Configuration dependent shapes in the 177 Re nucleus S. K. Chamoli, 1 P. Joshi, 1,2 A. Kumar, 1 R. P. Singh, 2 S. Muralithar, 2 R. K. Bhowmik, 2 Z. Naik, 3 C. R. Praharaj, 3 and I. M. Govil 1 1 Department of Physics, Panjab University, Chandigarh 160 014, India 2 Nuclear Science Centre, Post Box No. 10502, New Delhi 110 067, India 3 Institute of Physics, Bhubneshwar 751 005, India ~Received 6 January 2002; published 5 August 2002! The transition quadrupole moments for the proton h 9/2 @ 541# 1/2 2 , d 5/2 @ 402# 5/2 1 , and h 11/2 @ 514# 9/2 2 bands are measured in 177 Re using the recoil distance measurement technique. The high spin states in 177 Re were populated using the fusion evaporation reaction 165 Ho ( 16 O,4 n ) 177 Re at an energy of 84 MeV. The deformation for the h 9/2 band is found to be larger ( ;0.25) than the deformation for the d 5/2 ( ;0.20) and h 11/2 ( ;0.22) bands. The experimental transition probabilities for these bands are compared with those from projected Hartree-Fock microscopic calculations. For the h 9/2 ground state band the results are also compared with total Routhian surfaces calculations within the cranked Hartree-Fock-Bogoliubov framework. The experimental results are found to be in agreement with the theoretical predictions. DOI: 10.1103/PhysRevC.66.024307 PACS number~s!: 21.10.Tg, 21.10.Ky, 27.70.1q I. INTRODUCTION The odd Z nuclei below the spherical Z 582 closed shell gap provide an unique opportunity to study the properties of the single particle orbits that have different shape-driving effects in the g -soft nuclei @1,2#. In this mass region the Fermi surface is highly sloped for valence proton orbitals and therefore the general features of the rotational bands re- main unchanged. For neutron deficient Re nuclei, there have been predictions of the co-existence between different pro- late configurations such as due to the b stretching at low to moderate spins, accompanied by the shape transition in the yrast band at higher spins @3–6#. The level scheme for Re nuclei in this mass region is characterized by rotational bands based on different quasiparticle excitations. These consist of a highly decoupled band associated with the h 9/2 @ 541# 1/2 2 state, a highly coupled band built on h 11/2 @ 514# 9/2 2 , and a more normal d 5/2 @ 402# 5/2 1 band. Out of these configuration the low-K (1/2 2 ) h 9/2 intruder orbital is highly downsloping as a function of the deformation in the Nilsson plot and hence occupation of this orbital has the effect of increasing the deformation of the nucleus to higher values. On the contrary, the high-K (9/2 2 ) h 11/2 and (5/2 1 ) d 5/2 bands have positive slope as a function of deformation and therefore have a tendency for smaller b 2 values or soft g deformations. As the deformation affects the energy of the entire band, the band crossing frequencies corresponding to the alignment of the i 13/2 neutron pair may shift to higher values. This delay in the band crossing frequency for the h 9/2 band is reported for some other nuclei also in this mass re- gion @7–11#. On the contrary in high-K orbitals like h 11/2 @ 514# 9/2 2 and d 5/2 @ 402# 5/2 1 configurations, a gradual alignment gain is observed which is attributed due to b stretching @3–6#. Thus the n i 13/2 crossing for high-K orbitals is shifted to lower rotational frequencies relative to the cross- ing frequency for the p h 9/2 ( K 51/2 2 ) configuration @12#. This shift of n i 13/2 crossing frequency to lower values in high-K p h 11/2 and p d 5/2 bands, according to cranked shell model ~CSM! calculations, may be due to the small b 2 and negative g driving effects of these two configurations @13# or it may also be attributed due to the high interaction strength between the one- and three-quasiparticle bands in these con- figurations. So the shift of the band crossing frequency due to the alignment of a pair of i 13/2 neutrons for different qua- siproton configurations is a sensitive test of the single- quasiparticle basis of the nuclear shape. Particularly it is a useful probe for nuclei having neutron numbers around mid- shell as for these nuclei the neutron Fermi level is suffi- ciently away from the highly alignable low-V , high- j ( i 13/2 ) neutron configuration. For the 177 Re nucleus, the neutron number ~102! is near the midshell gap ~104!, so it is inter- esting to see the effect of the relative location of the qua- siproton orbitals with respect to the Fermi level on the shift of neutron band crossing frequency. The lifetime measure- ments of the high-spin states in this nucleus are done using the recoil distance Doppler shift technique ~RDM!@14# to understand the most plausible reason for the delay in the band crossing frequency in p h 9/2 band and the reduction of the same in p h 11/2 and p d 5/2 bands. The measured transition rates may provide important information about the configu- ration dependent shapes of the 177 Re nucleus. The experi- mental results are compared with the predictions of the cranked Hartree-Fock-Bogoliubov ~CHFB! model and with the microscopic HF model with angular momentum projec- tion. II. EXPERIMENTAL DETAILS The high-spin states of the 177 Re nucleus were populated using the fusion evaporation reaction 165 Ho ( 16 O,4 n ) 177 Re at a beam energy of 84 MeV provided by the 15 UD Pel- letron accelerator at Nuclear Science Center ~NSC!, New Delhi. This incident beam energy imparted the recoil velocity v / c .0.009 of the compound nucleus in the forward direc- tion. The target was a self-supporting stretched foil of 165 Ho of 780 m g/cm 2 thickness, while the stopper was made of a self-supporting stretched gold foil of 8 mg/cm 2 , sufficient to PHYSICAL REVIEW C 66, 024307 ~2002! 0556-2813/2002/66~2!/024307~8!/$20.00 ©2002 The American Physical Society 66 024307-1