We have compared the experimental data on charged-particle elliptic flow parameter ($v_2$) in Au $+$ Au collisions at midrapidity for $\sqrt{s_{\mathrm{NN}}}=9.2$, $19.6$, $62.4$, and $200$ GeV with results from various models in heavy-ion collisions such as the ultrarelativistic quantum molecular dynamics (UrQMD) model, a multiphase transport model (AMPT), and heavy-ion jet interaction generator (HIJING). We observe that the average $v_2$ ($\langle v_2\rangle$) from the transport model UrQMD agrees well with the measurements at $\sqrt{s_{\mathrm{NN}}}=9.2$ GeV but increasingly falls short of the experimental $\langle v_2\rangle$ values as the beam energy increases. The difference in $\langle v_2\rangle$ is of the order of $60\%$ at $\sqrt{s_{\mathrm{NN}}}=200$ GeV. The $\langle v_2\rangle$ results from HIJING are consistent with zero, while those from AMPT with default settings, a model based on HIJING with additional initial- and final-state rescattering effects included, give a $\langle v_2\rangle$ value of about $4\%$ for all the beam energies studied. This is in contrast to an increase in $\langle v_2\rangle$ with beam energy for the experimental data. A different version of the AMPT model, which includes partonic effects and quark coalescence as a mechanism of hadronization, gives higher values of $\langle v_2\rangle$ among the models studied and is in agreement with the measured $\langle v_2\rangle$ values at $\sqrt{s_{\mathrm{NN}}}=200$ GeV. These studies show that the experimental $\langle v_2\rangle$ has substantial contribution from partonic interactions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV, whose magnitude reduces with decrease in beam energy. We also compare the available data on the transverse momentum and pseudorapidity dependence of $v_2$ to those from these models.

High-spin states in the odd-odd nucleus ${}^{166}\mathrm{Ta}$ are investigated through the $5n$ channel of the ${}^{51}\mathrm{V}+{}^{120}\mathrm{Sn}$ reaction. Four new bands are observed and linked into the previous level scheme. Configurations for the bands are proposed, based on measured alignments and $B(M1)/B(E2)$ transition strength ratios.

We study whether the neutron skin thickness $\Delta r_{\mathit{np}}$ of ${}^{208}\mathrm{Pb}$ originates from the bulk or from the surface of the nucleon density distributions, according to the mean-field models of nuclear structure, and find that it depends on the stiffness of the nuclear symmetry energy. The bulk contribution to $\Delta r_{\mathit{np}}$ arises from an extended sharp radius of neutrons, whereas the surface contribution arises from different widths of the neutron and proton surfaces. Nuclear models where the symmetry energy is stiff, as typical of relativistic models, predict a bulk contribution in $\Delta r_{\mathit{np}}$ of ${}^{208}\mathrm{Pb}$ about twice as large as the surface contribution. In contrast, models with a soft symmetry energy like common nonrelativistic models predict that $\Delta r_{\mathit{np}}$ of ${}^{208}\mathrm{Pb}$ is divided similarly into bulk and surface parts. Indeed, if the symmetry energy is supersoft, the surface contribution becomes dominant. We note that the linear correlation of $\Delta r_{\mathit{np}}$ of ${}^{208}\mathrm{Pb}$ with the density derivative of the nuclear symmetry energy arises from the bulk part of $\Delta r_{\mathit{np}}$. We also note that most models predict a mixed-type (between halo and skin) neutron distribution for ${}^{208}\mathrm{Pb}$. Although the halo-type limit is actually found in the models with a supersoft symmetry energy, the skin-type limit is not supported by any mean-field model. Finally, we compute parity-violating electron scattering in the conditions of the ${}^{208}\mathrm{Pb}$ parity radius experiment (PREX) and obtain a pocket formula for the parity-violating asymmetry in terms of the parameters that characterize the shape of the ${}^{208}\mathrm{Pb}$ nucleon densities.

