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 theory which is based on the relativistic electron impact approximation for electron production and which accounts for angular deflection and energy loss but also energy straggling of the transmitted electrons. The measurements on electron ejection by 45 MeV u-1 Ni28+ projectiles colliding with carbon foils of thickness 10-8300 µg cm-2 were made on an absolute scale, providing a sensitive test of the transport theory. The theory gives a satisfactory description of earlier (relative) data from 13.6 MeV u-1 Ar18+ impact on carbon. Absolute singly differential cross sections for Ni28+ agree within 10% in the case of thin targets, but the width of the binary encounter 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 well reproduced.