Energy-Loss Spectra of Channeled Iodine and Oxygen Ions in Gold

Energy-loss spectra are reported for 15- and 21.6-MeV ¹²⁷I ions and for 10-MeV ¹⁶O ions transmitted through the {111} and {100} planar channels of thin gold crystals. In agreement with earlier observations on 60-MeV ¹²⁷I and 3-MeV ⁴He ions, the stopping power in each case is accurately proportional to the frequency with which the ions oscillate in traversing the channel. From the results of these experiments, it is concluded that the ⁴He and ¹⁶O ions behave in gold planar channels as test charges which sample the electron distribution of the medium. The ¹²⁷I ions behave nearly as test charges, but for them there is some evidence that the screening of the nuclear charge changes with the position of the ion in the channel.