Search

We studied the proton-rich T_{z}=-1 nucleus ^{70}Kr through inelastic scattering at intermediate energies in order to extract the reduced transition probability, B(E2;0^{+}→2^{+}). Comparison with the other members of the A=70 isospin triplet, ^{70}Br and ^{70}Se, studied in the same experiment, shows a 3σ deviation from the expected linearity of the electromagnetic matrix elements as a function of T_{z}. At present, no established nuclear structure theory can describe this observed deviation quantitatively. This is the first violation of isospin symmetry at this level observed in the transition matrix elements. A heuristic approach may explain the anomaly by a shape change between the mirror nuclei ^{70}Kr and ^{70}Se contrary to the model predictions.

International audience; Lifetimes of the low-energy levels in Nd136, populated in the reaction Te124(O16,4n), were measured with the ROSPHERE array at the Horia Hulubei National Institute for Physics and Nuclear Engineering (IFIN-HH), Bucharest-Magurele. The data were analyzed using the recoil distance Doppler shift method, and, in the cases where lifetimes were τ⩽1 ps, Doppler attenuation effects were taken into account. The deduced electromagnetic transition probabilities are discussed in the framework of the five-dimensional collective Hamiltonian (5DCH) theoretical model implemented with the D1S Gogny force, and detailed systematics of several observables in the even-even Nd isotopic chain are presented that highlight the transitional character of the neutron-deficient Nd isotopes. The 5DCH predictions are in overall good agreement with the present experimental results.

12 pags., 11 figs., 2 tabs., The N= Z= 36 nucleus Kr has been studied by inelastic scattering at intermediate energies. Two targets, Be and Au, were used to extract the nuclear deformation length, δ, and the reduced E2 transition probability, B(E2). The previously unknown non-yrast 2 and 4 states as well as a new candidate for the octupole 3 state have been observed in the scattering on the Be target and placed in the level scheme based on γ- γ coincidences. The second 2 state was also observed in the scattering on the Au target and the B(E2;22+→01+) value could be determined for the first time. Analyzing the results in terms of a two-band mixing model shows clear evidence for a oblate-prolate shape coexistence and can be explained by a shape change from an oblate ground state to prolate deformed yrast band from the first 2 state. This interpretation is corroborated by beyond mean field calculations using the Gogny D1S interaction., We would like to thank the RIKEN accelerator and BigRIPS teams for providing the high intensity beams. We thank T. Furumoto for providing us with the optical potentials and A. Moro for giving access to an unpublished version of the FRESCO code. This work has been supported by UK STFC under Grant numbers ST/L005727/1 and ST/P003885/1, the Spanish Ministerio de Economía y Competitividad under Grants FPA2011-24553, FPA2014-52823-C2- 1-P, and PGC2018-094583-B-I00, the Program Severo Ochoa (SEV2014-0398), the European Research Council through the ERC Grant No. MINOS-258567, NKFIH (NN128072), and by the ÚNKP-19-4- DE-65 New National Excellence Program of the Ministry of Human Capacities of Hungary. G. K. acknowledges support from the János Bolyai research fellowship of the Hungarian Academy of Sciences. K. W. acknowledges the support from the Spanish Ministerio de Economía y Competitividad RYC-2017-22007.

We present a microscopic description of neutron and proton elastic and inelastic scattering off $^{206,207,208}\mathrm{Pb}$ and $^{209}\mathrm{Bi}$ together with new medium-energy (7.5--15.5 MeV) neutron elastic and inelastic scattering measurements for various low-energy levels. The Jeukenne, Lejeune, Mahaux (JLM) semimicroscopic folding model provides the relevant optical and transition potentials used to calculate the elastic and inelastic cross sections. Rearrangement corrections that account for proton and neutron density variations during the transition are considered. The nuclear diagonal and transition densities are calculated from a (quasiparticle) random phase approximation [(Q)RPA] structure model implemented with the Gogny D1S interaction. Calculated differential elastic and inelastic cross sections are mostly in very good agreement with available data. Predicted nuclear structure properties as well as scattering calculations and measurements for the yrast quadrupole excitation in $^{206}\mathrm{Pb}$ are carefully discussed. The rearrangement corrections to inelastic scattering form factors are shown to reduce medium energy nucleon inelastic cross section by up to 55%. The magnitude of these corrections changes depending on the probe, incident energy, multipolarity, and nature of the transitions considered. The combined analysis of nuclear structure properties and those for nucleon scattering cross sections measured previously over a range of incident energies provides stringent tests of present microscopic models and helps distinguish those scattering data which most likely call for revision.

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.

