Ultrasonic Electron-Nuclear Double Resonance of CaF2:U4+

We report the first ultrasonic, electron-paramagnetic-nuclear double-resonance experiment. This experiment was performed on Ca${\mathrm{F}}_2$:${\mathrm{U}}^{4+}$, and the results indicate that the ultrasonic-paramagnetic-resonance absorption line is inhomogeneously broadened due to superhyperfine interaction. These results are compared with a theoretical model for superhyperfine interaction in Ca${\mathrm{F}}_2$:${\mathrm{U}}^{4+}$.