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Excited states in 137Xe have been studied by using the near-barrier single-neutron transfer reactions 13C(136Xe,12C )137Xe and 9Be(136Xe,8Be )137Xe in inverse kinematics.Particle- and particle- coincidence measurements have been performed with the Phoswich Wall and Digital Gammasphere detector arrays. Evidence is found for a 13/2+2 level (E = 3137 keV) and for additional high-lying 3/2– and 5/2– states. The results are discussed in the framework of realistic shell-model calculations. These calculations are also extended to the 13/2+1 and 13/2+2 levels in the N = 83 isotonic chain. Furthermore, they indicate that there is a need for a value of the neutron 0i13/2 single-particle energy (ESPE = 2366 keV) lower than the one proposed in the literature. It is also demonstrated that the population patterns of the j = l ± 1/2 single-particle states in 137Xe are different for the two targets used in these measurements and the implications of this effect are addressed.

International audience; High-spin states in Xe-124 have been populated using the Se-80(Ca-48,4n) reaction at a beam energy of 207 MeV and high-multiplicity, gamma-ray coincidence events were measured using the Gammasphere spectrometer. Six high-spin bands with large moments of inertia, similar to those observed in neighboring nuclei, have been observed. The experimental results are compared with calculations within the framework of the cranked Nilsson-Strutinsky model. It is suggested that the configurations of the bands involve excitations of protons across the Z = 50 shell gap coupled to neutrons within the N = 50-82 shell or excited across the N = 82 shell closure.

{\bf Background:} Level sequences of rotational character have been observed in several nuclei in the $A=60$ mass region. The importance of the deformation-driving $\pi f_{7/2}$ and $\nu g_{9/2}$ orbitals on the onset of nuclear deformation is stressed.\\ {\bf Purpose:} A measurement was performed in order to identify collective rotational structures in the relatively neutron-rich $^{62}$Ni isotope. \\ {\bf Method:} The $^{26}$Mg($^{48}$Ca,2$\alpha$4$n\gamma$)$^{62}$Ni complex reaction at beam energies between 275 and 320~MeV was utilized. Reaction products were identified in mass ($A$) and charge ($Z$) with the Fragment Mass Analyzer (FMA) and $\gamma$ rays were detected with the Gammasphere array. \\ {\bf Results:} Two collective bands, built upon states of single-particle character, were identified and sizable deformation was assigned to both sequences based on the measured transitional quadrupole moments, herewith quantifying the deformation at high spin. \\ {\bf Conclusions:} Based on Cranked Nilsson-Strutinsky calculations and comparisons with deformed bands in the $A=60$ mass region, the two rotational bands are understood as being associated with configurations involving multiple $f_{7/2}$ protons and $g_{9/2}$ neutrons, driving the nucleus to sizable prolate deformation.

Here, the decay of a Kπ = 8– isomer in 244Pu and the collective band structures populating the isomer were studied using deep inelastic excitations with 47Ti and 208Pb 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.

Research efforts ranging from studies of solid helium to searches for a neutron electric dipole moment require isotopically purified helium with a ratio of ^3He to ^4He at levels below that which can be measured using traditional mass spectroscopy techniques. We demonstrate an approach to such a measurement using accelerator mass spectroscopy, reaching the 10^(−14) level of sensitivity, several orders of magnitude more sensitive than other techniques. Measurements of ^3He/^4He in samples relevant to the measurement of the neutron lifetime indicate the need for substantial corrections. We also argue that there is a clear path forward to sensitivity increases of at least another order of magnitude.

International audience; Superheavy nuclei exist solely due to quantum shell effects,which create a pocket in the potential-energy surface of the nucleus, thusproviding a barrier against spontaneous fission. Determining the height ofthe fission barrier and its angular-momentum dependence is important toquantify the role that microscopic shell corrections play in enhancing andextending the limits of nuclear stability. In this talk, the first measurement ofa fission barrier in the very heavy nucleus 254No will be presented.

The neutron-rich nucleus $^{144}$Ba ($t_{1/2}$=11.5 s) is expected to exhibit some of the strongest octupole correlations among nuclei with mass numbers $A$ less than 200. Until now, indirect evidence for such strong correlations has been inferred from observations such as enhanced $E1$ transitions and interleaving positive- and negative-parity levels in the ground-state band. In this experiment, the octupole strength was measured directly by sub-barrier, multi-step Coulomb excitation of a post-accelerated 650-MeV $^{144}$Ba beam on a 1.0-mg/cm$^2$ $^{208}$Pb target. The measured value of the matrix element, $\langle 3_1^- \| \mathcal{M}(E3) \| 0_1^+ \rangle=0.65(^{+17}_{-23})$ $e$b$^{3/2}$, corresponds to a reduced $B(E3)$ transition probability of 48($^{+25}_{-34}$) W.u. This result represents an unambiguous determination of the octupole collectivity, is larger than any available theoretical prediction, and is consistent with octupole deformation., Comment: 5 pages, 2 figures, 1 table, Physical Review Letters 2016

