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Yamawaki, Masato*; Uesugi, Naoya*; Oka, Toshitaka; Nagasawa, Naotsugu*; Ando, Hirokazu*; O'Rourke, B. E.*; Kobayashi, Yoshinori*
Japanese Journal of Applied Physics, 59(11), p.116504_1 - 116504_5, 2020/11
Positron annihilation lifetime measurements were performed on polyethylene films with thickness of 15
m - 2000m using a Na-22 positron source enclosed in a Kapton film. For thin films, some positrons will pass through the film and annihilate behind it. Using a single film in a commercial anti-coincidence system, by placing an annealed stainless steel (SUS304) cover behind the sample, it is possible to sufficiently measure the long lifetime ortho-positronium (o-Ps) component even in thin films. Additionally, calculated intensities of the o-Ps component determined from the estimated film transmittance agreed well with the measured values. Furthermore, by applying this method to uniaxially stretched UHMWPE, we were able to observe structural changes owing to the stretching consistent with shorter measured o-Ps lifetime and increased o-Ps intensity.
Hirade, Tetsuya; O'Rourke, B. E.*; Kobayashi, Yoshinori*
Journal of Physics; Conference Series, 791(1), p.012029_1 - 012029_4, 2017/02
Times Cited Count：2 Percentile：62.67(Physics, Multidisciplinary)We tried to observe the positron annihilation rates near surface of (room temperature ionic liquids) IL's, such as N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI) by use of the perpendicular slow positron beamline installed at AIST. The vaper pressure of TMPA-TFSI is very small and hence it is possible to measure the positron annihilation rate in vacuum chamber directly. This represents the first energy variable experimental results of the positron annihilation rate at the near surface of an IL. The triplet positronium annihilation rate seems to be larger at nearer region to the surface of the IL's.
Jiang, L.*; Oshima, Nagayasu*; O'Rourke, B. E.*; Suzuki, Ryoichi*; Harada, Yoshihisa*; Suzuki, Takayuki*; Takatsu, Shuhei*; Hirade, Tetsuya; Takai, Kenichi*
no journal, ,
Positron annihilation spectroscopy (PAS) is a sensitive method for detection of defects such as vacancies, vacancy clusters and nano-voids. The positron probe microanalyzer (PPMA) in AIST can investigate defect distribution of materials using a scanning positron microbeam. For the application of the PPMA for analysis of such materials it is important to consider the defects introduced during the sample preparation. we are investigating two kinds of sample preparation process, electrical discharge machining (EDM) and colloidal silica polishing after EDM. We are studying the depth dependence of the density of the defects induced by these processes in various metals, including SUS316L, using PAS.
Jiang, L.*; O'Rourke, B. E.*; Harada, Yoshihisa*; Takatsu, Shuhei*; Ito, Kenji*; Okubo, Masataka*; Hirade, Tetsuya; Uedono, Akira*; Suzuki, Ryoichi*; Takai, Kenichi*; et al.
no journal, ,
We are studying the depth dependence of the density of the defects induced by the electrical discharge machining (EDM) in SUS316L, using the electron probe microanalysis (EPMA), Positron annihilation lifetime spectroscopy (PALS) and X-ray diffraction (XRD). EPMA results show a large change in the composition over the first 10 m. This layer can be assumed to correspond to the recast layer. PALS and XRD results suggest a defect layer with a thickness of around 50 m. This depth can be assumed to correspond to the heat affected zone where dislocations and vacancy clusters exists. For PALS (and other methods) analysis, it is recommended to remove the topmost 100 m of the samples by chemical polishing after EDM.
Hirade, Tetsuya; O'Rourke, B. E.*; Kobayashi, Yoshinori*
no journal, ,
A vertical slow positron beam was used to investigate the surface of a room temperature ionic liquid, N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI). Measurement of positron lifetimes indicated a higher Ps formation probability and shorter ortho-Ps annihilation lifetime in near surface of TMPA-TFSI than in the bulk. These changes are probably caused by the layered structure in near surface of TMPA-TFSI. Vertical slow positron beams are a strong tool to investigate the surface of room temperature ionic liquids.
