Microscopic studies of nuclear fission require the evaluation of the potential-energy surface as a function of the collective coordinates. A reasonable choice of constraints on multipole moments should be made to describe the topography of the surface completely within a reasonable amount of computing time. We present a detailed analysis of fission barriers in the self-consistent Hartree-Fock-Bogoliubov approach with the D1S parametrization of the Gogny nucleon-nucleon interaction. Two heavy isotopes representing different spontaneous fission modes, ${}^{252}\mathrm{Cf}$ (asymmetric) and ${}^{258}\mathrm{No}$ (bimodal), have been chosen for the analysis. We have shown the existence of complicated structures on the energy surface that cannot be fully described in two-dimensional calculations. We analyze apparent problems that can be encountered in this type of calculations: multiple solutions for given constraints and transitions between various overlapping potential-energy surfaces. These issues may be partially solved by the analysis of the potential-energy surface spanned by triple constraints, but even in this case one may find multiple solutions and surface discontinuities. Analysis of the potential-energy surface in two dimensions is often very successful but it must be carried out with special attention to possible discontinuities.

The transverse momentum spectra of seven identified hadrons produced in $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{s_{NN}}=2.76$ and 5.02 TeV at the CERN Large Hadron Collider have been investigated in the framework of the recombination model (RM). Soft, semihard, and hard partons all play important roles in our model and are uniformly treated for all hadrons produced. The investigation has been extended to noncentral collisions and the parameters controlling the momentum degradation of semihard partons have been tuned. Our study shows good agreement between theoretical results and experimental data. To be able to provide a coherent explanation for the production of all identified hadrons ($\pi , p, K, \mathrm{\Lambda }, \varphi , \mathrm{\Xi }, \mathrm{\Omega }$) for transverse momenta as high as 14 $\mathrm{GeV}/c$ (for $\pi , p$, and $K$), and for all centralities, is an unprecedented achievement that supports the RM as a sensible model to combine various mechanisms of parton production with a universal scheme of hadronization.

Two-particle long-range azimuthal correlations are measured in photonuclear collisions using $1.7{\mathrm{nb}}^{-1}$ of 5.02 TeV $\mathrm{Pb}+\mathrm{Pb}$ collision data collected by the ATLAS experiment at the CERN Large Hadron Collider. Candidate events are selected using a dedicated high-multiplicity photonuclear event trigger, a combination of information from the zero-degree calorimeters and forward calorimeters, and from pseudorapidity gaps constructed using calorimeter energy clusters and charged-particle tracks. Distributions of event properties are compared between data and Monte Carlo simulations of photonuclear processes. Two-particle correlation functions are formed using charged-particle tracks in the selected events, and a template-fitting method is employed to subtract the nonflow contribution to the correlation. Significant nonzero values of the second- and third-order flow coefficients are observed and presented as a function of charged-particle multiplicity and transverse momentum. The results are compared with flow coefficients obtained in proton-proton and proton-lead collisions in similar multiplicity ranges, and with theoretical expectations. The unique initial conditions present in this measurement provide a new way to probe the origin of the collective signatures previously observed only in hadronic collisions.

Background: Organic scintillators are widely used for neutron detection in both basic nuclear physics and applications. While the proton light yield of organic scintillators has been extensively studied, measurements of the light yield from neutron interactions with carbon nuclei are scarce.

Purpose: Demonstrate a new approach for the simultaneous measurement of the proton and carbon light yield of organic scintillators. Provide new carbon light yield data for the EJ-309 liquid and EJ-204 plastic organic scintillators.

Method: A 33-MeV ${}^2\mathrm{H}^{+}$ beam from the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory was impinged upon a 3-mm-thick Be target to produce a high-flux, broad-spectrum neutron beam. The double time-of-flight technique was extended to simultaneously measure the proton and carbon light yields of the organic scintillators, wherein the light output associated with the recoil particle was determined using $np$ and $n\mathrm{C}$ elastic scattering kinematics.

Results: The proton and carbon light yield relations of the EJ-309 liquid and EJ-204 plastic organic scintillators were measured over a recoil energy range of approximately 0.3 to 1 MeV and 2 to 5 MeV, respectively, for EJ-309, and 0.2 to 0.5 MeV and 1 to 4 MeV, respectively, for EJ-204.

