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Rotational structures have been measured using the Jurogam II and GAMMASPHERE arrays at low spin following the Gd155(α,2n)Dy157 and Nd148(C12,5n)Dy155 reactions at 25 and 65 MeV, respectively. We report high-K bands, which are conjectured to be the first candidates of a Kπ=2+γ vibrational band, built on the [505]11/2− neutron orbital, in both odd-ADy155,157 isotopes. The coupling of the first excited K=0+ states or the so-called β vibrational bands at 661 and 676 keV in Dy154 and Dy156 to the [505]11/2− orbital, to produce a Kπ=11/2− band, was not observed in both Dy155 and Dy157, respectively. The implication of these findings on the interpretation of the first excited 0+ states in the core nuclei Dy154 and Dy156 are also discussed.

The energy portfolio is changing for both the United States and Australia. Both countries are rich in fossil fuel reserves and both depend on burning them as a large source of energy. Both export coal and natural gas. Both are moving to more renewable supply of energy, although with different drivers and different degrees of government leadership. The United States has a sizeable nuclear component to its energy generation portfolio, but Australia does not due to a legal prohibition. How each country meets its goals of reduced carbon emissions (official or unofficial goals) is not clear at this time.

CITATION: Majola, S. N. T. et al. 2019. β and γ bands in N=88, 90, and 92 isotones investigated with a five-dimensional collective Hamiltonian based on covariant density functional theory: Vibrations, shape coexistence, and superdeformation. Physical Review C, 100(4). doi:10.1103/PhysRevC.100.044324.

CITATION: Majola, S. N. T., et al. 2019. Spectroscopy of low-spin states in 157Dy : Search for evidence of enhanced octupole correlations. Physical Review C, 100(6):034322, doi:10.1103/PhysRevC.100.034322.

Garrett et al. systematically investigated band-crossing frequencies resulting from the rotational alignment of the first pair of i13/2 neutrons (AB) in rare-earth nuclei. In that study, evidence was found for an odd-even neutron number dependence attributed to changes in the strength of neutron pairing correlations. The present paper carries out a similar investigation at higher rotational frequencies for the second pair of aligning i13/2 neutrons (BC). Again, a systematic difference in band-crossing frequencies is observed between odd-N and even-N Er, Yb, Hf, and W nuclei, but in the BC case, it is opposite to the AB neutron-number dependence. These results are discussed in terms of a reduction of neutron pairing correlations at high rotational frequencies and of the effects of Pauli blocking on the pairing field by higher-seniority configurations. Also playing a significant role are the changes in deformation with proton and neutron numbers, the changes in location of single-particle orbitals as a function of quadrupole deformation, and the position of the Fermi surface with regard to the various ω components of the neutron i13/2 shell.

The first rotational sequences have been assigned to the odd-odd nucleus $^{168}\mathrm{Re}$. Coincidence relationships of these structures with rhenium x rays confirm the isotopic assignment, while arguments based on the $\ensuremath{\gamma}$-ray multiplicity ($K$-fold) distributions observed with the new bands lead to the mass assignment. Configurations for the two bands were determined through analysis of the rotational alignments of the structures and a comparison of the experimental $B(M1)/B(E2)$ ratios with theory. Tentative spin assignments are proposed for the $\ensuremath{\pi}{h}_{11/2}\ensuremath{\nu}{i}_{13/2}$ band, based on energy level systematics for other known sequences in neighboring odd-odd rhenium nuclei, as well as on systematics seen for the signature inversion feature that is well known in this region. The spin assignment for the $\ensuremath{\pi}{h}_{11/2}\ensuremath{\nu}({h}_{9/2}/{f}_{7/2})$ structure provides additional validation of the proposed spins and configurations for isomers in the $^{176}\mathrm{Au} \ensuremath{\rightarrow} ^{172}\mathrm{Ir}\ensuremath{\rightarrow}^{168}\mathrm{Re} \ensuremath{\alpha}$-decay chain.