We discuss the nuclear EMC effect with particular emphasis on recent data for light nuclei including ${}^2\mathrm{H}$, ${}^3\mathrm{He}$, ${}^4\mathrm{He}$, ${}^9\mathrm{Be}$, ${}^{12}\mathrm{C}$, and ${}^{14}\mathrm{N}$. In order to verify the consistency of available data, we calculate the ${\chi }^2$ deviation between different data sets. We find a good agreement between the results from the NMC, SLAC E139, and HERMES experiments. However, our analysis indicates an overall normalization offset of about $2\%$ in the data from the recent JLab E03-103 experiment with respect to previous data for nuclei heavier than ${}^3\mathrm{He}$. We also discuss the extraction of the neutron/proton structure function ratio $F_2^n/F_2^p$ from the nuclear ratios ${}^3\mathrm{He}$/${}^2\mathrm{H}$ and ${}^2\mathrm{H}$/${}^1\mathrm{H}$. Our analysis shows that the E03-103 data on ${}^3\mathrm{He}$/${}^2\mathrm{H}$ require a renormalization of about $3\%$ in order to be consistent with the $F_2^n/F_2^p$ ratio obtained from the NMC experiment. After such a renormalization, the ${}^3\mathrm{He}$ data from the E03-103 and HERMES experiments are in a good agreement. Finally, we present a detailed comparison between data and model calculations, which include a description of the nuclear binding, Fermi motion, and off-shell corrections to the structure functions of bound proton and neutron, as well as the nuclear pion and shadowing corrections. Overall, a good agreement with the available data for all nuclei is obtained.

With the goal of constraining the phase of matter at high density, we study $r$-mode damping in the color-flavor-locked phase with kaon condensation (CFL-K0) and contrast it with the CFL phase. The mode frequencies in these phases are found to differ very slightly. While the bulk viscosity in either phase is only effective at damping the $r$-mode at temperatures $T\gtrsim {10}^{11}$ K, the shear viscosity in the CFL-K0 phase is the only effective damping agent all the way down to temperatures $T\gtrsim {10}^8$ K characteristic of cooling neutron stars. However, it cannot keep the star from becoming unstable to gravitational wave emission for rotation frequencies $\nu \approx 56$–11 Hz at $T\approx {10}^8$–${10}^9$ K. Stars composed almost entirely of CFL or CFL-K0 matter are ruled out by observation of rapidly rotating neutron stars, indicating that dissipation at the quark-hadron interface or nuclear crust interface must play a key role in damping the instability.

New neutron capture cross sections of ${}^{58,60}\mathrm{Ni}$ were measured in the energy range from 100 eV to 600 keV using the Oak Ridge Electron Linear Accelerator. The combination of these new neutron capture data with previous transmission data allowed a resonance analysis up to 900 keV using $\mathcal{R}$-matrix theory. The theoretically determined direct capture cross sections were included in the analyses. From these resonance parameters and the direct capture contribution, new ($n$,$\gamma$) astrophysical reaction rates were determined over the entire energy range needed by the latest stellar models describing the so-called weak $s$ process.

Level structures in ${}^{61,62}\mathrm{Mn}{}_{36,37}$ were studied with Gammasphere in the reaction of a $430$-MeV ${}^{64}\mathrm{Ni}$ beam and a thick ${}^{238}\mathrm{U}$ target. The newly identified levels decrease in excitation energy compared to the analogous structures in the lighter Mn isotopes and behave similarly to states in the corresponding Fe isotones that involve $g_{9/2}$ neutron excitations. This behavior illustrates the importance of the inclusion of the $\nu g_{9/2}$ orbital in any realistic shell-model calculations in this region.