Conclusions: These data provide new insight into the ionization quenching effect in organic scintillators and key input for simulation of the response of organic scintillators for both basic science and a broad range of applications.

Background: The peculiar properties of nuclei in the so-called “island of inversion” around $Z=10$ and $N=20$ are the focus of current nuclear physics research. Recent studies showed that ${}^{28}\mathrm{F}$ has a negative-parity ground state and thus lies within the southern shore of the island of inversion, and ${}^{29}\mathrm{F}$ presents a halo structure in its ground state, but it is unclear which effects, such as deformation, shell evolution due to tensor forces, or couplings to the continuum, lead to this situation.

Purpose: We investigate the role of quadrupole deformation and continuum effects on the single-particle structure of ${}^{28,29,31}\mathrm{F}$ from a relativistic mean-field approach and show how both phenomena can lead to a negative-parity ground state in ${}^{28}\mathrm{F}$ and halo structures in ${}^{29,31}\mathrm{F}$.

Methods: We solve the Dirac equation in the complex-momentum (Berggren) representation for a potential with quadrupole deformation at the first order obtained from relativistic mean-field calculations using the NL3 interaction and calculate the continuum level densities using the Green's function method.

Results: We extract single-particle energies and widths from the continuum level densities to construct the Nilsson diagrams of ${}^{28,29,31}\mathrm{F}$ in the continuum and analyze the evolution of both the widths and occupation probabilities of relevant Nilsson orbitals in ${}^{28}\mathrm{F}$ and find that some amount of prolate deformation must be present. In addition, we calculate the density distributions for bound Nilsson orbitals near the Fermi surface in ${}^{29,31}\mathrm{F}$ and reveal that, for a quadrupole deformation $0.3\le {\beta }_2\le 0.45$ (prolate), characteristic halo tails appear at large distances.

Conclusions: Using the relativistic mean-field approach in the complex-momentum representation with the Green's function method, we demonstrate that in neutron-rich fluorine isotopes, while in the spherical case the $pf$ shells are already inverted and close to the neutron emission threshold, a small amount of quadrupole deformation can dramatically reduce the gap between positive- and negative-parity states and increase the role of continuum states, ultimately leading to the negative parity in the ground state of ${}^{28}\mathrm{F}$ and the halo structures in ${}^{29,31}\mathrm{F}$.

We have performed a systematic study of the spectroscopic properties of the isotopic chain ${}^{214-226}\mathrm{Rn}$ using the $spdf$-IBM-2 interacting boson model. This model includes octupole degrees of freedom, what allows the description of negative- and positive-parity states with the same Hamiltonian. We discuss how this model is able to describe the transition from vibrational to rotational spectra in these nuclei with a rather small set of parameters, which were obtained to reproduce the properties of ${}^{214-222}\mathrm{Rn}$. Then the calculations regarding ${}^{224,226}\mathrm{Rn}$ can be considered a prediction, which compares very well with recent experimental data.

Background: The extent to which knockout, as opposed to a pickup reaction mechanism, contributes in pre-equilibrium $(p,\alpha )$ reactions is still not clear. Even with exclusive $(p,\alpha )$ reactions at conveniently low incident energies to well-defined final states, the issue often appears to be ambiguous. Recently Uozumi et al. [Y. Uozumi, Y. Fukuda, Y. Yamaguchi, G. Watanabe, and M. Nakano, Phys. Rev. C 102, 014604 (2020)] used the intranuclear cascade (INC) theory to study pre-equilibrium $(p,\alpha )$ reactions in a range of incident energies from 42 to 300 MeV. They conclude that, below a projectile energy of about 120 MeV, knockout contributes almost nothing to the upper half of the pre-equilibrium $(p,\alpha )$ yield. This result is in disagreement with several other studies.

Purpose: We investigate whether existing $(p,p\alpha )$ quasifree knockout results support the conclusion from the INC study.

Method: The distorted-wave impulse approximation (DWIA) is used. The theory is known to give a good reproduction of experimental energy distributions and angular distributions, as well as absolute cross sections of $(p,p\alpha )$ reactions at incident energies at and above 100 MeV. The DWIA is simply exploited as a convenient way of interpolation and extrapolation of the available experimental distributions.

Results: The experimental cross-section distributions of the coincidence knockout reactions predict contributions to the pre-equilibrium yield much higher than those estimated by the INC study. At small scattering angles of only ${30}^{\circ }$ to ${40}^{\circ }$ the knockout yield is already quite substantial. At ${60}^{\circ }$ it accounts for approximately all of the pre-equilibrium yield.