Excited states with seniority $\ensuremath{\nu}=3$, 5, and 7 have been investigated in odd neutron-rich $^{119,121,123,125}\text{Sn}$ isotopes produced by fusion-fission of 6.9-MeV/$A\phantom{\rule{4pt}{0ex}}^{48}\text{Ca}$ beams with $^{208}\text{Pb}$ and $^{238}\text{U}$ targets and by fission of a $^{238}\text{U}$ target bombarded with 6.7-MeV/$A\phantom{\rule{4pt}{0ex}}^{64}\text{Ni}$ beams. Level schemes have been established up to high spin and excitation energies in excess of 6 MeV, based on multifold gamma-ray coincidence relationships measured with the Gammasphere array. In the analysis, the presence of isomers was exploited to identify gamma rays and propose transition placements using prompt and delayed coincidence techniques. Gamma decays of the known $27/{2}^{\ensuremath{-}}$ isomers were expanded by identifying new deexcitation paths feeding $23/{2}^{+}$ long-lived states and $21/{2}^{+}$ levels. Competing branches in the decay of $23/{2}^{\ensuremath{-}}$ states toward two $19/{2}^{\ensuremath{-}}$ levels were delineated as well. In $^{119}\text{Sn}$, a new $23/{2}^{+}$ isomer was identified, while a similar $23/{2}^{+}$ long-lived state, proposed earlier in $^{121}\text{Sn}$, has now been confirmed. In both cases, isomeric half-lives were determined with good precision. In the range of $\ensuremath{\nu}=3$ excitations, the observed transitions linking the various states enabled one to propose with confidence spin-parity assignments for all the observed states. Above the $27/{2}^{\ensuremath{-}}$ isomers, an elaborate structure of negative-parity levels was established reaching the ($39/{2}^{\ensuremath{-}}$), $\ensuremath{\nu}=7$ states, with tentative spin-parity assignments based on the observed deexcitation paths as well as on general yrast population arguments. In all the isotopes under investigation, strongly populated sequences of positive-parity ($35/{2}^{+}$), ($31/{2}^{+}$), and ($27/{2}^{+}$) states were established, feeding the $23/{2}^{+}$ isomers via cascades of three transitions. In the $^{121,123}\text{Sn}$ isotopes, these sequences also enabled the delineation of higher-lying levels, up to ($43/{2}^{+}$) states. In $^{123}\text{Sn}$, a short half-life was determined for the ($35/{2}^{+}$) state. Shell-model calculations were carried out for all the odd Sn isotopes, from $^{129}\text{Sn}$ down to $^{119}\text{Sn}$, and the results were found to reproduce the experimental level energies rather well. Nevertheless, some systematic deviations between calculated and experimental energies, especially for positive-parity states, point to the need to improve some of the two-body interactions used in calculations. The computed wave-function amplitudes provide for a fairly transparent interpretation of the observed level structures. The systematics of level energies over the broad $A$ = 117--129 range of Sn isotopes displays a smooth decrease with mass $A$, and the observed regularity confirms most of the proposed spin-parity assignments. The systematics of the $B(E2)$ reduced transition probabilities extracted for the $23/{2}^{+}$ and $19/{2}^{+}$ isomers is discussed with an emphasis on the close similarity of the observed $A$ dependence with that of the $E2$ transition rates established for other $\ensuremath{\nu}=2$, 3, and 4 isomers in the Sn isotopic chain.

The structure of $^{133}\text{La}$ has been investigated using the $^{116}\text{Cd}(^{22}\text{Ne},4pn)$ reaction and the Gammasphere array. Three new bands of quadrupole transitions and one band of dipole transitions are identified and the previously reported level scheme is revised and extended to higher spins. The observed structures are discussed using the cranked Nilsson-Strutinsky formalism, covariant density functional theory, and the particle-rotor model. Triaxial configurations are assigned to all observed bands. For the high-spin bands it is found that rotations around different axes can occur, depending on the configuration. The orientation of the angular momenta of the core and of the active particles is investigated, suggesting chiral rotation for two nearly degenerate dipole bands and magnetic rotation for one dipole band. It is shown that the ${h}_{11/2}$ neutron holes present in the configuration of the nearly degenerate dipole bands have significant angular momentum components not only along the long axis but also along the short axis, contributing to the balance of the angular momentum components along the short and long axes and thus giving rise to a chiral geometry.

