A schematic calculation is given for the splitting of the $E1\mathrm{}$ giant resonance into (two) component peaks, taking into account the large collective energy shift. The observed intensity ratio of about 1:2 between the main peaks of ${\mathrm{O}}^{16}$ is calculated for the first time by assuming the quadrupole-quadrupole component of effective two-body forces in the nucleus to be enhanced by almost a factor 2 over the value given by a local potential of Yukawa shape. Similar calculations show this assumption to be compatible with the additional salient features of ${\mathrm{C}}^{12}$ and ${\mathrm{C}}^{13}$ photodisintegration, such as the "pygmy" resonance. These three nuclei are then simply generalized to serve as typical examples of the closed shell, closed shell minus a few particles, and closed shell plus a few particles. Detailed consideration of highly deformed nuclei by this method looks prohibitively laborious in detail but should generally yield the hydrodynamic intensity ratio of 1:2. The approach emphasizes that the peak splitting for such nuclei is a function of the $E1\mathrm{}$ excited state rather than of the ground state.

• Received 4 August 1961

DOI:https://doi.org/10.1103/PhysRev.129.808