Conclusions: Even a lower-limit estimate of the coincident contribution at forward angles to the cross section of pre-equilibrium reactions is already sizable at low excitation. The cross section is expected to increase very rapidly at higher excitation energies (equivalently, lower $\alpha$-particle energy).

Radial flow can be directly extracted from the azimuthal distribution of mean transverse rapidity. We apply the event-plane method and the two-particle correlation method to estimate the anisotropic Fourier coefficient of the azimuthal distribution of mean transverse rapidity. Using the event sample generated by a multiphase transport model with string melting, we show that both methods are effective. For the two-particle correlation method to be reliable, the mean number of particles in an azimuthal bin must be above a certain threshold. Using these two methods, anisotropic radial flow can be estimated in a model-independent way in relativistic heavy-ion collisions.

Švarc et al. [Phys. Rev. C 97, 054611 (2018)] have shown that without fixing the reaction-amplitude phase, different partial waves at neighboring energies in single-energy, single-channel partial wave analysis reproduce experimental data identically, but are discontinuous and disconnected. To obtain the continuous solution, the phase has to be fixed to some continuous value. In the same reference it has also been shown that the change of the angular part of the reaction-amplitude phase mixes partial waves, so the pole structure of any single-energy single-channel partial wave analysis depends on the chosen phase. As in any single-channel analysis the overall reaction-amplitude phase cannot be determined because of continuum ambiguity, it is in principle free and has to be taken from some coupled-channel model. Because of the difference in the angular part of the phase, choosing different phases results in the change of the pole content of the obtained solution. Therefore, single-energy single-channel partial wave analysis is inherently model dependent, and the number of poles it contains strongly depends on the choice of the phase. In that reference these facts have been illustrated on the pseudoscalar meson production toy model. This truth is now for the full set of measured observables demonstrated on the realistic model of $\eta$ photoproduction presented in Švarc, Wunderlich, and Tiator [Phys. Rev. C 102, 064609 (2020)].

We report measurements of the parity-conserving beam-normal single-spin elastic scattering asymmetries $B_n$ on ${}^{12}\mathrm{C}$ and ${}^{27}\mathrm{Al}$, obtained with an electron beam polarized transverse to its momentum direction. These measurements add an additional kinematic point to a series of previous measurements of $B_n$ on ${}^{12}\mathrm{C}$ and provide a first measurement on ${}^{27}\mathrm{Al}$. The experiment utilized the ${\mathrm{Q}}_{\mathrm{weak}}$ apparatus at Jefferson Lab with a beam energy of 1.158 GeV. The average laboratory scattering angle for both targets was $7.7^{\circ }$, and the average $Q^2$ for both targets was 0.024 37 ${\mathrm{GeV}}^2$ ($Q=0.1561$ GeV). The asymmetries are $B_n=-10.68\pm 0.90\left(\mathrm{stat}\right)\pm 0.57\left(\mathrm{syst}\right)$ ppm for ${}^{12}\mathrm{C}$ and $B_n=-12.16\pm 0.58\left(\mathrm{stat}\right)\pm 0.62\left(\mathrm{syst}\right)$ ppm for ${}^{27}\mathrm{Al}$. The results are consistent with theoretical predictions, and are compared to existing data. When scaled by $Z/A$, the $Q$ dependence of all the far-forward angle ($\theta <{10}^{\circ }$) data from ${}^1\mathrm{H}$ to ${}^{27}\mathrm{Al}$ can be described by the same slope out to $Q\approx 0.35$ GeV. Larger-angle data from other experiments in the same $Q$ range are consistent with a slope about twice as steep.

Background: ${}^{24}\mathrm{Mg}$ is a strongly deformed nucleus in the ground state. Deformation effects can be observed in the structure of the isoscalar giant monopole and quadrupole resonances. ${}^{24}\mathrm{Mg}$ is also a nucleus that is well known to present different types of cluster-oscillation modes. Both giant resonances and cluster states are strongly populated by isoscalar transitions.

Purpose: To extract the $E0$, $E1$, and $E2$ transition strengths via ${}^6\mathrm{Li}$ scattering. The ${}^6\mathrm{Li}$ probe is a powerful tool for investigating the isoscalar nuclear response with a very favorable ratio of resonance-to-continuum background.

