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The validity of the Brink-Axel hypothesis, which is especially important for numerous astrophysical calculations, is addressed for 116,120,124Sn below the neutron separation energy by means of three independent experimental methods. The $\gamma$-ray strength functions (GSFs) extracted from primary $\gamma$-decay spectra following charged-particle reactions with the Oslo method and with the Shape method demonstrate excellent agreement with those deduced from forward-angle inelastic proton scattering at relativistic beam energies. In addition, the GSFs are shown to be independent of excitation energies and spins of the initial and final states. The results provide a critical test of the generalized Brink-Axel hypothesis in heavy nuclei, demonstrating its applicability in the energy region of the pygmy dipole resonance., Comment: 6 pages, 4 figures, Phys. Rev. Lett. (in press)

Recent measurements of the nuclear level densities and γ-ray strength functions below the neutron thresholds in 180,181,182Ta are used as input in the nuclear reaction code TALYS. These experimental average quantities are utilized in the calculations of the 179,180,181Ta radiative neutron capture cross sections. From the latter, astrophysical Maxwellian-averaged (n,γ) cross sections (MACS) and reaction rates are extracted, which in turn are used in large astrophysical network calculations to probe the production mechanism of 180 Ta. These calculations are performed for two scenarios, the s-process production of 180,181Ta in Asymptotic Giant Branch (AGB) stars and the p-process nucleosynthesis of 180Tam in Type-II supernovae. Based on the results from this work, the s-process in stellar evolution is considered negligible in the production of 180Tam whereas 181Ta is partially produced by AGB stars. The new measurements strongly constrain the production and destruction rates of 180Tam at p-process temperatures and confirm significant production of nature’s rarest stable isotope 180Tam by the p-process., SCOPUS: ar.j, info:eu-repo/semantics/published

Prompt fission $\ensuremath{\gamma}$ rays (PFGs) resulting from the $^{240}\mathrm{Pu}(d,p\mathrm{f})$ reaction have been measured as a function of fissioning nucleus excitation energy ${E}_{\text{x}}$ at the Oslo Cyclotron Laboratory. We study the average total PFG multiplicity per fission, the average total PFG energy released per fission, and the average PFG energy. No significant changes in these characteristics are observed over the range $5.75l{E}_{\text{x}}l8.25$ MeV. The physical implications of this result are discussed. The experimental results are compared to simulations conducted using the computational fission model FREYA. We find that FREYA reproduces the experimental PFG characteristics within $8%$ deviation across the ${E}_{\text{x}}$ range studied. Previous excitation energy-dependent PFG measurements conducted below the second-chance fission threshold have large uncertainties, but are generally in agreement with our results within a $2\ensuremath{\sigma}$ confidence interval. However, both a published parametrization of the PFG energy dependence and the most recent PFG evaluation included in ENDF/B-VIII.0 were found to poorly describe the PFG excitation-energy dependence observed in this and previous experiments.

The nuclear level densities (NLDs) and the $\ensuremath{\gamma}$-ray strength functions ($\ensuremath{\gamma}\mathrm{SFs}$) of $^{153,155}\mathrm{Sm}$ have been extracted from ($d,p\ensuremath{\gamma}$) coincidences using the Oslo method. The experimental NLD of $^{153}\mathrm{Sm}$ is higher than the NLD of $^{155}\mathrm{Sm}$, in accordance with microscopic calculations. The $\ensuremath{\gamma}\mathrm{SFs}$ of $^{153,155}\mathrm{Sm}$ are in fair agreement with QRPA calculations based on the D1M Gogny interaction. An enhancement is observed in the $\ensuremath{\gamma}\mathrm{SF}$ for both $^{153,155}\mathrm{Sm}$ nuclei around 3 MeV in excitation energy and is attributed to the $M1$ scissors resonance (SR). Their integrated strengths were found to be in the range 1.3--2.1 and 4.4--6.4 ${\ensuremath{\mu}}_{N}^{2}$ for $^{153}\mathrm{Sm}$ and $^{155}\mathrm{Sm}$, respectively. The strength of the SR for $^{155}\mathrm{Sm}$ is comparable to those for deformed even-even Sm isotopes from nuclear resonance fluorescence measurements, while that of $^{153}\mathrm{Sm}$ is lower than expected.

High-spin states of the odd-odd nucleus $^{168}\mathrm{Lu}$ were populated in the $^{123}\mathrm{Sb}(^{48}\mathrm{Ca},3\mathrm{n})^{168}\mathrm{Lu}$ reaction at a beam energy of 203 MeV and decay $\ensuremath{\gamma}$ rays measured using the Gammasphere spectrometer array. The level scheme has been extended from spin 27 to 50 $\ensuremath{\hbar}$, and three new rotational bands have been added. A number of interband linking transitions were revealed, so that all but two bands could be connected with each other. High-spin band crossings, above the first $\ensuremath{\nu}{i}_{13/2}$ alignment, are delineated in most bands. Significant signature inversions are identified for the first time in the bands involving both favored and unfavored signatures of the $\ensuremath{\pi}{h}_{9/2}$ orbital, which are likely caused by a residual proton-neutron interaction. A signature inversion with small amplitude is also observed in the $\ensuremath{\pi}{d}_{5/2}\ensuremath{\bigotimes}\ensuremath{\nu}{i}_{13/2}$ band. Configurations are suggested for all bands based on their experimental properties, with the help of Cranked Shell Model calculations. No evidence is found for triaxial strongly deformed structures that were predicted by the calculations.

