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Development of positron annihilation induced X-ray spectroscopy

正电子湮灭诱导X射线光谱学的发展

基本信息

批准号：
12490006
负责人：
HYODO Toshio
金额：
$ 8.19万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-12490006/
关键词：
positron annihilation positron beam positron annihilation induced X-ray characteristic X-ray thin film positron moderator tungsten mesh electro-polish

项目摘要

In conventional Auger-electron spectroscopy and characteristic X-ray spectroscopy, particles with sufficient energy are incident on specimens to remove core electrons by collisional ionization. When positrons with the energy lower than the binding energy of the core electrons are incident on the specimens, core electrons are removed by matter-antimatter annihilation and not by collisional ionization. The Auger-electrons from this process have been detected and used to characterize the elemental content of solid surface. The purpose of this project is to detect the X-rays from this process.A slow positron beam was incident on a specimen and emitted X-rays were detected. The beam was produced using a new positron moderator made with a stack of electro-polished tungsten meshes. The moderation efficiency was measured to be 7.5×10^<-4>. This value is higher than any other transmission moderators except for inert gas solids. This moderator has the advantages over the inert gas solids that the treatment is easier, the cost is lower, and the long term stability is higher.The yield of the X-rays is considerably low because the probability of creation of inner core holes by positron annihilation is small. Therefore, the background must be reduced sufficiently. There are two kinds of background : characteristic X-rays induced by the positron annihilation γ-rays and signals created by Compton scattering in the X-ray detector. Thin specimens are used to reduce the former background. A detector with thin Si (Li) crystal is developed to reduce the latter background. It is also reduced by the measurement under the condition where the γ-rays are not incident on the X-ray detector by coincidence measurements with a scintillation detector of the γ-rays.However, we did not succeeded in detecting the X-rays in the term of the project.

在传统的俄歇电子能谱和特征x射线能谱中，有足够能量的粒子入射到样品上，通过碰撞电离去除核心电子。当能量低于核心电子结合能的正电子入射到样品上时，核心电子通过物质-反物质湮灭而不是通过碰撞电离被去除。该过程产生的俄歇电子已被检测并用于表征固体表面的元素含量。这个项目的目的是检测这个过程中的x射线。一个缓慢的正电子束入射到一个样品上，发射出的x射线被检测到。该光束是由一堆电抛光钨网制成的新型正电子慢化剂产生的。调节效率测量为7.5×10^<-4>。该值高于除惰性气体固体以外的任何其他传输缓和剂。与惰性气体固体相比，该慢化剂具有处理简单、成本低、长期稳定性高等优点。x射线的产率相当低，因为正电子湮灭产生内核空穴的可能性很小。因此，必须对背景进行充分的还原。背景有两种：正电子湮灭γ射线诱发的特征x射线和康普顿散射在x射线探测器中产生的信号。采用薄试样来减小前背景。为了减少后一背景，研制了一种薄硅（锂）晶探测器。在γ射线不入射到x射线探测器上的条件下，通过与γ射线闪烁探测器的重合测量，也降低了它的测量值。然而，在项目期间，我们没有成功地探测到x射线。