We investigate the role of the Coulomb interaction on the liquid-gas phase transition of nuclear matter with three different values of proton fraction ($Y_p=0.5,0.3$, and 0.1), relevant for heavy-ion physics as well as various astrophysical scenarios, within the framework of quantum molecular dynamics. We perform simulations for a wide range of density and temperature with and without the Coulomb interaction and calculate the two-point correlation functions of nucleon density fluctuations for all the configurations to determine the phase transition region. We also determine the critical end point of the liquid-gas phase transition for all three values of proton fraction considered. We observe that the Coulomb interaction reduces the transition temperature by $\gtrsim 2$ MeV for nuclear matter with $Y_p=0.5$ and $0.3$ and by $\sim 1$ MeV for nuclear matter with $Y_p=0.1$. However, the critical density is found to be more or less insensitive to the Coulomb interaction.

We have measured the $K$-shell and total internal conversion coefficients (ICCs), ${\alpha }_K$ and ${\alpha }_T$, for the 109.3-keV $M4$ transition in ${}^{125}\mathrm{Te}$ to be 185.0(40) and 350.0(38), respectively. Previously this transition's ICCs were considered to be anomalous, with measured values lying below calculated ones. When compared with Dirac-Fock calculations, our new results show good agreement. The ${\alpha }_K$ result agrees well with the version of the theory that takes account of the $K$-shell atomic vacancy and disagrees with the one that does not. This is consistent with our conclusion drawn from a series of measurements on high multipolarity transitions.

Excited states of ${}^{90,91}\mathrm{Kr}$ nuclei have been populated following the cold-neutron-induced fission of a ${}^{235}\mathrm{U}$ target. The $\gamma$ rays emitted following fission reactions were measured using the highly efficient array of high-purity Ge detectors, EXILL, at the Institute-Laue-Langevin, Grenoble. The surprisingly low population of ${}^{91}\mathrm{Kr}$ reported in the spontaneous fission of ${}^{252}\mathrm{Cf}$ measurement has been explained and new level schemes of ${}^{90,91}\mathrm{Kr}$ nuclei were established. Moderate $\gamma$ collectivity is observed in both nuclei. Large-scale shell-model calculations support the experimental picture of the $Z=36$, Kr isotopes forming a border line between lower-$Z$ nuclei showing moderate $\gamma$ collectivity and the heavier-$Z$ nuclei, where distinct shape changes are observed.

New excited states in ${}^{142}\mathrm{Ba}$ and ${}^{144}\mathrm{Ce}$ are investigated by means of prompt $\gamma \text{-ray}$ spectroscopy of the radiation following spontaneous fission of ${}^{252}\mathrm{Cf}$. Measurements of angular correlations and the observed branchings allowed the assignment of spins and parities with confidence. The new measurements are reinforced by shell-model calculations where energy levels, electric transitions, and magnetic moments are consistent with experimental data. The presence of collectivity in the $N=86$ isotones is confirmed by clear signatures of soft triaxial $\gamma$ bands in both nuclei.

Background: The heavy-ion induced reactions on intermediate mass targets are complex in nature, even at the low energies. To understand those nuclear reaction phenomena in detail, more experimental studies are required in a wide range of energies.

Purpose: Investigation of heavy-ion reactions by measuring production cross sections of the residues produced in the ${}^{11}\mathrm{B}$-induced reactions on ${}^{89}\mathrm{Y}$ and ${}^{93}\mathrm{Nb}$ at low energies, near and above the barrier, and to check the effectiveness of the different nuclear models to explain them. Further, aim is also to optimize the production parameters of neutron deficient medically relevant ${}^{97}\mathrm{Ru}$ and ${}^{101m}\mathrm{Rh}$ radioisotopes produced in those reactions, respectively.

Method: The ${}^{11}\mathrm{B}$ beam was allowed to impinge on ${}^{89}\mathrm{Y}$ and ${}^{93}\mathrm{Nb}$ foils supported by an aluminum (Al) catcher foil, arranged in a stack, in 27.5–58.7 and 30.6–62.3 MeV energy range, respectively. The off-line $\gamma$-ray spectrometry was carried out after the end of bombardment to measure the activity of the radionuclides produced in each foil and cross sections were calculated. Measured cross-sectional data were analyzed in terms of compound and precompound model calculations.

