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The nuclear equation of state (EOS) is explored with the constrained Hartree-Fock-Bogoliubov approach for self-conjugate nuclei. It is found that beyond a certain low, more or less universal density, those nuclei spontaneously cluster into A/4 α particles with A the nucleon number. The energy at the threshold density increases linearly with the number of a particles as does the experimental threshold energy. Taking off the spurious c.m. energy of each a particle almost gives agreement between theory and experiment. The implications of these results with respect to a clustering and the nuclear EOS at low density are discussed. [ABSTRACT FROM AUTHOR]

The combinatorial model of nuclear level densities has now reached a level of accuracy comparable to that of the best global analytical expressions without suffering from the limits imposed by the statistical hypothesis on which the latter expressions rely. In particular, it provides naturally, non-Gaussian spin distribution as well as nonequipartition of parities which are known to have a significant impact on cross section predictions at low energies. Our previous global model [S. Goriely, S. Hilaire, and A. J. Koning, Phys. Rev. C 78, 064307 (2008)] suffered from deficiencies, in particular in the way the collective effects--both vibrational and rotational--were treated. We have recently improved the level density calculations using simultaneously the single-particle levels and collective properties predicted by a newly derived Gogny interaction [S. Goriely, S. Hilaire, M. Girod, and S. Péru, Phys. Rev. Lett. 102, 242501 (2009)], therefore enabling a microscopic description of energy-dependent shell, pairing, and deformation effects. In addition, for deformed nuclei, the transition to sphericity is coherently taken into account on the basis of a temperature-dependent Hartree-Fock calculation which provides at each temperature the structure properties needed to build the level densities. This new method is described and shown to give reasonable results with respect to available experimental data. [ABSTRACT FROM AUTHOR]

In the present work, we have investigated an extension of the effective nucleon-nucleon Gogny interaction in which the zero-range density-dependent term has been replaced with a finite-range term. The parameters have been adjusted on both nuclear-matter properties and a few observables of stable nuclei. The traditional and unified fitting procedure of the Gogny force used in Bruyères-Ie-Châtel ensures common basic properties between the extended analytical form of the Gogny interaction, called D2, and the original one. In particular, symmetric infinite nuclear-matter and neutron-matter properties as well as pairing correlations have been investigated. A few static properties obtained in finite nuclei using the Hartree-Fock-Bogoiiubov approach and the D2 parametrization of the Gogny interaction are analyzed and compared to the results obtained with DI -type parametrizations and experiment when it is possible. The D2 parametrization makes it possible to reproduce nuclear structure properties with improved accuracy. [ABSTRACT FROM AUTHOR]

Background: The chain of Sm isotopes exhibits a wide range of nuclear shapes and collective behavior. While the onset of deformation for N>82 has been well studied both experimentally and theoretically, fundamental data is lacking for some Sm isotopes with N<82. 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 21+ state in 140Sm was measured with the recoil-distance Doppler shift technique using the reaction 124Te(20Ne, 4n)140Sm 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 21+ state in 140Sm was found to be 9.1(6) ps, corresponding to a B(E2;21+→0+1) value of 51(4) Weisskopf units. The theoretical calculations are in very good agreement with the experimental result. Conclusions: The B(E2;21+→0+1) value for 140Sm 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. [ABSTRACT FROM AUTHOR]

Background: The self-conjugate nuclei of the A ~ 70 mass region display rapid shape evolution over isotopic or isotonic chains. Shape coexistence has been observed in Se and Kr isotopes reflecting the existence of deformed subshell gaps corresponding to different shell configurations. As and Ge isotopes are located halfway between such deformed nuclei and the Z = 28 shell closure. Purpose: The present work aims at clarifying the low-lying spectroscopy of 66Ge and i,7As, and providing a better insight into the evolution of collectivity in light even-even Ge and even-odd As isotopes Methods: We investigate the low-lying levels and collectivity of the neutron deficient 67As and 66Ge through intermediate-energy Coulomb excitation, inelastic scattering, and proton knockout measurements. The experiment was performed using a cocktail beam of 68Se, 67As, and 66Ge nuclei at an energy of 70-80 MeV/nucleon. Spectroscopic properties of the low-lying states are compared to those calculated via shell model with the JUN45 interaction and beyond-mean-field calculations with the five-dimensional collective Hamiltonian method implemented using the Gogny DIS interaction. The structure evolution of the lower-mass Ge and As isotopes is discussed. Results: Reduced electric quadrupole transition probabilities B(E2) have been extracted from the Coulomb-excitation cross sections measured in 66Ge and 67As. The value obtained for the B(E2;01+ → 21+) in 66Cie is in agreement with a recent measurement, ruling out the existence of a minimum at N = 34 in the B(E2) systematics as previously observed. New transitions have been found in 67As and were assigned to the decay of low-lying negative-parity states. [ABSTRACT FROM AUTHOR]

