In Situ Positron Lifetime Measurement for the Strained Polyethylene

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.

Positron lifetime and Doppler broadening study of defects in hydrogen charged Al–Mg alloys

The results of positron lifetime and Doppler broadening spectrum of defects in the hydrogen charged non-heat treatable 5xxx Al alloys are presented in this work. The yield stress of the sample was reduced for about 20 MPa after hydrogen was charged. A similar trend was observed in positron lifetime measurement, as the average lifetime τav descended remarkably to almost the level of Al matrix. The change in coincidence Doppler broadening (CDB) spectroscopy was also significant, exhibited by the characteristic change in CDB radio curves of a sample before and after hydrogen was charged. After hydrogen charging, there is an obvious enhancement in the high momentum region compensating dehancement in the low momentum region. This indicates the existence of hydrogen filling effect. The vacancies around the Mg atoms should be preferential filling sites for hydrogen because Mg has a strong affinity for hydrogen. The formation of an Mg–H bond parallel to a grain boundary is an important factor in weakening the grain boundary cohesion.

The observation of the lattice defect formation during hydrogenation and dehydrogenation in La(Ni,Sn)5 by in-situ positron lifetime measurement

To clarify the effect of Sn substitution for Ni of LaNi5 on the lattice defect formation during the hydrogenation and dehydrogenation processes, in-situ positron lifetime measurements were per-formed in LaNi4.93Sn0.27. During the hydrogenation, the mean positron lifetime, τm, monotonically increased up to 175 ps which is almost same as calculated positron lifetime for vacancy. This shows vacancy introduction by hydrogenation. The τm mean positron lifetime decreased down to 135 ps with hydrogen content during the dehydrogenation. It shows that the vacancies are removed from the lattice during the dehydrogenation. These results show that vacancies in LaNi4.93Sn0.27 are intro-duced and removed reversibly during the hydrogenation and dehydrogenation. The concentra-tions of vacancy and dislocation were 1 × 10−5 and 6 × 109 cm−2, respectively. These values are two orders lower than those in LaNi5.

Vacancies in electron irradiated 6H silicon carbide studied by positron annihilation spectroscopy

ABSTRACTPositron lifetime spectroscopy was employed to study the as-electron-irradiated (10 MeV, 1×1018 cm-2) n-type 6H silicon carbide sample in the measuring temperature range of 15 K to 294 K. Isochronal annealing studies were also performed up to the temperature of 1373 K by carrying out the room temperature positron lifetime measurement. Negatively charged carbon vacancies and VCVSi divacancy were identified as the major vacancy type defects induced by the electron irradiation process. The concentration of the VCVSi divacancy was found to decrease dramatically after the 1973 K annealing.