Behaviors of d and f electrons in transition metals studied by positron annihilation

The background of the spectrum of Doppler broadening of positron annihilation radiation can be reduced remarkably by using a two-detector coincidence technique. With this setup, we get a peak to background ratio of about 104 on the high energy side of the peak. The d electron and f electron signal for the transition metals can be extracted from the coincidence Doppler broadening spectrum. The coincidence Doppler broadening spectra for the transition metals Zr, Nb, Mo, Ag, Hf, Pt, Au and single crystal of Si have been measured. The experimental results show that the height of the peak of the ratio curves (the reference sample is Si) for the transition metals Zr, Nb, Mo, Ag increases with the increase in the number of 4d electrons. There are 2 peaks in the ratio curves (the reference sample is Si) for the transition metals Ag, Hf, Pt. And the height of the peaks increases with the increase in atomic number. (authors)