Author(s): Crider, BP; Prokop, CJ; Liddick, SN; Al-Shudifat, M; Ayangeakaa, AD; Carpenter, MP; Carroll, JJ; Chen, J; Chiara, CJ; David, HM; Dombos, AC; Go, S; Grzywacz, R; Harker, J; Janssens, RVF; Larson, N; Lauritsen, T; Lewis, R; Quinn, SJ; Recchia, F; Spyrou, A; Suchyta, S; Walters, WB; Zhu, S | Abstract: Shape coexistence near closed-shell nuclei, whereby states associated with deformed shapes appear at relatively low excitation energy alongside spherical ones, is indicative of the rapid change in structure that can occur with the addition or removal of a few protons or neutrons. Near 68Ni (Z=28, N=40), the identification of shape coexistence hinges on hitherto undetermined transition rates to and from low-energy 0+ states. In 68,70Ni, new lifetimes and branching ratios have been measured. These data enable quantitative descriptions of the 0+ states through the deduced transition rates and serve as sensitive probes for characterizing their nuclear wave functions. The results are compared to, and consistent with, large-scale shell-model calculations which predict shape coexistence. With the firm identification of this phenomenon near 68Ni, shape coexistence is now observed in all currently accessible regions of the nuclear chart with closed proton shells and mid-shell neutrons.

Medium and high-spin states in $^{133}$Ce were investigated using the $^{116}$Cd($^{22}$Ne, $5n$) reaction and the Gammasphere array. The level scheme was extended up to an excitation energy of $\sim22.8$ MeV and spin 93/2 . Eleven bands of quadrupole transitions and two new dipole bands are identified. The connections to low-lying states of the previously known, high-spin triaxial bands were firmly established, thus fixing the excitation energy and, in many cases, the spin parity of the levels. Based on comparisons with cranked Nilsson-Strutinsky calculations and tilted axis cranking covariant density functional theory, it is shown that all observed bands are characterized by pronounced triaxiality. Competing multiquasiparticle configurations are found to contribute to a rich variety of collective phenomena in this nucleus., 20 pages, 11 figures

High-spin states in $^{134}\mathrm{Ce}$ have been investigated using the $^{116}\mathrm{Cd}(^{22}\mathrm{Ne},4n)$ reaction and the Gammasphere array. The level scheme has been extended to an excitation energy of $\ensuremath{\sim}30$ MeV and spin $\ensuremath{\sim}54\phantom{\rule{0.16em}{0ex}}\ensuremath{\hbar}$. Two new dipole bands and four new sequences of quadrupole transitions were identified. Several new transitions have been added to a number of known bands. One of the strongly populated dipole bands was revised and placed differently in the level scheme, resolving a discrepancy between experiment and model calculations reported previously. Configurations are assigned to the observed bands based on cranked Nilsson-Strutinsky calculations. A coherent understanding of the various excitations, both at low and high spins, is thus obtained, supporting an interpretation in terms of coexistence of stable triaxial, highly deformed, and superdeformed shapes up to very high spins. Rotations around different axes of the triaxial nucleus, and sudden changes of the rotation axis in specific configurations, are identified, further elucidating the nature of high-spin collective excitations in the $A=130$ mass region.

Background: Neutron-rich, even-mass chromium and iron isotopes approaching neutron number $N=40$ have been important benchmarks in the development of shell-model effective interactions incorporating the effects of shell evolution in the exotic regime. Odd-mass manganese nuclei have received less attention, but provide important and complementary sensitivity to these interactions.Purpose: We report the observation of two new $\ensuremath{\gamma}$-ray transitions in $^{63}\mathrm{Mn}$, which establish the $(9/{2}^{\ensuremath{-}})$ and $(11/{2}^{\ensuremath{-}})$ levels on top of the previously known $(7/{2}^{\ensuremath{-}})$ first-excited state. The lifetime for the $(7/{2}^{\ensuremath{-}})$ and $(9/{2}^{\ensuremath{-}})$ excited states were determined for the first time, while an upper limit could be established for the $(11/{2}^{\ensuremath{-}})$ level.Method: Excited states in $^{63}\mathrm{Mn}$ have been populated in inelastic scattering from a $^{9}\mathrm{Be}$ target and in the fragmentation of $^{65}\mathrm{Fe}$. $\ensuremath{\gamma}\ensuremath{\gamma}$ coincidence relationships were used to establish the decay level scheme. A Doppler line-shape analysis for the Doppler-broadened $(7/{2}^{\ensuremath{-}})\ensuremath{\rightarrow}5/{2}^{\ensuremath{-}}$, $(9/{2}^{\ensuremath{-}})\ensuremath{\rightarrow}(7/{2}^{\ensuremath{-}}),$ and $(11/{2}^{\ensuremath{-}})\ensuremath{\rightarrow}(9/{2}^{\ensuremath{-}})$ transitions was used to determine (limits for) the corresponding excited-state lifetimes.Results: The low-lying level scheme and the excited-state lifetimes were compared with large-scale shell-model calculations using different model spaces and effective interactions in order to isolate important aspects of shell evolution in this region of structural change.Conclusions: While the theoretical $(7/{2}^{\ensuremath{-}})$ and $(9/{2}^{\ensuremath{-}})$ excitation energies show little dependence on the model space, the calculated lifetime of the $(7/{2}^{\ensuremath{-}})$ level and calculated energy of the $(11/{2}^{\ensuremath{-}})$ level reveal the importance of including the neutron ${g}_{9/2}$ and ${d}_{5/2}$ orbitals in the model space. The LNPS effective shell-model interaction provides the best overall agreement with the new data.

