Investigation of the $\gamma -\alpha$ phase transition in cerium by Compton scattering

The change in Compton profile between pure phase $\gamma$ and $\alpha$ cerium has been measured and compared to electron momentum distributions calculated on the basis of renormalized-free-atom and tight-binding models. It turned out that any kind of promotion of the $4f$ electron into the conduction band is in striking contradiction to the experiment. The main contribution of the measured difference profile is due to the increased conduction-electron density in the collapsed phase.