We systematically study the nuclear level densities of superheavy nuclei, including odd systems, using the single-particle energies obtained with the Woods-Saxon potential diagonalization. We applied minimization over many deformation parameters for the global minima-ground states, and the “imaginary water flow” technique on a many-deformation energy grid for the saddle points, including nonaxial shapes. The level density parameters are calculated by fitting the obtained results with the standard Fermi gas expression. The total potential energy and shell correction dependencies of the level-density parameter are analyzed at the ground state and saddle point. These parameters are compared with the results of a phenomenological approach. As shown, this expression should be modified for the saddle points, especially for small excitation energy. The ratio of the level-density parameter at the saddle point to that at the ground state is shown to be crucial for the survival probability of a heavy nucleus.

A microscopic description of the interaction of atomic nuclei with external electroweak probes is required for elucidating aspects of short-range nuclear dynamics and for the correct interpretation of neutrino oscillation experiments. Nuclear quantum Monte Carlo methods infer the nuclear electroweak response functions from their Laplace transforms. Inverting the Laplace transform is a notoriously ill-posed problem; and Bayesian techniques, such as maximum entropy, are typically used to reconstruct the original response functions in the quasielastic region. In this work, we present a physics-informed artificial neural network architecture suitable for approximating the inverse of the Laplace transform. Utilizing simulated, albeit realistic, electromagnetic response functions, we show that this physics-informed artificial neural network outperforms maximum entropy in both the low-energy transfer and the quasielastic regions, thereby allowing for robust calculations of electron scattering and neutrino scattering on nuclei and inclusive muon capture rates.

The limiting mass is a significant characteristic for compact exotic stars. In the case of quark stars the limiting mass can be expressed in terms of fundamental constants and the bag constant. In the present paper, using bag model description, the maximum mass of a rotating quark star is found to depend on the rotational frequency apart from other fundamental parameters. The analytical results obtained agree with the results of several relevant numerical estimates as well as observational evidences.

Spectroscopic factors to low-lying negative-parity states in ${}^{11}\mathrm{Be}$ extracted from the ${}^{12}\mathrm{B}(d,{}^3\mathrm{He}){}^{11}\mathrm{Be}$ proton-removal reaction are interpreted within the rotational model. Earlier predictions of the $p$-wave proton-removal strengths in the strong-coupling limit of the Nilsson model underestimated the spectroscopic factors to the $3/2_1^{-}$ and $5/2_1^{-}$ states and suggested that deviations in the $1^{+}$ ground state of the odd-odd ${}^{12}\mathrm{B}$ due to Coriolis coupling should be further explored. In this work we use the particle rotor model to take into account these effects and obtain a good description of the level scheme in ${}^{11}\mathrm{B}$, with a moderate $K$ mixing of the proton Nilsson levels [110]1/2 and [101]3/2. This mixing, present in the $1^{+}$ bandhead of ${}^{12}\mathrm{B}$, is key to explaining the proton-pickup data.

Background: Neutron-rich nuclei in the $\mathrm{A}\approx 140–160$ mass region provide valuable information on nuclear structure such as quadrupole- and octupole-shape coexistence and the evolution of the collectivity. These nuclei have also a nuclear engineering interest because they contribute to the total decay heat after a fission burst. The information concerning ${}^{145}\mathrm{La}$ is very limited.

Purpose: The study of low-spin states in ${}^{145}\mathrm{La}$ will provide a more detailed level scheme and enable the determination of the half-lives of the excited states.

Methods: Low-spin excited states in ${}^{145}\mathrm{La}$ have been investigated from the ${}^{145}\mathrm{Ba}{\beta }^{-}$ decay. The ${}^{145}\mathrm{Ba}$ nuclei were directly produced by photofission in the ALTO facility or obtained from the ${\beta }^{-}$ decay of ${}^{145}\mathrm{Cs}$ also produced by photofission. Gamma spectroscopy and fast-timing techniques were used.

