We study the prolate-shape predominance of the nuclear ground-state deformation by calculating the masses of more than 2000 even-even nuclei using the Strutinsky method, modified by Kruppa, and improved by us. The influences of the surface thickness of the single-particle potentials, the strength of the spin-orbit potential, and the pairing correlations are investigated by varying the parameters of the Woods-Saxon potential and the pairing interaction. The strong interference between the effects of the surface thickness and the spin-orbit potential is confirmed to persist for six sets of Woods-Saxon potential parameters. The observed behavior of the ratios of prolate, oblate, and spherical nuclei versus potential parameters are rather different in different mass regions. The ratio of spherical nuclei is found to increase for weakly bound unstable nuclei. Differences from the results of calculations performed using the Nilsson potential are described in detail.

The microscopic optical potential model based on calculations of the mass operator of the single-particle Green function has been refined by using the extended Skyrme-force variant, which involves additional both density- and momentum-dependent terms, and is employed for describing simultaneously properties of nuclei, nuclear-matter characteristics, and the nucleon-nucleus scattering observables in a self-consistent approach. From analyzing a differential cross section and polarization for a chosen case of the elastic neutron-nucleus scattering while controlling the characteristics of nuclear matter and finite-nuclei structure, a few sets of parameters have been determined for new variants of the extended Skyrme forces. It has been shown that the allowance for both the density- and momentum-dependent terms makes it possible to significantly improve the agreement with experimental data. The proposed extended Skyrme-force variants provide a satisfactory description for cross sections and analyzing powers of the neutron and proton scattering in a wide range of the target-nucleus mass numbers at different incident nucleon energies, as well as for a variety of nuclear structure characteristics.

Background: The spatial distribution of charge and magnetization in the proton and neutron are encoded in the nucleon electromagnetic form factors. The form factors are all approximated by a simple dipole function, normalized to the charge or magnetic moment of the nucleon. The differences between the proton and neutron form factors and the deviation of $G_E^n$ from zero are sensitive to the difference between up- and down-quark contributions to the form factors.

Purpose: Recent measurements of $G_E^n$ up to 3.4 (GeV/$c$)${}^2$ allow for a much more detailed examination of the form factors. The flavor-separated form factors provide information on the quark flavor dependence of the nucleon structure and test theoretical models of the form factors.

Methods: We combine recent measurements of the neutron form factors with updated extractions of the proton form factors, accounting for two-photon exchange corrections and including an estimate of the uncertainties for all of the form factors to obtain a complete set of measurements up to $Q^2\approx 4$ (GeV/$c$)${}^2$. We use this to extract the up- and down-quark contributions which we compare to recent fits and calculations.

Results: We find large differences between the up- and down-quark contributions to $G_E$ and $G_M$, implying significant flavor dependence in the charge and magnetization distributions. The rapid falloff of the ratio $G_E^p/G_M^p$ does not appear in the individual quark form factors, but arises from a cancellation between the up- and down-quark contributions. We see indications that the down-quark contributions to the Dirac and Pauli form factors deviate from the suggested 1/$Q^4$ scaling behavior suggested by a previous analysis. While recent models provide a generally good qualitative description of the data, the down-quark contribution to $G_E/G_M$ and $F_2/F_1$ are not reproduced by any of the models. Finally, we note that, while the inclusion of recent $G_M^n$ data from the CLAS Collaboration modifies the high-$Q^2$ behavior slightly, the tension between these data and previous measurements at lower $Q^2$ has a more significant impact, suggesting the need for additional data in this region.

We present a direct measurement of the low-energy ${}^8\mathrm{Li}{(p,\alpha )}^5\mathrm{He}$ cross section, using a radioactive ${}^8$Li beam impinging on a thick target. With four beam energies, we cover the energy range between $E_{\mathrm{c}.\mathrm{m}.}=0.2$ and 2.1 MeV. An $R$-matrix analysis of the data is performed and suggests the existence of two broad overlapping resonances ($5/2^{+}$ at $E_{\mathrm{c}.\mathrm{m}.}=1.69$ MeV and $7/2^{+}$ at $E_{\mathrm{c}.\mathrm{m}.}=1.76$ MeV). At low energies our data are sensitive to the properties of a subthreshold state ($E_x=16.67$ MeV) and of two resonances above threshold. These resonances were observed in previous experiments. The $R$-matrix fit confirms spin assignments, and provides partial widths. We propose a new ${}^8\mathrm{Li}{(p,\alpha )}^5\mathrm{He}$ reaction rate and briefly discuss its influence in nuclear astrophysics.