Results: The measured cross sections of ${}^{97,95}\mathrm{Ru}$, ${}^{96,95,94}\mathrm{Tc}$, ${}^{93m}\mathrm{Mo}$, ${}^{90m}\mathrm{Y}$ radionuclides produced in the ${}^{11}\mathrm{B}$+${}^{89}\mathrm{Y}$ reaction, and ${}^{101,100,99}\mathrm{Pd}$, ${}^{101m,100,99m}\mathrm{Rh}$, ${}^{97}\mathrm{Ru}$ produced in the ${}^{11}\mathrm{B}$+${}^{93}\mathrm{Nb}$ reaction showed good agreement with the model calculations based on the Hauser-Feshbach formulation and exciton model. Unlike theoretical estimation, consistent production of ${}^{90m}\mathrm{Y}$ was observed in the ${}^{11}\mathrm{B}$+${}^{89}\mathrm{Y}$ reaction. Substantial pre-equilibrium contribution was noticed in the $3n$ reaction channel in both reactions.

Conclusions: Theoretical estimations confirmed that major production yields are mostly contributed by the compound reaction process. Pre-equilibrium emissions contributed at the high energy tail of the $3n$ channel for both reactions. Moreover, an indirect signature of a direct reaction influence was also observed in the ${}^{90m}\mathrm{Y}$ production.

We combine few- and many-body degrees of freedom in a new computationally efficient model applicable to both bound and continuum states and adaptable to different subfields of physics. We formulate a self-consistent three-body model for a core nucleus surrounded by two valence nucleons, where the core is treated in the mean-field approximation and the same effective Skyrme interaction is used between both core and valence nucleons. We apply the model to ${}^{26}\mathrm{O}$, where we reproduce the known experimental data as well as phenomenological models with more parameters. The decay of the ground state is found to proceed directly into the continuum without effect of the virtual sequential decay through the well-reproduced $d_{3/2}$ resonance of ${}^{25}\mathrm{O}$.

We discuss the applicability of the Wong formula for fusion cross sections in a single-channel problem. To this end, we carry out a systematic study and compare the approximate fusion cross sections with the exact results in a wide mass region of reaction systems. We show that the deviation of the approximate results from the exact cross sections is large for light systems, even though the Wong formula provides a reasonable approximation for heavy systems. We also discuss the energy dependence of the deviation, and show that for a given projectile nucleus the critical energy, at which the deviation exceeds 5% of the exact cross sections, increases as a function of the mass number of the target nucleus.

Background: The electromagnetic form factors of the proton measured by unpolarized and polarized electron scattering experiments show a significant disagreement that grows with the squared four-momentum transfer $\left(Q^2\right)$. Calculations have shown that the two measurements can be largely reconciled by accounting for the contributions of two-photon exchange (TPE). TPE effects are not typically included in the standard set of radiative corrections since theoretical calculations of the TPE effects are highly model dependent, and, until recently, no direct evidence of significant TPE effects has been observed.

Purpose: We measured the ratio of positron-proton to electron-proton elastic-scattering cross sections in order to determine the TPE contribution to elastic electron-proton scattering and thereby resolve the proton electric form factor discrepancy.

Methods: We produced a mixed simultaneous electron-positron beam in Jefferson Lab's Hall B by passing the 5.6-GeV primary electron beam through a radiator to produce a bremsstrahlung photon beam and then passing the photon beam through a convertor to produce electron-positron pairs. The mixed electron-positron (lepton) beam with useful energies from approximately 0.85 to 3.5 GeV then struck a 30-cm-long liquid hydrogen $\left({\mathrm{LH}}_2\right)$ target located within the CEBAF Large Acceptance Spectrometer (CLAS). By detecting both the scattered leptons and the recoiling protons, we identified and reconstructed elastic scattering events and determined the incident lepton energy. A detailed description of the experiment is presented.

Results: We present previously unpublished results for the quantity $R_{2\gamma }$, the TPE correction to the elastic-scattering cross section, at $Q^2\approx 0.85$ and 1.45 ${\mathrm{GeV}}^2$ over a large range of virtual photon polarization $\varepsilon$.

Conclusions: Our results, along with recently published results from VEPP-3, demonstrate a nonzero contribution from TPE effects and are in excellent agreement with the calculations that include TPE effects and largely reconcile the form-factor discrepancy up to $Q^2\approx 2{\mathrm{GeV}}^2$. These data are consistent with an increase in $R_{2\gamma }$ with decreasing $\varepsilon$ at $Q^2\approx 0.85$ and 1.45 ${\mathrm{GeV}}^2$. There are indications of a slight increase in $R_{2\gamma }$ with $Q^2$.

