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A Fermi-aligned ( i 13 2 ) 2 rotational band, with K≈8, has been observed in an even-even nucleus, 180W. Its structure corresponds to a t-band in the tilted-cranking representation. It crosses the ground-state band at I = 16 h , giving rise to backbending in the yrast sequence. Contrary to the usual interpretation, backbending in this case is not caused by the s-band. Comparison is made with other possible t-band crossings in the A ≈ 180 region.

High-spin states in 211Rn were populated using the reaction 198Pt(18O, 5n) at 96 MeV. Their decay was studied using γ-ray and electron spectroscopy. The known level scheme is extended up to a spin of greater than 69 2 and many non-yrast states are added. Semi-empirical shell-model calculations and the properties of related states in 210Rn and 212Rn are used to assign configurations to some of the non-yrast states. The properties of the high-spin states observed are compared to the predictions of the multi-particle octupole-coupling model and the semi-empirical shell model. The maximum reasonable spin available from the valence particles and holes in 77 2 and states are observed to near this limit.

The influence of particle-vibration coupling on the g-factors of the |(h 9 2 ) n 〉 isomers in the N = 126 isotones is assessed using the multiparticle-octupole-coupling model. According to the model, admixtures of the configuration |(h 9 2 ) n−1 f 7 2 〉 in the yrast 8+ and 21 2 − states, nominally associated with the configuration |(h 9 2 ) n 〉 , increase with n. On its own, the octupole mixing mechanism therefore predicts g-factors for these states that increase with the number of valence protons. This trend is the opposite of that predicted by core-polarization blocking. Combining multiparticle-octupole coupling and first-order core-polarization blocking significantly reduces the discrepancy between the experimental and theoretical g-factors of these states. We conclude that the observed breakdown in additivity for the g-factors of the |(h 9 2 n)〉 isomers in the N = 126 isotones arises primarily from first-order core-polarization blocking and the combination of configuration mixing due to multiparticle-octupole coupling and shell-model residual interactions.

An experimental value for the g-factor of the 7 2 proton is derived from the measured magnetic moment of the 141+ state in 214Ra (nominal configuration |( h 9 2 5 21 2 f 7 2 ; 14 + 〉) using the multiparticle-octupole-coupling model. The result, g( f 7 2 ) = 1.41(2) , is smaller than anticipated by theories which assume first-order core-polarization corrections to the proton spin g-factor together with an anomalous orbital magnetism of about 0.12. The experimental value suggests the proton spin g-factor gs may be quenched, in this orbital, to about half the bare-nucleon value, similar to that found for the 0 h 9 2 and 0 i 13 2 protons, or, alternatively, that the anomalous orbital magnetism is much reduced for the l f 7 2 orbital.

High spin states have been observed to excitation energies over 8 MeV in the odd-odd nucleus 214 Fr using in-beam γ-ray and electron spectroscopic techniques and heavy-ion induced reactions. Semi-empirical shell model calculations appear to provide a good description of the states observed, although some states expected within this model have yet to be identified.

The structure and decay properties of high-K isomers in {sup 176}Hf have been studied using beam sweeping techniques and the Gammasphere multidetector array. A new {Delta}K = 8 decay branch, from a K{sup {pi}} = 22{sup -}, six-quasiparticle, isomeric (t{sub 1/2} = 43 {micro}s) state at 4864 keV to the 20{sup -} state of a K{sup {pi}} = 14{sup -} band, has been identified. The reduced hindrance factor per degree of K forbiddenness for this decay is measured to be unusually low (f{sub ?} = 3.2), which suggests K mixing in the states involved. The deduced interaction matrix elements are discussed within the context of relevant K-mixing scenarios. The 3266-keV state, previously interpreted as a K{sup {pi}} = 16{sup +} intrinsic state, is reassigned as the J{sup {pi}} = 16{sup +} member of the band based on the K{sup {pi}} = 15{sup +} state at 3080 keV. The systematics of f{sub ?} values as a function of the degree of forbiddenness is discussed in light of this change.

