H.J. Jensen

More than thirty bands in 177Re

Abstract The level scheme of 177Re has been extended extensively, with fragments of more than thirty bands, characterised by a given signature, observed. Alignments at low frequency in one-quasiparticle bands are interpreted as deformation effects and compared with the predictions of cranking calculations. The previously assigned one-quasiparticle π i 13 2 band is shown to be a mixture of three-quasiparticle and vibrational character. The non-observation of the one-quasiparticle π i 13 2 band is explained as being due to crossings of its s-band by competing bands. A number of high-K bands are also reported, including five- and seven-quasiparticle bands. Configuration assignments for these bands are aided by comparing experimental gκ values with “effective” gκ values, calculated with a semi-classical expression taking Coriolis mixing into account. The population of the yrast band was observed to oscillate with every four units of spin.

Signature inversion in semi-decoupled bands: residual interaction between protons and neutrons ☆

Abstract Semi-decoupled bands based on the πh 9 2 ⊗ vi 13 2 configuration are observed in 162 Tm, 164 Tm and 174 Ta. Spins assigned to these bands imply an inversion of the expected signature splitting, which is interpreted as being the result of a residual proton-neutron interaction.

Triaxial Superdeformed Bands in

Abstract In a search for exotic structures in odd-odd 164 Lu, performed as one of the first Euroball experiments eight new, presumably triaxial, superdeformed bands were found. For the first time, evidence is presented for superdeformation in an odd-odd Lu isotope for which theory predicts large triaxiality. The data are compared to expectations from calculations with the code “Ultimate Cranker”. Two of the bands are connected to normal-deformed structures and the E1 strength of the decay-out appears to be enhanced over single particle expectations, possibly due to octupole correlations.

^164

Abstract 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.

Lu and Enhanced E1 Decay-Out Strength

Abstract The study of damping of rotational motion applying te rotational plane mapping (RPM) method is presented and discussed. The aim of this technique is to extract the distribution of the rotational transition strength from an analysis of the shape of the “central valley” of two- and three-dimensional γ-ray spectra. The method is applied to a triple γ-coincidence data set of 162,163Tm nuclei formed in 37Cl+130Te reactions. The rotational transition strength is obtained as a function of rotational frequency for selected regions of entry states, and the width is found to be rather constant and approximately equal to 80 keV. This value is significantly smaller than the value predicted theoretically for the rotational damping width Γrot. Also the ratio between the observed depth and width of both the 2D and 3D valleys does not agree with the simple model adopted in the RPM method. These discrepancies point to the presence of both a wide and a narrow component in the distribution of rotational strength as extracted by the RPM method. The analysis of simulated spectra obtained on the basis of realistic band-mixing calculations, including residual interactions, confirms this behaviour.

Band structures and proton-neutron interactions in 174Ta

Abstract Rotational bands in 169 Lu previously observed via (p, 3n) and (α, 4n) reactions were extended by 8–14 units of angular momentum using the 154 Sm( 19 F, 4n) reaction and the Nordball detector array. By analysis of γγ coincidence relations and γ-ray angular correlations we have established the [541] 1 2 − , α = + 1 2 band to 57 2 h , the [514] 9 2 − bands to 47 2 > the [404] 7 2 + bands to 53 2 h and the [411] 1 2 [su+ , α = − 1 2 to 47 2 ( 55 2 ) h . The bands belonging to the [411] 1 2 + and [402] 5 2 + configurations with α = + 1 2 appear to be rather mixed in the low spin region. One of these bands is established to 45 2 ( 49 2 ) units of spin. The transitions interconnecting the signature partners, in the bands based on the [514] 9 2 − and [404] 7 2 + Nilsson orbitais, as well as in and between the strongly mixed [411] 1 2 + and [402] 5 2 + bands are compared to particle-rotor model calculations. By DSAM analysis, lifetimes and thereby transition quadrupole moments for the band built on the configuration h 9 2 [541] 1 2 − , α = + 1 2 could be extracted. The abnormal alignment pattern at the ν i 13 2 crossing for the h 9 2 [541] 1 2 − ban analysed in terms of a difference in both deformation and neutron pairing compared to the other less polarizing configurations. The influence of octupole modes on the strength of observed [411] 1 2 + ⇒[541] 1 2 − E 1 transitions as well as on observed spin-flip, [514] 9 2 − ⇒[404] 7 2 + , E1 transitions is investigated theoretically and compared to the experimental data.

THE DISTRIBUTION OF THE ROTATIONAL TRANSITION STRENGTH IN WARM NUCLEI STUDIED THROUGH GAMMA-RAY CORRELATIONS

Abstract High-spin states in 182W have been studied using the 176Yb(13C,α3n) reaction at a beam energy of 65 MeV. The ground state band is found to backbend clearly at h ω ≈ 0.38 MeV and to gain more than 6 units of angular momentum. In addition, the Kπ = 10+ band is observed to decay into the g.s.b. 16+ state where the yrast sequence backbends. Three-band mixing calculations between the g-, s- and Kπ = 10+ bands have been performed to interpret the backbend. Comparison of the experimental gK factors with predictions confirms configuration assignments and allows new assignments for some of the bands. The level scheme of high-K four-quasiparticle states recently reported is corrected, and the intrinsic structures are discussed in more detail.

Shapes, electromagnetic properties and enhanced E1 strength in 169Lu

High-spin states in doubly odd nuclei of 124Cs, 126Cs and 124La have been investigated by gamma ray spectroscopy. Rotational bands of pih11/2 x nuh11/2 configuration have been assigned by the block ...

High-spin states in 182W

Abstract 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.

High-spin states in odd-odd nuclei

Abstract The number of excited superdeformed bands in 143 Eu is measured by use of the Fluctuation Analysis Method. Between 10 and 40 rotational bands, displaying typical rotational energy correlations over two consecutive transitions, are populated within a rather narrow range in transition energy, E γ ≈ 1300–1500 keV. These numbers are close to the values found for normally deformed nuclei and agree with microscopic cranking + band mixing calculations for the specific superdeformed nucleus, which predict the onset of rotational damping to occur at the excitation energy U 0 = 1.3–1.6 MeV above the yrast line.