The transition quadrupole moments. Q(t), of four weakly populated collective bands up to spin similar to 65h in Er-157,Er-158 have been measured to be similar to II eb demonstrating that these sequences are associated with large deformations. However, the data are inconsistent with calculated values from cranked Nilsson-Strutinsky calculations that predict the lowest energy triaxial shape to be associated with rotation about the short principal axis. The data appear to favor either a stable triaxial shape rotating about the intermediate axis or, alternatively, a triaxial shape with larger deformation rotating about the short axis. These new results challenge the present understanding of triaxiality in nuclei. (C) 2011 Elsevier B.V. All rights reserved. (Less)

The lifetimes of the first excited 2^{+} and 4^{+} states in ^{72}Ni were measured at the National Superconducting Cyclotron Laboratory with the recoil-distance Doppler-shift method, a model-independent probe to obtain the reduced transition probability. Excited states in ^{72}Ni were populated by the one-proton knockout reaction of an intermediate energy ^{73}Cu beam. γ-ray-recoil coincidences were detected with the γ-ray tracking array GRETINA and the S800 spectrograph. Our results provide evidence of enhanced transition probability B(E2;2^{+}→0^{+}) as compared to ^{68}Ni, but do not confirm the trend of large B(E2) values reported in the neighboring isotope ^{70}Ni obtained from Coulomb excitation measurement. The results are compared to shell model calculations. The lifetime obtained for the excited 4_{1}^{+} state is consistent with models showing decay of a seniority ν=4, 4^{+} state, which is consistent with the disappearance of the 8^{+} isomer in ^{72}Ni.

Excited states in the N = 88 nucleus Tb-153 were observed up to spin similar to 40 in an experiment utilizing the Gammasphere array. The Tb-153 states were populated in a weak alpha 4n evaporation channel of the Cl-37 + Sn-124 reaction. Two previously known sequences were extended to higher spins, and a new decoupled structure was identified. The pi h(11/2) band was observed in the spin region where other N = 88 isotopes exhibit effects of prolate to oblate shape changes leading to band termination along the yrast line, whereas Tb-153 displays a persistent collective behavior. However, minor perturbations of the very highest state in both signatures of this h(11/2) band are observed, which perhaps signal the start of the transition towards band termination. (Less)

The exact nature of the lowest Kπ=2+ rotational bands in all deformed nuclei remains obscure. Traditionally they are assumed to be collective vibrations of the nuclear shape in the γ degree of freedom perpendicular to the nuclear symmetry axis. Very few such γ bands have been traced past the usual backbending rotational alignments of high-j nucleons. We have investigated the structure of positive-parity bands in the N=90 nucleus Dy156, using the Nd148(C12,4n)Dy156 reaction at 65 MeV, observing the resulting γ-ray transitions with the Gammasphere array. The even- and odd-spin members of the Kπ=2+γ band are observed up to 32+ and 31+, respectively. This rotational band faithfully tracks the ground-state configuration to the highest spins. The members of a possible γ vibration built on the aligned yrast S band are observed up to spins 28+ and 27+. An even-spin positive-parity band, observed up to spin 24+, is a candidate for an aligned S band built on the seniority-zero configuration of the 0+2 state at 676 keV. The crossing of this band with the 0+2 band is at ℏωc=0.28(1)MeV and is consistent with the configuration of the 0+2 band not producing any blocking of the monopole pairing.

High-spin terminating bands in heavy nuclei were first identified in nuclei around Er-158(90). While examples of terminating states have been identified in a number of erbium isotopes, almost nothing is known about the states lying beyond band termination. In the present work, the high-spin structure of Er-156,Er-157,Er-158 has been studied using the Gammasphere spectrometer. The subject of triaxial superdeformation and 'wobbling' modes in Lu nuclei has rightly attracted a great deal of attention. Very recently four strongly or superdeformed (SD) sequences have been observed in Hf-174, and cranking calculations using the Ultimate Cranker code predict that such structures may have significant triaxial deformation. We have performed two experiments in an attempt to verify the possible triaxial nature of these bands. A lifetime measurement was performed to confirm the large (and similar) deformation of the bands. In addition, a high-statistics, thin-target experiment took place to search for linking transitions between the SD bands, possible wobbling modes, and new SD band structures.

High-spin terminating bands in heavy nuclei were first identified in nuclei around Er-158(90). While examples of special terminating states have been identified in a number of erbium isotopes, almost nothing is known about the states lying beyond band termination. In the present work the high-spin structure of Er-157 has been studied using the Gammasphere spectrometer. The subject of triaxial superdeformation and 'wobbling' modes in Lu nuclei has rightly attracted a great deal of attention. Very recently, four strongly or superdeformed (SD) sequences have been observed in Hf-174 and ultimate cranker calculations predict, such structures may have significant triaxial deformation. We have performed two experiments in an attempt to verify the possible triaxial nature of these bands. A lifetime measurement was performed to confirm the large (and similar) deformation of the bands. In addition, a high-statistics, thin-target experiment was run to search for linking transitions between the SD bands and possible wobbling modes.