We report on the first γ-ray spectroscopy of low-lying states in neutron-rich 98,100Kr isotopes obtained from 99,101Rb(p,2p) reactions at ∼ 220 MeV/nucleon. A reduction of the 2+ 1 state energies beyond N = 60 demonstrates a significant increase of deformation, shifted in neutron number compared to the sharper transition observed in strontium and zirconium isotopes. State-of-theart beyond-mean-field calculations using the Gogny D1S interaction predict level energies in good agreement with experimental results. The identification of a low-lying (0+ 2 , 2+ 2 ) state in 98Kr provides the first experimental evidence of a competing configuration at low energy in neutron-rich krypton isotopes consistent with the oblate-prolate shape coexistence picture suggested by theory

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

International audience; A multi-step Coulomb excitation measurement with the GRETINA and CHICO2 detector arrays was carried out with a 430-MeV beam of the neutron-rich $^{110}$Ru (t$_{1/2}$= 12 s) isotope produced at the CARIBU facility. This represents the first successful measurement following the post-acceleration of an unstable isotope of a refractory element. The reduced transition probabilities obtained for levels near the ground state provide strong evidence for a triaxial shape; a conclusion confirmed by comparisons with the results of beyond-mean-field and triaxial rotor model calculations.

The first measurement of the low-lying states of the neutron-rich 110 Zr and 112 Mo was performed via in-beam γ -ray spectroscopy after one proton removal on hydrogen at ∼ 200 MeV / nucleon . The 2 + 1 excitation energies were found at 185(11) keV in 110 Zr , and 235(7) keV in 112 Mo , while the R 42 = E ( 4 + 1 ) / E ( 2 + 1 ) ratios are 3.1(2), close to the rigid rotor value, and 2.7(1), respectively. These results are compared to modern energy density functional based configuration mixing models using Gogny and Skyrme effective interactions. We conclude that first levels of 110 Zr exhibit a rotational behavior, in agreement with previous observations of lighter zirconium isotopes as well as with the most advanced Monte Carlo shell model predictions. The data, therefore, do not support a harmonic oscillator shell stabilization scenario at Z = 40 and N = 70 . The present data also invalidate predictions for a tetrahedral ground state symmetry in 110 Zr .

The electromagnetic structure of 140Sm was studied in a low-energy Coulomb excitation experiment with a radioactive ion beam from the REX-ISOLDE facility at CERN. The 2+ and 4+ states of the ground-state band and a second 2+ state were populated by multistep excitation. The analysis of the differential Coulomb excitation cross sections yielded reduced transition probabilities between all observed states and the spectroscopic quadrupole moment for the 2+ 1 state. The experimental results are compared to large-scale shell model calculations and beyond-mean-field calculations based on the Gogny D1S interaction with a five-dimensional collective Hamiltonian formalism. Simpler geometric and algebraic models are also employed to interpret the experimental data. The results indicate that 140Sm shows considerable γ softness, but in contrast to earlier speculation no signs of shape coexistence at low excitation energy. This work sheds more light on the onset of deformation and collectivity in this mass region. 15 pages, 12 figures ispartof: Physical Review C vol:93 issue:5 status: published

International audience; We provide a sample of analyses for nuclear spectroscopic properties based on the five-dimensional collective Hamiltonian (5DCH) implemented with the Gogny force. The very first illustration is dating back to the late 70's. It is next followed by others, focusing on shape coexistence, shape isomerism, superdeformation, and systematics over the periodic table. Finally, the inclusion of Thouless-Valatin dynamical contributions to vibrational mass parameters is briefly discussed as a mean of strengthening the basis of the 5DCH theory.

The experiment was performed at the National Superconducting Cyclotron Laboratory (NSCL), at Michigan State University (USA).; We report on the first γ spectroscopy of 66Se and 65As from two-neutron removal at intermediate beam energies. The deduced excitation energies for the first-excited states in 66Se and 65As are compared to mean-field-based predictions within a collective Hamiltonian formalism using the Gogny D1S effective interaction and to state-of-the-art shell-model calculations restricted to the pf5/2 g9/2 valence space. The obtained Coulomb-energy differences for the first excited states in 66Se and 65As are discussed within the shell-model formalism to assess the shape-coexistence picture for both nuclei. Our results support a favored oblate ground-state deformation in 66Se and 65As. A shape transition for the ground state of even-odd As isotopes from oblate in 65As to prolate in 67,69,71As is suggested.

The light krypton isotopes were studied in a series of Coulomb excitation experiments using radioactive beams at GANIL. The static quadrupole moments found in these experiments give firm experimental evidence for the shape coexistence scenario that is based on theoretical calculations and on the systematics of low-lying excited 0+ states. The experimental results are interpreted within a phenomenological two-band mixing model. Configuration mixing calculations based on triaxial Hartree-Fock-Bogolyubov calculations with the Gogny D1S effective interaction have been performed and compared to experimental data.

