Papers by Keyword: Positron Annihilation

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Authors: Radosław Zaleski, Waldemar Dolecki, Jacek Goworek
Abstract: Positron annihilation lifetime spectroscopy study of n-heptane adsorption and desorption on silica gel Si-60 gives insight into a free volume evolution during those processes. Analysis of the lifetime distribution allows to ascribe particular ortho-positronium components to silica walls, mesopores and n-heptane. Hysteresis loop of the intensities of the mesopore and n-heptane related components similar to classic adsorption/desorption isotherms is observed. Transition from an adsorbate multilayer structure to liquid when pores become completely filled, manifests itself as an intensity change. Kinetics of desorption and adsorption studies allows to determine the time of reaching the equilibrium by the Si 60–n-heptane system at various pressures.
Authors: Masanori Fujinami, Ryutaro Minei, Chang Gui Liu, Kenta Hara
Abstract: The in situ positron annihilation spectroscopy measurement has been developed and applied to investigate the structural change in free volume on the tensile deformation of linear low-density polyethylene. The pick-off lifetime of ortho-positronium (Ps) decreases by applying the strain and an aging variation cannot be observed. On the contrary the fraction of Ps formation gradually decreases day by day and becomes constant after several days. Further, after release of strain, it returns to the original value. The reason is considered to be that the molecular chains become rigid gradually during deformation and they lose the flexibility.
Authors: Dušan Račko
Abstract: In the Present Contribution the Atomistic Structure of the Polymer Melt at 300 K Is Simulated by Means of Molecular Dynamics. the Agreement with an Experimental Density Is Obtained with a Deviation Lower than 1%. the Free Volume Is Analyzed in 1,000 Structures and 6.5 X 108 Cubic Å of Molecular Space. a Model for the Free Volume Cavities Is Proposed. in the Model the Size and Number of the Cavities Can Be Scaled by Three Parameters: Probe Radius, Cavity Depth and Cavity Threshold Volume. the Experimental Values of the Nano-Sized Cavity Volumes as Well as Ortho-Positronium Lifetimes Are Obtained, as Compared to Models with Cylindrical and Spherical Geometry. a Typical Value of the Number Density of Free Volume Cavities at 0.001 Å-3 Is Obtained. the Cavities Have Typically Elongated Shape with a Side-to-Length Ratio 1:2.
Authors: S. Roy Choudhury, R. Yadav, A.N. Maitra, P.C. Jain
Authors: Dawid Giebel, Jerzy Kansy
Abstract: LT 10 is a new version of LT program designed to analysis of Positron Annihilation Lifetime Spectra (PALS). The new program is equipped with a new user interface and other features unavailable in its previous versions. It has been created again in a modern programming language and is now compatible with the latest operating systems.
Authors: L.V. Jørgensen, M.J.T. Collier, K.S. Fine, T.L. Watson, D.P. van der Werf, M. Charlton
Authors: Y.Y. Shan, Ai Hong Deng, Y.W. Zhao, C.C. Ling, S. Fung, C.D. Beling
Authors: Jue Zhong, Peter Mascher, Werner Puff, A.H. Kitai
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