In a coupled-channel model, we explore the effects of coupling between configurations on the radial behavior of the wave function and, in particular, on the spectroscopic factor (SF) and the asymptotic normalization coefficient (ANC). We evaluate the extraction of a SF from the ratio of the ANC of the coupled-channel model to that of a single-particle approximation of the wave function. We perform this study within a $\mathrm{core}+n$ collective model, which includes two states of the core that connect by a rotational coupling. To get additional insights, we also use a simplified model that takes a $\delta$ function for the coupling potential. Calculations are performed for ${}^{11}\mathrm{Be}$. Fair agreement is obtained between the SF inferred from the single-particle approximation and the one obtained within the coupled-channel models. Significant discrepancies are observed only for large coupling strength and/or large admixture, that is, a small SF. This suggests that reliable SFs can be deduced from the wave-function asymptotics when the structure is dominated by one configuration, that is, for a large SF.

We undertake a quantitative comparison of multifragmentation reactions, as modeled by two different approaches: the antisymmetrized molecular dynamics (AMD) and the momentum-dependent stochastic mean-field (SMF) model. Fragment observables and pre-equilibrium (nucleon and light cluster) emission are analyzed, in connection with the underlying compression-expansion dynamics in each model. Considering reactions between neutron-rich systems, observables related to the isotopic properties of emitted particles and fragments are also discussed, as a function of the parametrization employed for the isovector part of the nuclear interaction. We find that the reaction path, particularly the mechanism of fragmentation, is different in the two models and reflects on some properties of the reaction products, including their isospin content. This should be taken into account in the study of the density dependence of the symmetry energy from such collisions.

The $\beta$-asymmetry parameter $\mathrm{Ã}$ for the Gamow-Teller decay of ${}^{60}\mathrm{Co}$ was measured by polarizing the radioactive nuclei with the brute-force low-temperature nuclear-orientation method. The ${}^{60}\mathrm{Co}$ activity was cooled down to milliKelvin temperatures in a ${}^3\mathrm{He}$-${}^4\mathrm{He}$ dilution refrigerator in an external $13$-T magnetic field. The $\beta$ particles were observed by a $500$-$\mu$m-thick Si PIN diode operating at a temperature of about $10$ K in a magnetic field of $0.6$ T. Extensive geant4 Monte Carlo simulations were performed to gain control over the systematic effects. Our result, $\mathrm{Ã}=-1.014(12){}_{\mathrm{stat}}(16){}_{\mathrm{syst}}$, is in agreement with the standard-model value of $-0.987(9)$, which includes recoil-order corrections that were addressed for the first time for this isotope. Further, it enables limits to be placed on possible tensor-type charged weak currents, as well as other physics beyond the standard model.

In this paper we study the possibility of spontaneous ferromagnetic and antiferromagnetic phase transitions of asymmetrical nuclear matter using the lowest-order constrained variational technique with ${\mathit{AV}}_{18}$ potential and employing a microscopic point of view. Our results show that the spontaneous transition to ferromagnetic and antiferromagnetic phases cannot occur for asymmetric nuclear matter.

We measured the production of ${}^{57}\mathrm{Co}$, ${}^{54}\mathrm{Mn}$, ${}^{68}\mathrm{Ge}$, ${}^{65}\mathrm{Zn}$, and ${}^{60}\mathrm{Co}$ in a sample of Ge enriched in isotope $76$ due to high-energy neutron interactions. These isotopes, especially ${}^{68}\mathrm{Ge}$, are critical in understanding background in Ge detectors used for double $\beta$ decay experiments. They are produced by cosmogenic-neutron interactions in the detectors while they reside on the Earth’s surface. These production rates were measured at neutron energies of a few hundred MeV. We compared the measured production to that predicted by cross-section calculations based on CEM03.02. The cross-section calculations overpredict our measurements by approximately a factor of $3$ depending on isotope. We then use the measured cosmic-ray neutron flux, our measurements, and the CEM03.02 cross sections to predict the cosmogenic production rate of these isotopes. The uncertainty in extrapolating the cross-section model to higher energies dominates the total uncertainty in the cosmogenic production rate.

