| NUKLEONIKA 2010, 55(1):91-96
POSITRON ANNIHILATION STUDY OF IRON OXIDE NANOPARTICLES
IN MESOPOROUS SILICA MCM-41 TEMPLATE
Zbigniew Surowiec1, Marek Wiertel1, Radosław Zaleski1, Mieczysław Budzyński1,
Jacek Goworek2
1 Institute of Physics, Maria Curie-Skłodowska University,
1 M. Curie-Skłodowskiej Sq., 20-031 Lublin, Poland
2 Faculty of Chemistry, Maria Curie-Skłodowska University,
1 M. Curie-Skłodowskiej Sq., 20-031 Lublin, Poland
The subject of investigation were the samples obtained by impregnation of MCM-41 template with an aqueous solution prepared from Fe(NO3)3.9H2O. As a result of such a procedure, iron oxides deposits on MCM-41 were formed. The Mössbauer studies revealed an occurrence of Fe3O4 nanocrystallites in the both ferri- and superparamagnetic states. Almost 80% small particles exist in a paramagnetic state. The positron annihilation lifetime spectroscopy (PALS) spectra were measured in air or in vacuum. The long-lived ortho-positronium (o-Ps) components and their intensities are time dependent due to air molecules interaction with iron oxide nanocrystallites and silica walls surfaces. The adsorption of air on the nanocrystallites surface causes a total screening of their surface and a raise of the o-Ps lifetime values. Observed anti-quenching effect is a result of competition of two phenomena: practically switching off a pick-off mechanism related to interaction of o-Ps with magnetite nanoparticles and considerably weaker usual
quenching by paramagnetic oxygen molecules.
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