Measurement of annihilation cross sections for positrons with inner-shell electrons

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The purpose of this project is to measure the cross sections for positron annihilation with inner-shell electrons by detecting the positron annihilation induced characteristic X-rays.There are two kinds of difficulties :(i)The positron annihilation rates with inner-shell electrons are extremely low.(ii)The γ-rays emitted from positron annihilation in the taregets deposit part of their energy in the X-ray detector crystal and produce a background in the X-ray spectra.In order to succeed in measuring the cross sections, the background must be suppressed and the positron annihilation induced characteristic X-rays must be detected.The background can be suppressed if an X-ray detector with a thin Si(Li) crystal is used. In this project, this kind of detector has been developed and employed to measure the cross sections. However, the cross sectiohs have not yet been measured in the term of this project.This project will be continued.In the project, the characteristic X-rays by positron impact have been successfully detected using the new detector.The inner-shell ionization cross sections by positron impact have also been measured successfully using this detector.The results have been submitted to ajoumal and accepted.