Charge dependent energy loss of 60 MeV Ni-58(q+) 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 me asurements show energy loss phenomena at argon gas thicknesses where the ch arge state distribution is not in equilibrium. For the charge state q = 8the stopping power at small target thickness deviates significantly from th e value at larger gas thickness. The stopping power of q = 18+ is almost th e same as for q = 14+ but energy loss shows a step at about 2 mu g/cm(2). T he 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 targ et thickness and a selection of impact parameter in collisions between proj ectiles and gas atoms. (C) 1998 Elsevier Science B.V. All rights reserved.