Understanding the evolution of level densities in the crossover from spherical to well-deformed nuclei has been a long-standing problem in nuclear physics. We measure nuclear level densities for a chain of neodymium isotopes $^{142,144-151}$Nd which exhibit such a crossover. These results represent to date the most complete data set of nuclear level densities for an isotopic chain between neutron shell-closure and towards mid-shell. We observe a strong increase of the level densities along the chain with an overall increase by a factor of $\approx 170$ at an excitation energy of 7.5 MeV and saturation around mass 150. Level densities calculated by the shell model Monte Carlo (SMMC) are in excellent agreement with these experimental results. Based on our experimental and theoretical findings, we offer an explanation of the observed mass dependence of the level densities in terms of the intrinsic single-particle level density and the collective enhancement., 7 pages, 4 figures

Research at the Oslo Cyclotron Laboratory at the University of Oslo is focused on spectroscopy experiments for nuclear structure and nuclear astrophysics using the Oslo Scintillator Array OSCAR. Light-ion beams from the$$K=35$$K=35cyclotron are furthermore used for studies in radiation biology and medical physics, for research and development related to medical isotope production, and for irradiation of materials and electronics components. Here we present an overview of the laboratory and its research infrastructure, give a brief discussion of the respective research programs and methods, and present recent highlights.

The Shape method, a novel approach to obtain the functional form of the $\gamma$-ray strength function ($\gamma$SF) in the absence of neutron resonance spacing data, is introduced. When used in connection with the Oslo method the slope of the Nuclear Level Density (NLD) is obtained simultaneously. The foundation of the Shape method lies in the primary $\gamma$-ray transitions which preserve information on the functional form of the $\gamma$SF. The Shape method has been applied to $^{56}$Fe, $^{92}$Zr, $^{164}$Dy, and $^{240}$Pu, which are representative cases for the variety of situations encountered in typical NLD and $\gamma$SF studies. The comparisons of results from the Shape method to those from the Oslo method demonstrate that the functional form of the $\gamma$SF is retained regardless of nuclear structure details or $J^\pi$ values of the states fed by the primary transitions., Comment: 13 pages, 8 figures

In this paper we present the first systematic analysis of the impact of the populated vs. intrinsic spin distribution on the nuclear level density and γ-ray strength function retrieved through the Oslo Method. We illustrate the effect of the spin distribution on the recently performed 239Pu(d,pγ)240Pu experiment using a 12 MeV deuteron beam performed at the Oslo Cyclotron Lab. In the analysis we couple state-of-the-art calculations for the populated spin-distributions with the Monte-Carlo nuclear decay code RAINIER to compare Oslo Method results to the known input. We find that good knowledge of the populated spin distribution is crucial and show that the populated distribution has a significant impact on the extracted nuclear level density and γ-ray strength function for the 239Pu(d,pγ)240Pu case.

Reliable neutron-induced reaction cross sections of unstable nuclei are essential for nuclear astrophysics and applications but their direct measurement is often impossible. The surrogate-reaction method is one of the most promising alternatives to access these cross sections. In this work, we successfully applied the surrogate-reaction method to infer for the first time both the neutron-induced fission and radiative-capture cross sections of 239Pu in a consistent manner from a single measurement. This was achieved by combining simultaneously-measured fission and gamma-emission probabilities for the 240Pu(4He,4He') surrogate reaction with a calculation of the angular-momentum and parity distributions populated in this reaction. While other experiments measure the probabilities for some selected gamma-ray transitions, we measure the gamma-emission probability. This enlarges the applicability of the surrogate-reaction method., Comment: 8 pages, 3 figures

6 pags., 4 figs., The γ-ray emission from the nuclei Fe following Coulomb excitation at bombarding energy of 400-440 AMeV was measured with special focus on E1 transitions in the energy region 4-8 MeV. The unstable neutron-rich nuclei Fe were produced at the FAIR-GSI laboratories and selected with the FRS spectrometer. The γ decay was detected with AGATA. From the measured γ-ray spectra the summed E1 strength is extracted and compared to microscopic quasi-particle phonon model calculations. The trend of the E1 strength with increasing neutron number is found to be fairly well reproduced with calculations that assume a rather complex structure of the 1 states (three-phonon states) inducing a strong fragmentation of the E1 nuclear response below the neutron binding energy., This work was partially supported by INFN (Italy) and STFC (UK), the Swedish Research Council (Vetenskapsrådet, VR 2010-147, 2011-5253, and 2016-3969), BMBF NuSTAR-AGATA 05P18RDFN9 and BMBF NuSTAR 05P18RDFN1. The project was co-funded by the European Commission under the 7th Framework Program for RTD (2007-2013) under the Capacities Program (Contract Number 262010, ENSAR). This work was par-tially supported by the Ministry of Science, and Generalitat Valenciana, Spain, under the Grants SEV-2014-0398, FPA2017-84756-C4, PROMETEO/2019/005 and by the EU FEDER funds.

The new Oslo Scintillator Array (OSCAR) has been commissioned at the Oslo Cyclotron Laboratory (OCL). It consists of 30 large volume (diameter 3.5 x 8 inches) LaBr$_3$(Ce) detectors that are used for $\gamma$-ray spectroscopy. The response functions for incident $\gamma$-rays up to 20 MeV are simulated with $\texttt{Geant4}$. In addition, the resolution, and the total and full-energy peak efficiencies are extracted. The results are in very good agreement with measurements from calibration sources and experimentally obtained mono-energetic in-beam $\gamma$-ray spectra., Comment: Changes to v2 (submitted version): Accepted for NIMA with minor revisions (implemented); Changes to v1: see v2 - major changes in experimental setup and simulations [stalled version]

The cascading 3.21 and 4.44 MeV electric quadrupole transitions have been observed from the Hoyle state at 7.65 MeV excitation energy in $^{12}\mathrm{C}$, excited by the $^{12}\mathrm{C}(p,{p}^{\ensuremath{'}})$ reaction at 10.7 MeV proton energy. From the proton-$\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ triple coincidence data, a value of ${\mathrm{\ensuremath{\Gamma}}}_{\mathrm{rad}}/\mathrm{\ensuremath{\Gamma}}=6.2(6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ was obtained for the radiative branching ratio. Using our results, together with ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\pi}}^{E0}/\mathrm{\ensuremath{\Gamma}}$ from Eriksen et al. [Phys. Rev. C 102, 024320 (2020)] and the currently adopted ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\pi}}(E0)$ values, the radiative width of the Hoyle state is determined as ${\mathrm{\ensuremath{\Gamma}}}_{\mathrm{rad}}=5.1(6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\text{ }\text{ }\mathrm{eV}$. This value is about 34% higher than the currently adopted value and will impact models of stellar evolution and nucleosynthesis.

