Ion beam-based coincidence Doppler broadening spectroscopy of positron annihilation radiation: The experiences of Tehran Van de Graaff lab

Abstract

Coincidence Doppler Broadening Spectroscopy of positron annihilation radiation is developed using high energy gamma-rays instead of standard positron source for defect assessment in thick samples. A 2.5 MeV proton beam of a Van de Graaff accelerator is used to generate high-energy gamma-ray through 19Fp,αγ16O nuclear reaction. The collimated gamma-ray is used to generate positron inside the sample. The performance of the technique to support the positron annihilation spectroscopy experiment is evaluated by investigation of the defect evolution of five low-carbon steel samples preloaded during the uniaxial tension test. The variation of the S-parameter versus strain is investigated and discussed considering the engineering stress-strain curve of the samples. Moreover, the advantages and limitations of the technique over the conventional CDBS are discussed. The developed spectrometer provides a systematic approach for the defect assessment in thick high-Z elements samples.