Transient-field precessions were measured simultaneously for the 2(1)+ states of Os-188, Os-190, Os-192 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 in Os-190, as disparities in measurements of the lifetimes of this level have led to uncertainties in its g-factor.

The high-spin structure of 129Ba was investigated via in-beam γ-ray spectroscopy allowing many new transitions to be placed in the level scheme. Two isometric states with lifetimes of τ = 23 (2) ns (182 keV level) and 68 (2) ns (2463 keV level) were identified. A high-K 3-quasineutron configuration [ 7 2 + [404]⊗ 7 2 − [523]⊗ 9 2 − [514]] is proposed for the latter. A discussion of the high-spin structure and the deformation driving effects in 129Ba is presented in terms of the cranked shell model. The conclusion reached is that the alignment gains are dominated by h 11 2 proton pairs.

Excited states in the N = 126 nucleus 214Ra have been studied using γ-ray and electron spectroscopy following reactions of 12C and 13C on 206Pb targets. Levels were identified to spins of ∼ 25 ħ and excitation energies of ∼ 7.8 MeV. Lifetimes and magnetic moments were measured for several levels, including a spin (25−) core-excited isomer at 6577.0 keV with τ = 184 ± 5 ns and g = 0.66 ± 0.01. The level scheme, lifetime and magnetic moment data are compared with, and discussed in terms of, empirical shell-model calculations and multiparticle octupole-coupled shell-model calculations. In general, the experimental data are well described by the empirical shell model.

This work was supported by the ANSTO program for Access to Major Research Facilities, grant No. 02/03-H-05, the Australian Research Council Discovery projects DP0343027 and DP0345844, and the U.S. Department of Energy, Office of Nuclear Physics, under contract No. DE-AC02-06CH11257 and No. DE-FG02-94ER40848. P.N. acknowledges funding from the Academy of Finland (Grant 121110).

The lifetimes of the yrast 6+, 8+, 10+ and 13- states in 216Ra and the 27/2+ state in 217Ra have been measured using direct timing and pulsed beams. The resulting B(E2) values cannot be explained by simple shell model configurations. Analysis of these transition strengths and those from similar states in related nuclei provides evidence for a relatively smooth increase in collectivity, correlated with the product of the numbers of valence protons and neutrons outside 208Pb.

Excited states in 175Ir and 177Ir have been identified using (heavy-ion, pxn) reactions and γ-ray spectroscopic techniques. Rotational bands based on intrinsic states arising from the odd-proton parents, h 9 2 , h 11 2 , i 13 2 and d 5 2 were established to high spin except for the 5 2 + [402] bands. Only the h 9 2 bands show sharp alignment gains compatible with alignment of ( i 13 2 ) 2 neutrons. The smooth apparent alignments of the i 13 2 proton bands can be attributed, at least qualitatively, to a much larger deformation. The complex alignment gains observed in the h 11 2 bands in these and other iridium isotopes in the range 173–181Ir are consistent with the effects of mixing with a deformed intruder (equivalently, a low-spin shape change). This conjecture is tested against the in-band decay properties using a three-band model. Examination of the band structure suggests a significant gamma deformation at very low spin, before the change to a more deformed configuration occurs.

Excited states in the very neutron-deficient nucleus {sup 174}Pt have been identified up to spin 14. An irregular yrast sequence was observed beginning with a high 2{sup +}{r arrow}0{sup +} energy. It can be interpreted as the result of a change from a weakly deformed ground-state band, to a well-deformed rotor, near spin 6.

Transient-field precessions were measured simultaneously for levels in the ground-state bands of156, 158, 160Gd as ions of these nuclei traversed a thin polarized Fe foil. Relative g-factors of levels up to 6 1 + were deduced, those of the 4 1 + levels being determined with greatest precision. In contrast with the conclusions of the recent report by Alzner et al. [1], our results are consistent with g(4 1 + ) having the same value in all three isotopes and imply g(2 1 + )=g(4 1 + ) in156Gd, consistent with nuclear structure models.

