Search

An extensive study of the level structure of Co62 has been performed following a complex multinucleon transfer reaction, Mg26(Ca48, 2α3npγ)Co62, at beam energies of 275, 290, and 320 MeV. The combination of the Gammasphere array, the fragment mass analyzer, and a focal-plane ionization chamber was used to identify and delineate excited levels in Co62. A considerable extension to the Co62 level scheme is proposed with firm spin-parity values assigned on the basis of angular distribution and correlation analyses. Various level sequences built upon states of single-particle character have been observed, and an interpretation of these structures in the framework of the spherical shell model is presented. At moderate spins, two dipole bands have been observed and, based on their phenomenological study, a possible magnetic rotation character is suggested. However, theoretical calculations performed using the particle rotor model support magnetic rotation for only one of these dipole bands.

Single-particle and collective excitations in Zn66 have been investigated via the multinucleon transfer reaction, Mg26(Ca48, α4nγ) using the Gammasphere multidetector array and the Fragment Mass Analyzer. In addition to confirming and complementing the previously known low-spin structure, a new quasirotational band comprising several stretched E2 transitions has been established to high spins. However, due to fragmentary nature of its decay, it was not possible to link this sequence to the low-lying states and, thus, determine the absolute excitation energies, spins, and parities unambiguously. Large-scale shell-model calculations employing the JUN45 and jj44b effective interactions are able to successfully describe the low-spin structure and herewith confirm that it is dominated by single-particle excitations. The newly established rotational cascade is compared with known superdeformed bands in the A≈60-70 mass region, and with results of calculations performed within the frameworks of the cranked shell model and the adiabatic and configuration-fixed constrained covariant density functional theory and the quantum particle-rotor model.

Rotational structures have been measured using the Jurogam II and GAMMASPHERE arrays at low spin following the 155Gd({\alpha},2n)157Dy and 148Nd(12C, 5n)155Dy reactions at 25 and 65 MeV, respectively. We report high-K bands, which are conjectured to be the first candidates of a K{\pi}= 2+ {\gamma} vibrational band, built on the [505]11/2- neutron orbital, in both odd-A 155, 157Dy isotopes. The coupling of the first excited K=0+ states or the so-called \b{eta} vibrational bands at 661 and 676 keV in 154Dy and 156Dy to the [505]11/2- orbital, to produce a K{\pi}=11/2- band, was not observed in both 155Dy and 157Dy, respectively. The implication of these findings on the interpretation of the first excited 0+ states in the core nuclei 154Dy and 156Dy are also discussed., Comment: Published in Physical Rev C

A previous study of symmetric collisions of massive nuclei has shown that current models of multinucleon transfer (MNT) reactions do not adequately describe the transfer product yields. To gain further insight into this problem, we have measured the yields of MNT products in the interaction of 977 (E/A=4.79 MeV) and 1143 MeV (E/A=5.60 MeV) Hg204 with Pb208. We find that the yield of multinucleon transfer products are similar in these two reactions and are substantially lower than those observed in the reaction of 1257 MeV (E/A=6.16 MeV) Hg204+Pt198. We compare our measurements with the predictions of the GRAZING-F, dinuclear systems (DNS), and improved quantum molecular dynamics (ImQMD) models. For the observed isotopes of the elements Au, Hg, Tl, Pb, and Bi, the measured values of the MNT cross sections are orders of magnitude larger than the predicted values. Furthermore, the various models predict the formation of nuclides near the N=126 shell, which are not observed.

The neutron-rich dysprosium isotopes $^{168}$Dy$_{102}$ and $^{169}$Dy$_{103}$ have been investigated using the EURICA γ-ray spectrometer, following production via in-flight fission of a high-intensity uranium beam in conjunction with isotope separation through the BigRIPS separator at RIBF in RIKEN Nishina Center. For $^{168}$Dy, a previously unreported isomer with a half-life of 0.57(7) μs has been identified at an excitation energy of 1378 keV, and its presence affirmed independently using γ-γ-γ coincidence data taken with Gammasphere via two-proton transfer from an enriched $^{170}$Er target performed at Argonne National Laboratory. This isomer is assigned Jπ=Kπ=(4−) based on the measured transition strengths, decay patterns, and the energy systematics for two-quasiparticle states in N=102 isotones. The underlying mechanism of two-quasiparticle excitations in the doubly midshell region is discussed in comparison with the deformed QRPA and multi-quasiparticle calculations. In $^{169}$Dy, the B(E2) value for the transition de-exciting the previously unreported Kπ=(1/2−) isomeric state at 166 keV to the Kπ=(5/2−) ground state is approximately two orders of magnitude larger than the E2 strength for the corresponding isomeric-decay transition in the N=103 isotone $^{173}$Yb, suggesting the presence of a significant γ-vibrational admixture with a dominant neutron one-quasiparticle component in the isomeric state.