Two Gammasphere experiments have been performed in order to establish the possible triaxial nature of strongly deformed (SD) bands in 174Hf. A lifetime measurement, using the Doppler-shift attenuation method, confirmed the large deformation of the four previously observed bands in this nucleus with transition quadrupole moments ranging from 12.6 to 13.8 b. These values are significantly larger than those predicted for triaxial minima by ultimate cranker (UC) calculations. A thin-target, high-statistics experiment was also carried out to search for linking transitions between the SD bands. No such transitions, which represent an experimental signature for wobbling modes, were observed. Four additional SD bands were found in 174Hf together with a single SD band in 173Hf. These results indicate that the strongly deformed sequences of N ≈ 102 Hf isotopes behave differently than the triaxial strongly deformed (TSD) bands found in Lu nuclei near N = 92 . The interpretation of these bands in terms of possible stable triaxial deformation is confronted with the experimental findings and UC predictions.

Entry distributions in angular momentum and excitation energy have been measured for several very proton-rich isotopes of Pt and Au. This is the first systematic study of the energy-spin phase space for nuclei near and beyond the proton drip line. Comparisons are made between the distributions associated with proton-unbound Au nuclei and more stable Pt isobars. In 173 Au the first evidence is seen for the limits of excitation energy and angular momentum which a nucleus beyond the proton drip line can sustain.

A significant extension of the level scheme for the odd-odd nucleus $^{172}\mathrm{Re}$ was accomplished through the use of the Gammasphere spectrometer. States up to a tentative spin assignment of 39 were observed and two new structures were identified. Configuration assignments are proposed based on alignment properties and observed band crossings.

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 properties of the nucleus 169Hf have been studied through the fusion evaporation reaction 96Zr(76Ge,3n)169Hf at a beam energy of 310 MeV. The known rotational bands have been extended considerably and 6 new bands have been established, four of which form coupled bands with pronounced M1 connections. Quasiparticle assignments are suggested for the new band structures, and it appears that coupling to vibrational degrees of freedom plays a role. Both coupled bands involve the excitation of quasiprotons. In the region of highest spin, a large alignment gain is interpreted in terms of a mixed crossing where an h 9/2 and an h 11/2 quasiproton provide the two signatures of the aligning configuration.

Excited states in the proton-unbound 173,175,177 Au nuclei were identified for the first time. Level structures associated with three different shapes were observed in 175 Au. While the yrast lines of 175 Au and 177 Au consist of a prolate band built upon the intruder 1/2 + [660] ( i 13/2 ) proton orbital, no sign of collectivity was observed in the lighter 173 Au isotope. Implications for the deformation associated with these structures are discussed with a focus on shape co-existence in the vicinity of the proton-drip line.

Three superdeformed (SD) bands have been found in 168Hf. Lifetime measurements revealed a large quadrupole moment, Q t ∼11.4 e b , for the strongest band (TSD1). Theoretical calculations using the Ultimate Cranker code predict high-spin SD minima (ϵ2∼0.43) with stable triaxial deformations of γ∼+20° and γ∼−15°. The measured Qt value suggests that band TSD1 corresponds, most likely, to a deformation with a positive γ value. This constitutes the first evidence for triaxial superdeformation in an even proton system.

Two excited well-deformed bands have been observed in the semi-magic nucleus Ni-58. One of the bands was observed to partially decay by emission of a prompt discrete alpha particle that feeds the 2949 keV 6(+) spherical yrast state in the daughter nucleus Fe-54. This constitutes the first observation of prompt alpha emission from states lying in the deformed secondary minimum of the nuclear potential. gamma -ray linking transitions via several parallel paths establish the spin. parity, and excitation energy of this deformed band in Ni-58.

Excited states in 171Ir have been observed for the first time. Gamma-rays were assigned to the nucleus by the recoil-decay tagging method. The ground-state band has a structure consistent with an h 11 2 proton coupled to a core of large triaxial deformation. At high spins, a bandcrossing occurs which is interpreted as a change in shape to a prolate deformation. Band-mixing calculations are performed for 171–175Ir. These show that shape-coexistence between triaxial and prolate states in these nuclei follows the same systematics found in their Pt and Os neighbours. The systematics are also compared with deformations calculated for 171–179Ir using the code “Ultimate Cranker”. Dipole bands were also observed, but tilted axis cranking calculations suggest that they are associated with a collective rotation.

