Free electron gas under high pressure

We have carried out Compton scattering studies on metallic sodium under var ious pressures up to 42 kbar utilizing high-energy x rays from a third gene ration synchrotron source. The high pressure was applied using a large volu me cell with a boron gasket. The induced change of free electron density (D elta V/V = 27%) is clearly detectable in the measured Compton profiles. The observed pressure effects are due to the change of the Fermi momentum, ele ctron-ion, and electron-electron correlations as the average distance betwe en electrons is reduced. The observed differences in the Compton profiles a re well explained by a RPA calculation.