We investigate the time evolution of prompt fission $\gamma$ emission due to the presence of ns to ms isomers in the fragments produced in the neutron-induced fission of ${}^{233,235}\mathrm{U}$ and in the spontaneous fission of ${}^{252}\mathrm{Cf}$. Calculations performed with the cgmf fission event generator are compared with recent experimental data on ${}^{252}\mathrm{Cf}\left(\mathrm{sf}\right)$ and ${}^{235}\mathrm{U}(n,\mathrm{f})$ obtained with the dance+neuance setup at the Los Alamos Neutron Science Center. Of particular interest are the average $\gamma$-ray energy spectrum as a function of time since scission, $\varphi ({\epsilon }_{\gamma },t)$; the increase of the average $\gamma$-ray multiplicity over time, ${\overline{N}}_{\gamma }\left(t\right)$; and its evolution in time as a function of the fission fragment mass, ${\overline{N}}_{\gamma }$($\mathrm{A},t$). The time evolution of isomeric ratios in postneutron emission fission fragments can be defined and used to test and reveal some deficiencies in our knowledge of the low-lying levels of neutron-rich nuclei produced in fission reactions.

Background: The fluctuation-dissipation mechanism underlying nonequilibrium transport in low-energy heavy-ion reactions remains unclear. Although the time-dependent Hartree-Fock (TDHF) method provides a reasonable description of average reaction outcomes and one-body dissipation, it is known to significantly underestimate fluctuations of observables.

Purpose: The purpose of this work is to investigate deep-inelastic collisions of ${}^{144}\mathrm{Sm}+{}^{144}\mathrm{Sm}$ and ${}^{154}\mathrm{Sm}+{}^{154}\mathrm{Sm}$ with microscopic mean-field approaches and to show a predominant role of one-body dissipation as well as one-body fluctuations and correlation in low-energy heavy-ion reactions.

Methods: Three-dimensional TDHF calculations are carried out for ${}^{144}\mathrm{Sm}+{}^{144}\mathrm{Sm}$ at $E_{\text{c.m.}}=500\mathrm{MeV}$ and ${}^{154}\mathrm{Sm}+{}^{154}\mathrm{Sm}$ at $E_{\text{c.m.}}=485\mathrm{MeV}$ for a range of impact parameters with the Skyrme SLy5 energy density functional. Backward time evolutions are performed as well to evaluate fluctuations and correlation in nucleon numbers within time-dependent random phase approximation (TDRPA).

Results: As results of TDHF calculations we obtain total kinetic energy loss (TKEL), scattering angles, and contact time, for a wide range of impact parameters. TKEL takes almost constant values in an impact parameter range of $0\le b\lesssim 6\mathrm{fm}$, indicating a fully damped character of the reactions. We find a systematically lower TKEL for ${}^{144}\mathrm{Sm}+{}^{144}\mathrm{Sm}$ collisions as compared with the other, presumably because of the shell effects of $N=82$. With TDRPA we calculate mass- and charge-number fluctuations, ${\sigma }_{AA}$ and ${\sigma }_{ZZ}$, as well as the correlation between neutron and proton transfers, ${\sigma }_{NZ}$, for each impact parameter. By combining these results, we make a comparison of the ${\sigma }^2$-TKEL plot with available experimental data. We demonstrate that TDRPA quantitatively reproduces the experimental ${\sigma }_{AA}^2$-TKEL distributions, whereas it systematically underestimates the charge fluctuation, ${\sigma }_{ZZ}$. The double-differential cross sections of reaction products are calculated, showing good agreement with the experimental data. We demonstrate a long sought-after characteristic property that the closed-shell structure limits nucleon transfer at small energy losses, based on our microscopic TDHF and TDRPA calculations.

Conclusions: It has been shown that one-body fluctuations and correlation in TDRPA, built on top of TDHF mean-field dynamics, are the predominant mechanisms in deep-inelastic collisions. TDRPA systematically overestimates proton-number fluctuations ${\sigma }_{ZZ}$ in both ${}^{144}\mathrm{Sm}+{}^{144}\mathrm{Sm}$ and ${}^{154}\mathrm{Sm}+{}^{154}\mathrm{Sm}$ reactions, which offers room for refining our understanding of reaction mechanisms in low-energy heavy-ion reactions.