Neutron-rich nuclei in the vicinity of ${}^{78}\mathrm{Ni}$ were produced using a ${}^{238}\mathrm{U}$ beam at the RIKEN Radioactive Isotope Beam Factory. The particle-identification plot for the in-flight fission fragments highlights the first observation of eight new isotopes: ${}^{73}\mathrm{Mn}$, ${}^{76}\mathrm{Fe}$, ${}^{77,78}\mathrm{Co}$, ${}^{80,81,82}\mathrm{Ni}$, and ${}^{83}\mathrm{Cu}$. Although the $\beta$-decay half-lives of ${}^{77}\mathrm{Co}$ and ${}^{80}\mathrm{Ni}$ were recently reported by Xu et al. [Phys. Rev. Lett. 113, 032505 (2014)] using data from the same experiment, the current work provides the first direct, quantitative evidence for the existence of these isotopes. The experimental production cross sections are reproduced in a satisfactory manner by theoretical predictions. An odd-even staggering of the cross sections was observed, and the effect appears to become more pronounced for the most exotic nuclei that were investigated. The staggering effect was interpreted as an increase of the neutron-evaporation probability for odd-$N$ isotopes, owing to the decrease of the neutron-separation energy, $S_n$. The predicted cross section for ${}^{80}\mathrm{Ni}$ is significantly overestimated, which may be related to a weak binding of the neutron pair above the $N=50$ shell closure.

Inspired by the low-density Lee-Yang expansion for the energy of a dilute Fermi gas of density $\rho$ and momentum $k_F$, we introduce here a Skyrme-type functional that contains only $s$-wave terms and provides, at the mean-field level, (i) a satisfactory equation of state for neutron matter from extremely low densities up to densities close to the equilibrium point, and (ii) a good-quality equation of state for symmetric matter at density scales around the saturation point. This is achieved by using a density-dependent neutron-neutron scattering length $a\left(\rho \right)$ which satisfies the low-density limit (for Fermi momenta going to zero) and has a density dependence tuned in such a way that the low-density constraint $|a\left(\rho \right)k_F|\le 1$ is satisfied at all density scales.

Background: An assessment done under the auspices of the Nuclear Energy Agency in 2007 suggested that the $\beta$ decays of abundant fission products in nuclear reactors may be incomplete. Many of the nuclei are potentially affected by the so called pandemonium effect and their $\beta \text{−}\gamma$ decay heat should be restudied using the total absorption technique. The fission products ${}^{137}\mathrm{I}$ and ${}^{137}\mathrm{Xe}$ were assigned highest priority for restudy due to their large cumulative fission branching fractions. In addition, measuring $\beta$-delayed neutron emission probabilities is challenging and any new technique for measuring the $\beta$-neutron spectrum and the $\beta$-delayed neutron emission probabilities is an important addition to nuclear physics experimental techniques.

Purpose: To obtain the complete $\beta$-decay pattern of ${}^{137}\mathrm{I}$ and ${}^{137}\mathrm{Xe}$ and determine their consequences for reactor decay heat and ${\overline{\nu }}_e$ emission. Complete $\beta$-decay feeding includes ground state to ground state $\beta$ feeding with no associated $\gamma$ rays, ground state to excited states $\beta$ transitions followed by $\gamma$ transitions to the daughter nucleus ground state, and $\beta$-delayed neutron emission from the daughter nucleus in the case of ${}^{137}\mathrm{I}$.

Method: We measured the complete $\beta$-decay intensities of ${}^{137}\mathrm{I}$ and ${}^{137}\mathrm{Xe}$ with the Modular Total Absorption Spectrometer at Oak Ridge National Laboratory. We describe a technique for measuring the $\beta$-delayed neutron energy spectrum, which also provides a measurement of the $\beta$-neutron branching ratio, $P_n$.

Results: We validate the current Evaluated Nuclear Structure Data File (ENSDF) evaluation of ${}^{137}\mathrm{Xe}\beta$ decay. We find that major changes to the current ENSDF assessment of ${}^{137}\mathrm{I}\beta$-decay intensity are required. The average $\gamma$ energy per $\beta$ decay for ${}^{137}\mathrm{I}\beta$ decay ($\gamma$ decay heat) increases by 19%, from 1050–1250 keV, which increases the average $\gamma$ energy per ${}^{235}\mathrm{U}$ fission by $0.11\%$. We measure a $\beta$-delayed neutron branching fraction for ${}^{137}\mathrm{I}\beta$ decay of $7.9\pm 0.2\left(\mathrm{fit}\right)\pm 0.4\left(\mathrm{sys}\right)\%$ and we provide a $\beta$-neutron energy spectrum.

