  Four theoretical approaches to calculate momentum densities of
electron-positron annihilation pairs (MDAP) in crystalline solids are
confronted with 3D densities reconstructed from two-dimensional angular
correlation (2D-ACAR) data for copper, chromium, and yttrium. It is shown that
the Bloch-modified ladder theory, in contrast to other approaches, is able to
describe - at least qualitatively - the MDAP profiles for all metals
investigated.
