The effect of the detector resolution on the Doppler broadening measurements of both valence and core electron-positron annihilation

The measured value of the Doppler profile of the electron-positron annihila tion radiation depends on the resolution function of the detectors used in the experiment. This is illustrated by the results of calculations of the p rofile convoluted with resolution functions of different FWHM. These result s are compared with Doppler broadening measurements for Al. The calculated results agree qualitatively with the experimental data. The positions of th e peaks in the curves which give the ratio of a Doppler profile to a refere nce profile are found to shift towards higher momenta when the width of the resolution for the reference material was increased. Since the peaks in th e ratio curves are used for identifying the chemical species, it is importa nt that the peak positions be unambiguously characterized. Hence, the detec tor resolution should be carefully measured and quoted when reporting and c omparing results of Doppler profiles. (C) 1999 Elsevier Science B.V. All ri ghts reserved.