Rotational bands in the odd-proton isotopes 175Ir, 177Ir, 179Ir and 181Ir based on the h 9 2 , h 11/NU> 2 , i 13 2 and d 11/NU> 2 orbitals have been identified, the first three to high spin. In all cases the h 9 2 band shows backbending with a crossing frequency and alignment gain consistent with that expected from the neutron i 2 13 2 alignment. In contrast the h 11/NU> 2 bands (and the fragments of d 11/NU> 2 bands observed) show complex alignment curves. These alignments can be explained using a phenomenological three-band model which incorporates a deformed intruder band, analogous to that proposed in the very light Pt and Os nuclei. Mixed wave functions from the model reproduce the observed B(M1)/B(E2) ratios. The presence of the intruder band in the h 11/NU> 2 and d 11/NU> 2 configurations and its absence in the h 9 2 band is compatible with its proposed association with an ( h 2 9 2 ) 0 pair excitation.

Rotational bands built on 1, 3 and 5 quasi-particle (qp) states in 173Hf have been populated to medium and high spins through the 160Gd(18O, 5n) reaction. The 1qp bands, previously identified as the 1 2 − [521], 5 2 − [512] and 7 2 + [633] ( mixed i 13 2 ) Nilsson configurations, have the first back-bend and show different alignment properties, possibly originating from deformation differences. The multi-particle states were identified from excitation energies, the properties of their associated band structures and decay patterns. The 3qp states are the previously known K π = 19 2 + and 23 2 − isomeric states originating from the 7 2 + [633] quasi-neutron coupled to 8−, 2-quasi-proton excitations and a K π =( 13 2 + ) state possibly containing the three lowest quasi-neutrons. A 5qp state with K π = ( 29 2 − ) was identified as the same three lowest lying quasi-neutrons coupled to the 8−, 2-quasi-proton excitation. The low excitation energies of these two related 3-and 5-quasi-particle states implies a reduced neutron pairing gap, which can be attributed to the effect of blocking.

New isomeric states with Jπ = 69/2+, τm = 13(1) ns in 211Rn and Jπ = 33−, πm = 7(1) ns in 212Rn have been identified. They decay by enhanced E3 transitions with strengths of 33(3) and 43(6) single particle units to the known 63/2− and 30+ isomers in 211Rn and 212Rn, respectively. The excitation energies and transition strengths agree well with predictions of the multiparticle, octupole-vibration coupled model.

Decay schemes of the nuclei 171 Os, 172 Os and 173 Os were studied using the reactions 144 Sm( 30 Si,3n) 171 Os, 144 Sm( 31 P, p2n) 172 Os and 149 Sm( 28 Si, 4n) 173 Os. The 5 − 2 [523] and i 13 2 bands were identified in the odd nuclei. Low-spin properties of these bands are analyzed using the particle-rotor model, while band-crossing frequencies and alignments are examined with the aid of the cranked shell model. A low-frequency band crossing was found in the 5 − 2 [523] band of 173 Os. At higher frequencies, the measured B( M 1) B( E 2) transition rates and signature splittings in the 5 − 2 [523] bands of both nuclei are consistent with a neutron alignment. In the i 13 2 band of 173 Os, an upbend, in the unfavoured sequence, possibly due to the AD crossing, occurs at a lower frequency than a similar upbend, presumably from the BC crossing, in the favoured sequence. These crossings were also analyzed with phenomenological three-band-mixing calculations.