The cross section for the knock-out of a deeply bound valence neutron from ${}^{37}$Ca at an incident beam energy of $60A\mathrm{MeV}$ has been measured along with momentum distributions of the residual nuclei and $\gamma$ rays from the de-excitation of the first excited state in ${}^{36}$Ca. As for other cases of deeply bound nucleons studied using knock-out reactions, the reduction of the measured cross section compared to theoretical predictions is stronger than those observed for near-magic stable nuclei. Both the momentum distributions and the excitation energy of the first excited state in ${}^{36}$Ca indicate a sizable $N=16$ gap.

We have studied the decay of actinide nuclear system ${}^{254}$Fm${}^{*}$ formed in ${}^{11}$B  $+$ ${}^{243}$Am reaction using the dynamical cluster decay model (DCM), with choices of spherical, quadrupole deformation ${\beta }_2$ alone and higher multipole deformations ${\beta }_2$–${\beta }_4$. For ${\beta }_2$ deformations, the optimum orientations ${\theta }_i^{\mathrm{opt}}$ are used whereas for higher multipole deformations the compact orientations ${\theta }_i^c$ of decaying fragments are taken in to account. Besides static-${\beta }_2$ deformations, the effects of dynamical-${\beta }_2$ deformations are also explored. The calculated cross sections find excellent agreement with the available experimental data with spherical as well as deformed choices of fragmentations, enabling us to account for the role of important nuclear deformation effects in the ${}^{11}$B-induced nuclear reaction. Spontaneous decay of ${}^{254}$Fm with cold elongated configuration and optimum orientation is also worked out. The mass distributions of excited fermium isotopes in the neighborhood of ${}^{254}$Fm${}^{*}$ are also explored. In addition, the roles of temperature, angular momentum, and fission fragment anisotropies are investigated in the context of the chosen reaction.

The dynamical cluster decay model (DCM) is used to study the decay of the ${}^{268}$Sg${}^{*}$ compound nucleus formed in the ${}^{30}$Si+${}^{238}$U reaction at above and below the Coulomb barrier energies. The neutron evaporation residues and fission cross sections are calculated in reference to the available data, including ${\beta }_{2i}$-static deformations with ‘optimum' orientations. The role of spherical and the ${\beta }_{2i}$-dynamic deformed choices of fragmentation are also studied explicitly at the highest 169 MeV energy. The fission fragment distribution is symmetric at above-barrier energies, where equatorial collisions are preferred, but becomes asymmetric when the nuclei approach in pole-to-pole configuration at sub-barrier energies. Therefore, at above-barrier energies the calculations are carried out by considering ‘hot fusion', equatorial collisions, whereas at sub-barrier energies the ‘cold fusion', polar configuration is considered. The asymmetric peaks at sub-barrier energies may be associated with some competing process, like quasifission. The analysis of polar and equatorial configurations suggests that larger barrier modification is required at sub-barrier energies for neutron evaporation residue and fission fragments, i.e., the contribution of barrier modification at sub-barrier energies is relatively higher for a cold elongated polar configuration as compared to a hot compact equatorial configuration. Finally, the potential energies surfaces for the Si-induced reaction are compared with the $S$-induced reaction on the ${}^{238}$U target, at comparable center of mass energies.

The beam polarization asymmetry in the reaction $ep\to e^{\prime }{K}^{+}\Lambda$ has been investigated in a tree-level effective Lagrangian model. The model incorporates most of the well-established baryon resonances with spins up to $\frac{5}{2}$, four less well-established nucleon resonances with larger mass, and the two kaon resonances $K^{☆}\left(892\right)$ and $K1\left(1270\right)$. The off-shell structure of the electromagnetic vertices was accounted for by the inclusion of electromagnetic form factors at those vertices. The free parameters of the model were fitted in a previous study to a large pool of photoproduction data from the CLAS, GRAAL, SAPHIR, and LEPS collaborations and to CLAS data for the virtual photoproduction structure functions ${\sigma }_U$, ${\sigma }_T$, ${\sigma }_L$, ${\sigma }_{TT}$, and ${\sigma }_{LT}$. Using this model, results were obtained for the beam polarization asymmetry structure function ${\sigma }_{L{T}^{\prime }}$ and compared with CLAS data. Two new fits to the combined photoproduction and electroproduction data with the ${\sigma }_{L{T}^{\prime }}$ data included were then generated. The first of these includes contributions from all of the resonances included in the previous study; the second excludes contributions from the $N\left(2080\right)$ and $N\left(2200\right)$ resonances. The results of both fits for both photoproduction and electroproduction observables are compared with the results of the previous fit and the data.

