Energy loss of silver ions in gadolinium

The energy loss of silver ions in metallic gadolinium foil at low velocities (2.7--4.3)v0, where v0 is the Bohr velocity, was measured with the Doppler shift technique. The results are about 20% smaller than the predictions of a semiempirical formulation [J. F. Ziegler, J. P. Biersack, and U. L. Littmark, in The Stopping and Ranges of Ions in Solids, edited by J. F. Ziegler (Pergamon, New York, 1985), Vol. 1] for the electronic stopping power