The structure of low-lying states in the light krypton isotopes 72Kr, 74Kr, and 76Kr has been studied with the finite-range Gogny D1S effective interaction via Hartree–Fock–Bogolyubov based calculations within a configuration-mixing formalism treating axial and triaxial quadrupole deformations. The good overall agreement with the experimental low-lying excitation spectra and matrix elements supports the shape coexistence scenario and a transition of the ground-state shape from oblate in 72Kr to prolate in 76Kr. The triaxial degree of freedom is shown to be crucial to reproduce the experimental data in general and the inversion of the oblate and prolate configurations in particular.

A fully microscopic calculation of inelastic proton scattering off {sup 208}Pb is presented, and compared to experimental scattering data for incident proton energies between 65 and 201 MeV. By constructing the nucleon-nucleus interaction through the folding of nuclear structure information with a reliable nucleon-nucleon effective interaction that has no adjusted parameter, a consistent framework is built, for probing the influence of different descriptions of nuclear structure on nucleon inelastic scattering predictions. The absence of phenomenological normalization in this framework guarantees a unique and unambiguous interpretation of our calculations in terms of quality of the underlying nuclear structure description: a feature that had been reserved, until recently, to the electron probe. This tool is used to investigate the effect of long range correlations embedded in excited states, on calculated inelastic observables, demonstrating the sensitivity of nucleon scattering predictions to details of the nuclear structure.

Two-dimensional Hartree-Fock-Bogoliubov (HFB) calculations have been performed from spherical shapes to large deformations with constraints on axial quadrupole and octupole deformations in 238 U , 256–260 Fm and 226 Th actinides. Scission configurations have then been identified in this subspace of collective coordinates and many nuclear properties of the nascent fragments have been derived, such as deformation, deformation energy or prompt neutron multiplicity. The HFB states have then served as basis states for time-dependent collective calculations based on the Time-Dependent Generator Coordinate Method and the Gaussian Overlap Approximation to derive fission fragment yields.

Background: The chain of Sm isotopes exhibits a wide range of nuclear shapes and collective behavior. While the onset of deformation for $Ng82$ has been well studied both experimentally and theoretically, fundamental data is lacking for some Sm isotopes with $Nl82$.Purpose: Electromagnetic transition rates represent a sensitive test of theoretical nuclear structure models. Lifetime measurements are furthermore complementary to Coulomb excitation experiments, and the two methods together can give access to spectroscopic quadrupole moments.Method: The lifetime of the ${2}_{1}^{+}$ state in $^{140}\mathrm{Sm}$ was measured with the recoil-distance Doppler shift technique using the reaction $^{124}\mathrm{Te}(^{20}\mathrm{Ne},4\mathrm{n})^{140}\mathrm{Sm}$ at 82 MeV. Theoretical calculations were performed based on a mapped collective Hamiltonian in five quadrupole coordinates (5DCH) and the Gogny D1S interaction.Results: The lifetime of the ${2}_{1}^{+}$ state in $^{140}\mathrm{Sm}$ was found to be 9.1(6) ps, corresponding to a $B(E2;{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})$ value of 51(4) Weisskopf units. The theoretical calculations are in very good agreement with the experimental result.Conclusions: The $B(E2;{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})$ value for $^{140}\mathrm{Sm}$ fits smoothly into the systematic trend for the chain of Sm isotopes. The new beyond-mean field calculations are able to correctly describe the onset of collectivity in the Sm isotopes below the $N=82$ shell closure for the first time.

Mean field and beyond mean field methods implemented with the D1S force are used in large scale calculations to study the structure properties of fifty five even–even actinides at normal and isomeric potential deformations. The mass region covered is spanned by the 226–236Th, 228–242U, 232–246Pu, 238–250Cm, 238–256Cf, 242–258Fm and 250–262No nuclides. Hartree–Fock–Bogolyubov (HFB) calculations performed with constraints placed on axial and triaxial quadrupole deformations as well as octupole deformations serve to build tensors of inertia and potential energy landscapes up to very large elongations. Long lived spin isomers are investigated through blocking calculations performed with and without breaking time reversal symmetry. Configuration mixing calculations are performed to make predictions for shape isomers and π = + vibrations in the isomeric potentials and to calculate moments of inertia at low spin. Moments of inertia are also investigated through cranking HFB calculations to high frequency so as to explore in this regime pairing properties of the D1S force in the heavy mass region. The WKB method is adopted in half-life calculations for the γ-back and fission decay modes of shape isomers. All these predictions are challenged through extensive comparisons with measurements for multipole moments, moments of inertia, spin and shape isomers as well as superdeformed phonons, inner and outer potential barrier heights, and shape isomer lifetimes. Most predictions match the experimental data. Finally we predict a shallow minimum on top of the triaxial inner barriers of N ≃ 154 nuclei. This topological property offers a possible explanation for the unexpected structures observed in fission transmissions measured a long time ago for 252Cf and neighboring nuclei.

