Search

165 Tm has been studied through the reactions 150 Nd( 19 F, 4n), E beam =85 MeV and 154 Sm ( 15 N, 4n), E beam =70 MeV. The level scheme has been extended to spin 71/2 − ℏ, and four new bands have been added. Two are assigned to the K =17/2, three-quasiparticle configurations, π [523]7/2 − ⊗ ν [642]5/2 + ⊗ ν [523]5/2 − and π [404]7/2 + ⊗ ν [642]5/2 + ⊗ ν [523]5/2 − , and the remaining two are assigned to γ -vibrations coupled to an h 9/2 proton. Lifetimes of high-spin states in the [541]1/2 − and [411]1/2 + bands have been measured using DSAM techniques, allowing transition quadrupole moments to be deduced. Furthermore, crossings between the [541]1/2 − and [523]7/2 − bands and between the [411]1/2 + and [404]7/2 + bands are analysed with a band-mixing calculation to obtain the quadrupole moments of the [523]7/2 − and [404]7/2 + bands. While the [523]7/2 − , [411]1/2 + and [404]7/2 + bands all have similar deformations, the [541]1/2 − band has a quadrupole moment approximately 15% larger. The relative deformations are in good agreement with diabatic potential energy surface calculations performed using the code “Ultimate Cranker”. The experimental crossing frequency, due to the alignment of i 13/2 neutrons, is found to be delayed in the [541]1/2 − band compared to the other bands. This is a universal feature in the rare-earth region, and extensive systematic Cranked Shell Model calculations have been performed to predict deformations and crossing frequencies for nuclei in the region. The model is unable to reproduce the full delay in crossing frequency, confirming that deformation alone is not responsible for the shift.

High-spin spectroscopy on odd-odd ${}^{164}\mathrm{Tm}$ has produced new illustrations of departures from the predictions of principal-axis cranking. Among the nine strongly coupled rotational bands observed, four are assigned to the parallel and antiparallel couplings of two configurations $\ensuremath{\pi}{h}_{11/2}\ensuremath{\nu}{i}_{13/2}$ and $\ensuremath{\pi}{g}_{9/2}\ensuremath{\nu}{i}_{13/2}.$ This represents the first time that the high-spin properties of both couplings can be explored. We find that the measured $B(M1)/B(E2)$ values in the $K=1(\ensuremath{\uparrow}\ensuremath{\downarrow})$ coupling of $\ensuremath{\pi}{h}_{11/2}\ensuremath{\nu}{i}_{13/2}$ are 50% larger than those in the $K=6$ (\ensuremath{\uparrow}\ensuremath{\uparrow}) coupling, and represent the largest seen in this nucleus. Tilted-axis cranking calculations successfully explain the $M1/E2$ ratios in these two bands, while the particle-rotor calculations did not reproduce the full low-K enhancement. No inversion in the signatures of the $K=6\ensuremath{\pi}{h}_{11/2}\ensuremath{\nu}{i}_{13/2}$ band is observed, but there is a small inversion in the $K=1$ coupling up to $I=17\ensuremath{\Elzxh}$ and a large inversion in the $\ensuremath{\pi}{h}_{9/2}\ensuremath{\nu}{i}_{13/2}$ band up to $I=19\ensuremath{\Elzxh}.$ Remarkably, particle-rotor calculations with a $p\ensuremath{-}n$ interaction included are able to reproduce these inversions. A stronger $p\ensuremath{-}n$ interaction is needed to explain an inversion in the $\ensuremath{\pi}{d}_{3/2}\ensuremath{\nu}{i}_{13/2}$ band.