γ-Ray emission probabilities from the decay of the long-lived (T(1/2)=160.44d) isomeric state in (177m)Lu were measured with planar (LEPS) and coaxial Ge detectors. The isomer γ-ray and β(-)-decay branching intensities were also determined. Measurements were carried out at low absolute efficiencies in order to minimize coincidence summing losses. The results are compared with the previous measurements.

A particle- γ coincidence technique has been used to measure the fusion cross-section in the system 12C+12C at low beam energies. Based on these results, it should be possible to measure this important fusion cross-section down to the 10 pb level within a week-long run.

Deep-inelastic reactions have been used to populate high-spin states in the iridium isotopes. New results include the identification of particularly long-lived three-quasiparticle isomers in 191Ir and 193Ir, with mean-lives of 8.2(7) s and 180(3) μs respectively, decaying into newly identified states of the h 11/2 proton bands and into other structures. Spins and parities of J π=31/2 + are suggested for both, consistent with coupling of the 11/2 -[505] proton to the 10 - two-neutron excitations in the cores. These and other configurations are discussed in the context of configuration constrained potential-energy-surface calculations. All calculated intrinsic states are expected to be associated with triaxial shapes and the extreme isomerism observed is attributed to spin-trapping rather than K-hindrance.

In recent models, the neutron-rich Ni isotopes around $N=40$ are predicted to exhibit multiple low-energy excited ${0}^{+}$ states attributed to neutron and proton excitations across both the $N=40$ and $Z=28$ shell gaps. In $^{68}\mathrm{Ni}$, the three observed ${0}^{+}$ states have been interpreted in terms of triple shape coexistence between spherical, oblate, and prolate deformed shapes. In the present work a new $({0}_{2}^{+})$ state at an energy of 1567 keV has been discovered in $^{70}\mathrm{Ni}$ by using $\ensuremath{\beta}$-delayed, $\ensuremath{\gamma}$-ray spectroscopy following the decay of $^{70}\mathrm{Co}$. The precipitous drop in the energy of the prolate-deformed ${0}^{+}$ level between $^{68}\mathrm{Ni}$ and $^{70}\mathrm{Ni}$ with the addition of two neutrons compares favorably with results of Monte Carlo shell-model calculations carried out in the large $fp{g}_{9/2}{d}_{5/2}$ model space, which predict a ${0}_{2}^{+}$ state at 1525 keV in $^{70}\mathrm{Ni}$. The result extends the shape-coexistence picture in the region to $^{70}\mathrm{Ni}$ and confirms the importance of the role of the tensor component of the monopole interaction in describing the structure of neutron-rich nuclei.

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)

Proton radioactivity from 117 La was re-investigated with much improved statistics and precision. Only the ground-state proton decay ( E p = 813 ( 3 ) keV , T 1 / 2 = 20.1 ( 25 ) ms ) was observed, no evidence for a previously reported isomeric proton decay was found. Prompt γ rays in 117 La were identified using the Recoil–Decay Tagging method. Overall the data indicate that the proton-emitting state is associated with a K π = 3 / 2 + configuration, in agreement with all the published proton-decay calculations and predictions for the ground-state configuration of 117 La calculated in the framework of either adiabatic or non-adiabatic particle models. However, this is not in agreement with the most recent state-of-the-art quasi-particle non-adiabatic model calculations which predict a K π = 7 / 2 − configuration.

A 985 MeV 178 Hf beam was Coulomb excited by a 208 Pb target at the ATLAS accelerator of Argonne National Laboratory. Gammasphere and the CHICO particle detector recorded particle-γ coincidence data. The aim was to populate and determine the mechanism of previously observed Coulomb excitation of the Kπ = 6+ (t1/2 = 77 ns ), 8- (4 s ) and 16+ (31 y ) isomer bands. New rotational bands were identified including an aligned band which appears to mix with the ground-state band (GSB) and the γ-vibrational band above ~ 12 ħ of angular momentum. Newly observed γ-decay transitions into the three isomer bands may elucidate the K-mixing which allows Coulomb excitation of these isomer bands, but direct decays from the GSB into the 16+ isomer band have not yet been confirmed.