The 104,106,108Ru nuclei have been produced as fission fragments following the fusion reaction 28Si + 176Yb at 145 MeV bombarding energy; prompt gamma rays emitted in the reaction were detected using the Eurogam II array. Their high-spin level schemes have been obtained, particularly several side bands have been extended or newly observed. Experimental results are discussed in the framework of both collective model and the rotating mean-field approach in which the Gogny force is the sole input. These calculations provide very good descriptions of both low-spin and high-spin structures observed in the neutron-rich even-A Ru isotopes.

An outline is presented of the status of nuclear data evaluation for accelerator driven systems. The international effort consists mainly of measuring, compiling and calculating nuclear data for elements and isotopes relevant for transmutation of radioactive waste, energy amplification and other accelerator-related nuclear applications. We argue that input for global, macroscopic calculation schemes for hybrid nuclear systems basically should consist of two types of nuclear data: (a) high-energy transport codes for energies above about 150 MeV, (b) neutron and proton data libraries, for both transport and activation, for energies below about 150 MeV. Our specific contribution to the field concerns (b). The evaluated data are calculated and stored in ENDF6-format with the computer codes ECIS96, GNASH and MINGUS. New phenomenological optical model potentials up to 200 MeV are presented and we illustrate the library production with a short outline of the other employed physical methods. The calculated results are compared with the available experimental data.

A nucleon-nucleus optical model potential (OMP) is built from the nuclear matter (NM) approach of Jeukenne, Lejeune, and Mahaux (JLM). The imaginary component of the on-shell NM mass operator, originally parametrized by these authors as a function of matter density and energy, is given a new representation suitable for energies from 1 to 200 MeV. The JLM model extended in this manner is then applied through an improved local density approximation (LDA) to treat nucleon scattering from closed- and near closed-shell nuclei with masses $40l~Al~209$. For proton, neutron, and charge radial densities, we use those obtained from Hartree-Fock-Bogoliubov calculations based on the finite range, density dependent Gogny force. Several LDA and spin-orbit potential prescriptions are tested to select those which provide the best overall description of elastic scattering and reaction measurements. Over three hundred datasets including differential cross sections, analyzing powers, spin rotation functions, and reaction cross sections are considered in the present analyses. The OMP components include normalization factors which are optimized for each incident energy, probe, and for most target nuclei. We give close forms which represent the energy variation of these factors for the $n+X$ and $p+X$ systems. The global OMPs built in this manner produce a good overall description of the neutron and proton scattering and reaction measurements available up to 200 MeV.

This work has been partly financed by the European Union Seventh Framework Program FP7/2007-2013 under Grant Agreement No. 262010 ENSAR, the Polish MNiSW under Grant No. DPN/N190/AGATA/2009, the Spanish Ministerio de Ciencia e Innovacion under Contract No. FPA2011-29854-C04, and ´ the BMBF under Grant Nos. 05P12RDFN8 and 06DA9040I.

In this paper we investigate the rotational band built upon a two-quasiparticle ${8}^{\ensuremath{-}}$ isomeric state of ${}^{252}$No up to spin ${I}^{\ensuremath{\pi}}$ $=$ ${22}^{\ensuremath{-}}$. The excited states of the band were populated with the ${}^{206}$Pb(${}^{48}\text{Ca},2n$) fusion-evaporation reaction. An unambiguous assignment of the structure of the ${8}^{\ensuremath{-}}$ isomer as a $7/{2}^{+}{[624]}_{\ensuremath{\nu}}\ensuremath{\bigotimes}9/{2}^{\ensuremath{-}}{[734]}_{\ensuremath{\nu}}$ configuration has been made on the basis of purely experimental data. Comparisons with triaxial self-consistent Hartree-Fock-Bogoliubov calculations using the D1S force and breaking time-reversal as well as $z$-signature symmetries are performed. These predictions are in agreement with present measurements. Mean-field calculations extended to similar states in ${}^{250}$Fm support the interpretation of the same two-neutron quasiparticle structure as the bandhead in both $N=150$ isotones.

Background: The nucleon-nucleus dispersive optical model (DOM) has been successful in providing good fits to scattering data and in making valuable predictions for bound-state properties in single- and double-closed shell nuclei. However, the generalizability of the DOM remains an ongoing issue.Purpose: We investigate the DOM in the continuum and bound-state regions of the open-shell, self-conjugate nuclei ${}^{28}$Si and ${}^{32}$S. We collect new differential cross section and analyzing power data for elastic scattering at incident neutron energies between 8.0 and 18.9 MeV.Methods: The measurements were conducted using a pulsed deuteron beam, the ${}^{2}$He($d$,$n$)${}^{3}$He source reaction, and time-of-flight techniques. All data were corrected for finite-geometry effects. Phenomenological DOM potentials were tailored to fit the differential and total cross section data, and then extrapolated to the bound-state regions. The DOM bound-state predictions were then compared to experimental data available for single-particle energies, occupation probabilities, root-mean-square radii, and spectroscopic factors.Results: The DOM bound-state predictions are in only fair agreement with experimental data and with USD shell-model predictions. Similar results are found after converting our neutron DOMs into proton DOMs. We investigate the separate effects of the dispersive surface and volume potential components on occupation probability and find that the volume component leads to a uniform depletion of the hole states, while the surface component acts mainly to deplete the valence orbitals. We compare these results to those of a variational multiparticle multihole configuration mixing (mp-mh CM) calculation using the Gogny D1S effective force.Conclusions: We find that the phenomenological DOM, which was originally designed for spherical nuclei, show certain deficiencies when applied to open-shell nuclei and suggest possible avenues of improvement. We also find that the predictions of occupation probability by the DOM using the dispersive surface component are similar to those by the mp-mh CM. This lends support to the interpretation that the surface absorption in the optical model originates from particle-vibration couplings, that is, long-range correlations.