The neutron-rich dysprosium isotopes ¹⁶⁸Dy₁₀₂ and ¹⁶⁹Dy₁₀₃ have been investigated using the EURICA γ-ray spectrometer, following production via in-flight fission of a high-intensity uranium beam in conjunction with isotope separation through the BigRIPS separator at RIBF in RIKEN Nishina Center. For ¹⁶⁸Dy, a previously unreported isomer with a half-life of 0.57(7) μs has been identified at an excitation energy of 1378 keV, and its presence affirmed independently using γ-γ-γ coincidence data taken with Gammasphere via two-proton transfer from an enriched ¹⁷⁰Er target performed at Argonne National Laboratory. This isomer is assigned Jπ = Kπ = (4⁻) based on the measured transition strengths, decay patterns, and the energy systematics for two-quasiparticle states in N = 102 isotones. The underlying mechanism of two-quasiparticle excitations in the doubly midshell region is discussed in comparison with the deformed QRPA and multi-quasiparticle calculations. In ¹⁶⁹Dy, the B(E2) value for the transition de-exciting the previously unreported Kπ = (1/2⁻) isomeric state at 166 keV to the Kπ = (5/2⁻) ground state is approximately two orders of magnitude larger than the E2 strength for the corresponding isomeric-decay transition in the N = 103 isotone ¹⁷³Yb, suggesting the presence of a significant γ-vibrational admixture with a dominant neutron one-quasiparticle component in the isomeric state.

© 2018 American Physical Society. Excited states in the neutron-rich isotopes P33 and P34 were populated by the O18+O18 fusion-evaporation reaction at Elab=24 MeV. The Gammasphere array was used along with the Microball particle detector array to detect γ transitions in coincidence with the charged particles emitted from the compound nucleus S36. The use of Microball enabled the selection of the proton emission channel. It also helped in determining the exact position and energy of the emitted proton; this was later employed in kinematic Doppler corrections. 16 new transitions and 13 new states were observed in P33 and 21 γ rays and 20 energy levels were observed in P34 for the first time. The nearly 4π geometry of Gammasphere allowed the measurement of γ-ray angular distributions leading to spin assignments for many states. The experimental observations for both isotopes were interpreted with the help of shell-model calculations using the (0+1)ω PSDPF interaction. The calculations accounted for both the 0p-0h and 1p-1h states reasonably well and indicated that 2p-2h excitations might dominate the higher-spin configurations in both P33 and P34.

Electromagnetic quadrupole transition strength is a sensitive probe of the evolution of the structure of nuclei, particularly the competition between collectivity and magicity. We have performed a new lifetime measurement of the 21+ state of 12Be to study the interplay of these phenomena. The lifetime was measured with the Doppler Shift Attenuation Method using the γ-ray detector GRETINA. Excited states of 12Be were produced via inelastic scattering at 55 MeV/nucleon, using several different targets to control for systematic uncertainties in the stopping powers. The lifetime is determined to be τ=1.38±0.10(stat)±0.19(sys) ps, which is about half the previously reported value at twice the precision. The reduced transition strength deduced from this result is B(E2;21+→01+)=14.2±1.0(stat)±2.0(sys) e2fm4, which supports the quenching of the N=8 shell gap in 12Be.

