On the reliability of various enhancement theories for a description of   electron-positron densities in metals
  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. 
H. Sormann, G. Kontrym-Sznajd, R.N. West