This paper reports on the results of $(n,n^{\prime }\gamma )$ and $(p,p^{\prime }\gamma )$ cross section measurements on nickel performed at the Geel Electron Linear Accelerator of the European Commission, Joint Research Centre (Geel) and at the 9-MV Tandem Accelerator of Horia Hulubei National Institute for Physics and Nuclear Engineering (Bucharest-Magurele), respectively. The main goal was to reliably measure with small uncertainty the most intense transitions arising from the inelastic channel. Comparisons are performed between the extracted results, nuclear reaction model calculations using default parameter values, and previously reported measurements, if available. The broader goal of this paper is related to our study on the possibility of inferring neutron inelastic cross sections from the proton-induced ones, in this case for ${}^{58}\mathrm{Ni}$. We show that—by making use of the Lane consistency of the nucleon optical model potential and of the constraints offered by the proton data—one can extract a neutron-target potential that better describes the experimental data, as compared to the calculation with default neutron parameters. We also discuss relevant issues and still open questions of our calculations along with future plans for mitigation.

Background: It is challenging to distinguish between fusion-fission and quasifission experimentally. To determine the characteristics of quasifission processes associated with dominant phenomena in heavy-ion collisions is important for estimating precisely the fusion cross section, which is relevant to the synthesis of new elements. We classified fusion-fission and quasifission processes theoretically in the past for an accurate assessment of the fusion cross section [Y. Aritomo and M. Ohta, Nucl. Phys. A 744, 3 (2004)]. However, no detailed analysis focused on each process was performed.

Purpose: In this work, we aimed to analyze the dynamical characteristics of quasifission processes in terms of the Langevin equation model. We specify the quasifission processes, and analyze the scission configuration. Finally, we clarify the origin of several modes included in quasifission.

Method: The calculation framework is the multidimensional dynamical model of nucleus-nucleus collisions based on the Langevin equations.

Results: It is shown that several quasifission modes exist leading to different fragment deformations. The timescale of the quasifission process differs for several different modes. Each scission configuration and total kinetic energy also differ.

Conclusions: The different quasifission modes are caused by the neck relaxation controlling the mass drift toward symmetry. This means that it is possible to discuss the time-dependent functional form of the neck parameter $\epsilon$ for the quasifission process in the framework of the dynamical model based on Langevin equations.

Three parametrizations DOPS1, DOPS2, and DOPS3 (named after the Department of Physics Shimla) of the relativistic mean field model have been proposed with the inclusion of all possible self and mixed interactions between the scalar-isoscalar ($\sigma$), vector-isoscalar ($\omega$), and vector-isovector ($\rho$) mesons up to quartic order. The generated parameter sets are in harmony with the finite and bulk nuclear matter properties. A set of equations of state (EOSs) composed of pure hadronic (nucleonic) matter and nucleonic with quark matter (hybrid EOSs) for superdense hadron-quark matter in $\beta$ equilibrium is obtained. The quark matter phase is calculated by using the three-flavor Nambu-Jona-Lasinio (NJL) model. The maximum mass of a nonrotating neutron star with DOPS1 parametrization is found to be around $2.6M\odot$ for the pure nucleonic matter, which satisfies the recent gravitational wave analysis of GW190814 [Abbott et al., Astrophys. J. Lett. 896, L44 (2020)] with possible maximum mass constraint indicating that the secondary component of GW190814 could be a nonrotating heaviest neutron star composed of pure nucleonic matter. EOSs computed with the DOPS2 and DOPS3 parametrizations satisfy the x-ray observational data [Steiner et al., Astrophys. J. 722, 33 (2010)] and the recent observations of GW170817 maximum mass constraint of a stable nonrotating neutron star in the range $2.01\pm 0.04–2.16\pm 0.03M\odot$ [Rezzolla et al., Astrophys. J. Lett. 852, L25 (2018)] and also in good agreement with constraints on mass and radius measurement for PSR $\mathrm{J}0740+6620$ (NICER) [Riley et al., Astrophys. J. Lett. 918, L27 (2021); Miller et al., Astrophys. J. Lett. 918, L28 (2021)]. The hybrid EOSs obtained with the NJL model also satisfy astrophysical constraints on the maximum mass of a neutron star from PSR J1614-2230 [Demorest et al., Nature (London) 467, 1081 (2010)]. We also present the results for dimensionless tidal deformability, $\mathrm{\Lambda }$ which are consistent with the waveform models analysis of GW170817.

