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

为了在极端条件下实现凝聚态物质的现场研究，我们研制了一种新的具有能量选择正电子和湮没光子符合的β~(2+)-伽马寿命能谱仪。整个装置是桌上型的，成本低，因为它不需要任何加速器，只需要一个小的密封正电子源和一对磁透镜。样品可以暴露在任何极端的环境条件下，不会受到放射性物质的污染，因为样品部分是独立的，并与密封的正电子源很好地分开。为了克服放射性同位素发射正电子的飞行时间(TOF)展宽带来的不可避免的时间分辨率下降，利用磁场选择一定能带内的正电子。总效率(来自源的正电子可以聚焦在一个样品上超过10^&lt；-3)远远优于慢化正电子再加速的情况。目前，用10mCi^&lt；22&gt；Na正电子源的整个系统的时间分辨率约为385ps(半高宽)，比传统的伽马符合法(通常约为200ps半高宽)要差，但与以前采用正电子源和样品之间紧密几何关系的β~(+)-伽马符合寿命谱仪的时间分辨率相当。

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.