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The problem of the very different E2 decay rates from the two-quasineutron Kπ = 6+ isomers in the N = 104 isotones 172Er, 174Yb, 176Hf, and 178W is investigated using the triaxial projected shell model with inclusion of multi-quasiparticle configurations. It is demonstrated that the highly K-forbidden transition from the 6+ isomer to the ground-state band is sensitive to mixing with the 6+ state of the γ-vibrational band. Thus the inter-band transitions, and lifetimes, depend on the relative position of the γ-band and the isomeric state in each isotone. [ABSTRACT FROM AUTHOR]

The nuclei 131I and 133I have been populated in multi-nucleon transfer reactions between 136Xe ions and various targets, and their structure investigated by time-correlated γ-ray coincidence spectroscopy and the measurement of γ-ray angular correlations. A 19/2- isomer at 1918 keV, with a half-life of 24(1) µs, has been identified in 131I, as well as nanosecond isomers with Jπ = 23/2+ in both isotopes. A T1/2 = 25(3) ns isomer at 4308 keV in 131I is suggested to have Jπ = (31/2-, 33/2-) and is primarily attributed to the coupling of an odd proton in the d5/2 or g7/2 orbit with the $(\pi^2)_{0^+} (\nu h_{11/2}^{-3} d_{3/2}^{-1})_{15^-}$ configuration in 130Te, responsible for the 15- isomer in that nucleus. The observed level properties are compared with predictions of a shell-model calculation. [ABSTRACT FROM AUTHOR]

Three low-lying 8+ states have been identified in 192Pb . A newly observed cascade of $ \gamma$ -rays built directly on the 8+ 1 state is compared to the previously identified, weakly rotational band above the 11- $ \pi$ i13/2 , h9/2 isomer in the same nucleus, and to analogous structures in 194Pb . The similarity of all four structures lends support to the suggestion that the 8+ 1 configurations are of a similar oblate deformation to the 11- isomers. The excitation energies of all three 8+ states in 192Pb and 190Pb are compared to systematics. The possibility that one of the 8+ states in 192Pb is associated with a prolate shape is discounted. [ABSTRACT FROM AUTHOR]

The nucleus $\ensuremath {\rm ^{127}Sb}$ , which is on the neutron-rich periphery of the $\ensuremath \beta$ -stability region, has been populated in complex nuclear reactions involving deep-inelastic and fusion-fission processes with $\ensuremath {\rm {}^{136}Xe}$ beams incident on thick targets. The previously known isomer at 2325 keV in $\ensuremath {\rm {}^{127}Sb}$ has been assigned spin and parity $\ensuremath 23/2^+$ , based on the measured $\ensuremath \gamma$ - $\ensuremath \gamma$ angular correlations and total internal conversion coefficients. The half-life has been determined to be 234(12) ns, somewhat longer than the value reported previously. The 2194 keV state has been assigned $\ensuremath J^{\pi} = 19/2^+$ and identified as an isomer with $\ensuremath T_{1/2} = 14(1) {\rm ns}$ , decaying by two $\ensuremath E2$ branches. The observed level energies and transition strengths are compared with the predictions of a shell model calculation. Two $\ensuremath 15/2^+$ states have been identified close in energy, and their properties are discussed in terms of mixing between vibrational and three-quasiparticle configurations. [ABSTRACT FROM AUTHOR]

Excited states in 208Fr have been identified using the 197Au(16O, 5n)208Fr reaction and a variety of time-correlated $ \gamma$ -ray and conversion electron spectroscopic techniques. Transitions above and below a $ \tau$ = 623(16) ns 10- isomer are placed in the level scheme. This isomer is analogous to that observed in the odd-odd isotone 206At for which additional spectroscopic information is also obtained, including a precise lifetime of $ \tau$ = 1173(30) ns. The $ \gamma$ -rays assigned to 208Fr are the same as the main transitions erroneously assigned to 209Fr in previous work. [ABSTRACT FROM AUTHOR]

