We analyze the origin of the unexpected deep subbarrier heavy-ion fusion hindrance in ${}^{64}\mathrm{Ni}+{}^{100}\mathrm{Mo}$, ${}^{64}\mathrm{Ni}+{}^{64}\mathrm{Ni}$, and ${}^{28}\mathrm{Si}+{}^{64}\mathrm{Ni}$ reactions. Our analysis is based on the improved coupled-channels description, implemented by means of the finite element method. With the aid of the Woods-Saxon potential the experimental cross sections and the $S$ factors of these reactions are remarkably well reproduced within the sudden approximation approach. We found that accounting for the nondiagonal matrix elements of the coupling matrix, traditionally neglected in the conventional coupled-channels approaches in setting the left boundary conditions inside the potential pocket, and its minimal value are crucially important for the interpretation of experimental data. We found as well a good agreement with the general trend of the experimental data for the $S$ factor of the fusion reaction ${}^{12}\mathrm{C}+{}^{12}\mathrm{C}$, which has no pronounced maximum for this system.

Fission fragments' charge and mass distribution is an important input to applications ranging from basic science to energy production or nuclear nonproliferation. In simulations of nucleosynthesis or calculations of superheavy elements, these quantities must be computed from models, as they are needed in nuclei where no experimental information is available. Until now, standard techniques to estimate these distributions were not capable of accounting for fine-structure effects, such as the odd-even staggering of the charge distributions. In this work, we combine a fully microscopic collective model of fission dynamics with a recent extension of the particle number projection formalism to provide the highest-fidelity prediction of the primary fission fragment distributions for the neutron-induced fission of ${}^{235}\mathrm{U}$ and ${}^{239}\mathrm{Pu}$. We show that particle-number projection is an essential ingredient to reproduce odd-even staggering in the charge yields and benchmark the performance of various empirical probability laws that could simulate its effect. This new approach also enables for the first time the realistic determination of two-dimensional isotopic yields within nuclear density functional theory.

We present a possibility of direct resonance production of pionic atoms (Coulomb bound states of a negative pion and a nucleus) with a rate of up to $\approx {10}^{10}$ per second using the gamma-ray beams from the Gamma Factory.

A detailed investigation on the relative isotopic distributions has been carried out for the first time in case of even-even correlated fission fragments for the ${}^{235}\mathrm{U}(n_{\text{th}},f$) fission reaction. High-statistics data were obtained in a prompt $\gamma$-ray spectroscopy measurement during the EXILL campaign at ILL, Grenoble, France. The extensive off-line analysis of the coincidence data have been carried out using four different coincidence methods. Combining the results from two-dimensional $\gamma \text{−}\gamma$ and three-dimensional $\gamma \text{−}\gamma \text{−}\gamma$ coincidence analysis, a comprehensive picture of the relative isotopic yield distributions of the even-even neutron-rich fission fragments has emerged. The experimentally observed results have been substantiated by the theoretical calculations based on a novel approach of isospin conservation, and a reasonable agreement has been obtained. The calculations following the semiempirical GEF model have also been carried out. The results from the GEF model calculations are found to be in fair agreement with the experimental results.

The interaction between medium-weight nuclei and a strong zeptosecond laser pulse of MeV photons is investigated theoretically. Multiple absorption of photons competes with nuclear equilibration. We investigate the sudden regime. Here the rate of photon absorption is so strong that there is no time for the nucleus to fully equilibrate after each photon absorption process. We follow the temporal evolution of the system in terms of a set of rate equations. These account for dipole absorption and induced dipole emission, equilibration (modeled in terms of particle-hole states coupled by the residual nuclear interaction), and neutron decay (populating a chain of proton-rich nuclei). Our results are compared with earlier work addressing the adiabatic regime where equilibration is instantaneous. We predict the degree of excitation and the range of nuclei reached by neutron evaporation. These findings are relevant for planning future experiments.

The lifetime of the $2^{+}$ and $9^{-}, {11}^{-}, {13}^{-}, {15}^{-}$ states in the neutron-deficient ${}^{110}\mathrm{Te}$ was measured for the first time using the recoil distance Doppler shift technique. The reported value of the reduced transition probability $B(E2;0_{g.s}^{+}\to 2^{+})=4.3\left(8\right)\times {10}^3{e}^{2}f{m}^4$ supports the systematic for even-mass Te isotopes and was interpreted in the framework of the large-scale shell model and cranked shell model calculations. The measured reduced transition probabilities in the negative-parity yrast band revealed the upward trend towards the high spins. The enhanced collectivity is discussed in terms of the tilted axis cranking approach and the symmetry configuration mixing method with the Gogny D1S interaction.

