SHAPE TRANSITION AND COLLECTIVE EXCITATIONS IN NEUTRON– RICH 170-178 Yb NUCLEI F. I. SHARRAD 1,β , HEWA Y. ABDULLAH γ,4 , N. AL-DAHAN β , A. A. MOHAMMED-ALI β , A. A. OKHUNOV 1 , H. ABU KASSIM 1 1 Department of Physics, Faculty of Science, University of Malaya, Kuala Lumpur, Malaysia E-mail: fadhilsharrad@um.edu.my β Department of Physics, College of Science, University of Kerbala, Karbala, Iraq E-mail: fadhilaltaie@uokerbala.edu.iq γ Department of Physics, Universiti Teknologi Malaysia, 81γ10 Skudai, Johor, Malaysia 4 Department of Physics, College of Science Education, Salahaddin University, Erbil, Iraq Received March 7, 2012 Energy levels, B(Eβ) values and potential energy surface for even-even 170-178 Yb isotopes have been calculated using the IBM-1. The predicted energy levels, B(Eβ) values and intrinsic quadrupole moments Q 0 results were reasonably consistent with the experimental data. The contour plot of the potential energy surfaces shows all interest nuclei were deformed and have rotational characters. Key words: IBM-1, neutron-rich, B(Eβ) values, energy levels, potential energy surface. 1. INTRODUCTION The quadrupole collectivity in atomic nucleus exhibits distinct regularities, where the nuclear shape can be spherical, deformed and the situation in between. Like other models and theories [1, β], the Interacting Boson Model [γ] has been successful in reproducing the nuclear collective levels in terms of s and d bosons, which are essentially the collective s and d pairs of valence nucleons [4], respectively. The IBM Hamiltonian has the so-called dynamical symmetry, and the shape of quadrupole deformation can be classified as a spherical vibrator (U(5)), axially symmetric deformation (SU(γ)), and γ−unstable deformation (O(6)), if the interaction strengths of the IBM Hamiltonian taken specific values. The medium-to heavy-mass Ytterbium (Yb) isotopes are located in the rear-earth mass region, most of these nuclei were well-deformed and it can be populated to very high spin. Much experimental information on even- odd- mass Yb isotopes has become more abundant [5-10]. For the heavier A=174 to 178 nuclei [11], previous work using deep inelastic reactions and Gammasphere have begun to reveal much information about the high-spin behavior of these neutron-rich Yb isotopes. The yrast states in Rom. Journ. Phys., Vol. 57, Nos. 9–10, P. 1γ46–1γ55, Bucharest, β01β