Conclusions: The Modular Total Absorption Spectrometer measurements of ${}^{137}\mathrm{I}$ and ${}^{137}\mathrm{Xe}$ demonstrate the importance of revisiting and remeasuring complex $\beta$-decaying fission products with total absorption spectroscopy. We demonstrate the ability of the Modular Total Absorption Spectrometer to measure $\beta$-delayed neutron energy spectra.

We investigate the effects of the pairing in spherical nuclei. We use the same finite-range interaction of Gogny type in the three steps of our approach, Hartree–Fock, Bardeen, Cooper, and Schrieffer, and quasiparticle random-phase-approximation calculations. We study electric- and magnetic-dipole and quadrupole and octupole excitations in oxygen and calcium isotopes and also in isotones with 20 neutrons. We investigate the pairing effects on single-particle energies and occupation probabilities, on the excitation energies, $B$ values, and collectivity of low-lying states including the isoscalar electric-dipole and magnetic-dipole excitations, and also the giant resonances. The inclusion of the pairing increases the values of the excitation energies in all the cases that we have studied. In general, the effects of the pairing are too small to noticeably improve the agreement with the available experimental data.

The high-spin nuclear structure of the odd-odd ${}^{66}\mathrm{Ga}$ nucleus was probed using heavy-ion induced fusion-evaporation reaction. The de-exciting $\gamma$ rays were detected by using the Indian National Gamma Array (INGA) consisting of high resolution Compton suppressed clover detectors. The level scheme of ${}^{66}\mathrm{Ga}$ was extended up to an excitation energy $\left(E_x\right)$ of $\sim 10.6$ MeV with spin parity of ${21}^{(+)}$. Two new quadrupole bandlike structures, one positive and one negative parity, based on the states having spin parity of $J^{\pi }={11}^{+}$ and ${10}^{-}$, respectively, were found. The experimental energy levels are compared with calculations within the framework of shell model calculation using $jj44bpn$ effective interaction. The agreement between experiment and theory is good. The total Routhian surface calculations were performed to understand the shape of the ${}^{66}\mathrm{Ga}$ nucleus associated with the configurations $\nu \left(g_{9/2}\right){}^3\nu \left(f_{5/2}\right){}^2\pi \left(g_{9/2}\right){}^1\pi \left(f_{5/2}\right){}^2$ and $\nu \left(g_{9/2}\right){}^2\nu \left(f_{5/2}\right){}^1\pi \left(g_{9/2}\right){}^1\pi \left(f_{5/2}\right){}^2$ assigned to the positive and negative parity bands, respectively. In the frequency domain $\omega =0.20\text{–}0.30$ MeV, both the negative and positive parity quadrupole structures, favor prolate deformation whereas at $\omega =0.50$ MeV there is a sudden change to noncollective oblate shape in both the bands.

The decay modes and half-lives of 96 isotopes of the superheavy element roentgenium (Rg) within the range of $255\le A\le 350$ come under investigation in the present paper. The isotopes which lie beyond the proton drip line are identified by calculating the one-proton and two-proton separation energies. The $\alpha$-decay half-lives are calculated using the Coulomb and proximity potential model for deformed nuclei (CPPMDN). For a theoretical comparison the $\alpha$ half-lives are also evaluated using the Viola-Seaborg semiempirical relation, the universal curve of Poenaru et al., the analytical formula of Royer, and the universal decay law of Qi et al. Spontaneous fission half-lives are computed with the shell-effect-dependent formula of Santhosh and Nithya and the semiempirical formula of Xu et al. The decay modes are predicted by comparing the $\alpha$-decay half-lives within the CPPMDN with the corresponding spontaneous fission half-lives computed by the shell-effect-dependent formula of Santhosh and Nithya. In our paper it is seen that the isotopes ${}^{255\text{–}271,273}\mathrm{Rg}$ lie beyond the proton drip line and hence decay through proton emission. The isotopes ${}^{272,274\text{–}277}\mathrm{Rg}$ exhibit long $\alpha$ chains. Three $\alpha$ chains are predicted from the isotopes ${}^{278\text{–}282}\mathrm{Rg}$. The isotopes ${}^{283\text{–}345}\mathrm{Rg}$ decay through spontaneous fission. The isotopes ${}^{346\text{–}350}\mathrm{Rg}$ are found to be stable against $\alpha$ decay. The theoretical results are compared with the available experimental results and are seen to be matching well. We hope that our predictions will be useful in future experimental investigations.

