  The 2-dimensional angular correlations of the positron annihilation radiation
(2D-ACAR) on a single crystal of LaB6 was measured for three projections. The
2D-ACAR spectra were subjected to the Van Citter-Gerhard deconvolution
alghorithm. From the experimental spectra we produced the 3D k-space density
rho(k) via three different methods: i) we reconstructed the 3D
electron-positron momentum density rho(p) via the Cormack method. rho(k) was
then obtained by applying the 3D LCW transformation to rho(p). ii) The same
steps of point i) were repeated adopting a modified Fourier-transform-based
algorithm. iii) The 3d k-space occupancy rho(k) was obtained directly by
parameterising the Fermi surface volume with prolate ellipsoids whose axes were
determined by a least-square fit to the 2D LCW transformations applied to two
high symmetry projections. The ellipsoids diameters along high symmetry
directions of the cubic Brillouin zone (BZ), as a fraction of the BZ size, were
0.64 (dir. X-M) and 0.82 (dir. Gamma-X). The resulting Fermi volume, as a
fraction of the BZ volume, was 0.55. These results agree within 1% with those
obtained via the de Haas van Alphen experiments.
