Charge dependent energy loss of 60 MeV 58Niq+ ions in argon gas

Energy loss and charge fractions of 60 MeV Ni-58(q+) ions in argon gas (0.1-16 mu g/cm(2)) have been measured by means of a Q3D magnetic spectrograph in dependence of the incident and analysed charge state of the ions. The measurements show energy loss phenomena at argon gas thicknesses where the charge state distribution is not in equilibrium. For the charge state q = 8+ the stopping power at small target thickness deviates significantly from the value at larger gas thickness. The stopping power of q = 18+ is almost the same as for q = 14+ but energy loss shows a step at about 2 mu g/cm(2). The deviation of the stopping power at small gas thickness is a combination of two effects. The evolution of the ion's mean charge with increasing target thickness and a selection of impact parameter in collisions between projectiles and gas atoms. (C) 1998 Elsevier Science B.V. All rights reserved.