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1. chinaXiv:201703.00587 [pdf]

Modification of source contribution in PALS by simulation using Geant4 code

Xia Ning; Xingzhong Cao; Chong Li; Demin Li; Peng Zhang; Yihao Gong; Rui Xia; Baoyi Wang; Long Wei
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties

The contribution of positron source for the results of a positron annihilation lifetime spectrum (PALS) is simulated using Geant4 code. The geometrical structure of PALS measurement system is a sandwich structure: the 22Na radiation source is encapsulated by Kapton films, and the specimens are attached on the outside of the films. The probabilities of a positron being annihilated in the films, annihilated in the targets, and the effect of positrons reflected back from the specimen surface, are simulated. The probability of a positron annihilated in the film is related to the species of targets and the source film thickness. The simulation result is in reasonable agreement with the available experimental data. Thus, modification of the source contribution calculated by Geant4 is viable, and it beneficial for the analysis of the results of PALS.

submitted time 2017-03-26 Hits1943Downloads1083 Comment 0

2. chinaXiv:201703.00584 [pdf]

Study of tunable monoenergy positron annihilation spectroscopy of polyethylene glycol thin-films?

Peng Kuang; Xiao-Long Han; Xing-Zhong Cao; Rui Xia; Peng Zhang; Bao-Yi Wang
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties

Doppler broadening and Coincidence Doppler broadening of annihilation radiation experiments have been performed in three kinds of polyethylene glycol (PEG) membrane formed with different average molecular weight using the tunable monoenergy slow positron probe as a function of implantion energy. The obtained positron annihilation parameters are interpreted from two aspects: surface effect and differences in micro-structure or chemical environment of positron annihilation. The experimental results show that the regulation of densification of PEG molecular packing and distribution uniformity from the near surface layer to bulk region in film forming process can be well realized by changing its molecular weight. Combining a variable monoenergetic slow positron beam and these two positron annihilation spectroscopy methods are powerful tool to study positron annihilation characteristics and for polymeric thin-film fine structure analysis.

submitted time 2017-03-26 Hits1568Downloads891 Comment 0

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