The domain of evaluated nuclear data involves at the same time, a close interaction between the field of nuclear applications and that of nuclear physics, and a close interaction between experiments and theory. The final product, the evaluated data file, synthesises vast amounts of information stemming from all of the above fields. In CEA DAM, all these aspects of nuclear data are investigated in a consistent way, making full use of experimental facilities and high-performance computing as well as numerous national and international collaborations, for the measurement, calculation, evaluation, and validation of nuclear data.

A decay spectroscopic study of the neutron-rich isotopes has been performed using fragmentation of a 86Kr primary beam. Fragments from this reaction have been selected by the LISE2000 spectrometer at the Grand Acc el erateur National d Ions Lourds (GANIL). Half-lives of 29 isotopes, including the first ones identified for 61Ti (15 4 ms), 64V (19 8 ms), and 71Fe (28 5 ms), have been determined and compared with model predictions. 67,68Mn -delayed rays were observed for the first time. The branching for the -delayed neutron emission was measured to be greater than 10(5)% in the 67Mn decay. The 67Fe isomeric level is firmly determined at higher energy than assigned in previous works. The excitation energies of the first (2+) and (4+) states of 68Fe are suggested to lie at 522(1) and 1389(1) keV, respectively, thus bringing confirmation of assignments based on in-beam -ray spectroscopy. Beyond-mean-field calculations with the Gogny D1S force have been performed for even-mass nuclei through the Fe isotopic chain. Not only 68Fe but most of the neutron-rich Fe isotopes with neutron numbers below N = 50 are interpreted as soft rotors. The calculated mean occupancy of the neutron g9/2 and d5/2 orbitals in correlated ground statesmore » is steadily growing with increasing neutron number throughout the isotopic chain. Interpretation of 67Fe data is based upon the present calculations for the 66Fe and 68Fe even cores.« less

We report on microscopic model calculations of the first step of direct pre-equilibrium (n,xn) emission in neutron interaction with {sup 90}Zr and {sup 208}Pb below 20 MeV. Our model is based on both an accurate description of the target excited states, provided by the self-consistent random-phase approximation (RPA) method implemented with the Gogny D1S force, and well-established in-medium two-body forces to represent the residual nucleon-nucleon interaction for the inelastic processes. Two goals have been achieved: The present microscopic approach provides a unified description of collective state excitations and the pre-equilibrium one-step process, and our reaction model reproduces the available data fairly well, without any parameter adjustment.

Differential scattering cross-section data have been measured at 43 angles from ${11}^{\ifmmode^\circ\else\textdegree\fi{}}$ to ${160}^{\ifmmode^\circ\else\textdegree\fi{}}$ for 37-MeV neutrons incident on $^{209}\mathrm{Bi}$. The primary motivation for the measurements is to address the scarcity of neutron scattering data above 30 MeV and to improve the accuracy of optical-model predictions at medium neutron energies. The high-statistics measurements were conducted at the China Institute of Atomic Energy using the $^{3}\mathrm{H}$($d,n$)$^{4}\mathrm{He}$ reaction as the neutron source, a pulsed deuteron beam, and time-of-flight (TOF) techniques. Within the resolution of the TOF spectrometer, the measurements included inelastic scattering components. The sum of elastic and inelastic scattering cross sections was computed in joint optical-model and distorted-wave Born approximation calculations under the assumption of the weak particle-core coupling. The results challenge predictions from well-established spherical optical potentials. Good agreement between data and calculations is achieved at 37 MeV provided that the balance between surface and volume absorption in a recent successful model [A. J. Koning and J. P. Delaroche, Nucl. Phys. A 713, 231 (2003)] is modified, thus suggesting the need for global optical-model improvements at medium neutron energies.

