R.A. Bark

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.

High-spin states in 182W

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.

The GDR width in the excited 147 Eu compound nucleus at high angular momentum

Abstract High-energy γ -rays emitted in the decay of the hot compound nucleus 147 Eu have been measured in coincidence with low-energy γ -rays. The γ transitions from the different residual nuclei were detected by a multiplicity filter and by Ge detectors. The employed reaction was 37 Cl + 110 Pd at bombarding energies of 160, 165 and 170 MeV. The measured high-energy γ -ray spectra were analysed within the framework of the statistical model using the Cascade code. The GDR width in the angular momentum interval between 35 and 50 ℏ was found to increase weakly and to be rather well predicted by the thermal shape fluctuation model. Also the deformation parameter β as a function of the average angular momentum extracted from the data was found to be in general agreement with the model.

Structure of the doubly odd nucleus 180Ta: Description of 23 bands

Abstract The structure of the doubly-odd nucleus 180 Ta has been studied by γ – γ coincidence measurements with a DC beam at 52 and 57 MeV and time-correlated γ – γ coincidence measurements with a pulsed beam at 55 MeV via the 176 Yb( 11 B, α 3n) 180 Ta reaction. In all measurements, γ -rays were detected in coincidence with charged particles. In the time-correlated γ – γ coincidence measurements with a pulsed 11 B beam, three rotational bands and one octupole vibrational band have been identified above the I π =15 − T 1/2 =30 μ s isomer. The configuration of three bands built on 8 + states has been discussed by means of three-band mixing calculations. BCS calculations with blocking have been used in support of configuration assignment of four- and six-quasiparticle structures. Totally, 19 rotational bands, one β -, one γ - and two octupole-vibrational bands, plus one intrinsic state have been identified with two-, four- and six-quasiparticle configurations. The K values of these bands range from 0 to 19. The K-forbidden transition rates are discussed on the basis of mixing between states with widely different K-values. The BBCS calculations predict a K π =22 − isomer not identified experimentally in this nor in previous works. A search for specific intermediate states which could explain the transformation from K π =9 − to 1 + during the astrophysical s- and r- processes was negative.

Interactions between a multitude of rotational bands in well deformed odd nuclei: A new method for spin and parity assignment

Abstract Using the ( 18 O,5n) 163 Er reaction a multitude of rotational bands have been established with firm spin and parity assignments in 163 Er. In 17 out of 24 band crossings E2 cross-band transitions have been observed. The interaction strength varies between ∼ 1 and ∼ 50 keV with many of the values in the range 10–15 keV. These interactions sample a variety of the lowest (multi) -quasiparticle configurations. For some bands, in particular those with high K -values, the configurations can be established rather well. Quite complicated changes in the wavefunctions must occur at these crossings, and to explain the observed interaction strengths coupling to various vibrational degrees of freedom, in addition to possible residual neutron-proton interactions, may be needed.

High-spin states in 171Lu

Abstract 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.

Back-bending in the πi132 band and proton-neutron interactions in 171Re

High-spin states in 171Re have been studied using the reaction 123Sb(52Cr, 4n)171Re. A back-bend in the i132 band of a Re nucleus has been fully delineated for the first time. A new back-bend has also been observed in the 52+[402] band and other bands have been extended to higher spin and added to the level scheme. Band crossings are interpreted using the CSM and three-band mixing calculations. These appear to show evidence for shape coexistence and configuration-dependent neutron pairing.

Structure of excited bands in 162Tm and residual interactions

Abstract The nucleus 162Tm has been populated by the 130Te(37Cl,5n) reaction, and the γ-cascades detected with the NORDBALL array. Eight coupled rotational bands involving the proton orbitals, g 7 2 [404] 7 2 + , d 3 2 [411] 1 2 + , d 5 2 [402] 5 2 + , h 11 2 [523] 7 2 − and h 9 2 [541] 1 2 − and neutron orbitals i 13 2 [642] 5 2 + , h 9 2 [523] 5 2 − and f 7 2 [521] 3 2 − have been established in 162Tm, to spins varying from 18 to 47ℏ. Various phenomena which can be related to residual neutron-proton interactions are discussed. In particular, signature inversion in the π [541]1 2 − ⊗ ν [642]5 2 + bands based on the h 9 2 quasiproton and i 13 2 quasineutron, rewpectively, may be explained by a fairly large p-n interaction. In addition, interactions at the crossings of bands with constituent quasiparticles differing both in parity and signature have been extracted with strength of the order of a few (4–12) keV. Such interactions also require terms beyond the standard mean field description.

Multi-quasiparticle states and K-forbiddenness in 177W

Abstract High-spin states in 177 W have been populated using the 164 Dy( 18 O,5n) reaction at a beam energy of 83 MeV. Six new high- K bands based on 3-, 5- and 7-quasiparticle excitations have been observed. Nilsson configurations for these bands are discussed, and experimental and calculated g -factors are compared. Decays of the K π = 29 2 + 5-quasiparticle state to the members of the K π = 7 2 + band have been observed. The decay rates are compared with predictions calculated within a tunneling model where the nuclear shapes are considered to change along the γ direction in the ( ϵ 2 , γ) deformation plane.

Erratum to “Collective and intrinsic structures in 183W” [Nucl. Phys. A 660 (1999) 171–196]☆

The structure of 183W has been studied by employing the 176Yb(14C,α 3n) reaction at 68 MeV. Five previously known rotational structure with one-quasiparticle configurations have been extended to higher spin states, and five new rotational bands with three- and five-quasiparticle configurations and a γ-vibration of a one-quasiparticle structure have been newly identified. In the ν7/2-[503] and ν11/2+[615] rotational structures, a signal of an admixture of an octupole- vibrational structure has been observed in their in-band B(M1)/B(E2) ratios and gΚ factors. In the Κπ = 19-M rotational band, a Coriolis effect on the ν1/2-[510] neutron has been identified. In all, 17 Κ-forbidden transitions have been observed. Energies of intrinsic states below 4 MeV have been calculated based on the Blocked BCS theory, and they are used in support of the configuration assignments.