Quantitative evaluation of hydrogen atoms trapped at single vacancies in tungsten using positron annihilation lifetime measurements: Experiments and theoretical calculations

Change in the Positron Annihilation Lifetime of Vacancies Containing Hydrogen Atoms in Electron-irradiated Tungsten

“…The decrease in τ 2 after hydrogen charging is 21 ps and 26 ps (on average 23.5 ps) at doses of 1.4 × 10 −4 dpa and 2.9 × 10 −4 dpa, respectively. The simulations show that the PAL decreases by approximately 15 ps and 10 ps when the first and second hydrogen atoms are added to the vacancies, respectively [7]. It is expected that one or two hydrogen atoms (on average 1.8 atoms) are captured by one vacancy in this study, which is similar to that seen in a previous study (on average 1.6 atoms, 5.8 MPa pressure) [7].…”

“…The de-trapping rate is defined as the product of the concentration of the vacant interstitial hydrogen sites, hydrogen jump frequency for de-trapping, and concentration of hydrogen trapped at the vacancies. Based on [7] and Sieverts' law, we set the maximum number of hydrogen atoms (Z) that the vacancies can capture at 6, while the binding energy of hydrogen to the vacancies and hydrogen concentration were 1.19 eV and 4.6 × 10 −12 (Pressure: 1 MPa, Temperature: 573 K), respectively. Furthermore, the jump frequencies for trapping and de-trapping were assumed to be equal.…”

“…High-pressure hydrogen charging was performed under a pressure of 1 MPa and temperature of 573 K for a duration of 240 h. The electron-irradiated samples were annealed at 573 K for 240 h in a vacuum prior to hydrogen charging to avoid the formation or growth of vacancy clusters during hydrogen charging. Hydrogen atoms diffused to sufficiently deep regions (>100 μm) during hydrogen charging and subsequent changes in the PAL were measured [7].…”

“…It has been reported by Troev et al that the positron annihilation lifetime (PAL) of vacancies or vacancy clusters containing hydrogen or helium atoms decreased as compared to those not containing any gas atoms [5,6]. The change in the PAL of vacancies containing hydrogen atoms in electron-irradiated tungsten has been experimentally determined by Sato et al [7]. The PAL of single vacancies with an initial value of ~175 ps decreased to ~155 ps following hydrogen charging under a high pressure of 5.8 MPa.…”

“…The PAL of single vacancies with an initial value of ~175 ps decreased to ~155 ps following hydrogen charging under a high pressure of 5.8 MPa. The PAL of single vacancies containing hydrogen atoms was also calculated using the electron density from the first principle calculation [7]. A comparison between the results from the experiments and simulations showed that one/each vacancy captured one or two hydrogen atoms (on average 1.6 atoms).…”