Development of gamma-ray-induced positron annihilation spectroscopy at UVSOR-III

Taira, Yoshitaka*; Okano, Yasuaki*; Hirade, Tetsuya  ; Yabuuchi, Atsushi*

High-energy ultrashort pulse gamma rays obtained by inverse Thomson/Compton scattering in UVSOR were applied to gamma-ray-induced positron annihilation spectroscopy. In gamma-ray-induced positron annihilation lifetime spectroscopy (GiPALS), a positron lifetime measurement system with a time resolution of 140 ps in full width at half maximum was developed using eight BaF scintillation detectors and two digital oscilloscopes. GiPALS is currently available for users and in situ measurements of positron lifetime under stress loading is conducted. The development of gamma-ray-induced age-momentum correlation (GiAMOC) system using Ge semiconductor detectors is also in progress. Furthermore, the effect of pulsed gamma-ray scattering on the positron lifetime spectra is evaluated computationally using the Monte Carlo simulation code EGS5, and the method is being refined. The development of spin-polarized positron annihilation spectroscopy using circularly polarized gamma rays is also planned in the future.