New positron lifetime spectrometer with the coincidence of energy selected positron and the annihilation photon

为了实现极端条件下凝聚态物质的原位研究，我们建造了新型的能量选择正电子与湮没光子符合的β ^+-γ符合寿命谱仪。整个装置不需要加速器，只需要一个小型密封正电子源和一对磁透镜，是台式的，成本低。样品可以暴露在任何极端的环境条件下，而没有被放射性物质污染的风险，因为样品部分是独立的，与密封的正电子源分离良好。为了克服由于放射性同位素发射的正电子的飞行时间（TOF）的扩展而导致的时间分辨率的不可避免的劣化，使用磁场来选择特定能带中的正电子。总的效率（超过10^<-3>的正电子从源可以集中在一个标本）是上级的情况下，预期的再加速慢化正电子。采用10 mCi ^ Na正电子源的整个系统的时间分辨率<22>约为385 ps（FWHM），比传统的γ-γ符合方法（FWHM约为200 ps）要差，但可以与正电子源和样品之间采用紧密几何结构的β ^+-γ符合寿命谱仪相比较。

In order to achieve in-situ studies of condensed matter under extremeconditions, new beta^+-gamma conicidence lifetime spectrometer with the coincidence of energy-selected positron and the annihilation photon has been constructed. The whole apparatus is desk-top and low cost, since it does not need any accelerators but a small sealed positron-source and a pair of magnetic lenses. Specimens can be exposed to any extreme surrounding conditions without the risk of contamination by radioactive materials, since the specimen part is independent and well-separated from the sealed positron-source. In order to overcome the inevitable deterioration of time resolution due to the spread of TOF (time of flight) of positrons emitted from radioisotopes, positrons in a certain energy band are selected using magnetic field. The total efficiency (more than 10^<-3> of positrons from the source can be focused on a specimen) is much superior to that expected for the case of re-acceleration of moderated positrons. The time resolution of the whole system with a 10mCi^<22> Na positron source is about 385ps (FWHM) as yet, which is worse than that of the conventional gamma-gamma coincidence method (around 200ps FWHM typically) but bears comparison with former beta^+-gamma coincidence lifetime spectrometers using close geometry between the positron source and a specimen.