The transitional nuclei $^{134}$Ba and $^{133}$Ba are investigated after multinucleon transfer employing the high-resolution Advanced GAmma Tracking Array coupled to the magnetic spectrometer PRISMA at the Laboratori Nazionali di Legnaro, Italy, and after fusion-evaporation reaction at the FN tandem accelerator of the University of Cologne, Germany. The Jπ=19/2+ state at 1942 keV in $^{133}$Ba is identified as an isomer with a half-life of 66.6(20)ns corresponding to a B(E1) value of 7.7(4)×10−6e2fm2 for the Jπ=19/2+ to Jπ=19/2− transition. The level scheme of $^{134}$Ba above the Jπ=10+ isomer is extended to approximately 6 MeV. A pronounced backbending is observed at ℏω=0.38 MeV along the positive-parity yrast band. The results are compared to the high-spin systematics of the Z=56 isotopes. Large-scale shell-model calculations employing the GCN50:82, SN100PN, SNV, PQM130, Realistic SM, and EPQQM interactions reproduce the experimental findings and elucidate the structure of the high-spin states. The shell-model calculations employing the GCN50:82 and PQM130 interactions reproduce alignment properties and provide detailed insight into the microscopic origin of this phenomenon in transitional $^{134}$Ba.

The Oslo method has been applied to particle-$\ensuremath{\gamma}$ coincidences following the $^{239}\mathrm{Pu}(d,p)$ reaction to obtain the nuclear level density (NLD) and $\ensuremath{\gamma}$-ray strength function ($\ensuremath{\gamma}\mathrm{SF}$) of $^{240}\mathrm{Pu}$. The experiment was conducted with a 12 MeV deuteron beam at the Oslo Cyclotron Laboratory. The low spin transfer of this reaction leads to a spin-parity mismatch between populated and intrinsic levels. This is a challenge for the Oslo method as it can have a significant impact on the extracted NLD and $\ensuremath{\gamma}\mathrm{SF}$. We have developed an iterative approach to ensure consistent results even for cases with a large spin-parity mismatch, in which we couple Green's function transfer calculations of the spin-parity dependent population cross-section to the nuclear decay code rainier. The resulting $\ensuremath{\gamma}\mathrm{SF}$ shows a pronounced enhancement between 2--4 MeV that is consistent with the location of the low-energy orbital $M1$ scissors mode.

The nuclear level density and $\ensuremath{\gamma}$-decay strength of $^{192}\mathrm{Os}$ have been extracted using particle-$\ensuremath{\gamma}$ coincidence data from the $^{192}\mathrm{Os}(\ensuremath{\alpha},{\ensuremath{\alpha}}^{\ensuremath{'}}\ensuremath{\gamma})^{192}\mathrm{Os}$ reaction by means of the Oslo method. The level density is found to be a rather smooth function of excitation energy, approximately following the constant temperature model. The $\ensuremath{\gamma}$-decay strength is compared to photoneutron cross-section data above the neutron separation energy, and to $E1$ and $M1$ strengths for nuclei in this mass region derived from primary transitions following neutron capture. Our results are in good agreement with these previous data and draw a consistent picture of the $\ensuremath{\gamma}$-strength function in the range ${E}_{\ensuremath{\gamma}}\ensuremath{\approx}1.5--6\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$. Using the measured nuclear level density and $\ensuremath{\gamma}$-decay strength as input to the nuclear-reaction code talys, we provide the first experimentally constrained Maxwellian-averaged cross section (MACS) for the $^{191}\mathrm{Os}(n,\ensuremath{\gamma})^{192}\mathrm{Os}$ reaction relevant to $s$-process nucleosynthesis. The systematic uncertainties introduced by the normalization procedure of the level density and $\ensuremath{\gamma}$-strength function were investigated and propagated to the calculated Maxwellian-averaged cross section. The obtained result of the Maxwellian-averaged cross section at ${k}_{B}T=30\phantom{\rule{0.28em}{0ex}}\mathrm{keV}$, ${\ensuremath{\langle}\ensuremath{\sigma}\ensuremath{\rangle}}_{n,\ensuremath{\gamma}}=1134\ifmmode\pm\else\textpm\fi{}375\phantom{\rule{0.28em}{0ex}}\mathrm{mb}$, is in very good agreement with the theoretical estimate provided by the KADoNiS project, giving experimental support to the adopted KADoNiS value. Good agreement is also found with MACS values obtained from other libraries, such as TENDL-2017, ENDF/B-VII.0, and JEFF.

CITATION: Brits, C. P., et al. 2019. Nuclear level densities and γ-ray strength functions of 180,181,182Ta. Physical Review C, 99(5):054330, doi:10.1103/PhysRevC.99.054330.

The high-spin structures of 136Ba and 137Ba are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. 136Ba is populated in a 136Xe+238U MNT reaction employing the high-resolution Advanced GAmma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA at the Laboratori Nazionali di Legnaro, Italy, and in two 9Be + 130Te fusion-evaporation reactions using the High-efficiency Observatory for -Ray Unique Spectroscopy (HORUS) at the FN tandem accelerator of the University of Cologne, Germany. Furthermore, both isotopes are populated in an elusive reaction channel in the 11B+130Te fusion-evaporation reaction utilizing the HORUS -ray array. The level scheme above the J� = 10+ isomer in 136Ba is revised and extended up to an excitation energy of approx. 5.5 MeV. From the results of angular-correlation measurements, the Ex = 3707- and Ex = 4920-keV states are identified as the bandheads of positive- and negative-parity cascades. While the high-spin regimes of both 132Te and 134Xe are characterized by high-energy 12+ ! 10+ transitions, the 136Ba E2 ground-state band is interrupted by negativeparity states only a few hundred keV above the J� = 10+ isomer. Furthermore, spins are established for several hitherto unassigned high-spin states in 137Ba. The new results close a gap along the highspin structure of N < 82 Ba isotopes. Experimental results are compared to large-scale shell-model calculations employing the GCN50:82, Realistic SM, PQM130 and SN100PN interactions. The calculations suggest that the bandheads of the positive-parity bands in both isotopes are predominantly of proton character.

