Electric Excitation of Certain Medium-Weight Nuclei by Protons

Electric excitation has been used to study energy levels in sixteen elements ranging from scandium to iodine. Seventeen $\gamma$ rays have been observed. Electric quadrupole transition probabilities for the energy levels corresponding to these $\gamma$ rays have been calculated from the measured electric-excitation cross sections. The results are substantially larger than those expected from transitions of single particles but are significantly and uniformly lower than those calculated from the energies of the levels by using the hypothesis of rotational excitation. Similar observations have been made previously for a series of heavy nuclei. It is suggested that this effect results from either a nonuniform distribution of charge and mass in the nucleus or from a breakdown of the assumption that the collective motion can be represented as an irrotational flow.