High-spin states have been identified in 174Os and 175Os using (HI, x>n) reactions and gamma-ray techniques. Rotational bands built on low-lying intrinsic states in 175Os have been observed for the first time. The intrinsic states are identified as a mixed i 13 2 neutron state (nominally 7 2 + [633] ) and the 1 2 − [521] and 5 2 − [512] Nilsson configurations. Differences in the alignment of the two signatures of the decoupled band built on the 1 2 − [521] state and the comparison between the signature splitting of routhians and if B(M1)/B(E2) values in the i 13 2 band suggest softness towards gamma deformation. Crossing transitions between the negative-parity bands at intermediate spin have been observed and the interaction strength derived from the branching ratios. A comparison of the properties of bands in 174Os and 175Os shows some expected similarities, but also surprising differences which point towards the need for a more comprehensive treatment in strong interaction cases. Depending on the choice of reference the alignment in the i l3 2 band might show degenerate BC and AD crossings at a relatively low frequency. This may be consistent with the alignment observed in the negative parity side bands in 174Os.

Rotational bands built on one- and three-quasiparticle states in 175 Ta have been populated through the 170 Er( 10 B,5n) reaction. The four previously known one-quasiproton bands based on intrinsic states arising from g 7 2 , d 5 2 , h 9 2 and h 11 2 parents were extended to higher spin. Two new three-quasiparticle states with K π = 17 2 + and 21 2 + and their rotational bands were established, as was the rotational band associated with the previously known K π = 21 2 − three-quasiparticle state at 1565.9 keV. B( M 1) B( E 2) and g K − g R values extracted from the in-band branching ratios, have been utilized, together with the decay properties and alignments, to assign configurations. A multi-quasiparticle calculation based on the Lipkin-Nogami method, including approximately the orbital-dependent residual nucleon-nucleon interactions, has been used to predict the multi-quasiparticle energies for comparison with experiment.

Internal conversion coefficients of transitions in 180 Os have been measured using a superconducting, solenoidal electron spectrometer, operated in the lens mode. The high energy resolution and efficiency allow a precise measurement of the conversion coefficients of the 528 keV yrast transition. The values obtained, α K = 0.015(2), α L = 0.004(1) define pure E2 multipolarity. Taken with the measured γ-ray angular distribution, the conversion coefficient leads to an unambiguous assignment of 16 + → 14 + for the 528 keV transition.

Independent yields of post-neutron emission, secondary fragments from the fission of 238U induced by fast neutrons have been measured using γ-γ coincidence data. The yields of these products are found to be centred on more neutron-rich isotopes than the yields from fission processes previously used for spectroscopic studies on neutron-rich nuclei. The average angular momentum in the fragments is found to be similar to that in fragments formed in other low-energy fission processes.

The yrast structure of 207Pb above the 13/2+ isomeric state has been investigated in deep-inelastic collisions of 208Pb and 208Pb at ATLAS, Argonne National Laboratory. New and previously observed transitions were measured using the Gammasphere detector array. The level scheme of 207Pb is presented up to ~ 6 MeV, built using coincidence and γ-ray intensity analyses. In addition, the spin and parity assignments of states were made, based on angular distributions and comparisons to shell model calculations.

An extended decay scheme for Xe-128 has been constructed by using data from the Sn-124(Be-9, 5n)Xe-128 reaction at a beam energy of 58 MeV. Bands have been identified as being built on several intrinsic states, including a proposed 9/2(-)[514] circle times 1/2(+)[400] two-quasineutron configuration that forms the K-pi=5(-) intrinsic state at 2228 keV, and on a previously assigned K-pi=8(-) intrinsic state at 2786 keV. A half-life of 73(3) ns has been measured for the latter. Theoretical calculations have been performed by using the configuration-constrained blocking method based on a nonaxial Woods-Saxon potential. Large gamma deformation and gamma softness are predicted for the ground state and the K-pi=5(-) intrinsic state, whereas a nearly axially symmetric shape is predicted for the K-pi=8(-) two-quasiparticle configuration. The low value of the hindrance factor for the E1 transition depopulating the K-pi=8(-) intrinsic state is discussed in the context of analogous transitions in neighbouring N=74 isotones.

