| The doubly-odd nucleus 158Tm, with Z=89 and N=89, lies at the begging edge of the well deformed A160 nuclear region. Due to the well-known shallow minima in energy as a function ofβ2 andγdeformations, it is expected to show various interesting features at high-spin states. Indeed, the phenomenon of signature inversion is an attractive topic for the doubly-odd nuclei in 158Tm region. Athough many attempts have been made using several theoretial methods, a commonly accepted explanation for signature inversion is still elusive. Moreover, the recent experimental studies on 160Lu and 164Ta revealed a new category of signature inversion behavior. Theπh11/2(?)νi13/2 bands in the two nuclei show inverted signature dependence of energy continuously to the highest spin observed, without showing a restoration of a normal dependence at the so-called signature inversion point expected from systematics. It is thus impotant to investigate whether such abnormal behavior occurs in other nuclei, and 158Tm, a nucleus having comparable soft shape to 160Lu and 164Ta is a good candidate in this regard.The A130 nuclear region is another one where the nuclei display attractive high-spin spectroscopy, such as band termanition, prolate and oblate shape coexistance and breaking of chiral symmetry. The odd-A nucleus 125Cs has been studied by several groups in the literature. However, the band built on d5/2 configuration has not been observed. For a more comprehensive understanding of its high spin properties, we have chosen 125Cs as a new object to study.I. Level structure, signature inversion and electromagnetic properties of 158TmThe experiment was performed at the HI-13 tandem accelerator of CIAE. The excited states of 158Tm was populated via the 144Nd( 19F,5n) reaction at bombarding energies of 108 and 112 MeV respectively. A self-supporting 5.2 mg/cm2 target was enriched in 144Nd to 96%. A detection array consisting of 14 Anti-Compton HPGe detectors was employed to record theγ-rays excited from the target chamber. Approximately 2×108γ-γcoincidence events were accumulated and sorted into a symmetric Eγ-Eγmatrix for analysis ofγ-γcoincidence relationships and an asymmetric Eγ-Eγmatrix for the analysis of mutipolarities ofγ-rays.A level scheme of 158Tm, containing two new bands and some extensions of previously-known bands, has been deduced from this work. Data of relativeγ-ray intensities ,ADO ratios and experimental B(M1)/B(E2) ratios were obtained.The spin-parities of the two new bands have been deduced from the additivity rule of alignment and ADO data. Configuration assignments were made for each of the rotational bands based on the prediction of additivity rule of Routhians, observed aligned angular momentum, band crossing frequencies, energy signature splitting and electromagnetic properties. A hanging band identified in a previous work was firmly connected to lower states through tree interband transitions, and was assigned to theπh11/2(?)νh9/2(α=-1/2) (?) (νi13/2)2 configuration. This band formed a pair of signature partners with another 4-quasiparticle band which was assigned to theπh11/2(?)νh9/2(α=+1/2)(?)(νi13/2)2 configuration in previous studies. The newly identified coupled and decoupled bands were assigned toπg7/2(?)νi13/2 andπd3/2(?)νi13/2 configurations respectively.Electromagnetic properties in yrast band and two 4-qp bands in 158Tm were discussed in detail together with comparisons of measured and theoretically expected B(M1)/B(E2) ratios. It was revealed that the yrast band built on theπh11/2(?)νi13/2 configuration might have positive triaxial deformation. Inπh11/2(?)νi13/2 configuration, no staggering in B(M1)/B(E2) was observered either in 158Tm or 160Lu,unlike in 162,164Lu.The yrast band, which is known as being built on theπh11/2(?)νi13/2 configuration at low spins and showing low-spin signature inversion, was observed to show a restoration of normal behavior of signature splitting at a spin I≈25 h, pronouncedly higher than the inversion point of 21h as expected from systematics.Configuration ofπh11/2(?)νh9/2(α=+1/2)(?)(νi13/2)2 band was observed to show high-spin signature inversion, presenting a striking contrast to the conventionally observed low-spin signature inversions that occur in many other configurations likeπh11/2(?)νi13/2,πh9/2(?)νi13/2, etc. A survey of similar phenomena was made in adjacent nuclei for an understanding of high-spin signature inversion. Results revealed thatπh11/2(?)νh9/2(?)(νi13/2)2 configuration in three isotones 156Ho,158Tm,160Lu showed signature inversion ,and keen softness in nuclear shape with respect to triaxial deformation was suspected to be an important role . In the mean time, the h9/2 neutron should not just be a spectator because of the increasing amplitude of signature inversion compared with 3-qp configuration without it. Configurations mixing from the f7/2 states might also play an important role in the signature inversion of the 4-qp bands. II. High spin study of odd-A nucleus 125CsThe excited states of 125Cs were populated via the 116Cd (14N, 5n) reaction at a bombarding energy of 65 MeV. The 14N beam was provided by the tandem accelerator complex at the Niels Bohr Instisute. The Cd target was a foil of thickness of 820μg/cm2 with a 1mg/cm2 Au backing. The resultantγrays were detected using the Nordball detector system consisting of up to 20 Compton-suppressed HPGe detectors and a 55 element BaF2 inner ball. One of the HPGe detectors was replaced by LEPS (low energy photon spectrometer) detector to ensure sensitivity to important low-energy transitions. A total of 8×108γ-γcoincidence events were accumulated in event-by-event mode.The level scheme was significantly improved; two new bands were established. Experimental data like relativeγ-ray intensities ,ADO ratios and B(M1)/B(E2) ratios were obtained.For the strongly coupled g9/2[404]9/2+ band, two transitions were replaced based on coincidence relationships, and three new interband transitions were established to lower excited states. On these basis, we revised the de-excitation mode and the excitation energy of the bandhead. With the help of ADO data and excitation energy systematics in the 55Cs isotopes, the spins of the states in this band were re-assigned.Based on data of ADO and systematics, one of the newly identified band was suggested to be the signature partner ofπg7/2 [ 422 ]3/2 + (α=-1/2)configuration. The comparisons of measured and theoretically expected B(M1)/B(E2) ratios confirmed our conclusion. Another new band was connected to lower excited states by three interband transitions. Based on the measured ADO ratios of the links, spin of the states in the band were assigned, and based on the systematics of excitation energies and the behavior of large signature splitting, configuration of this band was assigned d5/2[420]1/2+Experimental B(M1)/B(E2) ratios of the g9/2[404]9/2+ band have been extracted and compared with theoretical expectations. A good agreement has been obtained. However, appreciable staggering of Experimental B(M1)/B(E2) ratios was observed in spite of zero signature splitting in energy. The similar effect took place in isotopes of 119,121,123Cs and no explanation for this effect has been given so far. If the geometrical model was sufficiently precise, the observation could be considered as the strong evidence that the two signatures from the same configuration have different deformations,such asβ2 orγ.
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