Numerous scientific fields including astrophysics, nuclear power, and nuclear forensics require a knowledge of basic nuclear properties for large numbers of short-lived, radioactive isotopes far removed from stable nuclei. Neutron-capture cross sections are one such piece of nuclear data where direct measurements are not possible and theoretical predictions can vary by orders of magnitude. A recently developed indirect technique for inferring neutron capture rates, the β -Oslo method, has been introduced but not compared against a known, directly measured neutron capture cross section. To provide this benchmark, two indirect methods based on β decay and charged-particle reactions were used to extract the nuclear level density and γ -ray strength function of 51 Ti . The nuclear level density and γ -ray strength function from the two data sets were found to be equivalent and were used to extract the neutron capture cross section of 50 Ti which agrees with previous direct measurements at high neutron energies. The results demonstrate the validity of the β -Oslo method for extracting neutron capture cross sections of short-lived nuclei and provide a sufficiently small uncertainty to be used in various applications.

International audience; A Coulomb excitation campaign on $^{106,108,110}$Sn at 4.4–4.5 MeV/u was launched at the HIE-ISOLDE facility at CERN. Larger excitation cross sections and γ-ray statistics were achieved compared to previous experiments at ∼2.8 MeV/u. More precise $(B(E2;0_{1}^{ + } \to 2_{1}^{ + }))$ values, lifetimes of states via the Doppler shift attenuation method, and new $(B(E2;0_{1}^{ + } \to 2_{x}^{ + })), (B(E2;2_{1}^{ + } \to 4_{1}^{ + }))$ and $(Q(2_{1}^{ + }))$ values from the new Miniball data will be obtained and applied to test modern nuclear structure theories.

Photoneutron cross sections were measured for Ni58,Ni60,Ni61, and Ni64 at energies between the one-neutron and two-neutron thresholds using quasimonochromatic γ-ray beams produced in laser Compton scattering at the NewSUBARU synchrotron radiation facility. These photoneutron data are used to extract the γ-ray strength function above the neutron threshold, complementing the information obtained by the Oslo method below the threshold. We discuss radiative neutron-capture cross sections and the Maxwellian-averaged cross sections for Ni isotopes including Ni63, a branching point nucleus along the weak s-process path. The cross sections are calculated with the experimentally constrained γ-ray strength functions from the Hartree-Fock-Bogolyubov plus quasiparticle–random-phase approximation based on the Gogny D1M interaction for both E1 and M1 components and supplemented with the M1 upbend.

Detailed information on isomeric states in A ≈ 135 nuclei is exploited to benchmark shell-model calculations in the region northwest of doubly-magic nucleus 132Sn. The N = 79 isotones 133Xe and 135Ba are studied after multinucleon transfer (MNT) in the 136Xe + 208Pb reaction employing the high-resolution Advanced GAmma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA at the Laboratori Nazionali di Legnaro, Italy and in a pulsed-beam experiment at the FN tandem accelerator of the University of Cologne, Germany utilizing a 9Be+130Te fusion-evaporation reaction at a beam energy of 40 MeV. Isomeric states are identified via delayed γ-ray spectroscopy. Hitherto tentative excitation energy, spin, and parity assignments of the 2107-keV Jπ = 23/2+ isomer in 133Xe are confirmed and a half-life of T1/2 = 8.64(13) ms is measured. The 2388-keV state in 135Ba is identified as a Jπ = 23/2+ isomer with a half-life of 1.06(4) ms. The new results show a smooth onset of isomeric Jπ = 23/2+ states along the N = 79 isotones and close a gap in the high-spin systematics towards the recently investigated Jπ = 23/2+ isomer in 139Nd. The resulting systematics of M2 reduced transition probabilities is discussed within the framework of the nuclear shell model. Latest large-scale shell-model calculations employing the SN100PN, GCN50:82, SN100-KTH, and a realistic effective interaction reproduce the experimental findings generally well and give insight into the structure of the isomers.

The lifetimes of the first excited 2^{+}, 4^{+}, and 6^{+} states in ^{98}Zr were measured with the recoil-distance Doppler shift method in an experiment performed at GANIL. Excited states in ^{98}Zr were populated using the fission reaction between a 6.2 MeV/u ^{238}U beam and a ^{9}Be target. The γ rays were detected with the EXOGAM array in correlation with the fission fragments identified by mass and atomic number in the VAMOS++ spectrometer. Our result shows a very small B(E2;2_{1}^{+}→0_{1}^{+}) value in ^{98}Zr, thereby confirming the very sudden onset of collectivity at N=60. The experimental results are compared to large-scale Monte Carlo shell model and beyond-mean-field calculations. The present results indicate the coexistence of two additional deformed shapes in this nucleus along with the spherical ground state.

We are also grateful for the financial support received from the Research Council of Norway (NFR). S.S. and G.M.T. acknowledge funding under NFR project Grants No. 210007 and No. 262952/F20. A.C.L. acknowledges financial support from the ERC-STG2014 under Grant No. 637686.