The E3 decays of the 11- isomers in the isotopes Pb194 and Pb196 have been studied experimentally and evaluated in terms of configuration mixing due to the development of oblate deformation. New results include a remeasurement of the lifetime of the 11- isomer in Pb194 and clarification of the intensities of its main decay branches including the known 496 keV E3 branch. Its intensity is an order of magnitude weaker than previously reported, leading to an E3 transition strength of 29(4) W.u. Limits are placed on possible E3 decays of the 11- isomer in Pb196 to a previously assigned 8+ two-proton state. Neither the branch, nor the state is observed. An alternative 562 keV transition to a new state at 2630 keV is proposed, with an E3 strength of 26(2) W.u. The approximately constant E3 strength for the range of even-even isotopes Pb190-196 is consistent with an oblate deformation for the 11- state of similar magnitude. This is supported by K-constrained potential-energy-surface calculations for the 11- and 8+ configurations.

A beam of 28 MeV He-8 particles with an average intensity 2 x 10(5) ions s(-1), produced by the SPIRAL facility at GANIL, was used to initiate fusion-evaporation reactions in thick targets of Pb-201 and Bi-209. Excited states of Po-212 and At-213 were populated in (He-8,4n) reactions. The emitted gamma-rays were detected using the EXOGAM array composed of four Compton suppressed germanium Clover detectors in a close geometry configuration. Preliminary results show that Po-212 has been populated to high spin (I similar or equal to 14) with a significantly increased yield compared with our previous He-8 beam experiment. An apparently increased relative population of states up to 12(+) was observed compared with published results from a Pb-208(Be-9,alpha n)(212) Po reaction at 48 MeV. Evidence is presented for a previously unreported de-excitation pathway: 69 keV (13(-) -> 12(+)). States up to I-pi = (39/2(-)) have also been observed in At-213.

Two high-spin regularly spaced rotational bands with large dynamical moments of inertia have been identified in Hf-175 with the Gammasphere spectrometer. These new bands are very similar to the previously identified triaxial superdeformed bands in the hafnium nuclei. However, the new bands in Hf-175 have been linked into the known level scheme and thereby provide the first firm spin assignments for these structures in this region. In order to understand the new bands, theoretical calculations have been performed based on the ULTIMATE CRANKER code. The new bands in Hf-175 are deduced to be built upon highly deformed structures. No experimental evidence for triaxiality was established and this work suggests that the structure of the so-called "triaxial" superdeformed bands in the Hf nuclei may be quite different from those identified in the lighter mass Lu nuclei. Since the two highly deformed bands in Hf-175 are associated with different deformations, this work also identifies the role of the intruder orbits in polarizing the nuclear shape.

Nuclei in the A ≈ 180 region around Z = 72 exhibit well deformed prolate shapes, giving rise to isomeric states as a result of the partial conservation of K, the projection of the total angular momentum on the nuclear symmetry axis. As more protons are added, away from Z = 72, the prolate deformation decreases and the nuclear potential becomes susceptible to triaxial fluctuations, governed by the γ degree of freedom. In these so called γ-soft nuclei, K is no longer a conserved quantity, resulting in the reduction or even loss of K-isomerism. Based on the excitation energies of the 2+ γ-vibrational bandheads, osmium isotopes (Z = 76) have the most γ-soft potentials in the A ≈ 180 region. Here, new results are reported for the highspin structure of 184Os and comparisons with neighbouring even-even osmium nuclei are made.

An isomer with a half-life of 15 +/- 1 mus has been observed in the N = 74 nucleus Sm-136, populated following the reaction (Ag(S,p2n)Sm)-Ag-107-S-32-Sm-136. It is proposed to have a K(pi) = 8- two quasineutron configuration. The isomer decays via a DELTAK = 8, 466 keV E1 transition with a surprisingly low hindrance per degree of K forbiddenness, f(nu) = 25.

