| Abstract: | A high-performance positron age-momentum correlation (AMOC) spectrometer was newly developed.The counting rate is increased up to 200 cps much larger than the value 20 cps reported by other international groups.And at the same time,the time resolution still keeps at the international level of 220 ps.Furthermore,positronium (Ps) annihilation in silica aerogel was investigated by AMOC,which indicates:(1) Ps annihilation between the grains dominantly undergoes pick-off process and spin conversion from o-Ps to p-Ps;(2) Annealing below 400 ℃ changes the grain surface conditions,i.e.the desorption of hydrogen and the decrease of the defect centers concentration. |
