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

本课题的目的是通过探测正电子湮灭引起的特征x射线来测量正电子与内壳电子湮灭的截面。有两种困难：(1)正电子与内层电子的湮灭速率极低。（二）目标中正电子湮灭发出的γ射线将其部分能量沉积在x射线探测器晶体中，并在x射线光谱中产生背景。为了成功地测量截面，必须抑制背景和检测正电子湮灭引起的特征x射线。如果使用具有薄硅（锂）晶体的x射线探测器，则可以抑制背景。在本项目中，研制了这种探测器，并将其用于测量截面。然而，在这个项目的期限内，横截面还没有被测量。这个项目将继续进行。在该项目中，利用新型探测器成功地探测到了正电子撞击的特征x射线。利用该探测器还成功地测量了正电子撞击的内壳电离截面。结果已提交给期刊并被接受。

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.