Experimental study of flux peaking for channeled ions usingO18in Ti

An experimental study has been made of the flux-peaking effect for channeled ions in ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$-implanted Ti single crystals. Using 730-keV protons, as well as ${\mathrm{H}}_2^{+}$ and ${\mathrm{H}}_3^{+}$ ions of the same velocity, the angular dependence of the ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ $(p, \alpha ){}_{}{}^{15}{}_{}{}^{}\mathrm{N}$ reaction yield has been measured in scans across the [0001] and $〈11\overline{2}0〉$ axes and the (0001) plane. It is found that the implanted O occupies the same octahedral interstitial sites in Ti as in diffused samples. The dependence of the flux peak in the ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ yield on various factors has been investigated. While the magnitude of the peak is extremely sensitive to any factors which increase the transverse energy of the best-channeled ions, the width is relatively insensitive. For both the [0001] and $〈11\overline{2}0〉$ axes, the transition from axial to planar flux peaking has been examined. The magnitude of the flux peak for the (0001) plane is found to be greater than that for the $〈11\overline{2}0〉$ axis intersected by the plane. This is opposite to the behavior predicted by theoretical calculations, using both an analytical model and computer simulation, for channeling in Cu. Possible explanations for the discrepancy are discussed.