The transitional nucleus 131Xe is investigated after multinucleon transfer (MNT) in the 136Xe+208Pb and 136Xe+238U reactions employing the high-resolution Advanced GAmma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA at the Laboratori Nazionali di Legnaro, Italy and as an elusive reaction product in the fusion-evaporation reaction 124Sn(11B,p3n) 131Xe employing the HORUS γ-ray array coupled to a double-sided silicon strip detector (DSSSD) at the University of Cologne, Germany. The level scheme of 131Xe is extended to 5 MeV. A pronounced backbending is observed at ~ω ≈ 0.4 MeV along the negative-parity one-quasiparticle νh11/2(α = −1/2) band. The results are compared to the high-spin systematics of the Z = 54 isotopes and the N = 77 isotones. Large-scale shell-model calculations (LSSM) employing the PQM130, SN100PN, GCN50:82, SN100-KTH and a realistic effective interaction reproduce the experimental findings and provide guidance to elucidate the structure of the high-spin states. Further calculations in 129−132Xe provide insight into the changing nuclear structure along the Xe chain towards the N = 82 shell closure. Proton occupancy in the π 0h11/2 orbital is found to be decisive for the description of the observed backbending phenomenon.

Lifetimes of several short-lived excited states in Nd138 were measured with the ROSPHERE array at IFIN-HH, Bucharest, using the recoil-distance Doppler shift technique following the Sb123(F19,4n) reaction. The resulting electromagnetic transition probabilities are compared to large-scale shell model calculations and to constrained Hartree-Fock-Bogoliubov calculations with the Gogny D1S interaction, configuration mixing, and a five-dimensional collective Hamiltonian formalism. The onset of collectivity in Nd isotopes below the N=82 shell closure and the deformation induced by the alignment of protons and neutron holes in the h11/2 orbitals are discussed.

Transition probabilities of intermediate-spin yrast and non-yrast excitations in 80, 82Se were investigated in a recoil distance Doppler-shift (RDDS) experiment performed at the Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro. The Cologne Plunger device for deep inelastic scattering was used for the RDDS technique and was combined with the AGATA Demonstrator array for the γ-ray detection and coupled to the PRISMA magnetic spectrometer for an event-by-event particle identification. In 80Se, the level lifetimes of the yrast (6+1) and (8+1) states and of a non-yrast band feeding the yrast 4+1 state are determined. A spin and parity assignment of the head of this sideband is discussed based on the experimental results and supported by large-scale shell-model calculations. In 82Se, the level lifetimes of the yrast 6+1 state and the yrare 4+2 state and lifetime limits of the yrast (10+1) state and of the 5−1 state are determined. Although the experimental results contain large uncertainties, they are interpreted with care in terms of large-scale shell-model calculations using the effective interactions JUN45 and jj44b. The excited states' wave functions are investigated and discussed with respect to the role of the neutron g9/2 orbital.

Author(s): Jones, MD; MacChiavelli, AO; Wiedeking, M; Bernstein, LA; Crawford, HL; Campbell, CM; Clark, RM; Cromaz, M; Fallon, P; Lee, IY; Salathe, M; Wiens, A; Ayangeakaa, AD; Bleuel, DL; Bottoni, S; Carpenter, MP; Davids, HM; Elson, J; Gorgen, A; Guttormsen, M; Janssens, RVF; Kinnison, JE; Kirsch, L; Larsen, AC; Lauritsen, T; Reviol, W; Sarantites, DG; Siem, S; Voinov, AV; Zhu, S | Abstract: A model-independent technique was used to determine the γ-ray strength function (γSF) of Fe56 down to γ-ray energies less than 1 MeV for the first time with GRETINA using the (p,p′) reaction at 16 MeV. No difference was observed in the energy dependence of the γSF built on 2+ and 4+ final states, supporting the Brink hypothesis. In addition, angular distribution and polarization measurements were performed. The angular distributions are consistent with dipole radiation. The polarization results show a small bias towards magnetic character in the region of the enhancement.

A Coulomb-excitation experiment to study electromagnetic properties of Ca42 was performed using a 170-MeV calcium beam from the TANDEM XPU facility at INFN Laboratori Nazionali di Legnaro. γ rays from excited states in Ca42 were measured with the AGATA spectrometer. The magnitudes and relative signs of ten E2 matrix elements coupling six low-lying states in Ca42, including the diagonal E2 matrix elements of 21+ and 22+ states, were determined using the least-squares code gosia. The obtained set of reduced E2 matrix elements was analyzed using the quadrupole sum rule method and yielded overall quadrupole deformation for 01,2+ and 21,2+ states, as well as triaxiality for 01,2+ states, establishing the coexistence of a weakly deformed ground-state band and highly deformed slightly triaxial sideband in Ca42. The experimental results were compared with the state-of-the-art large-scale shell-model and beyond-mean-field calculations, which reproduce well the general picture of shape coexistence in Ca42.

High-spin states in 124 Cs were populated in the 64 Ni ( 64 Ni , p 3 n ) reaction and the Gammasphere detector array was used to measure γ -ray coincidences. Both positive- and negative-parity bands, including bands with chiral configurations, have been extended to higher spin, where a shape change has been observed. The configurations of the bands before and after the alignment are discussed within the framework of the cranked Nilsson-Strutinsky model. The calculations suggest that the nucleus undergoes a shape transition from triaxial to prolate around spin I≃ 22 of the positive-parity states. The alignment gain of 8ℏ , observed in the positive-parity bands, is due to partial alignment of several valence nucleons. This indicates the absence of band crossing due to paired nucleons in the bands. © 2018 American Physical Society

Statistical $\gamma$-decay from highly excited states is determined by the nuclear level density (NLD) and the $\gamma$-ray strength function ($\gamma$SF). These average quantities have been measured for several nuclei using the Oslo method. For the first time, we exploit the NLD and $\gamma$SF to evaluate the $\gamma$-width in the energy region below the neutron binding energy, often called the quasi-continuum region. The lifetimes of states in the quasi-continuum are important benchmarks for a theoretical description of nuclear structure and dynamics at high temperature. The lifetimes may also have impact on reaction rates for the rapid neutron-capture process, now demonstrated to take place in neutron star mergers., Comment: CGS16, Shanghai 2017, Proceedings, 5 pages, 3 figures

Lifetimes of excited states in 107Tc, 109Rh, 111Rh, and 113Rh were measured at GANIL using the Recoil-Distance Doppler Shift method. The neutron-rich nuclei were produced in fission reactions in inverse kinematics with a 238U beam impinging on a 9Be target. Fission fragments were identified event-by-event in the ray-tracing spectrometer VAMOS++ and correlated with prompt $\gamma$ rays observed around the target position with the EXOGAM Ge detector array. Several lifetimes were obtained for states in the positive-parity yrast bands in the four nuclei and compared to triaxial particle-rotor calculations. The results clarify the configuration for the strongest positive-parity band in 107Tc and suggest a gradual increase of triaxial deformation with atomic number Z, reaching almost maximum triaxiality for the neutron-rich Rh nuclei.