Lifetimes or lifetime limits of a small number of excited states of the sulfur isotopes with mass numbers $A=35$, 36, 37, and 38 have been measured using the differential recoil-distance method. The isotopes of sulfur were populated in binary grazing reactions initiated by a beam of ${}^{36}\mathrm{S}$ ions of energy 225 MeV incident on a thin ${}^{208}\mathrm{Pb}$ target which was mounted in the Cologne plunger apparatus. The combination of the PRISMA magnetic spectrometer and an early implementation of the AGATA $\gamma$-ray tracking array was used to detect $\gamma$ rays in coincidence with projectile-like nuclear species. Lifetime measurements of populated states were measured within the range from about 1 to 100 ps. The number of states for which lifetime measurements or lifetime limits were possible was limited by statistics. For ${}^{35}\mathrm{S}$, the lifetime was determined for the first $1/2^{+}$ state at 1572 keV; the result is compared with a previous published lifetime value. The lifetime of the $3^{-}$ state of ${}^{36}\mathrm{S}$ at 4193 keV was determined and compared with earlier measurements. No previous lifetime information exists for the ($6^{+}$) state at 6690 keV; a lifetime measurement with large associated error was made in the present work. For ${}^{37}\mathrm{S}$, the states for which lifetime limits were established were those at 646 keV with $J^{\pi }=3/2^{-}$ and at 2776 keV with $J^{\pi }=11/2^{-}$; there are no previously published lifetime values for excited states of ${}^{37}\mathrm{S}$. Finally, a lifetime limit was established for the $J^{\pi }=\left(6^{+}\right)$ state of ${}^{38}\mathrm{S}$ at 3675 keV; no lifetime information exists for this state in the literature. Measured lifetime values were compared with the results of state-of-the-art shell-model calculations based on the PSDPF, SDPF-U, and FSU effective interactions. In addition, nuclear magnetic-dipole and electric-quadrupole moments, branching ratios, mixing ratios, and electromagnetic transition rates, where available, have been compared with shell-model values. The current work suffers from poor statistics; nevertheless, lifetime values and limits have been possible, allowing a useful discussion of the ability of state-of-the-art shell-model calculations to reproduce the experimental results.

We present here a microscopic nuclear-structure calculation of a $\beta$-electron spectrum including all the $\beta$-decay branches of a high $Q$-value reactor fission product contributing significantly to the reactor antineutrino energy spectrum. We perform large-scale nuclear shell-model calculations of the total electron spectrum for the ${\beta }^{-}$ decay of ${}^{92}\mathrm{Rb}$ to states in ${}^{92}\mathrm{Sr}$ using a computer cluster. We exploit the $\beta$-branching data of a recent total absorption $\gamma$-ray spectroscopy (TAGS) measurement to determine the effective values of the weak axial-vector coupling, $g_{\mathrm{A}}$, and the weak axial charge, $g_{\mathrm{A}}\left({\gamma }_5\right)$. By using the TAGS data we avoid the bias stemming from the pandemonium effect which is a systematic error biasing the usual $\beta$-decay measurements. We take fully into account all the involved allowed and forbidden $\beta$ transitions, in particular the first-forbidden nonunique ones which have earlier been shown to be relevant in the context of the reactor-antineutrino flux anomaly and the unexplained spectral shoulder, the “bump,” the former one having been interpreted as one of the strongest evidence for the existence of sterile neutrinos. Here we are able to present quantitative evidence for the relevance of forbidden nonunique ${\beta }^{-}$ decays in a total $\beta$ spectrum of a fission product, in this case ${}^{92}\mathrm{Rb}$, which is one of the major contributors to the total reactor antineutrino spectral shape. We demonstrate that taking the forbidden spectral shapes fully into consideration leads for ${}^{92}\mathrm{Rb}$ to a 2.6%–4.6% reduction in the expected inverse $\beta$-decay rate at the reactor antineutrino telescopes. We also confirm by our calculation of a total $\beta$-electron spectrum that the forbidden transitions can contribute to the formation of the spectral bump in the reactor-antineutrino flux profile.