Method: Double-differential cross sections of ${}^6\mathrm{Li}$ inelastic scattering, at the beam energy of 100 MeV/u, were measured in the excitation-energy range $10\text{–}40\mathrm{MeV}$ and scattering angles $0-3{}^{\circ }$. A multipole-decomposition analysis was performed for extracting the isoscalar $E0$, $E1$, and $E2$ strength distributions.

Results: The extracted multipole strengths were compared with predictions from consistent quasiparticle random phase approximation calculations. The theoretical predictions are in fair agreement with the experimental data. The $E0$ strength was also compared with results from antisymmetrized molecular dynamics calculations found in the literature. A few peaks in the experimental data might be associated with clustering in ${}^{24}\mathrm{Mg}$.

Conclusions: Ground-state deformation effects were observed in the isoscalar giant monopole resonance (ISGMR) and isoscalar giant quadrupole resonance (ISGQR) distributions. The ISGMR strength is split in two peaks around 19 and 28 MeV. The ISGQR exhibits a pronounced peak at 20 MeV with a broadening at the low-energy region, similar to predictions from microscopic calculations. Signatures of excitation of cluster states were observed in the $E0$ response. Further studies including particle-decay measurements will be required to confirm the nature of the observed peaks.

We examine a description of available cross section data for symmetric space star (SST) configurations in the neutron-deuteron $\left(nd\right)$ and proton-deuteron $\left(pd\right)$ breakup reaction using numerically exact solutions of the three-nucleon $\left(3N\right)$ Faddeev equation based on two- and three-nucleon (semi)phenomenological and chiral forces. The predicted SST cross sections are very stable with respect to the underlying dynamics for incoming nucleon laboratory energies below $\approx 25$ MeV. We discuss possible origins of the surprising discrepancies between theory and data found in low-energy $nd$ and $pd$ SST breakup measurements.

In this paper we study the neutron-number dependence of $\delta R$ (difference of nuclear charge radii $R$ for two nuclei of one isotope chain), based on which we suggest an empirical formula of $\delta R$, called the $\delta R$ relations. The $\delta R$ relations of a number of theoretical models are also investigated in this work. We demonstrate that the $\delta R$ relations of this work are more competitive than the previously called $\delta R_{in-jp}$ relations, with the virtue of simplicity and flexibility. By using this approach we tabulate our predicted results of 1647 nuclear charge radii which are experimentally unaccessible, within theoretical uncertainty below 0.03 fm.

Neutron-rich nuclei in the vicinity of the $N=40$ island of inversion are characterized by shell evolution and exhibit deformed ground states. In several nuclei isomeric states have been observed and attributed to excitations to the intruder neutron $1g_{9/2}$ orbital. In the present paper we searched for isomeric states in nuclei around $N=40,Z=22$ produced by projectile fragmentation at the Radioactive Isotope Beam Factory. Delayed $\gamma$ rays were detected by the Euroball RIKEN Cluster Array germanium detector array. High statistics data allowed for an updated decay scheme of ${}^{60}\mathrm{V}$. The lifetime of an isomeric state in ${}^{64}\mathrm{V}$ was measured for the first time in the present experiment. A previously unobserved isomeric state was discovered in ${}^{58}\mathrm{Sc}$. The measured lifetime suggests a parity changing transition, originating from an odd number of neutrons in the $1g_{9/2}$ orbital. The nature of the isomeric state in ${}^{58}\mathrm{Sc}$ is, thus, different from isomers in the less exotic V and Sc nuclei.

The level schemes of the neutron-rich ${}^{37–42}\mathrm{P}$ isotopes are investigated via in-beam $\gamma$-ray spectroscopy following the fragmentation of a ${}^{45}\mathrm{Cl}$ projectile beam at intermediate beam energies. Information on $\gamma \gamma$ coincidence relationships complemented by comparisons to shell-model calculations in the $sd\text{−}pf$ model space were used to construct excitation level schemes for these neutron-rich nuclei. For the odd-mass ${}^{37,39}\mathrm{P}$ isotopes, a level scheme is presented that appears essentially complete at low energies and exhausts the states predicted by the SDPF-MU shell-model Hamiltonian. Simple Nilsson configurations are proposed for the low-lying excited states of ${}^{38,39,40,41}\mathrm{P}$ from an analysis of the $E2$ transition matrix elements and moments calculated within the shell model.