Yrast and near-yrast states in 30 Al and 30 Si have been populated to high spin with the O 18 + C 14 fusion–evaporation reaction in inverse kinematics. The level schemes for these two isobars have been extended up to J ∼ 9 ℏ at 9.4 and 15.5 MeV, respectively. Their decay schemes indicate that cross-shell excitations dominate at high spin, where negative-parity structures exist. Positive-parity states are compared to the results of shell-model calculations using the USD, USDA, and USDB effective interactions. The negative-parity levels are compared to predictions of the WBP interaction and the recently-developed WBP-a Hamiltonian, by allowing 1p–1h excitations to fp -shell orbitals. The results suggest that single-neutron excitations to the 0 f 7 / 2 orbital play a significant role at high spin.

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

Excited states in 124Xe have been studied via the 12C(124Xe, 124Xe∗) Coulomb excitation reaction. Their population cross-sections relative to the 2 1 + state have been determined from the γ-ray yields observed with Gammasphere. More than twenty absolute E2 strengths for seven off-yrast, low-spin states of 124Xe have been deduced for the first time. The absolute B ( E 2 ) values indicate pronounced O ( 5 ) symmetry, even for the off-yrast states with high O ( 5 ) quantum number τ, while the O ( 6 ) symmetry is substantially broken.

An inverse kinematics Coulomb excitation experiment was performed to obtain absolute E2 and M1 transition strengths in 134Xe. The measured transition strengths indicate that the 2 3 + state of 134Xe is the dominant fragment of the one-phonon 2 1 , ms + mixed-symmetry state. Comparing the energy of the 2 1 , ms + mixed-symmetry state in 134Xe to that of the 2 1 , ms + levels in the N = 80 isotonic chain indicates that the separation in energy between the fully-symmetric 2 1 + state and the 2 1 , ms + level increases as a function of the number of proton pairs outside the Z = 50 shell closure. This behavior can be understood as resulting from the mixing of the basic components of a two-fluid quantum system. A phenomenological fit based on this concept was performed. It provides the first experimental estimate of the strength of the proton–neutron quadrupole interaction derived from nuclear collective states with symmetric and antisymmetric nature.

Excited states in 124Xe were populated in the reaction 82Se(48Ca, 6n)124Xe and γ -ray coincidence relationships were measured with the Gammasphere spectrometer. Two new bands are observed and several of the previously known bands are extended in the high- as well as in the low-spin region. Two irregular high-spin structures are also added. The irregularities are a fingerprint of a transition from collective to non-collective behaviour. Configuration assignments to the new structures are proposed on the basis of systematics and by comparing experimental properties with calculations within the framework of the cranking model.

Zhu, S. Janssens, R. V. F. Fornal, B. Freeman, S. J. Honma, M. Broda, R. Carpenter, M. P. Deacon, A. N. Kay, B. P. Kondev, F. G. Krolas, W. Kozemczak, J. Larabee, A. Lauritsen, T. Liddick, S. N. Lister, C. J. Mantica, P. F. Otsuka, T. Pawlat, T. Robinson, A. Seweryniak, D. Smith, J. F. Steppenbeck, D. Tomlin, B. E. Wrzesinski, J. Wang, X.

The 242m Am isomer, a well-known candidate for photodepopulation research, has been studied in this first ever Coulomb excitation of a nearly pure (≈98%) isomer target. Thirty new states, including a new rotational band built on a K π = 6− state, have been identified. Strong K-mixing results in nearly equal populations of the K π=5− and 6− states. Newly identified states have been assigned to the K π=3− rotational band, the lowest states of which are known to decay into the ground-state band. Implications regarding K-mixing and Coulomb excitation paths to the ground state are discussed.

Two interacting, strongly-deformed triaxial (TSD) bands have been identified in the Z = 69 nucleus ^{163}Tm. This is the first time that interacting TSD bands have been observed in an element other than the Z = 71 Lu nuclei, where wobbling bands have been previously identified. The observed TSD bands in ^{163}Tm appear to be associated with particle-hole excitations, rather than wobbling. Tilted-Axis Cranking (TAC) calculations reproduce all experimental observables of these bands reasonably well and also provide an explanation for the presence of wobbling bands in the Lu nuclei, and their absence in the Tm isotopes., Comment: 13 pages, 7 figures

An oblate rotational sequence, built on an aligned, two-quasineutron isomeric state has been established in $^{196}\mathrm{Pt}$. The isomer has a half-life of 7.7(7) ns and is associated with the ${I}^{\ensuremath{\pi}}={12}^{+},\phantom{\rule{0.16em}{0ex}}{({i}_{13/2})}^{2}$ neutron configuration. Excited states, with angular momentum generated primarily through successive nucleon alignments, have been populated through $1\mathit{p}$ transfer from $^{197}\mathrm{Au}$. The nucleus $^{196}\mathrm{Pt}$ is the most neutron-rich Pt isotope for which high-spin states, beyond the ${12}^{+}$ isomeric state, have been established thus far. Cranked shell model calculations have been performed to understand shape evolution with spin, and the role of nucleons occupying specific Nilsson orbitals in generating aligned angular momentum for both prolate and oblate deformations has been explored.