We simulate the central reactions of ${}^{20}\mathrm{Ne}$$+$${}^{20}\mathrm{Ne}$, ${}^{40}\mathrm{Ar}$$+$${}^{45}\mathrm{Sc}$, ${}^{58}\mathrm{Ni}$$+$${}^{58}\mathrm{Ni}$, ${}^{86}\mathrm{Kr}$$+$${}^{93}\mathrm{Nb}$, ${}^{129}\mathrm{Xe}$$+$${}^{118}\mathrm{Sn}$, ${}^{86}\mathrm{Kr}$$+$${}^{197}\mathrm{Au}$, and ${}^{197}\mathrm{Au}$$+$${}^{197}\mathrm{Au}$ at different incident energies for different equations of state, different binary cross sections, and different widths of Gaussians. A rise-and-fall behavior of the multiplicity of intermediate mass fragments (IMFs) is observed. The system size dependence of peak center-of-mass energy $E_{\mathrm{c}.\mathrm{m}.}^{\max }$ and peak IMF multiplicity $\langle N_{\mathrm{IMF}}\rangle {}^{\max }$ is also studied, where it is observed that $E_{\mathrm{c}.\mathrm{m}.}^{\max }$ follows a linear behavior and $\langle N_{\mathrm{IMF}}\rangle {}^{\max }$ shows a power-law dependence. A comparison between two clusterization methods, the minimum spanning tree and the minimum spanning tree method with binding energy check (MSTB), is also made. We find that the MSTB method reduces the $\langle N_{\mathrm{IMF}}\rangle {}^{\max }$, especially in heavy systems. The power-law dependence is also observed for fragments of different sizes at $E_{\mathrm{c}.\mathrm{m}.}^{\max }$ and the power-law parameter $\tau$ is found to be close to unity in all cases except $A^{\max }$.

We examine the “naturalness” of the scaling of multiplicity and elliptic flow $v_2$ with rapidity in weakly and strongly coupled systems. We argue that multiplicity scaling is relatively straightforward to incorporate in existing ansatz, and that this scaling is insensitive to the transport properties of the system. On the other hand, we argue that the observed scaling of elliptic flow is problematic to describe within a hydrodynamic model (the Knudsen number $K\ll 1$), but arises more naturally within weakly coupled systems (where the Knudsen number $~1$). We conclude with an overview of ways proposed to make weakly coupled systems compatible with the absolute value of elliptic flow, and we indicate experimental probes that could clarify these issues.

Properties of quantum phase transitional systems in atomic nuclei are explored within the context of the interacting boson model 1 for both first and second order systems. A traditionally experimental approach is used to search for the effective finite-size critical point as a function of system size and angular momentum by studying derivatives of observables across the phase transition region. The effects of angular momentum on quantum phase transitions are investigated, and properties of first order phase transitions within the Casten triangle are examined.

High-spin states in the odd-odd $N=Z$ nucleus ${}^{54}\mathrm{Co}$ have been investigated by the fusion-evaporation reaction ${}^{28}\mathrm{Si}$(${}^{32}\mathrm{S}$,$1\alpha 1p1n$)${}^{54}\mathrm{Co}$. Gamma-ray information gathered with the Ge detector array Gammasphere was correlated with evaporated particles detected in the charged particle detector system Microball and a $1\pi$ neutron detector array. A significantly extended excitation scheme of ${}^{54}\mathrm{Co}$ is presented, which includes a candidate for the isospin $T=1$, $6^{+}$ state of the $1f_{7/2}^{-2}$ multiplet. The results are compared to large-scale shell-model calculations in the $\mathit{fp}$ shell. Effective interactions with and without isospin-breaking terms have been used to probe isospin symmetry and isospin mixing. A quest for deformed high-spin rotational cascades proved negative. This feature is discussed by means of cranking calculations.

Measurements of states excited by nuclear resonance fluorescence in ${}^{237}\mathrm{Np}$ were performed using a bremsstrahlung beam. Fifteen new states were observed in the region of 1.7 to 2.5 MeV. They can be used to detect or assay ${}^{237}\mathrm{Np}$ nondestructively for applications in security and safeguards. The states are populated with similar strength as those states found previously in ${}^{235}\mathrm{U}$ and ${}^{239}\mathrm{Pu}$ but are spread out more in energy.