The axial-shape asymmetry of yrast states in ${}^{246–256}\mathrm{Fm}$ is studied by performing the projected total-energy surface (PTES) calculations, which consider the beyond-mean-field effects associated with the restoration of rotational symmetry and shape variation at the same time. The results show a large elongation deformation but also a considerable large triaxiality for their ground and high spin states, the triaxial deformation $\gamma \approx {11}^{\circ }$ in average. In comparison, the TRS calculations have also been performed for these nuclei, and the results show a well-established axial quadrupole shape in their ground states. The presence of the significant triaxial deformation can be attributed to the beyond-mean-field effects generated by the angular-momentum projection. The axial asymmetric shape for the yrast states of nuclei with $Z=100$, suggested by the present variation after projection (VAP) calculations, indicates that the triaxial degree of freedom may also play a significant role in other transfermium and even superheavy nuclei. The present PTES calculations have well reproduced the available experimental energies of the ground-band states and predict the rest yrast states up to spin 30 in each nucleus. The calculated yrast bands of ${}^{246–256}\mathrm{Fm}$ present the back bending phenomenon at about the state ${18}^{+}$, caused by the alignment excitations of the two quasiparticle neutrons of $\nu j_{15/2}\left[743\right]7/2$ or of $\nu h_{11/2}\left[761\right]1/2$. It is worth confirming the predicted band structures by the future spectroscopic experiments in the transfermium nuclei for the study of the single-particle structure in the superheavy mass region.

A single crystal chemical vapor deposited (sCVD) diamond detector is used as an active target to measure neutron-induced reactions on natural carbon using the neutrons produced by spallation, with a broad energy spectrum at LANSCE. The neutron-induced reactions are detected in the diamond as low as ${\mathrm{E}}_n=400$ keV and up to approximately 100 MeV. Relative cross sections for ${}^{12}\mathrm{C}(n,{\alpha }_0),$ ${}^{12}\mathrm{C}(n,p_0),$ ${}^{12}\mathrm{C}(n,d_0+p_1),$ and ${}^{13}\mathrm{C}$$(n,{\alpha }_0)$ are reported up to ${\mathrm{E}}_n=22$ MeV and comparisons on detected pulse-height spectra and detector response of scattering reactions are made with GEANT4 simulations using the ENDF/B-VIII.0 evaluated nuclear data library up to 20 MeV. The results are compared with past experimental data, including other works that incorporate diamond detectors as an active carbon target. In addition, R-matrix calculations for the ${}^{13}\mathrm{C}$ $+$ n system are presented.

For fissioning isotopes of thorium and uranium, the simultaneous description of the charge, mass, total kinetic energy, and neutron multiplicity distributions of fission fragments is presented within the improved scission-point model. Correlations between all these observables are analyzed. The influence of the transition from symmetric to asymmetric fission mode on the shape of neutron multiplicity distribution is studied.

Background: Measurements of neutron-star macrophysical properties thanks to multimessenger observations offer the possibility to constrain the properties of nuclear matter. Indeed, cold and dense matter as found inside neutron stars, in particular in their core, is not accessible to terrestrial laboratories.

Purpose: We investigate the consequences of using equations of state that employ models for the core and the crust that are not calculated consistently on the neutron-star macrophysical properties, on some of the so-called universal relations and on the constraints obtained from gravitational-wave observations.

Methods: We use various treatments found in the literature to connect together nonconsistent core and crust equations of state. We then compute the mass, the radius, the tidal deformability, and the moment of inertia for each model. Finally, we assess the discrepancies in the neutron-star macrophysical properties obtained when consistent models for the whole star and nonconsistent ones are employed.

Results: The use of crust models nonconsistent with the core introduces an error on the macrophysical parameters which can be as large as the estimated accuracy of current and next-generation telescopes. The precision of some of the universal relations reported in the literature is found to be overestimated. We confirm that the equation of the crust has limited influence on the macrophysical properties.

Conclusions: The discrepancy between results obtained for a fully consistent equation of state and a nonconsistent one can be reduced if one connects the core and the crust models at baryon densities around 0.08–$0.1{\mathrm{fm}}^{-3}$. The equation of the crust cannot be probed with current multimessenger observations and near-future ones.