The ratio of shear viscosity over entropy density in low energy heavy-ion collision has been calculated by using the Green-Kubo method in the framework of an extended quantum molecular dynamics model. After the system almost reaches a local equilibration for a head-on ${}^{40}\mathrm{Ca}+{}^{100}\mathrm{Mo}$ collision, thermodynamic and transport properties are extracted. Meanwhile, the isovector giant dipole resonance (IVGDR) of the collision system also is studied. By the Gaussian fits to the IVGDR photon spectra, the peak energies of the IVGDR are extracted at different incident energies. The result shows that the IVGDR peak energy has a positive correlation with the ratio of shear viscosity over entropy density. This is a quantum effect and indicates a difference between nuclear matter and classical fluid.

Vorticity of matter generated in noncentral heavy-ion collisions at energies of the Nuclotron-based Ion Collider fAcility (NICA) at the Joint Institute for Nuclear Research (JINR) in Dubna is studied. Simulations are performed within the model of the three-fluid dynamics (3FD) which reproduces the major part of bulk observables at these energies. Comparison with earlier calculations is done. The qualitative pattern of the vorticity evolution is analyzed. It is demonstrated that the vorticity is mainly located at the border between participants and spectators. In particular, this implies that the relative $\mathrm{\Lambda }$-hyperon polarization should be stronger at rapidities of the fragmentation regions than that in the midrapidity region.

Background: Composed systems have become of great interest in the framework of ground-state quantum phase transitions (QPTs) and many of their properties have been studied in detail. However, in these systems, the study of the so-called excited-state quantum phase transitions (ESQPTs) has not received so much attention.

Purpose: A quantum analysis of the ESQPTs in the two-fluid Lipkin model is presented in this work. The study is performed through the Hamiltonian diagonalization for selected values of the control parameters in order to cover the most interesting regions of the system phase diagram.

Method: A Hamiltonian that resembles the consistent-Q Hamiltonian of the interacting boson model (IBM) is diagonalized for selected values of the parameters. Properties such as the density of states, the Peres lattices, the nearest-neighbor spacing distribution, and the participation ratio are analyzed.

Results: An overview of the spectrum of the two-fluid Lipkin model for selected positions in the phase diagram has been obtained. The location of the excited-state quantum phase transition can be easily singled out with the Peres lattice, with the nearest-neighbor spacing distribution, with Poincaré sections, or with the participation ratio.

Conclusions: This study completes the analysis of QPTs for the two-fluid Lipkin model, extending the previous study to excited states. The ESQPT signatures in composed systems behave in the same way as in single ones, although the evidences of their presence can be sometimes blurred. The Peres lattice turns out to be a convenient tool to look into the position of the ESQPT and to define the concept of phase in the excited states realm.

The deexcitation of alpha-conjugate nuclei produced in reactions of 35 MeV/nucleon ${}^{40}\mathrm{Ca}$ with ${}^{40}\mathrm{Ca}$ has been investigated. Particular emphasis is placed on examining the dynamics of collisions leading to projectile-like fragment exit channels. A general exploration of the reaction systematics reveals the binary dissipative character of the collisions and a hierarchy effect similar to that seen for heavier systems. Investigation of the subset of events characterized by a total $\alpha$-conjugate mass ($\alpha$ particles plus $\alpha$-conjugate fragments) equal to 40 and atomic number equal to 20 reveal a dominance of $\alpha$-conjugate exit channels. The hierarchy effect for these channels leads to the production of $\alpha$-clustered neck structures with potentially exotic geometries and properties.

The experimental fusion excitation functions of the reactions ${}^{48}\mathrm{Ti}+{}^{58}\mathrm{Fe}$ and ${}^{58}\mathrm{Ni}+{}^{54}\mathrm{Fe}$, measured down to the low sub-barrier energies, are described within the quantum diffusion approach and the universal fusion function representation. For these systems, the $s$-wave capture probabilities are extracted from the experimental excitation functions and are also analyzed. An enhancement of the sub-barrier fusion cross section observed in the ${}^{48}\mathrm{Ti}+{}^{58}\mathrm{Fe}$ reaction in comparison to the relatively close system ${}^{58}\mathrm{Ni}+{}^{54}\mathrm{Fe}$ is explained.

We propose a method to solve the eigenvalue problem with a two-center single-particle potential. This method combines the usual matrix diagonalization with the method of separable representation of a two-center potential; that is, an expansion of the two-center potential with a finite basis set. To this end, we expand the potential on a harmonic-oscillator basis, while single-particle wave functions on a combined basis with a harmonic oscillator and eigenfunctions of a one-dimensional two-center potential. To demonstrate its efficiency, we apply this method to a system with two ${}^{16}\mathrm{O}$ nuclei, in which the potential is given as a sum of two Woods–Saxon potentials.