Papers by Keyword: Positron Lifetime Spectroscopy

Abstract: Positron lifetime spectroscopy is a powerful non-destructive technique for characterizing open-volume lattice defects in solids at the atomic scale. This technique enables the identification of defects and the determination of defect concentration. This article provides a brief overview of the current state of development of positron lifetime spectrometers used for defect studies of bulk materials. It discusses advanced data analysis and recent methodological developments in positron lifetime spectroscopy.

Abstract: The strain-rate dependence of vacancy cluster sizes in hydrogen-charged martensitic steel AISI410 under tensile deformation was investigated using positron lifetime spectroscopy. The vacancy-cluster sizes in hydrogen-charged samples tended to increase with decreasing strain rates during the tensile deformations. The vacancy-cluster sizes significantly correlated to the tensile elongations to fracture. It was revealed that the presence of large-sized vacancy-clusters can cause the degradation of mechanical properties and followed by brittle fracture.

Abstract: The experimental study of the structure of commercially pure titanium after saturation with hydrogen from the gas phase by means of positron lifetime spectroscopy (PLS) and Doppler broadening spectroscopy (DBS) was carried out. In the result of penetration and accumulation of hydrogen, significant changes of annihilation characteristics occurred due to the defect structure changing. The investigated samples contained hydrogen in concentrations varying from 0 to 0.961 wt.%. Several stages of hydrogen interaction with the metal structure were revealed.

Abstract: Sealed radioactive sources of ²²Na for positron annihilation lifetime spectroscopy (PALS), free from the legal regulations, are commercially available from an American company. However, thick foils are used to seal ²²Na in these sources and large fractions of the positrons annihilate in the sealing materials. Further, it is pointed out that a long lifetime component over 1 ns appears in the positron lifetime spectrum acquired with the Kapton sealed source (POSK-22, IPL Inc.). In this research, attempts were made to develop high quality sealed positron sources, potentially free from regulations, for ubiquitous application of PALS. The sources prepared in the present work are of high quality and applicable to our new PALS, which does not require sample cutting and is potentially applicable to truly nondestructive, onsite inspection of various materials

Abstract: The defect structure of Fe28Al samples is examined with the Positron Annihilation Lifetime Spectroscopy. The studies are carried out for samples in as-cast state and after heat treatments: annealing for 24 hours at 900°C (or 1050°C) and either slow cooling with furnace or quenching to oil. The PALS spectra are analyzed using two-state trapping model. Only one type of defects is detected. The positron lifetime in these defects (V) suggests that they are quenched-in Fe-monovacancies (VFe). The vacancy concentration strongly depends on the rate of cooling. Besides, V also depends slightly on the rate of cooling of the material. This fact suggests, according to the predictions of latest theoretical calculations, that V is sensitive to the atomic configuration in the nearest neighborhood of VFe, which give hope to estimate the degree of atomic ordering in alloys by the PALS technique.

Abstract: In this work we used Positron Annihilation Spectroscopy (PAS) and Electron Paramagnetic Resonance (EPR) to investigate the properties of vacancy defects produced by low energy electron irradiation. N-doped 3C-SiC and 6H-SiC monocrystals have been irradiated with electrons at different energies from 240keV to 900keV. EPR measurements show that Frenkel pairs VSi 3-/Si are created in 6H-SiC when electron irradiation is performed at low energy (240-360 keV). EPR also indicates that the silicon displacement threshold energy is higher in 3C-SiC than in 6HSiC. Moreover, PAS results show that the size and concentration of the vacancy defects decrease when the electron energy decreases for both polytypes. PAS detects vacancy defects in 240keV electron irradiated 3C-SiC, and the detection of the carbon vacancy is proposed.