摘要
用大体积BaF_2(φ40mm×30mm)探测器组装正电子湮没的2γ和3γ寿命谱仪,在2γ方式下,两个BaF_2探测器构成双重符合,得到系统的时间分辨为FWHM=212ps,计数效率比塑料闪烁探测器组装的谱仪估计高10倍以上.在3γ方式下,NaI(Tl)探测器与两个BaF_2构成三重符合,合理安排三探头的几何及合理选择各能窗的位置以优化对3γ湮没事例的测量,实验表明,新系统可用于研究强度微弱的电子偶素在固体中湮没的3γ寿命谱.
We describe a high efficiency lifetime system for 2_γ as well as 3_γ positron annihilation experiments using large Ba_F(φ40 mm×30mm)detectors.In the usual 2_γ mode we obtain 212ps time resolution and a high efficiency yielding 400 counts/sec with a 5μci ^(22)Na source.For measuring only the 3_γ decay,a large NaI(Tl)detector is used in triple coincidence mode with the BaF_2 lifetime system.The energy window for the NaI(Tl) as well as the stop BaF_2,is arranged suitably to detect one of the three annihilation γ rays,while the energy window for the start BaF_2 is set higher,to only detect the sum signal of 1.28MeV γ and one Of the three γ rays.We will show examples of how the 2_γ-3_γ lifetime can be used for studying positron and positronium physics in solid.
出处
《高能物理与核物理》
CSCD
北大核心
1989年第12期1057-1063,共7页
High Energy Physics and Nuclear Physics
基金
美国国家科学基金