Fast-rotating N=151 isotones 245Pu, 247Cm and 249Cf have been studied through inelastic excitation and transfer reactions with radioactive targets. While all have a ground-state band built on a νj15/2[734]9/2− Nilsson configuration, new excited bands have also been observed in each isotone. These odd-N excited bands allow a comparison of the alignment behavior for two different configurations, where the νj15/2 alignment is either blocked or allowed. The effect of higher order deformations is explored through cranking calculations, which help clarify the elusive nature of νj15/2 alignments. Keywords: Superheavy, Neutron-rich, Inelastic and transfer reactions, Rotational alignments, Higher-order deformations

An experiment populating low/medium-spin states in Dy156 was performed to investigate the possibility of tetrahedral symmetry in this nucleus. In particular, focus was placed on the low-spin, negative-parity states since recent theoretical studies suggest that these may be good candidates for this high-rank symmetry. The states were produced in the Nd148(C12,4n) reaction and the Gammasphere array was utilized to detect the emitted γ rays. B(E2)/B(E1) ratios of transition probabilities from the low-spin, negative-parity bands were determined and used to interpret whether these structures are best associated with tetrahedral symmetry or, as previously assigned, to octupole vibrations. In addition, several other negative-parity structures were observed to higher spin and two new sequences were established.

States in Tl209 were populated using a multinucleon transfer reaction with a Xe136 beam impinging on a thick Pb208 target at E=785 MeV. The beam was pulsed at 825-ns intervals in order to perform isomer decay spectroscopy. The known Jπ=17/2+ isomer in Tl209 was located at 1228(4) keV and measured to have a half-life of T1/2=146(10) ns. A second isomer with Jπ=13/2+ was found to have T1/2=14(5) ns. The previously suggested low-energy X and Y transitions were found to have energies 57(2) and 47(2) keV respectively, while the measurement of conversion coefficients and a new decay path make the spin assignments below the isomers experimentally firm. Correlating the delayed γ transitions with the prompt beam flash allowed the decay of states above the isomer to be found. The longer-lived isomer represents full alignment of the simplest two-particle, one-hole configuration and illuminates the remarkably weak coupling of the proton hole to the Pb210 core.

States in Tl209 were populated using a multinucleon transfer reaction with a Xe136 beam impinging on a thick Pb208 target at E=785 MeV. The beam was pulsed at 825-ns intervals in order to perform isomer decay spectroscopy. The known Jπ=17/2+ isomer in Tl209 was located at 1228(4) keV and measured to have a half-life of T1/2=146(10) ns. A second isomer with Jπ=13/2+ was found to have T1/2=14(5) ns. The previously suggested low-energy X and Y transitions were found to have energies 57(2) and 47(2) keV respectively, while the measurement of conversion coefficients and a new decay path make the spin assignments below the isomers experimentally firm. Correlating the delayed γ transitions with the prompt beam flash allowed the decay of states above the isomer to be found. The longer-lived isomer represents full alignment of the simplest two-particle, one-hole configuration and illuminates the remarkably weak coupling of the proton hole to the Pb210 core.

The decay of a Kπ=8- isomer in Pu244 and the collective band structures populating the isomer were studied using deep inelastic excitations with Ti47 and Pb208 beams, respectively. Precise measurements of M1/E2 branching ratios in the band confirm a 9/2-[734]ν - 7/2+[624]ν configuration assignment for the isomer, validating the systematics of Kπ=8-, two-quasineutron isomers observed in even-Z, N=150 isotones. These isomers around the deformed shell gap at N=152 provide critical benchmarks for theoretical predictions of single-particle energies in this gateway region to superheavy nuclei.

The first rotational sequences have been assigned to the odd-odd nucleus Re168. Coincidence relationships of these structures with rhenium x rays confirm the isotopic assignment, while arguments based on the γ-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 πh11/2νi13/2 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 πh11/2ν(h9/2/f7/2) structure provides additional validation of the proposed spins and configurations for isomers in the Au176 → Ir172→Re168 α-decay chain.

The yields of over 200 projectile-like fragments (PLFs) and target-like fragments (TLFs) from the interaction of (Ec.m.=450 MeV) Xe136 with a thick target of Pb208 were measured using Gammasphere and off-line γ-ray spectroscopy, giving a comprehensive picture of the production cross sections in this reaction. The measured yields were compared to predictions of the grazing model and the predictions of Zagrebaev and Greiner using a quantitative metric, the theory evaluation factor tef. The grazing model predictions are adequate for describing the yields of nuclei near the target or projectile but they grossly underestimate the yields of all other products. The predictions of Zagrebaev and Greiner correctly describe the magnitude and maxima of the observed TLF transfer cross sections for a wide range of transfers (ΔZ=-8 to ΔZ=+2). However, for ΔZ=+4, the observed position of the maximum in the distribution is four neutrons richer than the predicted maximum. The predicted yields of the neutron-rich N=126 nuclei exceed the measured values by two orders of magnitude. Correlations between TLF and PLF yields are discussed.