The gamma-ray decay of excited states of the two-proton hole nucleus, 206Hg, has been identified using Gammasphere and 208Pb+238U collisions. The yrast states found include a T(1/2) = 92(8) ns 10(+) isomer located above the known 5(-) isomer. The B(E2;10(+)-->8(+)) strength is used to derive the quadrupole polarization charge induced by the h(11/2) proton hole. Also, the implied quadrupole moment has been used to provide an absolute scale for the electric field gradient of Hg in Hg metal.

The conversion coefficients for several bandhead decays in Ta-180 have been measured using pulsed-beam techniques and the Yb-176(Li-7,3n)Ta-180 reaction. The spin and parity of the 520 keV Intrinsic state is established as 4(+) and several earlier assignments are confirmed. Two-quasiparticle configurations for the 520 and 592 keV states are discussed and following reanalysis of the band properties, a consistent interpretation is reached. The 520 keV 4(+) state is associated with the favored coupling of the nu 1/2(-)[521]x pi 9/2(-)[514] configuration while the 592 keV (5(+)) state is identified with the nu 1/2(-)[510]x pi 9/2(-)[514] configuration.

Time-correlated, particle-tagged $\ensuremath{\gamma}$ spectroscopy of the stable nucleus ${}^{179}\mathrm{Hf}$ was undertaken with incomplete fusion reactions initiated by beams of ${}^{9}\mathrm{Be}$ and ${}^{7}\mathrm{Li}$ incident on targets of ${}^{176}\mathrm{Yb}.$ Intrinsic and rotational states above the three-quasiparticle ${K}^{\ensuremath{\pi}}{=25/2}^{\ensuremath{-}}, {T}_{1/2}=25 \mathrm{day}$ isomer, ${}^{179}\mathrm{Hf}{}^{m2},$ are reported. The rotational band based on ${}^{179}\mathrm{Hf}{}^{m2}$ has ${g}_{K}\ensuremath{-}{g}_{R}$ values that are consistent with the previously suggested $\ensuremath{\nu}{9/2}^{+}\ensuremath{\bigotimes}{\ensuremath{\pi}}^{2}[{7/2}^{+}{,9/2}^{\ensuremath{-}}]$ configuration assignment. A value of ${g}_{R}=0.34(5)$ was derived for the collective g factor of ${}^{179}\mathrm{Hf}{}^{m2},$ which is considerably higher than that found for the ${9/2}^{+}$ ground state. The difference is consistent with a reduction of the proton pairing strength due to blocking in the ${K}^{\ensuremath{\pi}}{=25/2}^{\ensuremath{-}}\ensuremath{\nu}\ensuremath{\bigotimes}{\ensuremath{\pi}}^{2}$ configuration. A number of ${\ensuremath{\nu}}^{3}{\ensuremath{\pi}}^{2}$ five-quasiparticle configurations were identified, the highest of which is an yrast ${K}^{\ensuremath{\pi}}{=43/2}^{+}, {T}_{1/2}=15(5) \ensuremath{\mu}\mathrm{s}$ isomer. It decays to an yrast ${K}^{\ensuremath{\pi}}{=39/2}^{\ensuremath{-}}$ state, which in turn decays to a rotational band based on a ${K}^{\ensuremath{\pi}}{=33/2}^{\ensuremath{-}}$ state. The ${K}^{\ensuremath{\pi}}{=33/2}^{\ensuremath{-}}$ state decays to the rotational band associated with ${}^{179}\mathrm{Hf}{}^{m2}.$ Semiempirical calculations reproduce the excitation energies of the three- and five-quasiparticle states above ${}^{179}\mathrm{Hf}{}^{m2}$ to within $\ensuremath{\sim}200 \mathrm{keV}.$ The calculations predict that the lowest seven-quasiparticle state will arise from a ${\ensuremath{\nu}}^{5}{\ensuremath{\pi}}^{2}$ configuration with ${K}^{\ensuremath{\pi}}{=47/2}^{\ensuremath{-}},$ which is just beyond the maximum spin accessible with the reactions employed here.

