  The model, introduced in a previous paper, for the description of the
octupole and quadrupole degrees of freedom in conditions close to the axial
symmetry, is used to describe the negative-parity band based on the first
octupole vibrational state in nuclei close to the critical point of the U(5) to
SU(3) phase transition. The situation of 150Nd and 152Sm is discussed in
detail. The positive parity levels of these nuclei, and also the in-band E2
transitions, are reasonably accounted for by the X(5) model. With simple
assumptions on the nature of the octupole vibrations, it is possible to
describe, with comparable accuracy, also the negative parity sector, without
changing the description of the positive-parity part.
