Performance of the new 2D ACAR spectrometer in Munich

TL;DR

This paper presents a new 2D ACAR spectrometer with an optimized source-sample stage that improves positron flux and resolution for studying the electric structure of materials, demonstrated on alpha-quartz.

Contribution

Development and evaluation of a novel source-sample stage with magnetic guidance that enhances positron flux and resolution in 2D ACAR measurements.

Findings

Achieved a spot size of 5.4 mm FWHM with high efficiency.

Demonstrated improved performance in 2D ACAR measurements of alpha-quartz.

Discussed implications for electric structure investigations.

Abstract

Angular Correlation of Annihilation Radiation (ACAR) is a well established technique for the investigation of the electric structure. A major limitation of ACAR studies is the available positron flux at a small spot on the sample. Fore this reason, the focus of this work is put on the discussion of a newly developed source-sample stage which uses an optimized static magnetic field configuration to guide the positrons onto the sample. The achieved spot size is $d_{\mathrm{FWHM}}=5.4\,$mm, with a high efficiency over the whole energy spectrum of the $^{22}$Na positron source. The implications of the performance of the source-sample stage are discussed with regard to 2D-ACAR measurements of single crystalline $\alpha$-quartz, which serves as a model system for the determination of the total resolution.