We present a model of electron-positron pair production in pion-nucleon collisions in the exclusive reaction $\pi N\to N{e}^{+}{e}^{-}$. The model is based on an effective field theory approach, incorporating 16 baryon resonances below 2 GeV. Parameters of the model are fitted to pion photoproduction data. We present the resulting dilepton invariant mass spectra for ${\pi }^{-}p$ collisions up to $\sqrt{s}=1.9$ GeV center-of-mass collision energy. These results are meant to give predictions for the planned experiments at the HADES spectrometer in GSI, Darmstadt.

The fish-bone potential of composite particles simulates the Pauli effect by nonlocal terms. We determined the $n$-$\alpha$ and $p$-$\alpha$ fish-bone potential by fitting to the experimental phase shifts. We found that with a double Gaussian parametrization of the local potential we can describe the $n$-$\alpha$ and $p$-$\alpha$ phase shifts simultaneously for all partial waves.

The experimental values of both branching ratios and hindrance factors for the alpha decay of even-even trans-lead nuclei, corresponding to the $2_1^{+}$, $4_1^{+}$, and $6_1^{+}$ excited states in the daughter nucleus, are examined within the valence correlation scheme. Existing calculations do not reproduce certain conspicuous features of these data in the deformed nuclei region, thus leaving open the question of what details of nuclear structure in this region are responsible for these effects.

The contribution of the chiral three-nucleon force to the strength of effective spin-orbit coupling is estimated. We construct a reduced two-body interaction by folding single-nucleon degrees of freedom of the three-nucleon force in nuclear matter. The spin-orbit strength is evaluated by the Scheerbaum factor obtained by a $G$-matrix calculation in nuclear matter with the two-nucleon interaction plus the reduced two-nucleon interaction. The inability of modern realistic two-nucleon interactions to account for the empirical spin-orbit strength is overcome. We found that spin-orbit coupling is weaker in a neutron-rich environment. Because the spin-orbit component of the three-nucleon force is determined by low-energy constants fixed in the two-nucleon sector, the present estimation has a small uncertainty.

Over a period of several years we have performed three separate experiments at Lawrence Berkeley National Laboratory's 88-Inch Cyclotron in which ${}^{235}$U (thick target) was Coulomb-excited. The program involved stand-alone experiments with Gammmasphere and with the 8pi Spectrometer using ${}^{136}$Xe beams at 720 MeV, and a CHICO-Gammasphere experiment with a ${}^{40}$Ca beam at 184 MeV. In addition to extending the known negative-parity bands to high spin, we have assigned levels in some seven positive-parity bands which are in some cases (e.g., $\left[631\right]1/2$, $\left[624\right]7/2$, and $\left[622\right]5/2$) strongly populated by $E3$ excitation. The CHICO data have been analyzed to extract $E2$ and $E3$ matrix elements from the observed yields. Additionally, many $M1$ matrix elements could be extracted from the $\gamma$-ray branching ratios. A number of new features have emerged, including the unexpected attenuation of magnetic transitions between states of the same Nilsson multiplet, the breakdown of Coriolis staggering at high spin, and the effect of $E3$ collectivity on Coriolis interactions.

Exact results of pair transfer probabilities for the Richardson model with equidistant or random level spacing are presented. The results are then compared either to particle-particle random-phase approximation (ppRPA) in the normal phase or quasiparticle random-phase approximation (QRPA) in the superfluid phase. We show that both ppRPA and QRPA are globally well reproducing the exact case although some differences are seen in the superfluid case. In particular, the QRPA overestimates the pair transfer probabilities to excited states in the vicinity of the normal-superfluid phase transition, which might explain the difficulty in detecting collective pairing phenomena as, for example, the giant pairing vibration. The shortcoming of QRPA can be traced back to the breaking of particle number that is used to incorporate pairing. A method based on direct diagonalization of the Hamiltonian in the space of two quasiparticles projected onto good particle number is shown to improve the description of pair transfer probabilities in superfluid systems.

