SYSTEMATICS AND SCALING OF DIFFERENTIAL IONIZATION CROSS-SECTIONS IN MULTICHARGED ION-ATOM COLLISIONS

Absolute doubly differential cross sections for electron emission are presented for 0.5-MeV/u multicharged ion-atom collisions. The collision systems investigated are B-q+, C-q+ (q = 2-5) and O-q+, F-q+ (q = 3-6) projectiles impacting on helium and C-q+ (q = 2-5) ions impacting on neon and argon targets. Laboratory electron emission angles between 10 degrees and 60 degrees were studied. Under the assumption that the cross sections scale with the square of an effective projectile charge, Z(eff)(epsilon,theta), the scaling was investigated as a function of emitted electron velocity and angle. For distant collisions (low-energy electron emission), we find that Z(eff)(epsilon,theta)>q for small q. For the highest values of q investigated, Z(eff)(epsilon,theta) was found to be smaller than the net projectile charge q. The effective projectile charges may be subject to a systematic underestimation since they were determined by referencing the partially stripped ion impact data to fully stripped boron, rather than proton, impact cross sections. In the binary-encounter region, the present data confirm previously observed features-namely that the emission increases as q decreases. For the helium target, the qualitative behavior is roughly in accordance with predictions by Schulz and Olson [J. Phys. B 24, 3409 (1991)]. Neon and argon targets also demonstrate these features, but less dramatically than helium.