Effect of rotation on the isovector giant dipole resonance in certain calcium isotopes

The isovector giant dipole resonances in certain rapidly rotating calcium isotopes wherein the bulk of the angular momentum is of an aligned nature are analyzed microscopically in the framework of the random phase approximation. The shape and deformation of the above nuclei at high spins are determined by the Mottelson-Nilsson method for rotating light nuclei. The allowed angular velocities for these deformations are obtained by the Fermi liquid drop model. The splitting of the resonance energies and the changes in the photoabsorption cross sections caused by rotation are studied in these nuclei by a simple schematic model of a rotating anisotropic harmonic oscillator which is justifiable in the case of the light nuclei considered. The results obtained show the general broadening of resonance widths in these light nuclei similar to that observed in the case of rare earth nuclei. The narrowing down of resonance widths in certain cases at higher angular momenta, suspected in lighter nuclei experimentally, is also theoretically observed and explained in the case of ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ as due to the shrinking effect of nuclear deformation at high spins.