Possible unified interpretation of low-lying negative parity states in lanthanide and actinide regions

The problem of the origin of low-lying negative parity states in radium and thorium isotopes is addressed via the examination of the systematic behavior of excitation energies of 11- and 31- states in the Z=82-94 region and the comparison of the observed trends to those seen in a systematic study of octupole vibrational states in the Z=56-82 region. These trends are qualitatively analyzed in terms of a simple description of octupole vibrations, and experimental approaches to discriminating among the several theoretical models proposed for the radium-thorium nuclei are suggested. (orig.)