QUADRUPOLE AND OCTUPOLE COLLECTIVITY IN ND-148

The role of quadrupole and octupole collectivity in the shape-transiti onal nucleus Nd-148 has been studied by Coulomb excitation using beams of Ni-58 and Mo-92, and a beam of Nd-148 (using a Pb-208 target). The extracted E1, E2 and E3 matrix elements involving states up to 12(+) in the ground band and 13(-) in the negative-parity band are presented , and compared to calculations that assume a vibrational and rotationa l octupole nature for the negative-parity band. The positive-parity gr ound-band states are well described in terms of a prolate deformed sha pe with Q(20) approximate to 400 e fm(2) (beta(2)(rms) approximate to +0.18). The present results suggest a vibrational octupole nature for the low-spin negative-parity states, with an intrinsic moment Q(30) ap proximate to 1500 e fm(3) (beta(3)(rms) approximate to 0.12). The E2 a nd E3 matrix elements connecting these bands to the beta- and gamma-vi brational bands (and within these bands) are also presented, and compa red to calculations incorporating the coupling between the rotational and vibrational modes. These calculations describe reasonably well the E2 matrix elements involving the gamma band, but do not reproduce the measured E2 matrix elements for the beta band, implying a complicated intrinsic structure for the beta band, The strong enhancement of the measured E3 matrix elements connecting the negative-parity band to the beta band could be indicative of a significant component of the two-p honon octupole vibration in the wavefunction of the so-called beta ban d. (C) 1997 Elsevier Science B.V.