109 / 2023-04-13 21:52:50

Single shot gamma-induced positron spectroscopy based on laser wakefield accelerator

极端光下的基础物理学 > 极端光下的基础物理学-海报

Recently, laser-plasma acceleration developed rapidly. Electrons accelerated by laser wakefields can be employed to produce high flux gamma rays via bremsstrahlung. Such a laser-driven gamma-ray source usually has a short pulse duration (∼100 fs), high energy (>1 MeV), and high yield, making single shot positron annihilation spectroscopy possible. In this study, single shot gamma-induced positron annihilation spectroscopy (GiPS) based on a laser wakefield accelerator is proposed. In this spectroscopy, a large number of gamma rays generated by laser-wakefield accelerated electrons are injected into a sample in a very short time (<2 ps), and the positron lifetime is detected by measuring the time profile of the annihilation radiation (511 keV gamma ray) from the sample. The processes including gamma-ray production, shielding, annihilation generation, and annihilation detection were simulated by using the Monte Carlo method. The results show that up to 10¹⁰ gamma rays with a duration of 1.4 ps can be produced per shot with a 45 TW laser system. A Cherenkov radiator PbF₂ was used to detect the annihilation radiation, and its optimal thickness of 15 mm was obtained. A whole process simulation with optimized parameters was conducted. A low statistical fluctuation lifetime spectrum can be produced, which confirms the feasibility of single shot GiPS with a typical 45 TW laser system.