We have developed microscopic models for nucleon induced inelastic scattering and one-step direct preequilibrium emission. These models are based on reliable effective in-medium two-body interactions and a microscopic description of the ground and excited states of target nuclei. No arbitrary renormalization process enters our analyzes and the predictions are directly compared to experimental data. The nuclear structure information are obtained in the Random Phase Approximation (RPA) framework with the Gogny force, which provides accurate descriptions of spherical nuclei without pairing. For medium energy (50-200 MeV) proton induced reactions, this approach gives very good predictions for direct inelastic scattering and for the first-step in direct preequilibrium emission. The one-step preequilibrium model has also been extended to fast neutron scattering (10-20 MeV) for the 90Zr target described with RPA theory, and for axially deformed nuclei with a simpler description of the excited states (i.e. particle-hole excitations). Predictions of the reaction model reproduce well experimental data for 90Zr. For deformed targets (232Th and 238U), our calculations underestimate the data at high emission energy. The cross section missing for both actinides may stem from the excitation of vibrational states with excitation energies lower than 5 MeV which are not described with incoherent particle-hole excitations. This defect might be cured if the target spectra are described within the Quasi-particle-RPA (QRPA) theory recently implemented with the Gogny force.

Angular correlations arising from particle‐particle propagation in nuclear matter are presented. Their account emerges from an exact treatment of the Pauli blocking on intermediate states while retaining the angular structure of the energy denominator. As a result, a correlation form factor appears from the Cauchy principal‐value of the particle‐particle propagator, while the imaginary part becomes structurally different from those in Lippmann‐Schwinger‐type equations. In selfconsistent runs these features alter the behavior of the mass operator near the Fermi surface, modifying the saturation properties of infinite nuclear matter.

The lifetimes of the first excited 2+ states in 62Fe and 64Fe have been measured for the first time using the recoil‐distance Doppler shift technique, at GANIL. A 238U beam of 6.5 AMeV impinged on 64Ni target, and the target like products were slowed down by a degrader foil positioned at micrometer distance downstream of the target and identified in the VAMOS spectrometer on an event‐by‐event basis. The lifetimes were then determined from the intensities of the degraded and fully Doppler shifted components of the 2+→0+ transition detected in EXOGAM detectors positioned at backward angles.The resulting lifetimes show a steep increase of the B(E2) values of the first excited 2+ state from 62Fe to 64Fe. A comparison with shell model calculations shows that the onset of collectivity is related to the occupation of neutron intruder orbitals. The large B(E2) value for 64Fe is only reproduced if the valence space includes both the neutron g9/2 and d5/2 orbitals. The transition from spherical 68Ni to more proton‐...

Three superdeformed (SD) bands including states with spins {ital I}{sup {pi}}{le}22{sup +} are predicted for {sup 192}Hg. The SD and normally deformed levels are calculated as eigenstates of the Griffin-Hill-Wheeler equation treated in the Gaussian overlap approximation. Potential and tensor of inertia are deduced from constrained Hartree-Fock-Bogoliubov calculations based on Gogny's force. Rates for {ital E}2 in-band transitions are deduced and compared with recent measurements. The decay out of SD bands is discussed.

A systematic study of low energy nuclear structure at normal deformation is carried out using the Hartree-Fock-Bogoliubov theory extended by the Generator Coordinate Method and mapped onto a 5-dimensional collective quadrupole Hamiltonian. Results obtained with the Gogny D1S interaction are presented from dripline to dripline for even-even nuclei with proton numbers Z=10 to Z=110 and neutron numbers N less than 200. The properties calculated for the ground states are their charge radii, 2-particle separation energies, correlation energies, and the intrinsic quadrupole shape parameters. For the excited spectroscopy, the observables calculated are the excitation energies and quadrupole as well as monopole transition matrix elements. We examine in this work the yrast levels up to J=6, the lowest excited 0^+ states, and the two next yrare 2^+ states. The theory is applicable to more than 90% of the nuclei which have tabulated measurements. The data set of the calculated properties of 1712 even-even nuclei, including spectroscopic properties for 1693 of them, are provided in CEA website and EPAPS repository with this article \cite{epaps}., 51 pages with 26 Figures and 4 internal tables; this version is accepted by Physical Review C

We report on the first measurement of the absolute transition strength $B(E2;{0}_{1}^{+}\ensuremath{\rightarrow}{2}_{1}^{+})$ in the self-conjugate nucleus $^{68}\mathrm{Se}$. It is found that the ${0}_{1}^{+}\ensuremath{\rightarrow}{2}_{1}^{+}$ transition displays a strength similar to that for the triaxial $^{64}\mathrm{Ge}$ nucleus, in sharp contrast to the much stronger collectivity observed for the oblate $^{72}\mathrm{Kr}$ nucleus. Shape evolution along the $N=Z$ line from zinc to strontium is analyzed through beyond-mean-field calculations using the D1S force. Over this narrow mass region the nuclear structure shows clear-cut transition from prolate to oblate and back to prolate, with $^{68}\mathrm{Se}$ standing as pivotal between triaxial and oblate deformations.