International audience; 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.

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 02+ state at 676 keV. The crossing of this band with the 02+ band is at ?ωc=0.28(1)MeV and is consistent with the configuration of the 02+ band not producing any blocking of the monopole pairing.

Fast-rotating N=151 isotones 245Pu, 247Cm and 249Cf have been studied through inelastic excitation and transfer reactions with radioactive targets. While all have a ground-state band built on a νj15/2[734]9/2- Nilsson configuration, new excited bands have also been observed in each isotone. These odd-N excited bands allow a comparison of the alignment behavior for two different configurations, where the νj15/2 alignment is either blocked or allowed. The effect of higher order deformations is explored through cranking calculations, which help clarify the elusive nature of νj15/2 alignments.

Expérience réalisée au NSCL

We report on the first measurement of the fission barrier height in a heavy shell-stabilized nucleus. The fission barrier height of No254 is measured to be Bf=6.0±0.5 MeV at spin 15 and, by extrapolation, Bf=6.6±0.9 MeV at spin 0. This information is deduced from the measured distribution of entry points in the excitation energy versus spin plane. The same measurement is performed for Th220 and only a lower limit of the fission barrier height can be determined: Bf(I)>8 MeV. Comparisons with theoretical fission barriers test theories that predict properties of superheavy elements.

Although the observation of wobbling was once thought to be possibly confined to lutetium isotopes in N≈94 nuclei, the identification of this exotic collective mode in 167Ta has raised the question of the role of the proton Fermi surface with regard to this phenomenon. To investigate this issue, an experiment was performed to populate high-spin states in the N=94 nucleus 169Re. The heavy-ion reaction 55Mn+118Sn was used in conjunction with Gammasphere to detect the emitted γ rays. More than 130 new transitions were added to the 169Re level scheme, including the first identification of the πi13/2 rotational sequence in this nucleus. This configuration is the structure on which all known wobbling sequences are based, but no wobbling band was observed, likely owing to the fact that the πi13/2 sequence is located at a relatively high energy in comparison with the other structures found in 169Re. Nine decay sequences are now established in this nucleus and are described within the context of the cranked shell model. In addition, significant extension of the level scheme of the odd-odd 170Re nucleus was possible and a discussion of the residual interactions for the πh 9/2νi13/2 and πi13/2νi13/2 configurations in this region is given as well.

Excited states of 76Ge have been populated in above-barrier Coulomb excitation and inelastic scattering of a 530-MeV 76Ge beam on a 238U target and studied using in-beam γ-ray spectroscopy with the Gammasphere array. The γ band was extended considerably and one new band was identified. Comparisons of the γ band with collective- and shell-model calculations suggest that 76Ge may be a rare example of a nucleus exhibiting rigid triaxial deformation in the low-lying states.

The nuclei 65,67Cu were studied in reactions between a 430-MeV 64Ni beam and a thick 238U target with the Gammasphere array. Decay schemes for both nuclei have been extended, with spin and parity assignments of observed states constrained by measured γ-ray angular distributions and correlations. Positive-parity level structures, based on p3/2 protons coupled to negative-parity states in the Ni cores, have been identified above the known 9/2+ states. In 67Cu, a negative-parity dipole band built upon a πf7/2-1 state has been observed, as were two shorter negative-parity sequences. A qualitative description of the level structures has been obtained through comparison with systematics of the odd-A57-71Cu isotopes and with states in the neighboring even-even Ni and Zn cores. Shell-model calculations using JUN45 and jj44b effective interactions were performed for 65,67Cu, with jj44b providing overall better agreement with the data. Both are limited, however, by the restriction that the f7/2 and g9/2 orbitals are not available simultaneously in the basis. Proton f7/2 and neutron g9/2 orbitals are required for the full negative-parity spectrum of states, while g9/2 protons and neutrons are both important for positive-parity levels. The latter states are found to be better described in terms of weak coupling of a proton to the Ni core.

Low-lying collective excited states of 194Pt have been studied via the 12C(194Pt,194Pt*) projectile Coulomb excitation reaction at 85% of the Coulomb barrier (850 MeV) using the Gammasphere Ge-detector array at Argonne National Laboratory. Absolute E2 transition strengths have been obtained from the Coulex cross sections that were deduced from the relative γ-ray yields. They are discussed with respect to the structure suggested by the O(6) symmetry of the Interacting Boson Model.