$^{111}\mathrm{Ag}$ and $^{113}\mathrm{Ag}$ were produced in induced fission reaction, where yrast and near-yrast states were populated. To interpret the new data the Interacting Boson-Fermion Model was used. A good agreement with the experimental data is achieved, suggesting that the two Ag nuclei have a well-developed collectivity, superimposed on $\ensuremath{\pi}{g}_{9/2}^{\ensuremath{-}3}$ excitations previously observed throughout the entire isotopic chain.

Author(s): Vogt, A; Siciliano, M; Birkenbach, B; Reiter, P; Hadynska-Klȩk, K; Wheldon, C; Valiente-Dobon, JJ; Teruya, E; Yoshinaga, N; Arnswald, K; Bazzacco, D; Blazhev, A; Bracco, A; Bruyneel, B; Chakrawarthy, RS; Chapman, R; Cline, D; Corradi, L; Crespi, FCL; Cromaz, M; De Angelis, G; Eberth, J; Fallon, P; Farnea, E; Fioretto, E; Fransen, C; Freeman, SJ; Fu, B; Gadea, A; Gelletly, W; Giaz, A; Gorgen, A; Gottardo, A; Hayes, AB; Hess, H; Hetzenegger, R; Hirsch, R; Hua, H; John, PR; Jolie, J; Jungclaus, A; Karayonchev, V; Kaya, L; Korten, W; Lee, IY; Leoni, S; Liang, X; Lunardi, S; MacChiavelli, AO; Menegazzo, R; Mengoni, D; Michelagnoli, C; Mijatovic, T; Montagnoli, G; Montanari, D; Muller-Gatermann, C; Napoli, D; Pearson, CJ; Podolyak, Z; Pollarolo, G; Pullia, A; Queiser, M; Recchia, F; Regan, PH; Regis, JM; Saed-Samii, N; Sahin, E; Scarlassara, F; Seidlitz, M; Siebeck, B; Sletten, G; Smith, JF; Soderstrom, PA; Stefanini, AM; Stezowski, O; Szilner, S; Szpak, B; Teng, R; Ur, C; Warner, DD; Wolf, K; Wu, CY; Zell, KO | Abstract: The transitional nuclei Xe132 and Xe133 are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. Both nuclei are populated (i) in Xe136+Pb208 MNT reactions employing the high-resolution Advanced GAmma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (ii) in the Xe136+Pt198 MNT reaction employing the GAMMASPHERE spectrometer in combination with the gas-detector array CHICO, and (iii) as an evaporation residue after a Te130(α,xn)Xe134-xn fusion-evaporation reaction employing the HORUS γ-ray array at the University of Cologne. The high-spin level schemes are considerably extended above the Jπ=(7-) and (10+) isomers in Xe132 and above the 11/2- isomer in Xe133. The results are compared to the high-spin systematics of the Z=54 as well as the N=78 and N=79 chains. Furthermore, evidence is found for a long-lived (T1/2â‰1μs) isomer in Xe133 which closes a gap along the N=79 isotones. Shell-model calculations employing the SN100PN and PQM130 effective interactions reproduce the experimental findings and provide guidance to the interpretation of the observed high-spin features.

Nuclear level densities (NLDs) and $\ensuremath{\gamma}$-ray strength functions ($\ensuremath{\gamma}\mathrm{SFs}$) have been extracted from particle-$\ensuremath{\gamma}$ coincidences of the $^{92}\mathrm{Zr}(p,{p}^{\ensuremath{'}}\ensuremath{\gamma})^{92}\mathrm{Zr}$ and $^{92}\mathrm{Zr}(p,d\ensuremath{\gamma})^{91}\mathrm{Zr}$ reactions using the Oslo method. The new $^{91,92}\mathrm{Zr}\phantom{\rule{4pt}{0ex}}\ensuremath{\gamma}\mathrm{SF}$ data, combined with photonuclear cross sections, cover the whole energy range from ${E}_{\ensuremath{\gamma}}\ensuremath{\approx}1.5\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$ up to the giant dipole resonance at ${E}_{\ensuremath{\gamma}}\ensuremath{\approx}17$ MeV. The wide-range $\ensuremath{\gamma}\mathrm{SF}$ data display structures at ${E}_{\ensuremath{\gamma}}\ensuremath{\approx}9.5$ MeV, compatible with a superposition of the spin-flip $M1$ resonance and a pygmy $E1$ resonance. Furthermore, the $\ensuremath{\gamma}\mathrm{SF}$ shows a minimum at ${E}_{\ensuremath{\gamma}}\ensuremath{\approx}2--3\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$ and an increase at lower $\ensuremath{\gamma}$-ray energies. The experimentally constrained NLDs and $\ensuremath{\gamma}\mathrm{SFs}$ are shown to reproduce known ($n,\ensuremath{\gamma}$) and Maxwellian-averaged cross sections for $^{91,92}\mathrm{Zr}$ using the talys reaction code, thus serving as a benchmark for this indirect method of estimating ($n,\ensuremath{\gamma}$) cross sections for Zr isotopes.