Results: A new level scheme was proposed including 67 excited levels up to about 3 MeV and 164 transitions. Half-lives in the few-nanosecond range were measured for the first excited states. Configurations for levels up to $\approx 600$ keV were discussed.

Conclusions: The available information on the low-spin states of ${}^{145}\mathrm{La}$ has been modified and considerably extended. The analysis of the properties of the first excited states, such as excitation energies, decay modes, log $\mathit{\text{ft}}$ values, reduced transition probabilities, and Weisskopf hindrance factors, has enabled the identification of the first members of the bands corresponding to the $g_{7/2},$ $d_{5/2},$ and $h_{11/2}$ proton configurations.

Background: Spatially correlated overabundances of ${}^{15}\mathrm{N}$ and ${}^{18}\mathrm{O}$ observed in some low-density graphite meteoritic grains have been connected to nucleosynthesis taking place in the helium-burning shell during core-collapse supernovae. Two of the reactions which have been identified as important to the final abundances of ${}^{15}\mathrm{N}$ and ${}^{18}\mathrm{O}$ are ${}^{18}\mathrm{F}(n,\alpha ){}^{15}\mathrm{N}$ and ${}^{18}\mathrm{F}(n,p){}^{18}\mathrm{O}$. The relative strengths of the ${}^{18}\mathrm{F}(n,\alpha ){}^{15}\mathrm{N}$ and ${}^{18}\mathrm{F}(n,p){}^{18}\mathrm{O}$ reactions depend sensitively on the relative ${\alpha }_0$ and $p_0$ decay branches from states above the neutron threshold in ${}^{19}\mathrm{F}$ in addition to other properties such as the spins, parities, and neutron widths. However, experimental data on the charged-particle decays from these highly excited states are lacking or inconsistent.

Purpose: We measure the charged-particle decay branches from states around the neutron threshold in ${}^{19}\mathrm{F}$.

Method: Two experiments were performed using proton inelastic scattering from LiF targets and magnetic spectrographs. The first experiment used the high-resolution Q3D spectrograph at Munich to constrain the properties of levels in ${}^{19}\mathrm{F}$. A second experiment using the Orsay split-pole spectrograph and an array of silicon detectors was performed in order To measure the charged-particle decay branches from states around the neutron threshold in ${}^{19}\mathrm{F}$.

Results: A number of levels in ${}^{19}\mathrm{F}$ have been identified along with their corresponding charged-particle decays. The first state above the neutron threshold which has an observed proton-decay branch to the ground state of ${}^{18}\mathrm{O}$ lies 68 keV ($E_x=10.5$ MeV) above the neutron threshold. The $\alpha$-particle decays from the neutron-unbound levels are generally observed to be much stronger than the proton decays.

Conclusion:Neutron-unbound levels in ${}^{19}\mathrm{F}$ are observed to decay predominantly by $\alpha$-particle emission, supporting the role of ${}^{18}\mathrm{F}(n,\alpha ){}^{15}\mathrm{N}$ in the production of ${}^{15}\mathrm{N}$ in the helium-burning shell of supernovae. Improved resonant-scattering reaction data are required in order to be able to determine the reaction rates accurately.

The ${}^{24}\mathrm{Mg}+{}^{12}\mathrm{C}$ fusion reaction was used to perform a detailed $\gamma$-ray spectroscopy study of the astrophysically important nucleus ${}^{34}\mathrm{Ar}$. In particular, an experimental setup, coupling the advanced $\gamma$-ray tracking array GRETINA with the well-established Argonne fragment mass analyzer (FMA), was employed to obtain excitation energies and spin-parity assignments for excited states in ${}^{34}\mathrm{Ar}$, both above and below the proton separation energy. For the first time, an angular distribution analysis of in-beam $\gamma$ rays from fusion-evaporation reactions, using a tracking array, has been performed and Coulomb energy differences of analog states in the $T=1,$ $A=34$ mirror system, explored from 0 to 6 MeV. Furthermore, we present a comprehensive discussion of the astrophysical ${}^{33}\mathrm{Cl}(p,\gamma )$ stellar reaction rate, together with implications for the identification of nova presolar grains from sulfur isotopic abundances.

