DETERMINATION OF THE V4-CENTER STRUCTURE IN KBr CRYSTAL BY MEANS OF DOUBLE ALIGNMENT CHANNELING TECHNIQUE

— The position of interstitial atoms involved in the Wcenter in KBr crystal has been determined with the double alignment channeling technique. An optical absorption measurement of KBr crystal irradiated with protons or heliums at liquid nitrogen temperature assured that the V4-center is the predominant radiation-induced interstitial defect. A well collimated beam of 1.25 Me V He ions was incident parallel to the [110] direction of KBr crystals. Angular dependence of the yield of the backscattered helium ions in the (100) plane around the [100] direction and the [110] direction was measured at liquid nitrogen temperature and found to have a broad peak at the center and a double peak, respectively. The Monte Carlo method was employed to calculate the angular dependence of the backscattering yield for several interstitial positions in the double alignment channeling. Comparison between the experimental and calculated results indicates that an interstitial Br atom of the VVcenter occupies a position near the body center. From the optical and channeling experiments, it was concluded that the VVcenter is a neutral halogen molecule, each atom of which is located at the position described above.