Chance near degeneracy of rotational states in the 1/2{sup {minus}}(521) and 5/2{sup {minus}}(512) bands in {sup 175}Os leads to mixing and connecting {ital E}2 transitions. Analysis of the observed branching ratios gives an interaction matrix element of about 4 keV, an order of magnitude smaller than the expected Coriolis interaction, deduced from particle-rotor calculations. A difference in deformation of 25% between the two configurations, as suggested by the larger unperturbed moment of inertia in the 1/2{sup {minus}}(521) band, would explain the quenched interaction.

Core excitations across the neutron shell gap in 207Tl E. Wilson a,∗,1, Zs. Podolyak a, H. Grawe b, B.A. Brown c, C.J. Chiara d,e,2, S. Zhu e, B. Fornal f, R.V.F. Janssens e, C.M. Shand a, M. Bowry a,3, M. Bunce a, M.P. Carpenter e, N. Cieplicka-Orynczak f,4, A.Y. Deo g,5, G.D. Dracoulis h, C.R. Hoffman e, R.S. Kempley a, F.G. Kondev i, G.J. Lane h, T. Lauritsen e, G. Lotay a,j, M.W. Reed a,6, P.H. Regan a,j, C. Rodriguez Triguero k, D. Seweryniak e, B. Szpak f, P.M. Walker a

This paper reports static moments and changes in mean-square charge radii of 175, 177, 177mYb measured using collinear laser spectroscopy at the IGISOL facility. The moments are compared to predictions made using the Nilsson model to determine the purity of the multi-quasiparticle T1/2 = 11.4 s, Iπ = 8− state of 176Yb and the ground state of 177Yb. The ground-state spins of 175, 177Yb and the T1/2 = 6.41 s, E = 331.5 keV isomeric state in 177Yb, have been measured from the hyperfine structure to be 7/2, 9/2 and 1/2 respectively.

Deep-Inelastic reactions have been used to populate high-spin states in the even-even osmium isotopes and in the iridium neighbors. New isomers have been identified in 190Os, 192Os, 194Os, 191Ir and 193Ir. These include a 2 ns 12+ state at 2865 keV and a 295 ns, 20+ state at 4580 keV in 192Os. Although a number of multi-quasiparticle states arising from prolate and triaxial deformations are expected in these nuclei, the main structures in 192Os can be interpreted as a two-stage alignment of i13/2 neutrons at oblate deformation, in close analogy with similar structures in the isotones 194Pt and 196Hg. The isomers are attributed to low-energy E2 transitions at the point of the alignment gains. The isomer observed in 191Ir is long-lived (τm ~8s) and probably arises from coupling of the h11/2 proton to the 10−ν/9/2− [505]11/2+ [615] prolate configuration that gives rise to long-lived isomers in 190Os and 192Os, although potential-energy-surface calculations indicate that the resultant three-quasiparticle state will be triaxial.

For prolate deformations around e 2 0.22 at neutron number N = 74 the neutron orbits 7/2 + [404] and 9/2 - [514] are close to the Fermi surface and may combine to give a K ϖ = 8-isomeric state. This K ϖ = 8- isomeric state decays to the 8 + member of the yrast band in 1 4 0 Dy, 1 3 8 Gd, 1 3 6 Sm, 1 3 4 Nd, 1 3 2 Ce and 1 3 0 Ba. There is no evidence for such a transition in 1 2 8 Xe and this will be explained in terms of the nuclear structure of the region.

The method of the level mixing spectroscopy (LEMS) was applied for the first time for the study of the static quadrupole moments of high-K isomers in the A ≈ 180 mass region. Results from a preliminary experiment for the static quadrupole moment of the Open image in new window (750 ns) isomer in 179W give a limit for its upper value Q < 7b, corresponding to a quadrupole deformation of β2< 0.343.

The high spin structure of the nucleus129Ba has been investigated using a18O induced reaction. The known bands could be followed up to a maximum spin (55/2) ħ. Some 56 states and 78 transitions could be placed in the level scheme. Band crossings were established in both positive and negative parity structures. They display features of strong polarization effects due to the alignment of h11/2 protons.