The lifetime of the Jπ=21+ state in 10C was measured using the Doppler shift attenuation method following the inverse kinematics p(10B ,n)10C reaction at 95 MeV. The 21+ state, at 3354 keV, has τ=219±(7)stat±(10)sys fs, corresponding to a B(E2)" of 8.8(3) e2 fm4. This measurement, combined with that recently determined for 10Be [9.2(3) e2 fm4], provides a unique challenge to ab initio calculations, testing the structure of these states, including the isospin symmetry of the wave functions. Quantum Monte Carlo calculations using realistic two- and three-nucleon Hamiltonians that reproduce the 10Be B(E2) value generally predict a larger 10C B(E2) probability but with considerable sensitivity to the admixture of different spatial symmetry components in the wave functions and to the three-nucleon potential used.

The available experimental information on 34P has been greatly increased through the analysis of γ decays in coincidence with protons from the interaction of an 18O beam at 24 MeV with an 18O target. Light charged particles from the reaction were detected with Microball, and multiple γ-ray coincidences with Gammasphere. Many observed γ transitions have been identified and placed in the level scheme. Additionally, for most states, spins have been assigned based on measured γ-ray angular distributions while parities were inferred from lifetimes determined through Doppler-broadened line-shape analysis. Most of the states observed have been interpreted in terms of shell-model calculations using the WBP-a and SDPF-NR interactions having one particle in the 0f7/2 or 1p3/2 orbital. The two calculations agree almost equally well with the data resulting in root-mean-square differences of about 200 keV. However, a few high-lying states observed with long lifetimes challenge current calculations. Two of these may be associated with stretched πf7/2⊗νf7/2 states, but the calculations overpredict their energies by 2-3 MeV. Furthermore, a long-lived 7919-keV state is established for which no explanation is available at present.

New high-spin microsecond isomers, with Jπ=(31+) and Jπ=(28), have been identified in 206Bi at 10170 and 9233keV, respectively, using γ-ray coincidence spectroscopy following deep-inelastic reactions with the 76Ge+208Pb system. Yrast and near-yrast levels populated in the decay of these isomers have been located and interpreted with the help of shell-model calculations. The states identified at energies up to approximately 7 MeV can be described well in terms of one-proton-particle, three-neutron-hole couplings.

Low-lying collective states of 154Sm are studied via the 12C(154Sm,154Sm*) Coulomb excitation reaction at 85% of the Coulomb barrier (570 MeV) using the Gammasphere Ge-detector array. Absolute transition strengths are obtained from the Coulomb excitation cross sections deduced from the relative γ-ray yields. The results include transition strengths for E2 decays of energy levels in the low-spin part of the first excited Kπ=0+ rotational band of 154Sm. The agreement of these results with the confined β-soft rotor model predictions establishes the assignment of this band as a β band.

Gamma rays assigned to 2872Ni44 have been identified with Gammasphere in deep-inelastic reactions involving a 450-MeV 76Ge beam and a 198Pt target. Using a combination of spectra produced by double gates on the known 454-, 843-, and 1095-keV members of the ground-state cascade, a coincident line at 199 keV has been identified and is tentatively assigned as the 8+→6 + transition. These γ-ray coincidences have been observed only in prompt events, indicating an 8+ half-life below 20 ns and requiring a large B(E2) enhancement compared to that expected from a seniority scheme. This value is consistent with models showing decay to a seniority ν=4, 6+ level that is depressed by the same two-body interaction responsible for the rather low 1095-keV 21+ energy, as compared to the valence-symmetry counterpart 4494Ru50.

The energy of the lowest deformed 2-particle 2-hole (2p2h) 0+ state in even-even N = 20 nuclei is a key observable directly related to the size of the neutron N = 20 shell closure. 34Si, with 14 protons and 20 neutrons, lies at the boundary of the "island of inversion", where the deformed 2p2h 0+ state is the ground state in even-A nuclei. In 34Si, the 2p2h 0+ state is expected to be particularly low lying - in some theories it is even predicted to lie below the first 2 + state. While there have been a number of attempts, using various techniques, no experiment to date has been able to firmly locate the 34Si 2p2h 0+ state although a number of candidates have been suggested. Here we present, for the first time, data obtained from a fusion-evaporation reaction 18O(18O, 2p) to produce 34Si. Gammasphere and Microball were used to detect γ-γ coincidences and charged particles (two protons), respectively. The increased sensitivity of this experiment using γ-γ coincidences and a high charged-particle detection efficiency helped to exclude previously reported candidates and provided a stringent limit on the anticipated γ decay from the first 2+ state to the 2p2h 0+ state.

