Z. Physik A 288, 373-381 (1978) Zeitschrift for Physik A (~: by Springer-Verlag 1978 Particle-Rotor Model for Doubly Odd Transitional Nuclei of the TI-Region A.J. Kreiner* Fachbereich Physik der Technischen Universit~it Miinchen, Garching, Fed. Rep. Germany Received October 26, 1977, Revised Version July 31, 1978 A model has been investigated describing a situation in which two noninteracting high-j Nilsson-BCS quasiparticles move in the deformed field of an axially and reflection symmetric rotor. According to the positions of the j-shells with respect to the proton and neutron Fermi surfaces structures of different character emerge referred to as semi- and doubly-decoupled. In particular, strongly Coriolis-distorted bands recently reported in doubly odd T1 nuclei are discussed. Also ~h9/2 bands in neighbouring odd mass TI isotopes are analysed on the same footing. It is shown that the pronounced odd even staggering of the transition energies can be understood as a specific quantal feature associated with the Coriolis interaction. 1. Introduction Several rotational bands based on high-j unique- parity quasiparticle (qp) states (ff h9/2, ~ h 11/2, ~ ix 3/2) have been reported in recent years in odd nuclei of the transitional region below the double shell closure at 2~ [1-7]. Hence, it is plausible to expect high spin structures, in the doubly odd nuclei built on intrinsic states just resulting from the vector addition of these qp excitations if the residual proton-neutron interaction does not obscures such a simple pic- ture. Thus, one may envisage two different cases in this part of the nuclidic chart. These two are 7~h9/z@Vi13/2 and "~hlt/2@~i13/2. The first one ac- tually appears to be realized in T1 [8, 9]. The second one is expected in more proton defficient nuclei like the Au isotopes where the 7zh11/2 qp state is known to come nearer to the Fermi surface [8, 10]. The main aim of the present work is to show that, indeed, the simple picture referred to above is able to provide an explanation for all especial features found in the experiments. * Present address: Departamento de Fisica, CNEA, Libertador 8250, Buenos Aires, Argentina 2. The Model A brief account of the model will be given first (further details may be found in [8]). The Hamil- tonian is: H=AR2 +hP +h~ o (A=h2/(20)). (1) R denotes the collective rotational angular momen- tum, only this degree of freedom is treated for the core. h~~") is the Hamiltonian for the odd valence proton (neutron) describing the motion in the intrin- sic coordinate system. It comprises a one-body op- erator for the average deformed field (a Nilsson Hamiltonian) and a two-body term which accounts for the pairing correlations treated in the BCS ap- proximation. Since we are going to work in the strong coupling basic the usual substitution is made: R=I-J (J=jp+j,). (2) Thus, the rotational angular momentum becomes: R2=I2_IZ_2I• .• .• -• +j. +2j. -jp. (3) The superscript _1_ denotes those parts of the vectors 0340-2193/78/0288/0373/$01.80