Theory and measurement of absolute doubly differential cross sections of binary encounter electron ejection in collisions of swift heavy ions with solids

Measurements of the momentum distribution of high-energy electrons emitted in weakly relativistic ion-solid collisions are compared with a transport t heory which is based on the relativistic electron impact approximation for electron production and which accounts for angular deflection and energy lo ss but also energy straggling of the transmitted electrons. The measurement s on electron ejection by 45 MeV u(-1) Ni28+ projectiles colliding with car bon foils of thickness 10-8300 mug cm(-2) were made on an absolute scale, p roviding a sensitive test of the transport theory. The theory gives a satis factory description of earlier (relative) data from 13.6 MeV u(-1) Ar18+ im pact on carbon. Absolute singly differential cross sections for Ni28+ agree within 10% in the case of thin targets, but the width of the binary encoun ter peak is underestimated by theory. For the thickest targets the measured doubly differential cross sections are overpredicted by up to one order of magnitude, particularly at forward emission angles, but peak shapes are we ll reproduced.