The negative-parity band structure built on the proton $h{}_{9/2}$ state in ${}^{199}\mathrm{Tl}$ has been established up to an excitation energy of 7 MeV and spin of (51/2)$\hslash$. The level scheme has been extended with the inclusion of fourteen new transitions de-exciting levels at high spin. The $\mathrm{\Delta }\mathit{I}=1$ $\gamma$ rays are found to be more prominently visible in the spectra when comparing to $\mathrm{\Delta }\mathit{I}=2$ transitions. Rotation alignments are evident at frequencies of 0.22 and 0.30 MeV with both being attributed to the breaking of pairs of neutrons in the $i{}_{13/2}$ subshell. Since ${}^{199}\mathrm{Tl}$ is expected to have weak oblate deformation, and lies in a transitional region where competing contributions to the spin are expected from collective rotation and the angular momentum of high-$j$ nucleons, calculations using both the principal axis cranking (PAC) and tilted axis cranking (TAC) formalisms have been performed to understand its structure. Both the PAC and TAC calculations are found to provide a satisfactory description of the evolution of excitation energies with spin. The PAC calculations give a good account of the experimental crossing frequencies and associated spins. The structure of the yrast, negative-parity band in ${}^{199}\mathrm{Tl}$ may be primarily understood in terms of the collective rotation of a moderately deformed oblate nucleus, along with contributions to the angular momentum from two pairs of rotation-aligned $i{}_{13/2}$ neutrons.

The $\alpha$-decay half-life of heavy and superheavy nuclei has been investigated using a potential barrier penetration model that adapts semiclassical WKB calculations to incorporate a coordinate-dependent effective mass for the $\alpha$ particle. This effect is a consequence of a dynamic property of nonlocality in the particle-nucleus interaction, as implemented in the barrier tunneling calculations of [N. Teruya, S. B. Duarte, and M. M. N. Rodrigues, Phys. Rev. C 93, 024606 (2016)]. Calculations have been performed for a recent set of experimental data of 255 $\alpha$-emitting nuclides, all selected with angular momentum $\ell =0$ experimentally assigned. Results show a good agreement when compared to experimental half-life data, obtaining a standard deviation of $\sigma =0.306$ and fully satisfying the universal systematics, namely, new universal plot and universal decay law systematics, of $\alpha$ decay. Additionally, the present model has been applied to make half-life predictions for 34 possible new $\alpha$-decay cases.

An existing parametrization of the simple effective interaction (SEI) that is able to reproduce the experimentally known crossing between the $2p_{3/2}$ and $1f_{5/2}$ single-particle (s.p.) proton levels in neutron-rich Ni isotopes has been generalized. We have added a short-range tensor force in order to describe the observed gaps between the $1h_{11/2}$ and $1g_{7/2}\mathrm{s}.\mathrm{p}.$ proton levels in the Sn isotopic chain and between the $1i_{13/2}$ and $1h_{9/2}\mathrm{s}.\mathrm{p}.$ neutron levels in $N=82$ isotones without compromising the good agreement with the splittings in the Ni isotopes. Different scenarios where tensor effects are relevant are considered with the new interaction and its predictions are compared with results from other mean-field models and experimental data where available.