Absolute $\ensuremath{\gamma}$-ray emission probabilities in the ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of $^{67}\mathrm{Cu}$ were measured by means of $\ensuremath{\gamma}$-ray and ${\ensuremath{\beta}}^{\ensuremath{-}}$-decay singles and ${\ensuremath{\beta}}^{\ensuremath{-}}\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidences. The new results, together with the known decay scheme of $^{67}\mathrm{Cu}$, were used to determine absolute ${\ensuremath{\beta}}^{\ensuremath{-}}$-decay branching intensities. The present data differ significantly from previously published values. In addition, the half-life of the ${I}^{\ensuremath{\pi}}={\frac{1}{2}}^{\ensuremath{-}}$ isomer in $^{67}\mathrm{Zn}$ was measured as ${T}_{1/2}=9.37(4) \ensuremath{\mu}\mathrm{s}$, in a good agreement with earlier measurements. From the analysis of the Fermi--Kurie plots, ${Q}_{{\ensuremath{\beta}}^{\ensuremath{-}}}(\text{g.s.})=560.3(10)$ keV was deduced, which differs from the previously measured value of 577(8) keV but is in good agreement with ${Q}_{{\ensuremath{\beta}}^{\ensuremath{-}}}(\text{g.s.})=561.3(15)$ keV recommended in the latest Atomic Mass Evaluation.

A high-spin isomer with $\ensuremath{\tau}g700$ ns has been found in $^{204}\mathrm{Hg}$, populated in reactions of 1360-MeV $^{208}\mathrm{Pb}$ and 330-MeV $^{48}\mathrm{Ca}$ beams with a thick $^{238}\mathrm{U}$ target and a 1450-MeV $^{208}\mathrm{Pb}$ beam on a thick $^{208}\mathrm{Pb}$ target. The observed $\ensuremath{\gamma}$-ray decay of the isomer has established the yrast states below it, including another isomer with $\ensuremath{\tau}=33(3)$ ns. The experimental results are compared with shell-model calculations that include four holes in the configuration space between $^{132}\mathrm{Sn}$ and $^{208}\mathrm{Pb}$. The available spectroscopic information, including transition strengths, total conversion, and angular correlation coefficients, together with the observed agreement with the calculations, allows spin, parity, and configuration assignments to be proposed for the experimental states. The $\ensuremath{\tau}g700$ ns isomer is the ${22}^{+}$ state of maximum spin available from the alignment of the four valence holes with the configuration $\ensuremath{\pi}{h}_{11/2}^{\ensuremath{-}2}\ensuremath{\nu}{i}_{13/2}^{\ensuremath{-}2}$.

week ending 16 OCTOBER 2015 PHYSICAL REVIEW LETTERS PRL 115, 169902 (2015) Publisher’s Note: Decay and Fission Hindrance of Two- and Four-Quasiparticle K Isomers in 254 Rf [Phys. Rev. Lett. 115, 132502 (2015)] H. M. David, J. Chen, D. Seweryniak, F. G. Kondev, J. M. Gates, K. E. Gregorich, I. Ahmad, M. Albers, M. Alcorta, B. B. Back, B. Baartman, P. F. Bertone, L. A. Bernstein, C. M. Campbell, M. P. Carpenter, C. J. Chiara, R. M. Clark, M. Cromaz, D. T. Doherty, G. D. Dracoulis, N. E. Esker, P. Fallon, O. R. Gothe, J. P. Greene, P. T. Greenlees, D. J. Hartley, K. Hauschild, C. R. Hoffman, S. S. Hota, R. V. F. Janssens, T. L. Khoo, J. Konki, J. T. Kwarsick, T. Lauritsen, A. O. Macchiavelli, P. R. Mudder, C. Nair, Y. Qiu, J. Rissanen, A. M. Rogers, P. Ruotsalainen, G. Savard, S. Stolze, A. Wiens, and S. Zhu (Received 7 October 2015; published 16 October 2015) DOI: 10.1103/PhysRevLett.115.169902 PACS numbers: 23.20.Lv, 21.10.Tg, 23.35.+g, 27.90.+b, 99.10.Fg This paper was published online on 24 September 2015 with a tagging error resulting in an incorrect author footnote. J. Chen’s footnote should read as “ ‡ Present address: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.” The paper has been corrected as of 29 September 2015. The footnote is correct in the printed version of the journal. © 2015 American Physical Society