The ${}^{238}\mathrm{U}\left({}^{54}\mathrm{Cr},4n\right){}^{288}\mathrm{Lv}$ and ${}^{242}\mathrm{Pu}({}^{50}\mathrm{Ti},3n\text{–}4n){}^{288,289}\mathrm{Lv}$ reactions have been studied at the gas-filled separator DGFRS-2 at the SHE Factory at Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research. Three new isotopes were discovered: two α-decaying nuclei ${}^{288}\mathrm{Lv}$ with α-particle energy $E_{\alpha }=11.08$ MeV and half-life $T_{1/2}=2.0$ ms, ${}^{289}\mathrm{Lv}$ with $E_{\alpha }=10.90$ MeV, $T_{1/2}=2.4$ ms, and granddaughter of ${}^{288}\mathrm{Lv}$, spontaneously fissioning ${}^{280}\mathrm{Cn}$ with $T_{1/2}=10\mu \mathrm{s}$, which was observed after the first registration of α decay of ${}^{284}\mathrm{Fl}$ with $E_{\alpha }=10.57$ MeV. Besides, for the first time we reliably registered the pxn channel of the ${}^{242}\mathrm{Pu}+{}^{50}\mathrm{Ti}$ reaction which was not evidently observed in the ${}^{48}\mathrm{Ca}$-induced reactions in previous studies. The cross sections of the $3n$ and $4n$ channels of the ${}^{242}\mathrm{Pu}+{}^{50}\mathrm{Ti}$ reaction of ${0.32}_{-0.18}^{+0.34}$ pb and ${0.22}_{-0.15}^{+0.27}$ pb, respectively, were measured at excitation energy of the ${}^{292}\mathrm{Lv}$ compound nucleus $E^{*}=41$ MeV. The cross section of the $4n$-evaporation channel of the ${}^{238}\mathrm{U}+{}^{54}\mathrm{Cr}$ reaction, leading to the same compound nucleus, at $E^{*}=42$ MeV of ${32}_{-24}^{+46}$ fb turned out to be approximately 15 times lower than the total cross section of the ${}^{242}\mathrm{Pu}+{}^{50}\mathrm{Ti}$ reaction at close excitation energy. Thus, for the first time, it was convincingly proved in an experiment that the reactions of isotopes of actinide elements with ${}^{50}\mathrm{Ti}$ are, by an order of magnitude, preferable to reactions with ${}^{54}\mathrm{Cr}$ for the synthesis of new elements 119 and 120.

Low-energy fusion of heavy ions is a fascinating coupling-assisted quantum tunneling problem, whose understanding is crucial for advancing the synthesis of new elements and isotopes. Quantum dynamical coupled-channels calculations of laser-assisted ${}^{16}\mathrm{O}+{}^{238}\mathrm{U}$ fusion are presented for both a central collision and the total fusion cross sections, suggesting that laser-nucleus interaction can enhance the average ${}^{16}\mathrm{O}+{}^{238}\mathrm{U}$ fusion probability by $6\text{–}60\%$ at sub-barrier energies using quasistatic laser fields of intensity ${10}^{27}\text{–}{10}^{29}$ ${\mathrm{W}\mathrm{cm}}^{-2}$ and photon's energy of 1 eV. Femtosecond laser pulses are shown to reduce this enhancement by many orders of magnitude.

Cross sections of the reaction ${}^{54}\mathrm{Fe}(p,\gamma ){}^{55}\mathrm{Co}$ were measured using the activation technique within the proton energy range of 1.3 to 15.0 MeV employing a low-energy tandem accelerator and a small cyclotron. The obtained results are comparable to those previously obtained via prompt γ counting. The excitation function was reproduced well by a model calculation using the code talys and some adjusted input parameters. Additionally, the excitation function of the competing reaction ${}^{54}\mathrm{Fe}(p,\alpha ){}^{51}\mathrm{Mn}$ was measured up to 15.8 MeV. Also, for this reaction, theoretical calculations using the talys code reproduced the experimental data well after appropriate selection of input parameters. The model calculations using global parameters (given in TENDL-2015 and TENDL-2023) were only partially successful in reproducing the experimental data. This study identified the (p,α) reaction as the dominant process, while the (p,γ) reaction appeared weakest, possibly due to a higher probability of particle emission compared to γ-ray emission. Notably, the ${}^{54}\mathrm{Fe}\left(p,\alpha \right){}^{51}\mathrm{Mn}$ reaction was found to be a viable route for producing the radioisotopically pure positron emitter ${}^{51}\mathrm{Mn}$ using a small cyclotron, highlighting its potential for medical applications.

