Observation of resonant coherent excitation of highly charged heavy ions

This study is aimed at detecting deexcited photons emitted from resonantly excited ions and obtaining knowledge on the origin of so-called convoy electrons. A self-supported thin single crystal of (110) gold is prepared. Ratios of the low-energy loss ions to the total transmitted ions are measured while changing the crystal orientation. Observation is made of the change in the ratios of 9 + to 9 + plus 10 + charge state fractions for random and aligned incidences. While the ratio for random incidence shows a smooth tendency, that for aligned incidence shows a dip around incident energy of 88 to 89 MeV. This agrees with calculated resonance energy. For convoy electrons, energy spectra of secondary electrons caused by <110> channeling of 1.0- and 1.0-MeV He+ ions are measured. Convoy peaks are clearly seen. Another observation is made on the change in the convoy intensity with incident energy. In this case, however, no distinct change in convoy intensity is found at the resonance energy even if the energy loss of the incident ions in the target crystal is taken into account. This may be due to the fact that the radius of the excited state He+ has an orbital radius of 1.1 A which is larger than the inter string distance of the Au <110> atomic rows and consequently the resonance width may be too large to be observed. (Nogami, K.)