Recent developments of the Scanning Positron Microscope SPM for depth- and position-resolved positron lifetime measurement

摘要

To investigate inhomogeneous defect distributions, e.g. close to fatigue cracks or dispersive alloys with positron annihilation lifetime spectroscopy a pulsed positron beam with a diameter in the range of 1 μm and with a time resolution in the order of 250ps is needed. The Scanning Positron Microscope (SPM) fulfills the requirements for position resolved positron lifetime measurements and was operated by the Universitat der Bundeswehr München. To increase the countrate, the SPM is currently transferred to the intense positron source NEPOMUC. The SPM Interface connects the SPM to the NEPOMUC source and enhances the beam quality to the needs of the SPM. In this contribution we will give an overview of the SPM Interface and its performance. The finale stage of the SPM Interface is the positron elevator which has been further developed. We will discuss the apparatus in detail and show measurements of the beam quality with a beam elevation of 8 keV. From our measurements we are able to predict the performance of the SPM at NEPOMUC. In the future position resolved measurements will be possible with an improved spatial resolution of about 0.3 μm and an event rate of about 3.7 kHz.