The electric multipole strength distributions for transitions from the ${}^{12}\mathrm{C}\left(0_1^{+}\right)$ ground state to $3\alpha$ ($0^{+}$, $1^{-}$, $2^{+}$, and $3^{-}$) continuum states are studied in terms of $3\alpha$ model. Several sets of the $3\alpha$ Hamiltonian are introduced phenomenologically with conventional $\alpha \text{−}\alpha$ interaction potentials and $3\alpha$ potentials with different range parameters. The transition strength distributions are obtained from wave functions of $3\alpha$ bound and continuum states calculated by the Faddeev three-body formalism. From these strength distributions, the resonance parameters (energy, $3\alpha$-decay width, and transition strength) of $3\alpha$ resonance states are extracted. Dependencies of these observables on interaction potential models are studied to examine the introduced interaction models. Using the transition strength distributions, excitation-energy spectra in the ${}^{12}\mathrm{C}(\alpha ,{\alpha }^{\prime })3\alpha$ reaction are calculated to compare with experimental data.

The cross sections for the $pp\to pp\eta$ reaction are evaluated at energies relevant for the HADES, PANDA, and SIS100 experiments at GSI-FAIR (Facility for Antiproton and Ion Research). Consideration includes the $\eta$-bremsstrahlung mechanism involving intermediate proton exchange via the ${\pi }^0$, $\eta$, ${\rho }^0$, and $\omega$ exchanges and the mechanism involving the nucleon resonances $N\left(1535\right)$, $N\left(1650\right)$, $N\left(1710\right)$, and $N\left(1880\right)$ excited via the pseudoscalar- and/or vector-meson exchanges, depending on the model. The role of the $\omega \omega$- and ${\rho }^0{\rho }^0$-fusion processes with the Reggeized vector-meson exchanges is also discussed. The calculation is done in an effective Lagrangian approach. To determine the parameters of the model, the $\gamma p\to \eta p$ and ${\pi }^{-}p\to \eta n$ reactions are studied and the results are then compared with the Crystal Ball and CLAS data. For the $pp\to pp\eta$ reaction, the model results are compared with the energy dependence of the cross section measured far from the threshold and with the differential distributions $d\sigma /dcos{\theta }_{\eta }$ and $d\sigma /d{p}_{\eta }$ measured by the DISTO Collaboration. The comparison shows that the $N\left(1535\right)$ resonance is the dominant contribution and that other contributions are also important due to interference effects. Assuming that the $\rho$ exchange is the dominant resonant excitation process, the model is able to describe the available data, e.g., it reproduces the shape of the angular distributions measured by the DISTO Collaboration. Predictions are given for the HADES experiment at center-of-mass energy of $\sqrt{s}=3.46$ GeV, which can be verified in the near future, and for planned PANDA and SIS100 experiments at higher energies.

The quantum-mechanical description of the collective angular motion in a system of two touching fission fragments is proposed. The main features of excitation spectrum and the structure of the wave functions are investigated. As found, the angular motion approximately corresponds to independent vibrations of fragments around the pole-to-pole configuration. The model allows us to explain the experimentally observed lack of correlation between the angular momenta of two fission fragments. The correlation between angular momentum and fragment mass is primarily linked to the change of fragments deformation. The saw-tooth behavior of angular momentum distribution with respect to the fragment mass is explained.

The correlations between event-by-event fluctuations of symmetry planes are measured in Pb-Pb collisions at a center-of-mass energy per nucleon pair $\sqrt{s_{NN}}=5.02\mathrm{TeV}$ recorded by the ALICE detector at the Large Hadron Collider. This analysis is conducted using the Gaussian estimator technique, which is insensitive to biases from correlations between different flow amplitudes. The study presents, for the first time, the centrality dependence of correlations involving up to five different symmetry planes. The correlation strength varies depending on the harmonic order of the symmetry plane and the collision centrality. Comparisons with measurements from lower energies indicate no significant differences within uncertainties. Additionally, the results are compared with hydrodynamic model calculations. Although the model predictions provide a qualitative explanation of the experimental results, they overestimate the data for some observables. This is particularly true for correlators that are sensitive to the nonlinear response of the medium to initial-state anisotropies in the collision system. As these new correlators provide unique information—independent of flow amplitudes—their usage in future model developments can further constrain the properties of the strongly interacting matter created in ultrarelativistic heavy-ion collisions.