A superdeformed band has been observed in theN= 108 isotope190Pb. This is the most neutron-deficient Pb isotope in which superdeformed states have been observed. Several theoretical approaches have predicted thatN= 108 will mark the limit of observable superdeformation in the Pb isotopes. The band, which consists of five (possibly six) transitions, is observed to feed at least one isomeric level in its decay to the ground state. This decay pattern supports a spin assignment of 10? for the lowest observed level. [ABSTRACT FROM AUTHOR]

A seven-quasiparticle isomer withandT1/2 = 53 ( + 3-7) ns has been identified in179Ta. By comparing its excitation energy with results from multi-quasiparticle calculations that include the effects of blocking and residual nucleon-nucleon interactions, the isomer is assigned the(5/2 +[402], 7/2 +[404],(5/2-[512], 7/2-[514], 7/2-[503], 9/2 +[624]) configuration. The decay of this isomer is found to be unusually fast, a feature that is attributed to a mixing with a specific collective level. The interaction strength is found to be orders of magnitude lower than that observed between interacting collective levels. [ABSTRACT FROM AUTHOR]

New data have been obtained for 185Os following the 176Yb(13C,4n)185Os reaction, extending the pseudo-Nilsson &fracl;12-, -&frac;32- [&4tilde;&1tilde;&1tilde;] doublet structure and the &frac;72- [&4tilde;&0tilde;&4tilde; band to significantly higher spins. Gamma-ray branching ratio data have been analysed to obtain extensive B(M1) and B(E2) ratios for intraband and inter band transitions. The data are compared with particle-rotor calculations based on the pseudo-Nilsson potential and the Woods-Saxon potential. The results indicate that the pseudo-Nilsson approximation provides a good description of the &fracl;12-, -&frac;32-[&4tilde;&1tilde;&1tilde;] bands up to the first band crossing; the difference in magnitude between the model predictions and data for the &frac;72-[&4tilde;&0tilde;&4tilde;] band may be attributed to a lower deformation for the higher-K structure. [ABSTRACT FROM AUTHOR]

The nuclear structure of the stable nucleus 18476Os has been studied including five newly identified rotational bands built on 2-quasiparticle Kπ=0+, 6−, 8− couplings. The excitation energies of the proposed multi-quasiparticle excitations are in good agreement with predictions of blocked BCS calculations. The interaction responsible for the first band crossing, caused by a high-K tilted 2-neutron configuration, is calculated and a new interpretation presented for the yrast states after the interaction. A second crossing with an aligned s–β band is also reported. The yrast behaviour at high spins is dominated by a wealth of short-lived (nanoseconds and shorter) high-K levels. The low reduced hindrances for intrinsic state decays are discussed, and attributed to the triaxial shapes and fluctuations predicted by configuration-constrained potential-energy-surface calculations. Comparisons with neighbouring nuclei are made. [Copyright &y& Elsevier]

Transient-field precessions were measured simultaneously for the 2 states ofOs as ions of these nuclei traversed a thin polarized iron foil. In contrast with most earlier measurements, the relative gyromagnetic ratios deduced here are independent of the level lifetimes. Emphasis is placed upon determination of the g-factor of the first excited state inOs, as disparities in measurements of the lifetimes of this level have led to uncertainties in its g-factor. [ABSTRACT FROM AUTHOR]

Excited states in the range of even tungsten isotopes, from170W to178W, populated in the β-decay of170–178Re parents have been identified using γ-ray singles and coincidence techniques, utilising the high efficiency of a Compton-suppressed array, and conversion electron systems. Many new states at low excitation energies have been identified, complementing the level schemes previously established from in-beam studies. The new states include excited O+ states in170W,172W,174W,176W and178W. A large body of data on decay properties, spins and parities, and relative E2 and E0 matrix elements has been obtained. The properties of the K π=0+ (quasi-β) bands are compared with similar bands observed in light osmium, platinum and mercury isotopes, which have been attributed to shape coexistence. [ABSTRACT FROM AUTHOR]