The development of deformation and shape coexistence in the vicinity of doubly magic $^{48}\mathrm{Ca}$, related to the weakening of the $N=28$ shell closure, was addressed in a low-energy Coulomb excitation experiment using a radioactive $^{44}\mathrm{Ar}$ beam from the SPIRAL facility at GANIL. The ${2}_{1}^{+}$ and ${2}_{2}^{+}$ states in $^{44}\mathrm{Ar}$ were excited on $^{208}\mathrm{Pb}$ and $^{109}\mathrm{Ag}$ targets at two different beam energies. $B(E2)$ values between all observed states and the spectroscopic quadrupole moment of the ${2}_{1}^{+}$ state were extracted from the differential Coulomb excitation cross sections, indicating a prolate shape of the $^{44}\mathrm{Ar}$ nucleus and giving evidence of an onset of deformation already two protons and two neutrons away from doubly magic $^{48}\mathrm{Ca}$. New Hartree-Fock-Bogoliubov based configuration mixing calculations have been performed with the Gogny D1S interaction for $^{44}\mathrm{Ar}$ and neighboring nuclei using two different approaches: the angular momentum projected generator coordinate method considering axial quadrupole deformations and a five-dimensional approach including the triaxial degree of freedom. The experimental values and new calculations are furthermore compared to shell-model calculations and to relativistic mean-field calculations. The new results give insight into the weakening of the $N=28$ shell closure and the development of deformation in this neutron-rich region of the nuclear chart.

The structure of even-even $N=40$ isotones is studied from drip line to drip line through the systematic investigation of their quadrupole modes of excitation. Calculations are performed within the Hartree-Fock-Bogoliubov approach using the Gogny D1S effective interaction. Where relevant, these calculations are extended beyond mean field within a generator-coordinate-based method. An overall good agreement with available experimental data is reported, showing that collectivity increases from the neutron to the proton drip line. Whereas $^{60}\mathrm{Ca}$ and $^{68}\mathrm{Ni}$ display a calculated spherical shape in their ground states, all other isotones show a prolate-deformed ground-state band and a quasi-$\ensuremath{\gamma}$ band. Coexistence features are predicted in the neutron-deficient $N=40$ isotones above $^{74}\mathrm{Se}$.

Lifetimes of states in the ground-state bands of {sup 70}Se and {sup 72}Se were measured using the recoil-distance Doppler shift method. The results deviate significantly from earlier measurements, requiring a revision of the conclusions drawn from a recent Coulomb excitation experiment concerning the shape of {sup 70}Se. The new results lead to a coherent picture of shape coexistence in the neutron-deficient selenium and krypton isotopes. The coexistence and evolution of oblate and prolate shapes in this mass region is for the first time consistently described by new Hartree-Fock-Bogolyubov-based configuration-mixing calculations which were performed using the Gogny D1S interaction.

The constrained Hartree-Fock-Bogoliubov method is used with the Gogny interaction D1S to calculate potential energy surfaces of fissioning nuclei $^{226}\mathrm{Th}$ and $^{256,258,260}\mathrm{Fm}$ up to very large deformations. The constraints employed are the mass quadrupole and octupole moments. In this subspace of collective coordinates, many scission configurations are identified ranging from symmetric to highly asymmetric fragmentations. Corresponding fragment properties at scission are derived yielding fragment deformations, deformation energies, energy partitioning, neutron binding energies at scission, neutron multiplicities, charge polarization, and total fragment kinetic energies.

Data on elastic scattering of 96 MeV neutrons from 56Fe, 89Y, and 208Pb in the angular interval 10-70° are reported. The previously published data on 208Pb have been extended, as a new method has been developed to obtain more information from data, namely to increase the number of angular bins at the most forward angles. A study of the deviation of the zero-degree cross section from Wick's limit has been performed. It was shown that the data on 208Pb are in agreement with Wick's limit while those on the lighter nuclei overshoot the limit significantly. The results are compared with modern optical model predictions, based on phenomenology and microscopic nuclear theory. The data on 56Fe, 89Y, and 208Pb are in general in good agreement with the model predictions.

We calculate potential energy surfaces in the elongation‐asymmetry plane, up to very large deformations, with the Hartree‐Fock‐Bogoliubov method and the Gogny nucleon‐nucleon effective interaction DIS, for the 226Th and 256,258,260Fm fissioning systems. We then define a criterion based on the nuclear density, in order to discriminate between pre‐ and post‐scission configurations. Using this criterion, many scission configurations are identified, and are used for the calculation of several fragment properties, like fragment deformations, deformation energies, energy partitioning, neutron binding energies at scission, charge polarization, total fragment kinetic energies and neutron multiplicities.