We investigate the entanglement in two-quasiparticle plus triaxial-rotor model for the particle-hole configuration $\pi {\left(1h_{11/2}\right)}^1\otimes \nu {\left(1h_{11/2}\right)}^{-1}$, the particle-particle configuration $\pi {\left(1h_{11/2}\right)}^1\otimes \nu {\left(1h_{11/2}\right)}^1$, and two-proton particles configuration $\pi {\left(1h_{11/2}\right)}^2$ for different values of the triaxiality parameter. The entanglement between the angular momenta of the two quasiparticles and the total angular momentum is quantified by the three bipartite concurrences $\mathcal{C}$ of one type of angular momentum with the other two angular momenta and the area $\mathcal{F}$ of the triangle formed by the bipartite concurrences. Collective chiral and wobbling modes are identified for $\gamma >{15}^{\circ }$ via spin coherent state (SCS) maps and spin squeezed state (SSS) plots. Their entanglement increases from moderate values at the band head to near-maximal values at $I=20$. The area $\mathcal{F}$ of the chiral partners changes order as function of $I$ which reflects the crossing of the partner bands as a signature of chirality. For the $\pi {\left(1h_{11/2}\right)}^2$ configuration, the antisymmetrization required by the Pauli exclusion principle causes strong entanglement between the two protons, which significantly amplifies the area $\mathcal{F}$. For $\gamma <{15}^{\circ }$, the lowest bands become various uniformly rotating quasiparticle configurations, which have large values of $\mathcal{F}$ for all values $I$.

The superheavy nuclei push the periodic table of the elements and the chart of the nuclides to their limits, providing a unique laboratory for studies of the electron-nucleus interactions. The most important weak decay mode in known superheavy nuclei is electron capture (EC). In the standard calculations of EC, the lepton wave functions are usually considered in the lowest-order approximation. In this work, we investigate the sensitivity of EC rates on the choice of the electron wave functions by (i) assuming the single-particle approximation for the electron wave functions, and (ii) carrying out Dirac-Hartree-Fock (DHF) calculations. The nuclear response is generated based on the state-of-the-art quasiparticle random phase approximation employing relativistic nuclear energy density functional theory. We show that using the improved lepton wave functions reduces the EC rates up to 40% in the superheavy nucleus oganesson ($Z=118$). Interestingly, because of screening effects, the difference between the EC rates obtained with the DHF and single-particle calculations is fairly small.

The exploration of low-lying excitation energies of atomic nuclei remains a pivotal area of nuclear physics research due to its unique capacity to uncover new physics phenomena, especially in regions far from stability. In this work, the state-of-the-art efficiency machine-learning algorithm Light Gradient Boosting Machine is applied for the first time to investigate low-lying excitation energies of $0_2^{+}$, $0_3^{+}$, and $3_1^{-}$ states in even-even nuclei. These particular excitations serve as crucial probes for quantifying shape coexistence and octupole deformation of nuclei. Our results are in good agreement with experimental data, achieving accuracy factors of 1.10, 1.12, and 1.07 for the $0_2^{+}$, $0_3^{+}$, and $3_1^{-}$ states, respectively. This represents a significant improvement over the predictions using the theoretical models calculations, as well as over previous machine learning approaches. The predictive capability of our machine learning methodology is further validated using 14 newly measured data points that are not used in the training set, demonstrating good agreement between the machine learning predictions and experimental data. Additionally, we encoded the significance ranking of input physics features relevant to the properties of low-lying excited states. The interpretable nature of present algorithm showcased robust performance, enabling timely and effective interventions that could enhance outcomes.

In this work, we address the problem of longitudinal spin polarization of the $\mathrm{\Lambda }$ hyperons produced in relativistic heavy-ion collisions. We combine a relativistic kinetic-theory framework that includes spin degrees of freedom treated in a classical way with the freeze-out parametrization used in previous investigations. The use of the kinetic theory allows us to incorporate dissipative corrections (due to the thermal shear and gradients of thermal vorticity) into the Pauli-Lubanski vector that determines spin polarization and can be directly compared with the experimental data. As in earlier similar studies, it turns out that a successful description of data can only be achieved with additional assumptions—in our case, they involve the use of projected thermal vorticity and a suitably adjusted time for spin relaxation (${\tau }_s$). From our analysis, we find that ${\tau }_s\sim 5\mathrm{fm}/c$, which is comparable with other estimates.

