Analysis on components of characteristic X-ray yield of pure thick targets by positron impact near threshold energy

Abstract

In the process of low-energy positron impact with pure thick target, the atomic inner-shell ionization is induced by not only the incident positrons whose energy is completely deposited in the target but also the other particles produced during positron-target collision, namely, the backscattered positrons that deposited part of their energy before escaping the target, the annihilation photons and the secondary electrons. In this paper, the W-M characteristic X-ray yields of two pure thick targets with different diameters impacted by a positron accelerated by the negative high voltage to 5–9 keV have been measured. The contributions from annihilation photons, secondary electrons, backscattered positrons, and the non-uniform electromagnetic field in the target chamber to the characteristic X-ray yields have been evaluated by the realistic Monte Carlo simulation. Besides, Nagashima et al. (Phys. Rev. Lett., 92 (2004) 223201) neglected the contribution from annihilation photons, secondary electrons and backscattered positrons to the yields when calculating the cross-section by the characteristic X-ray yields of thick target impacted by a positron. Here we also caculated the contribution share of the above particles to the Cu-K and the Ag-L characteristic X-ray yields of pure thick target impact by positrons below 30 keV. The results show that the contributions from the above components are non-negligible. Hence, it is necessary to modify the experimental yields for obtaining the accurate yields of pure thick targets by non-backscattered positron impact.