The Gamow shell model has shown to efficiently describe weakly bound and unbound nuclear systems, as internucleon correlations and continuum coupling are both taken into account in this model. In the present work, we study neutron-dripline oxygen isotopes. It is hereby demonstrated that the presence of continuum coupling is important for the description of oxygen isotopes at dripline, and especially to assess the eventual bound or unbound character of ${}^{28}\mathrm{O}$. Our results suggest that the ground state of ${}^{28}\mathrm{O}$ is weakly unbound and is similar to the narrow resonant ${}^{26}\mathrm{O}$ ground state. Predictions of weakly bound and resonance excited states in ${}^{24\text{–}26}\mathrm{O}$ are also provided. The asymptotes of the studied many-body states are analyzed via one-body densities, whereby the different radial properties of well bound, loosely bound, resonance states are clearly depicted.

The fusion-evaporation reaction ${}^{28}\mathrm{Si}+{}^{40}\mathrm{Ca}$ at 122 MeV beam energy was used to populate excited states in the $N=Z+1$ nucleus ${}^{63}\mathrm{Ga}$. With the combination of the Gammasphere spectrometer and the Microball CsI(Tl) charged-particle detector array, the level scheme of ${}^{63}\mathrm{Ga}$ was extended by more than a factor of two in terms of number of $\gamma$-ray transitions and excited states, excitation energy $(E_x>30\mathrm{MeV})$, and angular momentum $(I>30\hslash )$. Nine regular sequences of states were newly established in the high-spin part of the level scheme. The majority of these rotational band structures could be connected to the previously known part of the level scheme by high-energy $\gamma$-ray transitions in the energy range $E_{\gamma }=4–6\mathrm{MeV}$. Low-spin states were assessed by shell-model calculations. The high-spin rotational bands were interpreted and classified by means of cranked Nilsson-Strutinsky calculations.

We investigate the interactions of weakly interacting massive particles (WIMPS) with nucleons in nuclear medium by taking into account the effect of nuclear dynamics. We derive the nonrelativistic effective operators starting from the relativistic mean-field approximation. Certain interactions receive non-negligible corrections, which may significantly change the sensitivities of the WIMP-nucleus scattering cross section to these effective operators.

Medium-spin excited states of the neutron-rich nucleus ${}^{87}\mathrm{Br}$ were observed and studied for the first time. They were populated in fission of ${}^{235}\mathrm{U}$ induced by the cold-neutron beam of the PF1B facility of the Institut Laue-Langevin, Grenoble. The measurement of $\gamma$ radiation following fission was performed using the EXILL array of Ge detectors. The observed level scheme was compared with results of large valence space shell model calculations. The medium-spin level scheme consists of three bandlike structures, which can be understood as bands built on the $\pi f_{5/2}$, $\pi (p_{3/2}+f_{5/2})$, and $\pi g_{9/2}$ configurations. The behavior of the observed $\pi g_{9/2}$ band at high spins shows a considerable deviation from the shell model predictions. This deviation in this band is probably the result of an increased collectivity, which can be understood assuming that the $\pi g_{9/2}$ high-$\mathit{j}$ proton polarizes the core.

The empirical coupled-channel model and the statistical model are used to analyze the measured evaporation-residue cross sections of 48 fusion reactions. The experimental data of these reactions are systematically well reproduced (within one order of magnitude). It is found that the ratio of $a_{\mathrm{f}}$ (level density parameter in fission channel) to $a_{\mathrm{n}}$ (level density parameter in neutron-evaporation channel) plays an important role in reproducing the data appropriately. Furthermore, a good exponential holds between the ratio $a_{\mathrm{f}}/a_{\mathrm{n}}$ and the fissility parameter.