Two isomers decaying by electromagnetic transitions with half-lives of 4.7(1.1) and 247(73) μs have been discovered in the heavy ^{254}Rf nucleus. The observation of the shorter-lived isomer was made possible by a novel application of a digital data acquisition system. The isomers were interpreted as the K^{π}=8^{-}, ν^{2}(7/2^{+}[624],9/2^{-}[734]) two-quasineutron and the K^{π}=16^{+}, 8^{-}ν^{2}(7/2^{+}[624],9/2^{-}[734])⊗8^{-}π^{2}(7/2^{-}[514],9/2^{+}[624]) four-quasiparticle configurations, respectively. Surprisingly, the lifetime of the two-quasiparticle isomer is more than 4 orders of magnitude shorter than what has been observed for analogous isomers in the lighter N=150 isotones. The four-quasiparticle isomer is longer lived than the ^{254}Rf ground state that decays exclusively by spontaneous fission with a half-life of 23.2(1.1) μs. The absence of sizable fission branches from either of the isomers implies unprecedented fission hindrance relative to the ground state.

Near shell closures, the presence of unexpected states at low energies provides a critical test of our understanding of the atomic nucleus. New measurements for the $N=42$ isotones $_{27}^{69}\mathrm{Co}$ and $_{29}^{71}\mathrm{Cu}$, along with recent data and calculations in the Ni isotopes, establish a full set of complementary, deformed, intruder states astride the closed-shell $_{28}\mathrm{Ni}$ isotopes. Nuclei with a one-proton hole or one-proton particle adjacent to $Z=28$ were populated in $\ensuremath{\beta}$-decay experiments and in multinucleon transfer reactions. A $\ensuremath{\beta}$-decaying isomer, with a 750(250)-ms half-life, has been identified in $_{27}^{69}\mathrm{Co}_{42}$. It likely has low spin and accompanies the previously established $7/{2}^{\ensuremath{-}}$ state. Complementary data for the levels of isotonic $_{29}^{71}\mathrm{Cu}_{42}$ support the presence of a deformed, $\mathrm{\ensuremath{\Delta}}J=1$ band built on the proton intruder $7/{2}^{\ensuremath{-}}$ level at 981 keV. These data, together with recent studies of lower-mass Co and Cu isotopes and extensive work near $^{68}\mathrm{Ni}$, support the view that intruder states based on particle-hole excitations accompany all closed proton shells with $Z\ensuremath{\ge}28$.

This is an Open Access article distributed under the terms of Creative Commons Attribution Licence 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.; International audience; In this work we present the results from two experiments dedicated to search for quadrupole-collective isovector valence-shell excitation, the states with so-called mixed proton-neutron symmetry (MSS), in nuclei around the doubly magic nucleus $^{208}$Pb. $^{212}$Po was studied in an α-transfer reaction. $^{204}$Hg was studied in an inverse kinematics Coulomb excitation reaction on a carbon target. Both experiments provide indications for existence of one-phonon MSSs. Those are the first experimentally identified MSSs in the mass A ≈ 208 region.

The yields of over 200 projectile-like fragments (PLFs) and target-like fragments (TLFs) from the interaction of (${E}_{\mathrm{c}.\mathrm{m}.}=450$ MeV) $^{136}\text{Xe}$ with a thick target of $^{208}\text{Pb}$ were measured using Gammasphere and off-line $\ensuremath{\gamma}$-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 $\mathit{t}ef$. 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 ($\mathrm{\ensuremath{\Delta}}Z=\ensuremath{-}8$ to $\mathrm{\ensuremath{\Delta}}Z=+2$). However, for $\mathrm{\ensuremath{\Delta}}Z=+4$, 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 cross section of the ^12C+^12C fusion reaction at low energies is of paramount importance for models of stellar nucleosynthesis in different astrophysical scenarios, such as Type Ia supernovae and Xray superbursts, where this reaction is a primary route for the production of heavier elements. In a series of experiments performed at Argonne National Laboratory, using Gammasphere and an array of Silicon detectors, measurements of the fusion cross section of ^12C+^12C were successfully carried out with the gamma and charged-particle coincidence technique in the center-of-mass energy range of 3-5 MeV. These were the first background-free fusion cross section measurements for ^12C+^12C at energies of astrophysical interest. Our results are consistent with previous measurements in the high-energy region; however, our lowest energy measurement indicates a fusion cross section slightly lower than those obtained with other techniques.

