Die Vernichtung von Positronen im Fluge

Abstract

The differential cross section at 0° for annihilation in flight of positrons has been measured with foils of lucite, Al, Cu, Ag, Sn, Au, and Pb. Positrons from Cu⁶⁴ and Co⁵⁶ with energies of 400, 600, 800, and 1000 keV were selected by means of a magnetic spectrometer of the Kofoed-Hansen type, and the annihilation was detected in a telescope consisting of three scintillation counters. The experimental results were compared with theoretical values computed from the two-quantum cross section by taking into account the effect of multiple scattering of the positrons. The agreement is good for light elements within a statistical accuracy of 10%. For heavy elements the experimental value was found to be 15% greater than the theoretical value which perhaps could be attributed to the one-quantum annihilation.