In the context of the ongoing search for the QCD critical point at the Relativistic Heavy-Ion Collider, we study the equation of state near the critical point in the temperature and baryon chemical potential plane. We use the parametric representation introduced in earlier literature, which maps the universal three-dimensional Ising equation of state onto the QCD phase diagram using several non-universal parameters. We focus on the quartic cumulant of the baryon number, or baryon number susceptibility ${\chi }_4^B$, which can be accessed experimentally via net-proton fluctuation kurtosis measurements. It was originally predicted, through universality arguments based on the leading singular contribution, that ${\chi }_4^B$ and net-proton kurtosis should show a specific nonmonotonic behavior due to the critical point. In particular, when following the freeze-out curve on the phase diagram by decreasing beam energy, the kurtosis is expected to dip, and then peak, when the beam energy scan passes close to the critical point. We study the effects of the nonuniversal and thus far unknown parameters of the Ising-to-QCD mapping on the behavior of ${\chi }_4^B$. We find that, while the peak remains a solid feature, the presence of the critical point does not necessarily cause a dip in ${\chi }_4^B$ on the freeze-out line below the transition temperature. The critical point contribution to the dip appears only for a narrow set of mapping parameters, when subleading singular terms are sufficiently suppressed.

Description of relativistic heavy-ion collisions at the energies of the BNL Relativistic Heavy Ion Collider (RHIC) Beam Energy Scan program with fluid dynamic approach poses several challenges, one of which being a complex geometry and a longer duration of the prehydrodynamic stage. Therefore, existing fluid dynamic models for heavy-ion collisions at the RHIC Beam Energy Scan energies rely on rather complex initial states, such as urqmd cascade or multifluid dynamics. In this study, we show that functionally simpler, nondynamical initial states can be employed for the fluid-dynamical simulations of Au-Au collisions at $\sqrt{s_{{}_{NN}}}=27$ and 62.4 GeV. We adapt the initial states based on the Monte Carlo Glauber model (glissando 2) and $\sqrt{T_A{T}_B}$ ansatz based on reduced thickness (${\mathrm{t}}_{\mathrm{r}}$ ento $p=0$), extended into the longitudinal direction and finite baryon density. We find that both initial states, when coupled to a three-dimensional event-by-event viscous fluid dynamic $+$ cascade model, result in an overall fair reproduction of basic experimental data: pseudorapidity distributions, transverse momentum spectra, and elliptic flow, at both collision energies. This is rather surprising given that the $\sqrt{T_A{T}_B}$ ansatz is functionally similar to the EKRT and IP-Glasma models, which are successful at much larger energies and rely on a partonic picture of the initial state.

We compute various nucleon polarizabilities in chiral perturbation theory implementing the $\mathrm{\Delta }$-full ($\mathrm{\Delta }$-less) approach up to order ${\epsilon }^3+q^4$ ($q^4$) in the small-scale (chiral) expansion. The calculation is carried out using the covariant formulation of $\chi \mathrm{PT}$ by utilizing the extended on-mass shell renormalization scheme. Except for the spin-independent dipole polarizabilities used to fix the values of certain low-energy constants, our results for the nucleon polarizabilities are pure predictions. We compare our calculations with available experimental data and other theoretical results. The importance of the explicit treatment of the $\mathrm{\Delta }$ degree of freedom in the effective field theory description of the nucleon polarizabilities is analyzed. We also study the convergence of the $1/m$ expansion and analyze the efficiency of the heavy-baryon approach for the nucleon polarizabilities.

The electric dipole moments (EDMs) of diamagnetic atoms are expected to be sensitive to charge-parity violation, particularly in nuclei through the nuclear Schiff moment. I explicitly demonstrate that the well-known form of the Schiff moment operator originating from the nucleon EDM is obtained by considering the screening of the nucleon EDMs in a neutral atom. Consequently, an additional contribution to the Schiff moment arises from the screening of the nuclear EDM induced by the interaction of the nucleon EDMs with the protons. This correction to the Schiff moment of ${}^{199}\mathrm{Hg}$ is evaluated in the independent particle model.