The {ital p}-{sup 40}Ca mean field is derived from an optical-model (OM) analysis that explicitly incorporates the dispersion relation connecting the real and imaginary parts of the mean field. This analysis is based on differential cross-section, analyzing power, and reaction cross-section data available in the energy range between 20 and 180 MeV. The extrapolation of the OM potential from positive to negative energies provides the shell-model potential. This extrapolation is guided by known single-particle energies. The deeply bound 1{ital p} and 1{ital s} orbits clearly indicate the need for a linear rather than an exponential energy dependence of the Hartree-Fock potential at large negative energies. The analysis also provides root-mean-square radii, occupation probabilities, spectral functions, and absolute spectroscopic factors for proton single-particle orbits in {sup 40}Ca. Our calculated 15% depletion of the hole states in {sup 40}Ca is lower than that suggested for {sup 208}Pb from theoretical and experimental studies. We also find that a substantial amount of single-particle strength in {sup 40}Ca is located at rather high excitation energy.

We examine the global performance of an extended self-consistent mean field theory of 2+ excitations in even-even nuclei. 518 nuclei are included in our survey, comprising all but 39 of the known nuclei tabulated by Raman et al. The theory is based on a quantal collective Hamiltonian in five dimensions in which the potential energy and the tensor of inertia are obtained from constrained triaxial Hartree-Fock-Bogoliubov calculations. The only parameters in theory are those of the finite-range, density-dependent Gogny D1S interaction. The following properties of the lowest 2+ excitations are calculated: excitation energy, reduced transition probability, and spectroscopic quadrupole moment. We find that the theory is very reliable to classify the nuclei by shape. Quantitatively the performance of the theory in deformed nuclei is excellent: average excitation energies and transition quadrupole moments are within 5% of the experimental values, and the dispersion about the averages are 20% and 10%, respectively. The performance is not as good on spherical and soft nuclei. Including all nuclei in the performance evaluation, the average transition quadrupole moment is 10% too high and the dispersion about the mean is 20%. For the energies, the average is 13% too high and the dispersion is 40%., 4 pages with 5 figures and 1 table; this version is a resubmission to Phys. Rev. Lett. including changes in response to referee comments

This paper demonstrates the feasibility of quadrupole moment measurements on isomeric levels populated in projectile fragmentation reactions. The neutron-rich $^{61}\mathrm{Fe}$$(9/{2}^{+})$ [${E}^{*}=$ 861 keV, ${T}_{1/2}=$ 239(5) ns] isomer was produced and spin aligned by the intermediate energy fragmentation of a $^{64}\mathrm{Ni}$ beam and implanted in a Cd single crystal. Its spectroscopic quadrupole moment $|{Q}_{s}|=41(6)\phantom{\rule{0.3em}{0ex}}e\phantom{\rule{0.3em}{0ex}}{\mathrm{fm}}^{2}$ agrees with mean-field based calculations using the finite-range Gogny force, suggesting a moderately deformed shape characterized by an intrinsic charge quadrupole moment ${Q}_{0}=\ensuremath{-}85\phantom{\rule{0.3em}{0ex}}e\phantom{\rule{0.3em}{0ex}}{\mathrm{fm}}^{2}$ or ${Q}_{0}=+115\phantom{\rule{0.3em}{0ex}}e\phantom{\rule{0.3em}{0ex}}{\mathrm{fm}}^{2}$. The present measurement paves the way for future determinations of isomeric quadrupole moments in more exotic nuclei.

GANIL E344aS; Shape coexistence in the light krypton isotopes was studied in two low-energy Coulomb excitation experiments using radioactive $^{74}$Kr and $^{76}$Kr beams from the SPIRAL facility at GANIL. The ground-state bands in both isotopes were populated up to the $8^+$ state via multi-step Coulomb excitation, and several non-yrast states were observed. Large sets of matrix elements were extracted for both nuclei from the observed $\\gamma$-ray yields. Diagonal matrix elements were determined by utilizing the reorientation effect. In both isotopes the spectroscopic quadrupole moments for the ground-state bands and the bands based on excited $0_2^+$ states are found to have opposite signs. The experimental data are interpreted within a phenomenological two-band mixing model and model-independent quadrupole invariants are deduced for the relevant $0^+$ states using the complete sets of matrix elements and the formalism of quadrupole sum rules. Configuration mixing calculations based on triaxial Hartree-Fock-Bogolyubov calculations with the Gogny D1S effective interaction have been performed and are compared both with the experimental results and with recent calculations using the Skyrme SLy6 effective interaction and the full generator-coordinate method restricted to axial shapes.

Reliable nuclear structure predictions are needed for reaction data evaluations, whenever experimental information is missing. Even if full parameter-free evaluations are not possible nowadays, some noteworthy progress in both structure and reaction fields has been accomplished recently. We present here some results on fission barriers and shape isomers partial γ-back decay and fission lifetimes. Calculations have been performed using the effective D1S Gogny force and the Generator Coordinate Method with the Gaussian Overlap Approximation based on Hartree- Fock-Bogoliubov results.

PTH; International audience; Microscopic results on fission barriers, partial gamma-back and fission lifetimes of shape isomers are presented. They have been obtained from mean-field and beyond mean-field calculations using the effective D1S Gogny force.