Positron annihilation in flight: experiment with slow and fast positrons

13th International Workshop on Slow Positron Beam Techniques and Applications

Cízek, J.^1 ; Vlek, M.^1 ; Lukác, F.^1 ; Melikhova, O.^1 ; Procházka, I.^1 ; Anwand, W.^2 ; Wagner, A.^2 ; Butterling, M.^2,3 ; Krause-Rehberg, R.^3

Charles University in Prague, Faculty of Mathematics and Physics, V Holeovikách 2, 180 00 Praha 8, Czech Republic^1

Institut für Strahlenphysik, Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, D-01328 Dresden, Germany^2

Martin-Luther University, Department of Physics, 06099 Halle, Germany^3

关键词: Coincidence doppler broadening;    Gamma-ray energy;    Hyperbolic curves;    Low background;    Monoenergetic;    Positron annihilation in flights;    Positron energy;    Slow positron beam;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/505/1/012043/pdf
DOI  :  10.1088/1742-6596/505/1/012043

来源: IOP

【 摘 要 】

A novel digital coincidence Doppler broadening (D-CDB) spectrometer was employed for energy resolved investigations of two-quantum annihilation-in- flight (TQAF). The TQAF phenomenon was studied using monoenergetic positrons produced in a slow positron beam and also using fast positrons. Because of a low background the measurements on the slow positron beam could be performed in a close geometry and the TQAF contribution in the two-dimensional gamma ray energy spectra fills a 'bowl-like' area delimited by a hyperbolic curve and a kinematical cut-off determined by the kinetic energy of positrons. With decreasing positron energy the area of TQAF contribution becomes smaller and disappears completely for slow positrons with energies below ∼ 100 eV. The measurements with fast positrons were restricted to a limited range of angles between the annihilation gamma rays and the TQAF events contribute to a hyperbolic band in gamma ray energy spectrum.