Fermi surface of yttrium
  Electron-positron momentum densities in Y, reconstructed from two-dimensional angular correlation of annihilation radiation spectra, are compared with the theoretical predictions of fully-relativistic augmented plane-wave calculations. Knowledge of the theoretical densities and of the effects on them of certain symmetry selection rules has allowed us to separate two hole Fermi sur-faces in the third and fourth bands and to establish some Fermi momenta for each of them. 
G. Kontrym-Sznajd, H. Sormann and R.N. West