Angular distribution of positron annihilation radiation in vanadium and niobium

The angular correlation curves due to the two photon positron annihilation process in vanadium and niobium are calculated by APW method. The agreement between theory and experiment is found to be excellent, and especially, the substantial anisotropy is well reproduced by the calculation, although the experimental values are a little higher than the theoretical ones in the region of small momentum. It is concluded that the electronic distribution in these transition metals is well explained by an independent-particle model of APW method when a proper effective one-electron potential is adopted. It is also concluded that positron probes do not seem to perturb the system much. Therefore, the experimental results of the positron annihilation are useful in providing information about electronic structures in transition metals. (auth.)