Rotational bands in the odd-proton nucleus 171 Lu have been populated with the 160 Gd( 19 F, α4n) reaction. High-spin states were observed to a maximum spin of 73 2 − using the NORD-BALL array. Several new three-quasiparticle bands were observed, including one based on the π 1 2 − [541]⊗ν 7 2 + [633]⊗ν 1 2 − [521] configuration. The signature splitting of this band is inverted from the expected splitting, and this is interpreted as being due to a residual proton-neutron interaction. The contribution of this interaction to the increased crossing frequency observed for the alignment of i 13 2 neutrons in the π 1 2 − [541] band is considered. Strong E1 transitions from high-spin levels in the π 1 2 + [411] band to the π 1 2 − [541] band are observed.

Six rotational bands in the odd-odd nucleus 174Ta have been populated with the 160Gd(19F,5n) reaction. High-spin states were identified using the NORDBALL array. Both signatures of the doubly decoupled π 1 2 − [541] ⊗ ν 1 2 − [521] band and semi-decoupled π 1 2 − [541] ⊗ ν 7 2 − [633] band are observed, in addition to the high-K couplings of the π 9 2 − [514] ⊗ ν 7 2 + [633] , π 9 2 − [514] ⊗ ν 5 2 − [512] , π 7 2 + [404] ⊗ ν 7 2 + [633] , and π 5 2 + [402] ⊗ ν 5 2 − [512] configurations. The signature splitting of the π 1 2 − [541] ⊗ ν 7 2 + [633] band is inverted from the expected splitting, and this is interpreted as being due to a residual proton-neutron interaction. It is shown empirically that this interaction, together with deformation changes, can account for the increased crossing frequency associated with the alignment of i 13 2 neutrons in the π 1 2 − [541] bands of odd-Z nuclei.

An experimental investigation of the nucleus 165Lu, using the reactions 138Ba(31P,4n) 165Lu and 150Sm(19F,4n) 165Lu at beam energies of E = 155 and 95 MeV, respectively, has been performed. Among other additions to the existing level scheme, a new band, with transition energies almost identical to a strongly deformed (β2 0.42) πi13/2[660 1/2+] band recently discovered in 163Lu has been established. A theoretical analysis of the structure of the two Lu isotopes, 165Lu and 163Lu is carried out by detailed calculations of total potential energy surfaces for specific configurations. By a diabatic treatment of crossings specific proton configurations as πi13/2[660 1/2+] are identified throughout the deformation space and as a function of spin. It is found as a general feature that well deformed local minima of considerable nonaxial symmetry coexist with a normal deformed global minimum. The depth of these local minima depend on configuration. The structure of the different global and local minima found in these surfaces are analysed and discussed in terms of occupation of available basis configurations and their orientation relative to the rotation axis. The strongly deformed minima are found to belong to a group of superdeformed triaxial structures, expected to appear at low energies for certain favourable combinations of proton and neutron numbers.

High-spin properties of rotational bands are studied in 173Ta using the 160Gd(19F,6n) reaction at bombarding energies of 103–105 MeV. With the existing bands being extended, and new bands established, a total of 16 rotational sequences are interpreted in terms of their (multi) quasiparticle structure. Measurements of electromagnetic properties for these bands include E2 M1 mixing ratios, branching ratios and lifetimes of isomeric states close to band heads, for which all energies have now been determined. Particular emphasis is devoted to (i) the band structures related to the 1 2 − [541] intruder configuration, for which both favoured, and unfavoured partners as well as the extended g- and S-bands in the (delayed) crossing region have been established, (ii) the reduced E1 transition strength between the (new) 1 2 + [411] and 1 2 − [541] bands, which is strongly enhanced, most likely due to coupling to octupole degrees of freedom, and show a ΔI = 4 staggering, (iii) the observation of weak interband transitions between the two partners of a pseudo-spin doublet composed of the 5 2 + [402] and 7 2 + [404] bands together with accurately measured intraband mixing ratios enable an analysis of the mixing of these bands through comparisons to particle-rotor calculations, (iv) the observed three-quasiparticle bands which are assigned to specific configurations coupling the lowest protons to lowest two-quasineutrons with negative parity.