Collective states in 129La

Abstract Low-spin states of the odd-proton nucleus 129 La have been investigated by means of in-beam γ-ray spectroscopy. Many new low-lying levels have been established. Of special interest are three new negative-parity bands which are identified as the unfavored yrast- and the favored and unfavored yrare-bands based on a π h 11 2 quasiparticle configuration. The negative-parity states are discussed within the framework of the rigid triaxial rotor plus particle model (RTRP) considering excitation energies, branching and multipole mixing ratios. We are able to establish a value of γ ≈ 16° for the triaxial deformation parameter for 129 La.