The doubly magic superdeformed band in the N = Z nucleus Zn-60 has been identified. Linking transitions connecting this band to the yrast line provide the first spin, parity, and excitation energy measurements for superdeformed states in the A similar to 60 region. The stretched-E2 character and relatively large B(E2) values of these transitions suggest a nonstatistical decay-out process.

High-spin states were studied in ${}^{181,183}\mathrm{Au}$ and resulted in the identification of several new prolate rotational bands based on $\ensuremath{\pi}{i}_{13/2},$ $\ensuremath{\pi}{h}_{9/2},$ $\ensuremath{\pi}{f}_{7/2},$ and $\ensuremath{\pi}{h}_{11/2}$ configurations. The alignment and moment of inertia features of the intruder bands are compared with ground-state bands in Pt nuclei. From these features, it can be concluded that a strongly interacting $(\ensuremath{\pi}{h}_{9/2}{)}^{2}$ alignment is occurring in the $\ensuremath{\pi}{i}_{13/2}$ bands in Au and the ground-state bands in Pt. In addition, bandhead energies and deformation parameters are calculated for deformed configurations in the framework of a microscopic-macroscopic shell-correction model. These calculations are compared with experimental values in Re and Ir, as well as, Au isotopes. Interaction properties between known $\ensuremath{\pi}{h}_{9/2}$ and $\ensuremath{\pi}{f}_{7/2}$ rotational bands are also discussed and compared with results from a cranked-shell model. Experimental $B(M1)/B(E2)$ ratios between these bands are compared with results from a particle-rotor calculation.

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.

High-spin states in {sup 97,98}Rh (Z=45) were populated via the {sup 65}Cu({sup 36}S,xn){sup 97,98}Rh (x=4,3) fusion-evaporation reactions. More than 40 additional transitions have been identified and placed in the decay schemes of these nuclei. The level scheme of {sup 97}Rh has been extended up to tentative spins of J{sup {pi}}=39/2{sup +},37/2{sup {minus}}, and the placement of some of the previously known transitions has been revised. The level structure of {sup 97}Rh indicates a single-particle nature and the observed levels are reproduced well by spherical shell-model calculations. The level scheme of {sup 98}Rh has been extended up to spins J{approximately}20{h_bar} and up to an excitation energy of {approximately}10 MeV. The low-spin structure of {sup 98}Rh (J{le}10{h_bar}), appears to indicate also a single-particle structure, as supported by the stretched coupling scheme [{sup 97}Rh(J{sup {prime}}){circle_times}{nu}(d{sub 5/2})={sup 98}Rh (J)]. {copyright} {ital 1998} {ital The American Physical Society}

We observe for the first time rotational bands of enhanced deformation (ED) in 127 Pr and 128 Pr, and suggest that these bands are built upon πg9/2 ( [404] 9 2 ) in 127 Pr and on the πg9/2νh11/2 orbitals in 128 Pr. These are the lightest isotopes of Pr for which ED bands have been observed. A contrasting trend in the dynamical moments of inertia ( J (2) ) versus N is observed at low frequencies for the “normal-deformed” πh11/2 and “enhanced-deformed” πg9/2 bands of 127 – 131 Pr both experimentally and in self-consistent Woods-Saxon calculations. The trends in J (2) and β2 are correlated with a decreasing probability for pair scattering into the deformation-driving νh9/2/f7/2 ( [541] 1 2 ) orbital.

Gamma rays in the N=Z + 1 nucleus Y-79 were identified using the reaction Si-28(Fe-54, p2n)Y-79 at a 200 MeV beam energy and an experimental setup consisting of an array of Ge detectors and the Recoil Mass Spectrometer at Oak Ridge National Laboratory. With the help of additional gamma-gamma coincidence data obtained with Gammasphere, these gamma rays were found to form a strongly coupled rotational band with rigid-rotor-like behavior. Results of conventional Nilsson-Strutinsky cranked shell model calculations, which predict a deformation of beta(2)similar to 0.4, are in excellent agreement with the properties of this band. Similar calculations for the neighboring N=Z and N=Z + 1 nuclei are also in good agreement with experimental data. This suggests that the presence of the putative T=0 neutron-proton pairing does not significantly affect such simple observables as the moments of inertia of these bands at low spins. [S0556-2813(98)50612-7].