The semimicroscopic particle-hole dispersive optical model is adopted for a description of main properties of isoscalar giant multipole resonances (up to $L=3$) in medium-heavy closed-shell nuclei. The main properties are characterized by the strength distribution, transition density, and partial and total probabilities of direct one-nucleon decay. The model is implemented to describe characteristics of the mentioned resonances in the ${}^{208}\mathrm{Pb}$ nucleus, taken as an example. Calculation results are compared with available experimental data.

Background: The presence of nuclear ground states with stable reflection-asymmetric shapes is supported by rich experimental evidence. Theoretical surveys of odd-multipolarity deformations predict the existence of pear-shaped isotopes in several fairly localized regions of the nuclear landscape in the vicinity of near-lying single-particle shells with $\mathrm{\Delta }\ell =\mathrm{\Delta }j=3$.

Purpose: We analyze the role of isoscalar, isovector, neutron-proton, neutron-neutron, and proton-proton multipole interaction energies in inducing the onset of reflection-asymmetric ground-state deformations.

Methods: The calculations are performed in the framework of axial reflection-asymmetric Hartree-Fock-Bogoliubov theory using two Skyrme energy-density functionals and density-dependent pairing force.

Results: We show that reflection-asymmetric ground-state shapes of atomic nuclei are driven by the odd-multipolarity neutron-proton (or isoscalar) part of the nuclear interaction energy. This result is consistent with the particle-vibration picture, in which the main driver of octupole instability is the isoscalar octupole-octupole interaction giving rise to large $E3$ polarizability.

Conclusions: The necessary condition for the appearance of localized regions of pear-shaped nuclei in the nuclear landscape is the presence of parity doublets involving $\mathrm{\Delta }\ell =\mathrm{\Delta }j=3$ proton or neutron single-particle shells. This condition alone is, however, not sufficient to determine whether pear shapes actually appear, and, if so, what the corresponding reflection-asymmetric deformation energies are. The predicted small reflection-asymmetric deformation energies result from dramatic cancellations between even- and odd-multipolarity components of the nuclear binding energy.

Background: At energies above the capture barrier, coupled-channels (CC) calculations with a standard nuclear potential diffuseness (0.65 fm) increasingly overestimate experimental capture cross section as the charge product ($Z_1{Z}_2$) of the colliding nuclei increases. It has been suggested this may be linked to energy dissipation outside the capture barrier.

Purpose: We investigate quantitatively the role of energy dissipation in suppressing capture in heavy ion fusion reactions.

Method: The yields of sequential fission, including that resulting from deep inelastic collisions, and of fission following capture were determined simultaneously for collisions of ${}^{18}\mathrm{O}, {}^{30}\mathrm{Si}, {}^{34}\mathrm{S}$, and ${}^{40}\mathrm{Ca}+{}^{232}\mathrm{Th}$ at a range of energies around the respective capture barriers.

Results: The ratio of experimental to CC capture cross sections was found to decrease with increasing $Z_1{Z}_2$. Conversely, the ratio of sequential fission to capture-fission increased with increasing $Z_1{Z}_2$. The sum of sequential and capture fission agrees quite well with the CC cross sections.

Conclusions: The experimental capture fission and sequential fission cross sections, and their comparison with CC calculations, give a consistent picture that the increase in density overlap at the capture barrier with increasing $Z_1{Z}_2$ of the colliding nuclei is correlated with increasing energy dissipative processes. These compete increasingly strongly with capture as the $Z_1{Z}_2$ of the reaction increases. For the ${}^{40}\mathrm{Ca}$ reaction, the total fission yield exceeds expectations from capture model calculations, indicating that deep inelastic processes occur both from trajectories that would have led to capture and also from more peripheral trajectories.