Previously we proposed a new approach of exciting the ${}^{229}\mathrm{Th}$ nucleus using laser-driven electron recollision [Wang, Zhou, Liu, and Wang, Phys. Rev. Lett. 127, 052501 (2021)]. The current article is aimed at elaborating the method by explaining further theoretical details and presenting extended new results. The method has also been improved by adopting the electronic excitation cross sections calculated recently by Tkalya [Tkalya, Phys. Rev. Lett. 124, 242501 (2020)]. The new cross sections are obtained from Dirac distorted-wave calculations instead of from Dirac plane-wave calculations as we used previously. The distorted-wave cross sections are shown to be 5 to 6 orders of magnitude higher than the plane-wave results. With the excitation cross sections updated, the probability of isomeric excitation of ${}^{229}\mathrm{Th}$ from electron recollision is calculated to be on the order of ${10}^{-12}$ per nucleus per (femtosecond) laser pulse. The dependency of the excitation probability on various laser parameters is calculated and discussed, including the laser intensity, the laser wavelength, and the laser pulse duration.

Breakup reactions are one of the favored probes to study loosely bound nuclei, particularly those in the limit of stability forming a halo. In order to interpret such breakup experiments, the continuum discretized coupled channel method is typically used. In this study, the first Bayesian analysis of a breakup reaction model is performed. We use a combination of statistical methods together with a three-body reaction model (the continuum discretized coupled channel method) to quantify the uncertainties on the breakup observables due to the parameters in the effective potential describing the loosely bound projectile of interest. The combination of tools we develop opens the path for a Bayesian analysis of not only breakup processes, but also a wide array of complex processes that require computationally intensive reaction models.

Nuclear mass measurements of isotopes are key to improving our understanding of nuclear structure across the chart of nuclides, in particular, for the determination of the appearance or disappearance of nuclear shell closures. We present high-precision mass measurements of neutron-rich Ca, Ti, and V isotopes performed at TRIUMF's Ion Trap for Atomic and Nuclear science (TITAN) and the Low Energy Beam and Ion Trap (LEBIT) facilities. These measurements were made using the TITAN multiple-reflection time-of-flight mass spectrometer (MR-ToF-MS) and the LEBIT 9.4T Penning trap mass spectrometer. In total, 13 masses were measured, 8 of which represent increases in precision over previous measurements. These measurements refine trends in the mass surface around $N=32$ and $N=34$, and support the disappearance of the $N=32$ shell closure with increasing proton number. Additionally, our data do not support the presence of a shell closure at $N=34$.

In the decay of an excited heavy nucleus, both the fission or evaporation residue (ER) cross sections and the fission time are determined by the competition between the various evaporation channels and fission. Statistical model (SM) calculations for several heavy-ion-induced fusion-fission reactions are presented which reproduce the fission or ER excitation functions. The corresponding calculated fission times are found to depend upon the compound nuclei and their excitation energies. The multichance fission probabilities and the corresponding fission times are also obtained, and they are shown to depend sensitively on the shell correction energies and the neutron separation energies of the compound nuclei involved. The experimental neutron multiplicities are reproduced by adjusting the saddle-to-scission transition time interval. An additional delay time for compound nuclear formation is found necessary to fit the experimental neutron multiplicities for a system with higher entrance channel mass symmetry.