In this paper we investigate the rotational band built upon a two-quasiparticle 8- isomeric state of 252No up to spin Iπ = 22-. The excited states of the band were populated with the206Pb(48Ca, 2n) fusion-evaporation reaction. An unambiguous assignment of the structure of the 8- isomer as a 7/2+[624]v ⊗ 9/2-[734]v configuration has been made on the basis of purely experimental data. Comparisons with triaxial self-consistent Hartree-Fock-Bogoliubov calculations using the DIS 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 250Fm support the interpretation of the same two-neutron quasiparticle structure as the bandhead in both N = 150 isotones. [ABSTRACT FROM AUTHOR]

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 Accélérateur 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 β-delayed γ rays were observed for the first time. The branching for the β-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 γ-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 states 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. [ABSTRACT FROM AUTHOR]

We report on two complementary delayed gamma-ray spectroscopic studies on 16464Gd100. The nucleus is produced via spontaneous fission of 252Cf sources used in selective experimental setups. An isomeric state at 1095 keV with a half-life of 605 (30) ns is confirmed as well as its decay path toward the ground state band. From comparison to other N=100 isotones and with calculations based on the axially symmetric-deformed quasiparticle random phase approximation (QRPA) using the up-to-date Gogny interaction a 4- spin and parity is proposed for the isomer. The state is interpreted as a two-quasi-neutron excitation in line with available data for others N=100 isotones. The variation of the lifetime of the isomeric state along the N=100 isotones is interpreted in terms of Coriolis mixing implemented for the first time within axially symmetric-deformed QRPA microscopic calculations. [ABSTRACT FROM AUTHOR]

We studied the proton-rich T&#95;{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&#95;{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.

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&#95;{1}^{+}→0&#95;{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 report on the first γ-ray spectroscopy of low-lying states in neutron-rich ^{98,100}Kr isotopes obtained from ^{99,101}Rb(p,2p) reactions at ∼220  MeV/nucleon. A reduction of the 2&#95;{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-the-art 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&#95;{2}^{+}, 2&#95;{2}^{+}) state in ^{98}Kr 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.

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&#95;{1}^{+} excitation energies were found at 185(11) keV in ^{110}Zr, and 235(7) keV in ^{112}Mo, while the R&#95;{42}=E(4&#95;{1}^{+})/E(2&#95;{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.

We present the first Gogny-Hartree-Fock-Bogoliubov (HFB) model which reproduces nuclear masses with an accuracy comparable with the best mass formulas. In contrast with the Skyrme-HFB nuclear-mass models, an explicit and self-consistent account of all the quadrupole correlation energies are included within the 5D collective Hamiltonian approach. The final rms deviation with respect to the 2149 measured masses is 798 keV. In addition, the new Gogny force is shown to predict nuclear and neutron matter properties in agreement with microscopic calculations based on realistic two- and three-body forces.

We report on the g-factor measurement of the first isomeric state in (16)43S27 [Ex=320.5(5) keV, T1/2=415(5) ns, and g=0.317(4)]. The 7/2- spin-parity of the isomer and the intruder nature of the ground state of the nucleus are experimentally established for the first time, providing direct and unambiguous evidence of the collapse of the N=28 shell closure in neutron-rich nuclei. The shell model, beyond the mean-field and semiempirical calculations, provides a very consistent description of this nucleus showing that a well deformed prolate and quasispherical states coexist at low energy.

Lifetimes of states in the ground-state bands of (70)Se and (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 (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.

We report the first comprehensive calculations of 2(+) excitations with a microscopic theory applicable to over 90% of the known nuclei. The theory uses a quantal collective Hamiltonian in five dimensions. 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. For deformed nuclei, average excitation energies and transition quadrupole moments are within 5% of the experimental values, and the dispersion about the averages are roughly 20% and 10%, respectively. Including all nuclei in the performance evaluation, the average transition quadrupole moment is 11% too high and the average energy is 13% too high.