In terms of the parton hadron string dynamics (PHSD) approach—including the retarded electromagnetic field—we investigate the role of fluctuations of the correlation function in the azimuthal angle $\psi$ of charged hadrons that is expected to be a sensitive signal of local strong parity violation. For the early time we consider fluctuations in the position of charged spectators resulting in electromagnetic field fluctuations as well as in the position of participant baryons defining the event plane. For partonic and hadronic phases in intermediate stages of the interaction we study the possible formation of excited matter in electric charge dipole and quadrupole form as generated by fluctuations. The role of the transverse momentum and local charge conservation laws in the observed azimuthal asymmetry is investigated, too. All these above-mentioned effects are incorporated in our analysis based on event-by-event PHSD calculations. Furthermore, the azimuthal angular correlations from Au+Au collisions observed in the recent STAR measurements within the Relativistic Heavy Ion Collider (RHIC) Beam Energy Scan (BES) program are studied. It is shown that the STAR correlation data at the collision energies of $\sqrt{s_{NN}}=7.7$ and 11.5 GeV can be reasonably reproduced within the PHSD. At higher energies the model fails to describe the $\psi$ correlation data resulting in an overestimation of the partonic scalar field involved. We conclude that an additional transverse anisotropy fluctuating source is needed which with a comparable strength acts on both in- and out-of-plane components.

We study the consistency of parton distribution functions in the presence of target mass corrections (TMCs) at low $Q^2$. We review the standard operator product expansion derivation of TMCs in both $x$ and moment space, and present the results in closed form for all unpolarized structure functions and their moments. To avoid the unphysical region at $x>1$ in the standard TMC analysis, we propose an expansion of the target mass corrected structure functions order by order in $M^2/Q^2$, and assess the convergence properties of the resulting forms numerically.

Background: Neutron-induced reactions are a significant concern for experiments that require extremely low levels of radioactive backgrounds. Measurements of $\gamma$-ray production cross sections over a wide energy range help to predict and identify neutron backgrounds in these experiments.

Purpose: The purpose of this experiment is to determine partial $\gamma$-ray production cross sections for neutron-induced reactions in natural neon.

Methods: The broad spectrum neutron beam at the Los Alamos Neutron Science Center (LANSCE) was used for the measurement. Gamma rays from neutron-induced reactions were detected using the GErmanium Array for Neutron Induced Excitations (GEANIE).

Results: Partial $\gamma$-ray cross sections were measured for the first excited-state transitions in ${}^{20}$Ne and ${}^{22}$Ne. The measured cross sections were compared to the talys and CoH${}_3$ nuclear reaction codes.

Conclusions: These are the first experimental data for ($n,n^{\prime }$) reactions in neon. In addition to providing data to aid in the prediction and identification of neutron backgrounds in low-background experiments, these new measurements will help refine cross-section predictions in a mass region where models are not well constrained.

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.

The ${}^{64}$Co $\beta$-decay feeding levels in the well-studied ${}^{64}$Ni nucleus were investigated. Whereas the previously known ${}^{64}$Co decay scheme merely contained 2 $\gamma$ rays, the decay scheme established in this work contains $18,$ of which 5 are observed in this work and 6 were previously observed in an ($n$,$\gamma$) study but not placed in the ${}^{64}$Ni level scheme. Surprisingly, one additional level—placed at an excitation energy of $3578.7$ keV—could be determined. The observed $\beta$-decay paths involve allowed $\nu f_{5/2}\to \pi f_{7/2}$ and $\nu p_{1/2}\to \pi p_{3/2}$ transitions. Three strongly fed levels around 4 MeV are interpreted to possess possible proton-intruder character.

We calculate the electromagnetic form factors of the nucleon to third chiral order in manifestly Lorentz-invariant effective field theory. The $\rho$ and $\omega$ mesons as well as the $\Delta \left(1232\right)$ resonance are included as explicit dynamical degrees of freedom. To obtain a self-consistent theory with respect to constraints we consider the proper relations among the couplings of the effective Lagrangian. For the purpose of generating a systematic power counting, the extended on-mass-shell renormalization scheme is applied in combination with the small-scale expansion. The results for the electric and magnetic Sachs form factors are analyzed in terms of experimental data and compared to previous findings in the framework of chiral perturbation theory. The pion-mass dependence of the form factors is briefly discussed.