International audience; Analyses of data from both deep inelastic reactions at Argonne National Laboratory and single-and multiple-particle knockout reactions at Michigan State University revealed new gamma-ray transitions in even-even Ni-66,68,70,72(38,40,42,44) and in Co-67(40) that provide strong evidence for multiple shape coexistence at N = 38 and 40 and deep prolate minima in Ni-70(42) and isotonic Cu-71(42). A new transition at 642 keV is proposed for Ni-66 as the prolate 2(+) to 0(+) transition. Two new transitions in Ni-72 at 915 and 1225 keV were identified in the knock-out reaction study and could represent de-population of prolate states. Taken together with recent theoretical work using the Monte Carlo shell model, a well defined region of shape coexistence can be seen existing precisely between 38

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 Sn-124(Cl-37, 6n gamma) fusion-evaporation reaction at a bombarding energy of 180 MeV has been used to significantly extend the excitation level scheme of Ho-155(67)88. The collective rotational behavior of this nucleus breaks down above spin I similar to 30 and a fully aligned noncollective (band terminating) state has been identified at I-pi = 79/2(-). Comparison with cranked Nilsson-Strutinsky calculations also provides evidence for core-excited noncollective states at I-pi = 87/2(-) and (89/2(+)) involving particle-hole excitations across the Z = 64 shell gap. A similar core-excited state in Er-156(68)88 at I-pi = (46(+)) is also presented.

An extensive study of the level structure of $^{61}\mathrm{Co}$ has been performed following the complex $^{26}\mathrm{Mg}(^{48}\mathrm{Ca},2\ensuremath{\alpha}4np\ensuremath{\gamma})^{61}\mathrm{Co}$ reaction at beam energies of 275, 290, and 320 MeV using Gammasphere and the Fragment Mass Analyzer (FMA). The low-spin structure is discussed within the framework of shell-model calculations using the GXPF1A effective interaction. Two quasirotational bands consisting of stretched-$E2$ transitions have been established up to spins $I=41/2$ and $(43/2)$, and excitation energies of $\ensuremath{\sim}17$ and $\ensuremath{\sim}20$ MeV, respectively. These are interpreted as signature partners built on a neutron $\ensuremath{\nu}{({g}_{9/2})}^{2}$ configuration coupled to a proton $\ensuremath{\pi}{p}_{3/2}$ state, based on cranked shell model (CSM) calculations and comparisons with observations in neighboring nuclei. In addition, four $\ensuremath{\Delta}I=1$ bands were populated to high spin, with the yrast dipole band interpreted as a possible candidate for the shears mechanism, a process seldom observed thus far in this mass region.

The structure of semi-magic Ni-70(28)42 was investigated following complementary multinucleon-transfer and secondary fragmentation reactions. Changes to the higher-spin, presumed negative-parity states based on observed gamma-ray coincidence relationships result in better agreement with shell-model calculations using effective interactions in the neutron f(5/2)pg(9/2) model space. The second 2(+) and (4(+)) states, however, can only be successfully described when proton excitations across the Z = 28 shell gap are included. Monte Carlo shell-model calculations suggest that the latter two states are part of a prolate-deformed intruder sequence, establishing an instance of shape coexistence at low excitation energies similar to that observed recently in neighboring Ni-68.

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.

A pair of transverse wobbling bands is observed in the nucleus ^{135}Pr. The wobbling is characterized by ΔI=1, E2 transitions between the bands, and a decrease in the wobbling energy confirms its transverse nature. Additionally, a transition from transverse wobbling to a three-quasiparticle band comprised of strong magnetic dipole transitions is observed. These observations conform well to results from calculations with the tilted axis cranking model and the quasiparticle rotor model.

New γγ -coincidence relations and E 2 decay transition rates in the isotopes 194,196 Pt have been deduced from γ -ray spectroscopy experiments using the Gammasphere spectrometer in projectile-Coulomb excitation reactions of beams of 194,196 Pt ions provided by the ATLAS accelerator facility. The results give access to observables that are crucial for a classification of excited quadrupole-collective states in terms of quantum numbers associated with the analytically solvable O(6) dynamical symmetry of the interacting boson model. The data on 196 Pt corroborate the qualitative pattern of excitation energies and E 2 transition rates expected from the O(6) solution but the excitation energies significantly deviate from it on a quantitative level.

Physics letters / B 747, 88 - 92 (2015). doi:10.1016/j.physletb.2015.04.055, Published by North-Holland Publ., Amsterdam

An exploratory experiment performed at REX-ISOLDE to investigate cluster-transfer reactions with radioactive beams in inverse kinematics is presented. The aim of the experiment was to test the potential of cluster-transfer reactions at the Coulomb barrier as a mechanism to explore the structure of exotic neutron-rich nuclei. The reactions Li7(Rb98,αxn) and Li7(Rb98,txn) were studied through particle-γ coincidence measurements, and the results are presented in terms of the observed excitation energies and spins. Moreover, the reaction mechanism is qualitatively discussed as a transfer of a clusterlike particle within a distorted-wave Born approximation framework. The results indicate that cluster-transfer reactions can be described well as a direct process and that they can be an efficient method to investigate the structure of neutron-rich nuclei at medium-high excitation energies and spins., SCOPUS: ar.j, info:eu-repo/semantics/published