The $\ensuremath{\gamma}$ decay of $^{65}\mathrm{Ni}$ has been studied from particle-$\ensuremath{\gamma}$ coincidence data on the $^{64}\mathrm{Ni}(d,p\ensuremath{\gamma})^{65}\mathrm{Ni}$ reaction. $\ensuremath{\gamma}$-ray spectra at excitation energies below ${E}_{x}\ensuremath{\approx}2\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$ have been studied and compared with previous measurements. Coincidences corresponding to ${E}_{x}\ensuremath{\approx}4.4--6.1\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$ have been used to constrain the shape of the nuclear level density and $\ensuremath{\gamma}$-strength function of $^{65}\mathrm{Ni}$ by means of the Oslo method. The experimental $\ensuremath{\gamma}$-strength function presents an enhancement at $\ensuremath{\gamma}$ energies below ${E}_{\ensuremath{\gamma}}\ensuremath{\approx}3\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$. In addition, a resonance-like structure centered at ${E}_{\ensuremath{\gamma}}\ensuremath{\approx}4.6\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$ is seen together with accumulated strength at ${E}_{\ensuremath{\gamma}}\ensuremath{\approx}2.6--3.6\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$. The obtained results contribute to the systematic study of $\ensuremath{\gamma}$ decay in the Ni isotopes, which is of great interest for the understanding of both single-particle and collective nuclear structure phenomena.

Author(s): Rose, SJ; Zeiser, F; Wilson, JN; Oberstedt, A; Oberstedt, S; Siem, S; Tveten, GM; Bernstein, LA; Bleuel, DL; Brown, JA; Crespo Campo, L; Giacoppo, F; Gorgen, A; Guttormsen, M; Hadynska, K; Hafreager, A; Hagen, TW; Klintefjord, M; Laplace, TA; Larsen, AC; Renstrom, T; Sahin, E; Schmitt, C; Tornyi, TG; Wiedeking, M | Abstract: Prompt-fission γ rays are responsible for approximately 5% of the total energy released in fission, and therefore important to understand when modeling nuclear reactors. In this work we present prompt γ-ray emission characteristics in fission as a function of the nuclear excitation energy of the fissioning system. Emitted γ-ray spectra were measured, and γ-ray multiplicities and average and total γ energies per fission were determined for the U(d,pf)233 reaction for excitation energies between 4.8 and 10 MeV, and for the Pu(d,pf)239 reaction between 4.5 and 9 MeV. The spectral characteristics show no significant change as a function of excitation energy above the fission barrier, despite the fact that an extra ∼5 MeV of energy is potentially available in the excited fragments for γ decay. The measured results are compared with model calculations made for prompt γ-ray emission with the fission model code gef. Further comparison with previously obtained results from thermal neutron induced fission is made to characterize possible differences arising from using the surrogate (d,p) reaction.

The level structure of the neutron-rich ^{77}Cu nucleus is investigated through β-delayed γ-ray spectroscopy at the Radioactive Isotope Beam Factory of the RIKEN Nishina Center. Ions of ^{77}Ni are produced by in-flight fission, separated and identified in the BigRIPS fragment separator, and implanted in the WAS3ABi silicon detector array, surrounded by Ge cluster detectors of the EURICA array. A large number of excited states in ^{77}Cu are identified for the first time by correlating γ rays with the β decay of ^{77}Ni, and a level scheme is constructed by utilizing their coincidence relationships. The good agreement between large-scale Monte Carlo shell model calculations and experimental results allows for the evaluation of the single-particle structure near ^{78}Ni and suggests a single-particle nature for both the 5/2_{1}^{-} and 3/2_{1}^{-} states in ^{77}Cu, leading to doubly magic ^{78}Ni.

CITATION: Kheswa, B. V., et al. 2017. ¹³⁷,¹³⁸,¹³⁹La(n,γ) cross sections constrained with statistical decay properties of ¹³⁸,¹³⁹,¹⁴⁰La nuclei. Physical Review C, 95(4):1-9, doi:10.1103/PhysRevC.95.045805.

The high-spin structures of the N = 81 isotones 135Xe and 137Ba are investigated after multinucleontransfer (MNT) and fusion-evaporation reactions. Both nuclei are populated in (i) 136Xe+238U and (ii) 136Xe+208Pb MNT reactions employing the high-resolution Advanced Gamma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (iii), in the 136Xe+198Pt MNT reaction employing the -ray array GAMMASPHERE in combination with the gas detector array Chico, and (iv) via a 11B+130Te fusion-evaporation reaction. The high-spin level schemes of 135Xe and 137Ba are considerably extended to higher energies. The 2058-keV (19=2 ) state in 135Xe is identified as an isomer, completing the systematics for the N = 81 isotones. Its half-life is measured to be 8.6(10) ns, corresponding to a transition probability of B(E2; 19=2 ! 15=2 ) = 0:539(69) W.u. Latest shell model calculations considering 132Sn as a closed core reproduce the experimental findings and provide guidance to the interpretation of the new levels. The experimentally deduced reduced quadrupole transition probabilities of the isomeric states are compared to shell-model predictions.

M. Klintefjord et al. -- 11 pags., 8 figs., 1 tab. -- Open Access funded by Creative Commons Atribution Licence 4.0

L. Pellegri et al. ; 5 pags. ; 6 figs. ; open access article under the CC BY license. Funded by SCOAP3, © 2014 The Authors. The γ decay from the high-lying states of 124Sn was measured using the inelastic scattering of 17O at 340 MeV. The emitted γ rays were detected with high resolution with the AGATA demonstrator array and the scattered ions were detected in two segmented δE-E silicon telescopes. The angular distribution was measured both for the γ rays and the scattered 17O ions. An accumulation of E1 strength below the particle threshold was found and compared with previous data obtained with (γ, γ') and (α, α'γ) reactions. The present results of elastic scattering, and excitation of E2 and E1 states were analysed using the DWBA approach. From this comprehensive description the isoscalar component of the 1- excited states was extracted. The obtained values are based on the comparison of the data with DWBA calculations including a form factor deduced using a microscopic transition density., Grant No. 2011/03/B/ST2/01894; (iii) the National Superconducting Cyclotron Laboratory at MSU; (iv) the US NSF Grant PHY-1204486; and the German BMBF under Grant 06KY9136.