A new Nilsson single-particle structure is proposed for neutron-rich nuclei near ${}^{132}\mathrm{Sn}$. In general, a large reduction in spin-orbit interaction is required and the neutron $N=82$ gap persists in the new set of parameters. The ground state deformations for several isotopic chains are studied with this set and compared with the results of the standard set and with measured ones. Collective bands in two even-even, neutron-rich nuclei are calculated using the projected shell model with the new set of parameters and improved agreement with existing data is found.

Two superdeformed bands of 10 transitions each have been found in {sup 189}Tl extending the mass 190 region of superdeformation down to neutron number N=108. The new bands can be interpreted as signature partners and are proposed to be based on a proton i{sub 13/2} ({Omega}=5/2) configuration, in analogy with the yrast superdeformed band structures in the heavier odd-mass Tl isotopes. The dynamic moments of inertia of all these bands show no noticeable differences as function of N, consistent with an essentially constant quadrupole deformation from the center of the island to its edges. {copyright} {ital 1998} {ital The American Physical Society}

We investigate the independent quasiparticle picture for superdeformed nuclei of the mass-190 region, which is expected to lead to additivity in certain physical quantities. Obvious deviations from additivity are found from both experimental data and projected shell model calculations. The cause of the deviation can be decomposed and identified through this model. Our study suggests that the independent quasiparticle picture may not be fully appropriate for this mass region. {copyright} {ital 1998} {ital The American Physical Society}

Excited states have been identified in neutron-deficient ${}_{ 58}^{125}{\mathrm{Ce}}_{67}$ using the ${}^{58}\mathrm{Ni}{(}^{70}\mathrm{Ge}{,2pn)}^{125}\mathrm{Ce}$ reaction at 280 and 310 MeV. The experiment was performed at the Holifield Radioactive Ion Beam Facility, Oak Ridge National Laboratory. A $\ensuremath{\gamma}$-ray array of six clover plus four single-crystal HPGe detectors was used in conjunction with the Recoil Mass Spectrometer, which had a position sensitive avalanche counter (mass $A$ identification) at its focal plane, together with an ionization chamber (charge $Z$ identification). Two band structures assigned to ${}^{125}\mathrm{Ce}$ are interpreted as based on the $\ensuremath{\nu}{h}_{11/2}[523]{7/2}^{\ensuremath{-}}$ and $\ensuremath{\nu}{d}_{5/2}[402]{5/2}^{+}$ Nilsson orbitals, respectively.

The high-spin level structures of {sup 94,95}Mo (N=52,53) have been investigated via the {sup 65}Cu({sup 36}S, {alpha}p2n){sup 94}Mo and {sup 65}Cu({sup 36}S, {alpha}pn){sup 95}Mo reactions at 142 MeV. The level schemes have been extended up to spin J{approx}19{h_bar} and excitation energies E{sub x}{approx}12 MeV. Spherical shell-model calculations have been performed and compared with the experimental energy levels. The level structure of {sup 94}Mo exhibits a single-particle nature and the higher-angular-momentum states are dominated by the excitation of a g{sub 9/2} neutron across the N=50 shell gap. The level sequences observed in {sup 95}Mo have been interpreted on the basis of the spherical shell model and weak coupling of a d{sub 5/2} or a g{sub 7/2} neutron to the {sup 94}Mo core. {copyright} {ital 1998} {ital The American Physical Society}

An excited well-deformed rotational band has been observed in the N = Z odd-odd nucleus Cu-58. The first excited state in this band decays via gamma emission to the spherical states associated with the first minimum in the potential, thus providing for its unambiguous assignment to Cu-58. I, contrast, its bandhead decays via emission of a prompt 2.4(1) MeV proton to an excited state in the daughter nucleus Ni-57. This is the first observation of proton decay from states associated with a deformed secondary minimum in the potential. Self-consistent Hartree-Fock calculations reproduce well both the large collectivity of this band and the general trend of its moment of inertia.

Two sets of strongly coupled rotational bands have been identified in Zn-62. These bands have been observed up to the terminating states of their respective configurations. Lifetime measurements indicate that the transition quadrupole moments in these bands decrease as termination is approached. These results establish the first terminating states of rotational bands in the A similar to 60 mass region and confirm the predicted loss of collectivity associated with smooth band termination.