High-spin rotational states in 182Os have been studied using singles and coincidence γ-ray techniques and the 170Er(16O, 4n) reaction. The yrast sequence of states has been extended to spin 24+ and 7 sidebands identified. These are the γ-vibrational and K = 3− octupole bands and five two-quasiparticle bands including the K = 8−(τ = 1.1 ms) isomer band. The octupole vibrational band is rotation aligned and may also mix with two-quasiparticle configurations involving an i 13 2 neutron or an h 9 2 proton orbit. The bands with K = 5(−) and 8− also involve an i 13 2 neutron and have high apparent moments of inertia. As well as the ( i 13 2 ) 2 s-band, two other rotation aligned positive-parity bands are observed and they are suggested to be the yrare ( i 13 2 ) 2 neutron bands. The bands are characterized in terms of their most probable Nilsson configurations. The level scheme of 181Os was reinvestigated and the i 13 2 neutron band extended to spin 49 2 + .

Five rotational bands in 172Hf have been observed to high spin following the 160Gd(16O, 4n)172Hf reaction, using γ-γ coincidence techniques. The ground-state band is extended to spin 20+ without backbending, in contrast to the neighbouring even-even isotones. The most strongly populated side-band, consisting of separated odd-spin and even-spin sequences, appears to result from the partial decoupling of an i132 neutron. Three other bands are identified with the following band-heads: an 8− state at 2006 keV with 163 ns half-life; a 6+ state at 1685 keV with a half-life < 16 ns; and a level at 1857 keV with spin 4, 5, 6 or 7 and a half-life < 16 ns. The differences between the bands are discussed in terms of the influence of Coriolis forces and the two-quasiparticle level structure.

The $\ensuremath{\gamma}$-decay and nuclear structure of low-lying yrast and near yrast levels in $^{210}\mathrm{Rn}$ and $^{211}\mathrm{Rn}$ have been investigated. The cascade from the yrast ${6}^{+}$ state in $^{210}\mathrm{Rn}$ branches to two close-lying ${4}^{+}$ states, deduced to be complete mixtures of the ${4}^{+}$ states arising from the proton configuration, and from the neutron-hole intruder configuration. The influence of this proton-neutron-hole interaction on the yrast cascades in $^{211}\mathrm{Rn}$ and $^{206}\mathrm{Rn}$, $^{208}\mathrm{Rn}$ is discussed.

The decay sequence based on the 5/2+(402) proton orbital has been identified in 171Re up to spin 41/2. An anomalous upbend in the alignment is observed below the expected backbend, a phenomenon similar to that observed in the yrast sequence of 172Os. The properties of the 5/2+(402) band can be understood in terms of two crossings, one at low spin with a band based on a deformed intruder configuration, the second at higher spin with a band composed of aligned i13/2 neutrons.

The relative intensities of ground-state rotational band transitions in 158 Dy, 164 Er, 168 Yb, 174 Hf and 180 W have been studied with particular emphasis on the identification of delayed feeding from high- K isomers. The results are interpreted in terms of a simple formulation of the K -conservation model which is introduced to explain the discrepancy between the observed intensity distributions and those expected from the statistical model.

The study of Coulomb excitation in 147Sm has provided improved B(E2) values for six low-lying excited states. The results have been interpreted in the cluster-vibration model as a collective quasi- f 7 2 multiplet with two intruder states. Special attention has been paid to the discussion of the theoretical crossing of the 9 2 1 − and 9 2 2 − states, which leads to a pronounced decrease of the B( E 2; 9 2 1 − → 7 2 1 − ) / B( E 2 ; 9 2 2 − → 7 2 1 − ) ratio at a critical interaction strength. Accordingly, it has been suggested that the 1108 keV state with a large B(E2) value for the transition to the ground state has a 9 2 − spin and parity.