In this article we investigate ${}^{40,48}\mathrm{Ca}+{}^{40,48}\mathrm{Ca}$ peripheral and semiperipheral reactions at 35 MeV/nucleon. Data were obtained using the unique coupling of the VAMOS high acceptance spectrometer and the INDRA charged particle multidetector. The spectrometer allowed high-resolution measurement of charge, mass, and velocity of the cold projectile-like fragment (PLF), while the INDRA detector recorded coincident charged particles with nearly $4\pi$ acceptance. The measured isotopic composition of the PLF identified in VAMOS and the average light charged particle (LCP) multiplicities are promising observables to study the isospin diffusion. The detection of the PLF in coincidence with LCP allows the reconstruction of the mass, charge, and excitation energy of the associated initial quasiprojectile nuclei (QP), as well as the extraction of apparent temperatures. We investigate the suitability of the isoscaling method with the PLF and the experimental reconstructed QP. The extracted $\alpha$ and $\mathrm{\Delta }$ isoscaling parameters present a dependence on the considered system combination that could justify their use as a surrogate for isospin asymmetry in isospin transport studies. The reconstruction of the QP allows us to observe an evolution of the $\alpha /\mathrm{\Delta }$ with the size of the QP, the latter being consistent with a strong surface contribution to the symmetry energy term in finite nuclei. This leads to the conclusion that the reconstruction of the primary source is mandatory for the study of the symmetry energy term based on the isoscaling method for such reactions.

Background: A nonperturbative charm production contribution, known as intrinsic charm, was predicted in the early 1980s. Recent results have provided new evidence for its existence but further confirmation is needed.

Purpose: $J/\psi$ and $\overline{D}$ meson production are calculated with a combination of perturbative QCD and intrinsic charm to determine the best energy range to study intrinsic charm production.

Methods: $J/\psi$ and $\overline{D}$ meson production are calculated in perturbative QCD to next-to-leading order in the cross section. Cold nuclear matter effects, including nuclear modification of the parton densities and $p_T$ broadening by multiple scattering, are taken into account in the production of both; absorption by nucleons is also included for the $J/\psi$. Contributions from intrinsic charm are calculated assuming production from a $|uudc\overline{c}\rangle$ Fock state.

Results: The $J/\psi$ and $\overline{D}$ meson rapidity and $p_T$ distributions are calculated as a function of rapidity and transverse momentum $p_T$ over a wide range of center-of-mass energies with and without intrinsic charm in $p+p$ collisions. The nuclear modification factor, $R_{pA}$, is also calculated for $p+\mathrm{Pb}$ interactions at appropriate energies. Previous fixed-target data as a function of Feynman $x$, $x_F$, are also compared to calculations within the approach. Good agreement with the data is found when intrinsic charm is included.

Conclusions: The intrinsic charm signal may be largest at midrapidity for future low energy fixed target experiments such as the proposed $\mathrm{NA}60+$.

${}^{180m}\mathrm{Ta}$ is a naturally abundant quasistable nuclide and the longest-lived nuclear isomer known to date. It is of interest, among others, for the search for dark matter, for the development of a $\gamma$ laser, and for astrophysics. So far, its excitation energy has not been measured directly but has been based on an evaluation of available nuclear reaction data. We have determined the excitation energy of this isomer with high accuracy using the Penning-trap mass spectrometer JYFLTRAP. The determined mass difference between the ground and isomeric states of ${}^{180}\mathrm{Ta}$ yields an excitation energy of 76.79(55) keV for ${}^{180m}\mathrm{Ta}$. This is the first direct measurement of the excitation energy and provides a better accuracy than that of the previous evaluation value, 75.3(14) keV.

We extend the improved density-dependent cluster model (DDCM+) of our recent work [Wang et al., Phys. Rev. C 105, 024327 (2022)] to study the favored $\alpha$ decays of odd-$A$ and odd-odd nuclei with $Z⩾82$. In this work, the effective $\alpha$-core interactions are determined using the double-folding potential with a realistic M3Y-Reid nucleon-nucleon interaction plus proton-proton Coulomb interaction, in which a deformation-dependent diffuseness correction is validated to address the surface anisotropy and polarization effects in nucleon density distribution. It is found that calculations within the anisotropic diffuseness would yield longer calculated $\alpha$ decay half-lives and suggest larger estimated $\alpha$-preformation factors, which is quite consistent with the conclusions obtained for the even-even $\alpha$ emitters. Meanwhile, the theoretical half-lives agree very well with the experimental data for the favored $\alpha$ decays of the odd-$A$ and odd-odd nuclei with a mean factor of 1.94 and 1.61, respectively. Remarkably, the experimental $\alpha$-decay half-life of the new thorium isotope ${}^{207}\mathrm{Th}$ [Yang et al., Phys. Rev. C 105, L051302 (2022)] is also well reproduced with a factor of about 2.50. Furthermore, we present the quantitative predictions on the favored $\alpha$-decay half-lives of ${}^{293,294}119$ and ${}^{294,295}120\alpha$-decay chains in this work, which are expected to serve as useful references for the synthesis of new isotopes in the future.

