Helium implantation in metals investigated by monoenergetic positrons

Abstract

Helium-implanted metals and alloys were investigated with a positron beam system capable of producing positrons with energies ranging between 150 eV and 28 keV. Such a system is superior to the classical positron annihilation methods using high energy positrons from radioactive sources, since, for the first time, near-surface defects and defect agglomerates at high concentrations can be studied. Results are reported on crystalline nickel and amorphous nickel alloys irradiated at room temperature with helium up to doses of 1.8 × 10¹⁸ cm⁻² at different energies. The Doppler broadening technique of the annihilation radiation is applied, and the lineshape parameter I_c is used to characterize the various defect configurations. In some favourable cases information about defect concentrations could be obtained.