Excited states in the neutron-deficient nucleus Ta167 were studied through the Sn120(V51,4n) reaction. Twelve rotational bands have been observed and the relative excitation energy of each sequence is now known owing to the multiple interband connections. Several quasineutron alignments were observed that aided in the quasiparticle assignments of these bands. The resulting interpretation is in line with observations in neighboring nuclei. Trends in the wobbling phonon energy seen in Lu161,163,165,167 and Ta167 are also discussed and particle-rotor model calculations (assuming constant moments of inertia) are found to be inconsistent with the experimental data.

A three-quasiparticle isomer with τ=170(8) μs and Kπ= (19/2 +) has been identified in the neutron-rich isotope Ho169. The isomer decays with K-forbidden transitions to members of a band associated with the 7/2-[523] proton configuration, whose structure is characterized through analysis of the in-band γ-ray branching ratios. In the isotone Tm171, the rotational band based on the known 19/2+, three-quasiparticle isomer has also been observed. Alternative one-proton two-neutron configurations for the isomer in Ho169 are discussed in terms of multiquasiparticle calculations and through a comparison with the structures observed in Tm171.

High-spin states in the odd-odd nucleus Ta168 have been populated in the Sn120(V51,3n) reaction. Two multi-quasiparticle structures have been extended significantly from spin ~20 to above 40. As a result, the first rotational alignment has been fully delineated and a second band crossing has been observed for the first time in this nucleus. Configurations for these strongly coupled rotational bands are proposed based on signature splitting, B(M1)/B(E2) ratio information, and observed rotation-alignment behavior. Properties of the observed bands in Ta168 are compared to related structures in the neighboring odd-Z, odd-N, and odd-odd nuclei and are discussed within the framework of the cranked shell model.

High-spin states in the odd-odd nucleus Ta166 are investigated through the 5n channel of the V51+Sn120 reaction. Four new bands are observed and linked into the previous level scheme. Configurations for the bands are proposed, based on measured alignments and B(M1)/B(E2) transition strength ratios.

Isomers in the neutron-rich nucleus W190 have been characterized. A 10 - state from the 9/2-[505] 11/2+[615] two-neutron configuration with a 240-μs lifetime decays via a K-allowed, 97-keV, M2 transition to an 8+ state with a 160-ns lifetime from the 9/2-[505] 7/2-[503] neutron configuration. New states have also been identified in W188, including a Kπ=8-, 158-ns isomer from the 9/2-[614] 7/2+[404] two-proton configuration. The K hindrance is observed to decrease with increasing neutron number, consistent with a trend toward increasing triaxial softness.

The stable and neutron-rich isotopes Er168, Er170, and Er172 have been studied with Gammasphere using inelastic excitation with energetic Xe136 beams. The previously assigned structures based on the proposed Kπ=4- isomeric intrinsic states in both Er168 and Er170 have been re-evaluated and an equivalent band identified in Er172. In Er170, the identification of a Kπ=6- band with transitions close in energy to those of the 4 - band leads to a modified interpretation, since the overlap would have compromised previous analyses. The gK-gR values for the 4- bands deduced from the in-band γ-ray intensities for the sequence of isotopes suggest a predominantly two-neutron configuration in Er168, an equally mixed two-neutron, two-proton configuration in Er170, and a two-proton configuration in Er172. A comprehensive decay scheme for the previously proposed 6+ isomer in Er172 has also been established, as well as band structures built on this isomer that closely resemble the 6+ and 7- two-neutron structures known in the isotone Yb174. The implied K hindrances are discussed. The main decay path of the 6+ isomer occurs through the newly identified 4- isomer. The measured lifetimes of the 4 - and 6+ isomers in Er172 are 57(3) and 822(90) ns, respectively. Multiquasiparticle calculations support the suggested configuration changes across the isotopic chain.

