Precise Radiation Energy and Core Electron Contribution of Positron Annihilation in Al Studied with Two Ge(Li) Detectors

The average energy of positron annihilation radiation from Al has been determined by the Doppler-broadening summing technique with two detectors. Energy differences of annihilation radiation from the electron rest mass are 8.2±3.1 eV and 8.9±3.3 eV for the single and coincidence measurements, respectively. According to the analysis by using the electron binding energy, half of the intensity of the momentum distribution outside the Fermi momentum is due to high-momentum components of the conduction electrons. The contribution of the core electrons to the total annihilation is estimated to be 5∼6%, and the core enhancement factor is 1.2∼1.5. The average energy of annihilation radiation estimated with this contribution is consistent with the above measured values within the experimental accuracy.