Papers by Keyword: Positronium

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Authors: A.I. Ryzhkov, Victor P. Shantarovich
Authors: Radosław Zaleski, Jacek Goworek
Abstract: The ordering of n-nonadecane confined in the pores of MCM-41 silica was investigated by Positron Annihilation Lifetime Spectroscopy. No irradiation effects caused by the positron source were observed. The ortho-positronium components found in the lifetime spectra correspond to the free volumes observed in the bulk alkane plus additional space at the interface between n-nonadecane and the silica wall. Phase transitions rigid-rotator and rotator-liquid were shifted towards lower temperatures by 28 and 16 degrees respectively.
Authors: Laszlo Lizkay, C. Corbel, P. Perez, P. Desgardin, Marie France Barthe, Toshiyuki Ohdaira, Ryoichi Suzuki, P. Crivelli, Ulisse Gendotti, A. Rubbia, M. Etienne, A. Walcarius
Abstract: Positron annihilation gamma energy distribution, lifetime spectroscopy and time-of-flight method were used to study surfactant-templated mesoporous silica films deposited on glass. The lifetime depth profiling was correlated to Doppler broadening and 3γ annihilation fraction measurements to determine the annihilation characteristics inside the films. A set of consistent fingerprints for positronium annihilation, o-Ps reemission into vacuum, and pore size was directly determined. The lifetime measurements were performed in reflection mode with a specially designed lifetime spectrometer mounted on a slow positron beam system. The intensity of the 142 ns vacuum lifetime component was recorded as a function of the energy of the positron beam. In a film with high porosity a reemission efficiency of as high as 40 % was found at low positron energy. Positron lifetime in samples capped by a thin silica layer was used to determine the pore size. The energy of the reemitted o-Ps fraction was measured by a time-of-flight detector, mounted on the same system, allowing determination of both o-Ps re-emission efficiency and energy in the same sample. We demonstrate the potential of the simultaneous use of different positron annihilation techniques in the study of thin porous films.
Authors: P.E. Mijnarends, C.V. Falub, S.W.H. Eijt, A. van Veen
Authors: Sergey V. Stepanov, Dmitry Zvezhinskiy, Gilles Duplâtre, Vsevolod Byakov, V.S. Subrahmanyam
Abstract: A new strategy for the treatment of positron annihilation lifetime (PAL) spectra in viscous liquids is proposed, enabling to extract values of the Ps reaction rate constants with intratrack radiolytic products as well as parameters of the free volume distribution in viscous media.
Authors: Fiorenza Quasso, Giovanni Consolati, M. Pegoraro, F. Severini
Authors: R. Khatri, Kelvin G. Lynn, Allen P. Mills, L.O. Roellig
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