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The very neutron-deficient strongly deformed 119Cs nucleus has been studied using the 58Ni(64Zn,3p) reaction and the JUROGAM 3 γ-ray detector array coupled to the MARA recoil-mass separator setup. The excitation energies of all observed bands have been determined, spins and parities have been firmly assigned to most of the observed states. The previously known and the newly identified rotational bands have been extended to very high spin and excitation energy. The configurations of the observed bands are discussed using the particle number conserving cranked shell model. The present study establishes the largest set of rotational bands observed in the proton-rich A≈120 mass region.
Prolate-oblate shape coexistence close to the ground state in the strongly-deformed proton-rich A≈120 nuclei is reported for the first time. One of the four reported bands in 119Cs, built on a 11/2− state at 670 keV, consists of nearly degenerate signature partners, and has properties which unequivocally indicate the strongly-coupled πh11/2[505]11/2− configuration associated with oblate shape. Together with the decoupled πh11/2[541]3/2− band built on the 11/2− prolate state at 110 keV, for which a half-life of T1/2=55(5)μs has been measured, the new bands bring evidence of shape coexistence at low spin in the proton-rich strongly deformed A≈120 nuclei, a phenomenon predicted since long time, but not yet observed. Calculations using the particle-number conserving cranked shell model and two dimensional tilted axis cranking covariant density functional theory support and well reproduce the observed oblate and prolate coexisting low-energy states in 119Cs.
The neutron-deficient 119Ba nucleus has been studied using the 58Ni(64Zn,2pn) reaction and the JUROGAM 3 γ-ray detector array coupled to the MARA recoil-mass separator setup. One new rotational band and several low-lying states are newly identified. A half-life of T1/2=0.36(2)μs has been measured for the 5/2− bandhead of the νh11/2 band. The two previously known rotational bands are confirmed, except for the higher part of the +1/2 signature partner of the positive-parity band. Configurations are assigned based on the analysis of the observed quasiparticle alignments whose nature is unveiled by the calculations using the particle number conserving cranked shell model.
One of the largest sets of collective excitations built on two-quasiparticle configurations in odd-odd nuclei of the proton-rich A≈120 mass region is reported in 118Cs. Several new rotational bands and long-lived isomers have been identified. The 8+ bandhead of the πh11/2⊗νh11/2 band is a short-lived isomer with a half-life in the nanosecond range, while the 7+ state below it is a long-lived isomer with a half-life of T1/2=0.55(6)μs. Two other long-lived isomers have been identified: a 66-keV transition detected at the MARA focal plane depopulates one of them, indicating a half-life in the microsecond range, while no depopulating transitions have been identified for the other, indicating a much longer half-life. Extensive particle number conserving cranked shell model calculations and alignment analysis have been employed to investigate the rich band structure of 118Cs, which exhibits one of the most complete sets of two-quasiparticle configurations in nuclei close to the proton drip line.
Three new negative-parity bands have been identified in 120Ba, two of them forming a strongly coupled band. The previously known negative-parity band is significantly extended to high spin, while the lower part of the yrare positive-parity band has been modified. From the analysis of the band properties and comparison with the neighboring nuclei a coherent description of all bands is achieved. In particular, a simple explanation of the evolution of the positive-parity bands at high spin is proposed, including the possible occupation of the νf7/2[541]1/2− intruder orbital. Cranked Nilsson-Strutinsky calculations reveal similar quadrupole deformations but different triaxiality of the bands, while particle number conserving cranked shell model calculations qualitatively reproduce the experimental data and support the assigned configurations. The new measured ratios of reduced transition probabilities B(E1)/B(E2) complete the systematics in the 118–124Ba nuclei, exhibiting a decrease with decreasing neutron number, and are compared with the known values in the 116–120Xe nuclei, which are larger. Extended calculations with the quadrupole and octupole collective Hamiltonian based on the relativistic Hartree-Bogoliubov model employing the relativistic DD-PC1 density functional nicely reproduce the decreasing trend towards lower neutron numbers for Ba and Xe nuclei, as well as the larger values in Xe nuclei, but are much larger in amplitude than the experimental values. On the other hand, particle number conserving cranked shell model calculations without octupole deformation overestimate the low-spin values, while those with octupole deformation included reproduce the experimental values in 120Ba, suggesting the possible existence of moderate octupole collectivity in the negative-parity bands of nuclei in this mass region.
Lifetimes of negative-parity states have been determined in the neutron deficient semi-magic (N = 50) nucleus 95Rh. The fusion-evaporation reaction 58Ni(40Ca,3p) was used to populate high-spin states in 95Rh at the Grand Accélérateur National d’Ions Lourds (GANIL) accelerator facility. The results were obtained using the Doppler Shift Attenuation Method (DSAM) based on the Doppler broadened line shapes produced during the slowing down process of the residual nuclei in a thick 6mg/cm2 metallic target. B(M1) and B(E2) reduced transition strengths are compared with predictions from large-scale shell-model calculations.
Linear polarization measurements have been performed for γ rays in 91Ru produced with the 58Ni(36Ar, 2p1nγ ) 91Ru reaction at a beam energy of 111 MeV. The EXOGAM Ge clover array has been used to measure the γ -γ coincidences, γ -ray linear polarization, and γ -ray angular distributions. The polarization sensitivity of the EXOGAM clover detectors acting as Compton polarimeters has been determined in the energy range 0.3–1.3 MeV. Several transitions have been observed for the first time. Measurements of linear polarization and angular distribution have led to the firm assignments of spin differences and parity of high-spin states in 91Ru. More specifically, calculations using a semiempirical shell model were performed to understand the structures of the first and second (21/2+) and (17/2+) levels. The results are in good agreement with the experimental data, supporting the interpretation of the nonyrast (21/2+) and (17/2+) states in terms of the Jmax and Jmax − 2 members of the seniority-three ν(g9/2) −3 multiplet.