An investigation of the isospin equilibration process in the reactions ${}^{58,64}\mathrm{Ni}+{}^{58,64}\mathrm{Ni}$ at two bombarding energies in the Fermi regime (32 and 52 MeV/nucleon) is presented. Data have been acquired during the first experimental campaign of the coupled INDRA-FAZIA apparatus in GANIL. Selecting from peripheral to semicentral collisions, both the neutron content of the quasiprojectile residue and that of the light ejectiles coming from the quasiprojectile evaporation have been used as probes of the dynamical process of isospin diffusion between projectile and target for the asymmetric systems. The isospin transport ratio technique has been employed. The relaxation of the initial isospin imbalance with increasing centrality has been clearly evidenced. The isospin equilibration appears stronger for the reactions at 32 MeV/nucleon, as expected due to the longer projectile-target interaction time than at 52 MeV/nucleon. Coherent indications of isospin equilibration come from the quasiprojectile residue characteristics and from particles ascribed to the quasiprojectile decay.

Recent beam energy scan experiments at the BNL Relativistic Heavy Ion Collider by the STAR Collaboration [Phys. Lett. B 827, 137003 (2022) and Phys. Rev. Lett. 128, 202303 (2022)] found that hadronic interactions dominate the collective flow and the proton cumulant ratios are driven by baryon number conservation in a region of high baryon density in $\sqrt{s_{NN}}=3$ GeV $\mathrm{Au}+\mathrm{Au}$ reactions, indicating that the dense medium formed in such collisions is likely hadronic matter. Within an updated a relativistic transport model with momentum dependent isoscalar and isovector single-nucleon mean-field potentials corresponding to different symmetry energies at suprasaturation densities, the $n/p, {\pi }^{-}/{\pi }^{+}, K_s^0/K^{+}, {\mathrm{\Sigma }}^{-}/{\mathrm{\Sigma }}^{+}$, and ${\mathrm{\Xi }}^{-}/{\mathrm{\Xi }}^0$ ratios are studied for central $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=3$ GeV, where the maximum central density reaches about $(3.6–4.0){\rho }_0$. The doubly strange ${\mathrm{\Xi }}^{-}/{\mathrm{\Xi }}^0$ ratio is found to have the strongest sensitivity to the variation of high-density nuclear symmetry energy. Thus, the ${\mathrm{\Xi }}^{-}/{\mathrm{\Xi }}^0$ ratio in relativistic heavy-ion reactions at $\sqrt{s_{NN}}\sim 3$ GeV may help probe sensitively the poorly known symmetry energy of dense neutron-rich matter critically important for understanding various properties of neutron stars.

Nuclear masses are predicted with the Bayesian neural networks by learning the mass surface of even-even nuclei and the correlation energies to their neighboring nuclei. By keeping the known physics in various sophisticated mass models and performing the delicate design of neural networks, the proposed Bayesian machine learning mass model achieves an accuracy of $84\mathrm{keV}$, which crosses the accuracy threshold of the $100\mathrm{keV}$ in the experimentally known region. It is also demonstrated the corresponding uncertainties of mass predictions are properly evaluated, while the uncertainties increase by about $50\mathrm{keV}$ each step along the isotopic chains towards the unknown region. The shell structures in the known region are well described and several important features in the unknown region are predicted, such as the new magic numbers around $N=40$, the robustness of $N=82$ shell, the quenching of $N=126$ shell, and the smooth separation energies around $N=104$.