Ne K x-ray and Auger-electron production cross sections have been measured in 50-MeV Cl + Ne collisions for incident charge states of 5+ to 15+ . The ionization cross section and mean fluorescence yield were derived from the data. A factor 20 rise in the xray cross section over the charge-state range studied is primarily due to a factor 7.2 increase in the mean fluorescence yield. The factor 2.8 rise in the ionization cross section can be explained by a decreased screening of the projectile nuclear charge.Macdonald et al} and Mowat et al. 2 * 3 have recently reported that x-ray production cross sections in heavy-ion collisions at a fixed energy increase rapidly with the projectile charge state: In 80-MeV Ar +Ne and 50-MeV Cl + Ne collisions the x-ray cross sections rise exponentially with the incident charge state above 6+. This important discovery clearly showed the need for more detailed studies of the ionization mechanisms in heavy-ion collisions, and placed severe limitations on the interpretation of solid-target x-ray studies since they measure only the effects of an equilibrium charge-state distribution. Related studies of multiple ionization in Ne have recently been reported by Kauffman et al., 4 Burch et al., 5 and Brown et al. 6 A test of any ionization theory, however, requires a measurement of the total ionization cross section cr=cr x +a A ("x" for x ray, "A" for Auger) or equivalently, of the mean 7 fluorescence yield u)=cr x /(j m The exponential rise observed in a x can be the result of a change in cr and/or cu. An increase in a would require a modification of direct inner-shell ionization models, which to first order are independent of the charge state, or the inclusion of additional mechanisms such as electron capture. An increase in a>, on the other hand, could be due to a charge-state dependence of the outer-shell cross sections alone since cu is a strong function of the number of electrons available to fill the inner vacancy.To test this we have measured , for the Ne K shell in 50-MeV Cl + Ne collisions at incident charge states of 5+ to 15+. Partial results of this work are summarized as follows: (1) Both a and uJ increase with increasing charge state. From 5+ to 15+, a increases by a factor of 2.8 and w increases by a factor of 7.2 showing that the factor 20 (2.8x7.2) rise in a x is primarily due to the rise in . The relative importance of the fluorescence yield change observed here is the opposite of that deduced previously 6 from a semiempirical analysis, based on theoretical fluorescence yields, of the charge-state dependence of the Ne x-ray spectrum. We emphasize, however, that there is no discrepancy between the present measurements and the x-ray data of Brown et al. 6 ; the two experimental results are consistent with regard to the fraction of x-ray transitions which must originate from states having co = 1. (2) Very large L x-ray emission cross sections from the