Nuclear level densities and $\gamma$-ray strength functions of $^{56,57}$Fe have been extracted from proton-$\gamma$ coincidences. A low-energy enhancement in the $\gamma$-ray strength functions up to a factor of 30 over common theoretical E1 models is confirmed. Angular distributions of the low-energy enhancement in $^{57}$Fe indicate its dipole nature, in agreement with findings for $^{56}$Fe. The high statistics and the excellent energy resolution of the large-volume LaBr$_{3}$(Ce) detectors allowed for a thorough analysis of $\gamma$ strength as function of excitation energy. Taking into account the presence of strong Porter-Thomas fluctuations, there is no indication of any significant excitation-energy dependence in the $\gamma$-ray strength function, in support of the generalized Brink-Axel hypothesis., Comment: 24 pages, 17 figures, accepted for publication in J. Phys. G: Nucl. Phys; Special Issue

International audience; Lifetimes of excited states in ${}^{99}$Y , ${}^{101}$Y, ${}^{101}$Nb, ${}^{103}$Nb, and ${}^{105}$Nb were measured in an experiment using the recoil distance Doppler shift method at GANIL (Grand Accélérateur National d’Ions Lourds). The neutron-richnuclei were produced in fission reactions between a ${}^{238}$U beam and a ${}^9$Be target. Prompt γ rays were measuredwith the EXOGAM array and correlated with fission fragments that were identified in mass and atomic numberwith the VAMOS$\ {++}$ spectrometer. The measured lifetimes, together with branching ratios, provide $\it B(M1)$ and$\it B(E2)$ values for the strongly coupled rotational bands built on the [422]5/2$^+$ ground state in the Y and Nb nucleiwith neutron number N $\geq$ 60. The comparison of the experimental results with triaxial particle-rotor calculationsprovides information about the evolution of the nuclear shape in this mass region.

A program to study the γ-ray decay from the region of high-level density has been established at iThemba LABS, where a high-resolution gamma-ray detector array is used in conjunction with silicon particle-telescopes. Results from two recent projects are presented: 1) The 74 Ge(α,α′γ) reaction was used to investigate the Pygmy Dipole Resonance. The results were compared to (γ,γ′) data and indicate that the dipole states split into mixed isospin and relatively pure isovector excitations. 2) Data from the 95 Mo(d,p) reaction were used to develop a novel method for the determination of spins for low-lying discrete levels utilizing statistical γ-ray decay in the vicinity of the neutron separation energy. These results provide insight into the competition of (γ,n) and (γ,γ′) reactions and highlights the need to correct for angular momentum barrier effects.

The structure of neutron-rich 96,98Sr nuclei was investigated by low-energy safe Coulomb excitation of radioactive beams at the REX-ISOLDE facility, CERN, with the MINIBALL spectrometer. A rich set of transitional and diagonal E2 matrix elements, including those for non-yrast structures, has been extracted from the differential Coulomb-excitation cross sections. The results support the scenario of a shape transition at N = 60, giving rise to the coexistence of a highly deformed prolate and a spherical configuration in 98Sr, and are compared to predictions from several theoretical calculations. The experimental data suggest a significant contribution of the triaxal degree of freedom in the ground state of both isotopes. In addition, experimental information on low-lying states in 98Rb has been obtained.

Particle-$\ensuremath{\gamma}$ coincidence data have been analyzed to obtain the nuclear level density and the $\ensuremath{\gamma}$-strength function of $^{64}\mathrm{Ni}$ by means of the Oslo method. The level density found in this work is in very good agreement with known energy levels at low excitation energies as well as with data deduced from particle-evaporation measurements at excitation energies above ${E}_{x}\ensuremath{\approx}5.5$ MeV. The experimental $\ensuremath{\gamma}$-strength function presents an enhancement at $\ensuremath{\gamma}$ energies below ${E}_{\ensuremath{\gamma}}\ensuremath{\approx}3$ MeV and possibly a resonancelike structure centered at ${E}_{\ensuremath{\gamma}}\ensuremath{\approx}9.2$ MeV. The obtained nuclear level density and $\ensuremath{\gamma}$-strength function have been used to estimate the $(n,\ensuremath{\gamma})$ cross section for the $s$-process branch-point nucleus $^{63}\mathrm{Ni}$, of particular interest for astrophysical calculations of elemental abundances.

One of the greatest questions for modern physics to address is how elements heavier than iron are created in extreme, astrophysical environments. A particularly challenging part of that question is the creation of the so-called p-nuclei, which are believed to be mainly produced in some types of supernovae. The lack of needed nuclear data presents an obstacle in nailing down the precise site and astrophysical conditions. In this work, we present for the first time measurements on the nuclear level density and average strength function of $^{92}$Mo. State-of-the-art p-process calculations systematically underestimate the observed solar abundance of this isotope. Our data provide stringent constraints on the $^{91}$Nb$(p,{\gamma})^{92}$Mo reaction rate, which is the last unmeasured reaction in the nucleosynthesis puzzle of $^{92}$Mo. Based on our results, we conclude that the $^{92}$Mo abundance anomaly is not due to the nuclear physics input to astrophysical model calculations., Comment: Submitted to PRC

We investigated the U238(d,p) reaction as a surrogate for the n+U238 reaction. For this purpose we measured for the first time the γ-decay and fission probabilities of U∗239 simultaneously and compared them to the corresponding neutron-induced data. We present the details of the procedure to infer the decay probabilities, as well as a thorough uncertainty analysis, including parameter correlations. Calculations based on the continuum-discretized coupled-channels method and the distorted-wave Born approximation (DWBA) were used to correct our data from detected protons originating from elastic and inelastic deuteron breakup. In the region where fission and γ emission compete, the corrected fission probability is in agreement with neutron-induced data, whereas the γ-decay probability is much higher than the neutron-induced data. We have performed calculations of the decay probabilities with the statistical model and of the average angular momentum populated in the U238(d,p) reaction with the DWBA to interpret these results.