The description of quantum many-body dynamics is extremely challenging on classical computers, as it can involve many degrees of freedom. However, the time evolution of quantum states is a natural application for quantum computers that are designed to efficiently perform unitary transformations. In this paper, we study quantum algorithms for response functions, relevant for describing different reactions governed by linear response. We focus on nuclear-physics applications and consider a qubit-efficient mapping on the lattice, which can efficiently represent the large volumes required for realistic scattering simulations. For the case of a contact interaction, we develop an algorithm for time evolution based on the Trotter approximation that scales logarithmically with the lattice size and is combined with quantum phase estimation. We eventually focus on the nuclear two-body system and a typical response function relevant for electron scattering as an example. We also investigate ground-state preparation and examine the total circuit depth required for a realistic calculation and the hardware noise level required to interpret the signal.

Low-energy spectra in the isotopic chain ${}^{250-262}\mathrm{No}$ are systematically investigated within the fully self-consistent Quasiparticle Random-Phase-Approximation (QRPA) using Skyrme forces SLy4, SLy6, SkM*, and SVbas. QRPA states of multipolarity $\lambda \mu =20$, 22, 30, 31, 32, 33, 43, 44, and 98 are considered. The main attention is paid to isotopes ${}^{252}\mathrm{No}$ and ${}^{254}\mathrm{No}$ where the most extensive experimental spectroscopic information is available. In these two nuclei, a reasonable description of $K^{\pi }=8^{-},2^{-}$, and $3^{+}$ isomers is obtained with forces SLy4 and SLy6. The disputed $8^{-}$ isomer in ${}^{254}\mathrm{No}$ is assigned as neutron two-quasiparticle configuration $nn[734\uparrow ,613\uparrow ]$. The isomers are additionally analyzed using Skyrme functionals UNEDF1, UNEDF2, and ${\mathrm{UNEDF1}}^{\mathrm{SO}}$. At the energies 1.2–1.4 MeV, the 2qp $K$ isomers $4^{-},7^{-}$ in ${}^{252}\mathrm{No}$ and $4^{-},6^{-},7^{-}$ in ${}^{254}\mathrm{No}$ are also predicted. In ${}^{254}\mathrm{No}$, the $K^{\pi }=3^{+}$ isomer should be accompanied by the nearby $K^{\pi }=4^{+}$ counterpart. It is shown that, in the chain ${}^{250-262}\mathrm{No}$, some features of ${}^{252}\mathrm{No}$ and ${}^{254}\mathrm{No}$ should exhibit essential irregularities caused by a noticeable shell gap in the neutron single-particle spectrum and corresponding reduction of the neutron pairing. In particular, low-energy pairing vibrational $K^{\pi }=0^{+}$ states in ${}^{252,254}\mathrm{No}$ are predicted.

The elementary fragmentation function that describes the process $q\to \pi$ is predicted by applying crossing and charge symmetry to the cut diagram of the pion valence quark distribution function. This elementary probability distribution defines the ladder-kernel of a quark jet fragmentation equation, which is solved self-consistently to obtain the full pion fragmentation function. The hadronization into a pion employs the complete Poincaré invariant Bethe-Salpeter wave function, though the overwhelming contribution to the fragmentation function is due to the leading Bethe-Salpeter amplitude. Compared to a Nambu–Jona–Lasinio model prediction, the fragmentation function we obtain is enhanced in the range $z\lesssim 0.8$ but otherwise in good qualitative agreement. The full pion fragmentation function is overall greater than the elementary fragmentation function below $z\lesssim 0.6$.

A time-dependent wave-packet method is devised to compute three-particle rearrangement and breakup amplitudes over a wide range of collision energies from a single wave-packet solution of the time-dependent Faddeev equations (TDFE). The TDFE is solved in momentum space for a given initial wave packet using finite-element-type discretizations of the Jacobi momenta in terms of local basis functions. Central difference formula for the time derivative is used for the time propagation step. Projection of the postcollision wave packet on the two-particle bound and continuum states yield state-to-state (sharp energy) rearrangement and breakup S matrices, respectively. The proposed method is tested on a three-body model that is often used as a benchmark to compare different computational approaches to three-particle problem. The wave-packet results for rearrangement are in good agreement with the reference results from a time-independent calculation. With the rather coarse discretization grid used in the present calculations, one is able to recover the general qualitative features of the breakup process, but quantitatively the state-to-state breakup results are not on par with the rearrangement results.