifetime for zeolite Y was only 2-4 ns with an intensity of15-25%. However, when the experiments were carried out in vacuum, the very longlifetime components could be observed for both samples, although with differentintensities, ~30% for MCM-41 and ~10% for zeolite Y. For MCM-41 in air,the longest lifetime (τ4) is ~42 ns, corresponding to theortho-positronium (o-Ps)annihilation lifetime in MCM-41 cavities. This value is slightly longer butvery close to the value of 39 ns, which was estimated by using a bouncingquantum particle model. These peculiar positron annihilation characteristicswere explained by air quenching mechanism of o-Ps annihilation in MCM-41. Itwas suggested that because of the existence of the very long lifetime componenteven in air, positron lifetime spectroscopy could be a very useful toolfor nondestructive measurement of the cavity size of mesoporous solids such asMCM-41.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
