Nuclear Okorokov effect of heavy ions with relativistic energy

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Channeling ions have a possibility to be excited in the internal levels by a periodic potential of a crystal. It is called Resonant Coherent Excitation (PCE). The condition of RCE in nuclear levels is satisfied with relativistic heavy ions supplied by HIMAC.A channeling experiment in a relativistic energy region requires a beam with extremely small angular divergence. We have developed a parallel beam, and observed the reductions of the energy deposition and the angular spread of channeling ions under several channeling conditions. channeling ions under several channeling conditions.We have succeeded in observing the atomic RCE from 1s to n=2 states with 390MeV/u Ar^<17+> ions planar channeled in a Si crystal, by measuring the charge state distribution after transmission through the crystal. Under several RCE conditions, the fraction of survived Ar^<17+> ions was observed to decrease drastically. We also measured the energy deposition of channeling ions adopting a totally depleted silicon detector as a target crystal. The energy deposition of the plannar channeling ion is closely related to the trajectory in the crystal, and provides the information of the position dependent crystal field. The resonance profiles are well explained by the L・S interaction and the Stark effect originated in the crystal field.