Resonant Scattering of Gamma Rays from Nuclear Levels with a Linear Accelerator

Several elements have been irradiated with a high-intensity bremsstrahlung beam and a search has been made for $\gamma$ rays scattered from nuclear levels. A 6-in.×5-in.-diameter NaI(Tl) crystal was used as the detector. Resonant scattering was seen from ${\mathrm{Li}}^6$, ${\mathrm{B}}^{11}$, ${\mathrm{C}}^{12}$, ${\mathrm{O}}^{16}$, Mg, and Si. Pulse-height spectra for $\gamma$ rays scattered from each of these are shown. Application of these spectra to previous experiments in which level widths and branching ratios were calculated is discussed. Levels in ${\mathrm{B}}^{11}$, ${\mathrm{C}}^{12}$, and ${\mathrm{O}}^{16}$ were observed which have not been seen with this technique previously.