Kae Ito

Interlaboratory Comparison of Positron Annihilation Lifetime Measurements

An interlaboratory comparison for positron annihilation lifetime (PAL) measurements for pure nickel and fused silica was performed. Based on the reported positron (for nickel) and positronium (for fused silica) lifetimes, the uncertainties in the PAL measurements were estimated.

Positron and positronium annihilation in silica-based thin films studied by a pulsed positron beam

Abstract Positron and positronium annihilation in silica-based thin films has been investigated by means of measurement techniques with a monoenergetic pulsed positron beam. The age–momentum correlation study revealed that positron annihilation in thermally grown SiO 2 is basically the same as that in bulk amorphous SiO 2 while o -Ps in the PECVD grown SiCOH film predominantly annihilate with electrons of C and H at the microvoid surfaces. We also discuss time-dependent three-gamma annihilation in porous low- k films by two-dimensional positron annihilation lifetime spectroscopy.

Defect profiles in ion-irradiated metal samples by slow positron beams in comparison with simulation profiles

Metal (Fe and Ni) samples ion-irradiated at 100 – 773 K were characterized by Doppler broadening measurements with slow positron beams to investigate depth profiles of irradiation-induced defects. Obtained results were compared with defect profiles calculated by Monte-Carlo simulation. Defects profiles obtained by positron measurements were always deeper than those by the simulation. The difference between measured and simulated profiles was observed even in the case of the Fe sample irradiated at 100 K where vacancies are immobile. The origin of such differences was discussed with respect to vacancy diffusion, depth calculation, surface contamination and ion channeling.

Low energy positron annihilation study of composite reverse osmosis membranes

Positron annihilation with a slow positron beam was applied to the characterization of composite reverse osmosis membranes. The results, obtained at different positron incident energies, indicated that the membranes are asymmetric with respect to the pore structure, consisting of a thin top layer with little porosity and an underlying thick porous layer. A relationship between the longest positron lifetime near the membrane surface and the salt rejection rate was discussed in terms of the free-volume hole size for the thin top layer.

Study of Cs-loaded SiO2 glass by thermal analysis and positron annihilation spectroscopy

SiO2 glass with Cs clusters was investigated by differential scanning calorimetry (DSC), thermogravimetric differential analysis (TG-DTA), and positron age-momentum-correlation (AMOC) spectroscopy. No significant peaks arising from Cs clusters were observed in TG-DTA and DSC curves, suggesting Cs clusters in smaller amount than the detection limit of thermal analysis. In contrast to that, AMOC spectroscopy showed ortho-positronium (o-Ps) pick-off annihilation influenced by the presence of Cs clusters. The results demonstrate the feasibility of probing an electronic state of small metal clusters loaded into a disordered system by o-Ps.