Chopped-beam techniques and γ-ray spectroscopy with Gammasphere have been used to measure the lifetime of the 1112-keV 8- isomeric state in Er174. The value obtained of τ=5.8(4) s corresponds to a reduced hindrance of fν=98 for the 163-keV E1 transition to the 8+ state of the ground-state band, in good agreement with the systematics of the corresponding E1 strengths in the N=106 isotones. The K-mixing in the 8- states is calculated in the context of the particle-rotor model and used to extract the underlying reduced hindrances.

High-spin states in the neutron-rich nucleus Ta185, populated in the decay of a long-lived, three-quasiparticle state, have been studied using deep-inelastic reactions with Xe136 ions and a W186 target. The lifetime of the isomer has been measured as 17(2) ms and the spin and parity determined to be Kπ=21/2-, leading to a π7/2+[404]ν3/2-[512]11/2+[615] configuration assignment. The isomer decays into the rotational band built upon the π9/2-[514] intrinsic state via K-forbidden transitions with reduced hindrances of 52 and 71. The π9/2-[514] state is itself an isomer with a lifetime of 17(3) ns. It decays via K-allowed E1 transitions to states in the π7/2+[404] band with strengths that are similar to equivalent transitions in the lighter tantalum isotopes.

The collective wobbling mode, the strongest signature for the rotation of a triaxial nucleus, has previously been seen only in a few Lu isotopes in spite of extensive searches in nearby isotopes. A sequence of transitions in the N=94 Ta167 nucleus exhibiting features similar to those attributed to the wobbling bands in the Lu nuclei has now been found. This band feeds into the πi13/2 band at a relative energy similar to that seen in the established wobbling bands and its dynamic moment of inertia and alignment properties are nearly identical to the i13/2 structure over a significant frequency range. Given these characteristics, it is likely that the wobbling mode has been observed for the first time in a nucleus other than Lu, making this collective motion a more general phenomenon.

Excited states in the odd-AGa71,73,75,77 nuclei have been populated in deep-inelastic reactions of a Ge76 beam at 530 MeV with a thick U238 target. High-spin sequences built upon the 9/2+, 5/2-, and 3/2- states were identified in all four isotopes. A comparison of the observed structures with the yrast positive-parity states in the neighboring even-even Zn cores indicates that the newly identified levels may be regarded as arising from the relatively weak coupling of the odd proton to the core states. However, significant contributions from broken pairs are expected to be present in this region of excitation energy. The present data set also provides clarification of previously reported decay paths of the low-energy levels in Ga71,73,75,77.

The nucleus Ge77 was studied through the Ge76(C13,C12)Ge77 reaction at a sub-Coulomb energy. The angular distributions of γ rays depopulating excited states in Ge77 were measured in order to constrain spin and parity assignments. Some of these assignments are of use in connection with neutrinoless double beta decay, where the population of states near the Fermi surface of Ge76 was recently explored using transfer reactions.

Identification of near-yrast states in the β-stable nucleus 91Zr51 has been carried out using the fusion evaporation reaction, 82Se(13C,4n)91Zr at an incident beam energy of 50 MeV. States above the reported r = 6 μs, Iπ = 21/2+ isomeric level at Ex = 3167 keV have been identified for the first time in this work, a tentative decay scheme of near-yrast states to excitation energies in excess of 10 MeV has been constructed. These states are of relevance to shell model structures formed via limited valence-space configurations in this semi-magic N = 51 nucleus.

We describe the new ENDF/B-VIII.0 evaluated nuclear reaction data library. ENDF/B-VIII.0 fully incorporates the new IAEA standards, includes improved thermal neutron scattering data and uses new evaluated data from the CIELO project for neutron reactions on 1H, 16O, 56Fe, 235U, 238U and 239Pu described in companion papers in the present issue of Nuclear Data Sheets. The evaluations benefit from recent experimental data obtained in the U.S. and Europe, and improvements in theory and simulation. Notable advances include updated evaluated data for light nuclei, structural materials, actinides, fission energy release, prompt fission neutron and γ-ray spectra, thermal neutron scattering data, and charged-particle reactions. Integral validation testing is shown for a wide range of criticality, reaction rate, and neutron transmission benchmarks. In general, integral validation performance of the library is improved relative to the previous ENDF/B-VII.1 library.