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 collisio n 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 o n 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-ener gy 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 p rojectile 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 sectio ns. In the binary-encounter region, the present data confirm previousl y observed features-namely that the emission increases as q decreases. For the helium target, the qualitative behavior is roughly in accorda nce with predictions by Schulz and Olson [J. Phys. B 24, 3409 (1991)]. Neon and argon targets also demonstrate these features, but less dram atically than helium.