High-spin states of a number of nuclei near Ni-56 have been studied by means of the Si-28(Ar-36,x alpha ypzn) reaction. The GAMMASPHERE array in conjunction with light charged particle and neutron detectors were used to identify and cleanly select the fusion-evaporation products. In addition to significantly extending the level schemes of many previously known N = Z nuclei from Fe-52 to Cu-58, excited states in the one-neutron-hole nucleus Ni-55 and high-spin rotational bands in the vicinity of the doubly-magic Ni-56 have been established for the first time. Spherical-fp shell model and cranked Hartree-Fock calculations employing several Skyrme-type effective interactions have been used to interpret these data. The calculated moments of inertia of the rotational bands show considerable sensitivity to the details of the effective interactions.

Superdeformation studies in {sup 189,191,192}Tl at Gammasphere are discussed. New results on {sup 191}Tl are the observation of interband transitions between the signature partner E2 bands and the measurement of an average quadrupole moment (Q{sub 0} = 18 {+-} 1 eb) for these superdeformed structures. These data enable them to derive absolute M1 strengths and confirm that the 81st proton occupies the [642]5/2 orbital. Tentative data for one superdeformed sequence in {sup 189}Tl are consistent with the prediction of a decrease in quadrupole deformation for the lightest nuclei at the limit of this island of superdeformation.

The high-spin level structures of {sup 96,97,98}Ru (Z=44) have been investigated using the {sup 65}Cu({sup 36}S,pxn){sup 96,97,98}Ru (x=4,3,2) reactions. About 130 new transitions have been observed and unambiguously placed in the decay schemes of these nuclei. The level schemes have been extended up to spin J{approx}22{endash} 34{h_bar}, and excitation energies E{sub x}{approx}20{minus}24 MeV. Spherical shell model calculations have been performed and theoretical level energies compared with experimental values. Calculations using {sup 88}Sr as the core give a reasonable agreement for the observed energy levels up to J{le}16{h_bar} (the maximum angular momentum possible within this restricted model space). The higher angular momentum states are dominated by the {nu}(g{sub 9/2}){sup {minus}1} configuration, associated with breaking of the N=50 core. The experimental indications for this `core breaking` are (i) the observation of {gamma} rays with energies E{sub {gamma}}{approx} 2 MeV at intermediate spins and (ii) the fragmentation of {gamma}-ray intensity into a number of branches. A cascade of E2 transitions of nearly equal transition energies has been observed in {sup 98}Ru after the core breaking (J{ge}16{h_bar}), possibly manifesting vibrational behavior. {copyright} {ital 1998} {ital The American Physical Society}

A high-spin rotational cascade of six gamma rays has been observed in Zn-62. The quadrupole moment of 2.7(-0.5)(+0.7) e b measured for this band corresponds to a deformation beta(2) = 0.45(-0.07)(+0.10). The properties of this band are in excellent agreement with calculations that predict high-spin superdeformed bands in Zn-62 with deformations beta(2) = 0.41-0.49. These results establish a new region of superdeformation for nuclei with neutron and proton numbers N, Z approximate to 30-32.

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.

Excited states in {sup 182}Pt have been studied via the heavy-ion reactions {sup 170}Yb({sup 16}O,4n), {sup 162}Dy({sup 24}Mg,4n), and {sup 163}Dy({sup 24}Mg,5n). {gamma}-ray coincidence measurements were performed with arrays of HPGe detectors at the McMaster University Tandem Accelerator Laboratory ({sup 16}O-induced reaction) and the Institut de Physique Nucl{acute e}aire, Orsay ({sup 24}Mg-induced reactions). The ground-state rotational band has been extended to I=26{h_bar}, and six new band structures have been identified and assigned quasiparticle configurations. The {gamma}-vibrational band and the band built upon the first excited 0{sup +} state have also been extended. Properties of the rotational bands are compared with cranked-shell-model and total-Routhian-surface calculations. Evidence concerning shape coexistence at low spin and band crossings at high spin is discussed. {copyright} {ital 1997} {ital The American Physical Society}

The occurrence of an energy inversion of the signatures of a rotational band in odd-odd deformed nuclei is discussed. A survey of this signature inversion in πh 11 2 νh 11 2 bands in A = 120 – 130 nuclei is given, and also for the πh 11 2 νi 13 2 bands around A = 160. New data on 164Tm indicates that the signature inversion is almost absent for the yrast πh 11 2 νi 13 2 band, but present in three other structures. Suggestions for the selective origin of this effect is given in terms of a particle-rotor calculation.