Development of a positron annihilation measurement system by implantation of 17 MeV gamma beam into bulk materials

We have developed a new positron annihilation measurement system via electron-positron pair creation using by laser Compton scattering (LCS) gamma beam direct implantation into bulk materials at NewSUBARU synchrotron radiation facility, LASTI, University of Hyogo, Japan. LCS gamma beam is easy to control energy, and its energy is quasi-monochromatic and high directivity. These parameters are determined by laser wavelength and electron kinetic energy. In this study, maximum energy 16.9 MeV LCS gamma beam generation by Nd:YVO₄ laser (wavelength 1064 nm) and circling electron (982 MeV) directly irradiated into samples for Doppler broadening measurement in an atmosphere. The gamma beam created high energetic positrons to MeV order. This measurement could be a simple setup consisting of a single HP-Ge detector, amplifier, and multi-channel analyzer. As a demonstration, we have tried to measure the Doppler broadening spectra of pure iron, electron irradiated iron and silicon by this system.