Direct observation of energy loss of charge-frozen hydrogen-like Ar ions

We measured the energy loss of charge-frozen clothed ions (i.e., partially stripped ions which maintain their charge states throughout the passage) in a Si solid employing a totally depleted silicon detector with 4.1 mu m thi ckness as a target, to measure the energy deposition of 390 MeV/u Ar17+ dir ectly. Under the present conditions, the probability of the electron loss i s not so large, and that of the electron capture is negligibly small. Accor dingly, the energy loss of charge-frozen Ar17+ ions in a rather thick targe t can be measured. Charge states of ions transmitted through the target wer e observed by a 2D-position sensitive detector in coincidence with the ener gy deposition. We have obtained an effective charge of Ar17+ ions for the s topping power, as Z(eff) = 17.36 (+/-0.03).