The total fusion cross section for the ${}^{17}\mathrm{F}+{}^{12}\mathrm{C}$ system at incident energies near the top of the Coulomb barrier was studied using the newly developed Encore active-target detector at Florida State University. The ${}^{17}\mathrm{F}$ nucleus exhibits interesting nuclear structure properties in that although it has a low threshold against ${}^{17}\mathrm{F}\to {}^{16}\mathrm{O}+p$ breakup $(S_p=600\mathrm{keV})$, the valence proton is in the $1d_{5/2}$ shell in the ground state so that the nuclear matter radius is predicted to be similar to that of the ${}^{16}\mathrm{O}$ core. By contrast, the low-lying $1/2^{+}$ first excited state (bounded by 105 keV) with the valence proton in the $2s_{1/2}$ shell is considered to be a proton halo. In this paper possible influences of both the weak binding and the halo nature of the excited state on the total fusion cross section were investigated. The new data reported here complement existing measurements for the total fusion of ${}^{17}\mathrm{F}$ with heavy $\left({}^{208}\mathrm{Pb}\right)$ and medium mass (${}^{58}\mathrm{Ni}$) targets by extending the range of systems studied to one where Coulomb effects should be minimal. Total fusion cross sections for the stable counterpart systems ${}^{16}\mathrm{O}+{}^{12}\mathrm{C}$ and ${}^{19}\mathrm{F}+{}^{12}\mathrm{C}$ were also measured to enable a systematic comparison. No significant influence of either the weak binding or the halo nature of the ${}^{17}\mathrm{F}1/2^{+}$ first excited state on the above barrier total fusion excitation function was observed when compared with the stable counterpart systems.

We study the fragmentation (far forward/backward) region of heavy-ion collisions by considering an at-rest nucleus which is struck by a relativistic sheet of colored glass. By means of a simple classical model, we calculate the subsequent evolution of baryons and the associated radiation. We confirm that the struck nucleus undergoes a compression and that the dynamics of the early times of the collision are best described by two separate fluids as the produced radiation's velocity distribution is very different to the velocity distribution of the matter in the struck nucleus.

Proton-rich nuclei possess unique properties in the nuclear chart. Due to the presence of both continuum coupling and Coulomb interaction, phenomena such as halos, Thomas-Ehrman shift, and proton emissions can occur. Relevant experimental data are difficult to obtain, so that theoretical calculations are needed to understand nuclei at drip lines and to guide experimentalists. In particular, the ${}^{16}\mathrm{Ne}$ and ${}^{18}\mathrm{Mg}$ isotopes are supposed to be one-proton and/or two-proton emitting nuclei, but associated experimental data are either incomplete or even unavailable. Consequently, we performed Gamow shell model calculations of carbon isotones bearing $A=15\text{–}18$. Isospin-symmetry breaking occurring in carbon isotones and isotopes is also discussed. It is hereby shown that the mixed effects of continuum coupling and Coulomb interaction at drip lines generate complex patterns in isospin multiplets. Added to that, it is possible to determine the one-proton and two-proton widths of ${}^{16}\mathrm{Ne}$ and ${}^{18}\mathrm{Mg}$. Obtained decay patterns are in agreement with those obtained in previous experimental and theoretical works. Moreover, to our knowledge, this is the first theoretical calculation of binding energy and partial decay widths of ${}^{18}\mathrm{Mg}$ in a configuration interaction picture.

Background: The neutron-rich $A\approx 100, N\approx 62$ mass region is important for both nuclear structure and nuclear astrophysics. The neutron-rich segment of this region has been widely studied to investigate shape coexistence and sudden nuclear deformation. However, the absence of experimental data of more neutron-rich nuclei poses a challenge to further structure studies. The derivatives of the mass surface, namely, the two-neutron separation energy and neutron pairing gap, are sensitive to nuclear deformation and shed light on the stability against deformation in this region. This region also lies along the astrophysical $r$-process path, and hence precise mass values provide experimental input for improving the accuracy of the $r$-process models and the elemental abundances.

Purpose: (a) Changes in deformation are searched for via the mass surface in the $A=104$ mass region at the $N=66$ mid-shell crossover. (b) The sensitivity of the astrophysical $r$-process abundances to the mass of Rb and Sr isotopic chains is studied.

Methods: Masses of radioactive Rb and Sr isotopes are precisely measured using a Multiple-Reflection Time-of-Flight Mass Separator (MR-TOF-MS) at the TITAN facility. These mass values are used to calculate two-neutron separation energies, two-neutron shell gaps and neutron pairing gaps for nuclear structure physics, and one-neutron separation energies for fractional abundances and astrophysical findings.

Results: We report the first mass measurements of ${}^{103}\mathrm{Rb}$ and ${}^{103–105}\mathrm{Sr}$ with uncertainties of less than 45 keV/$c^2$. The uncertainties in the mass excess value for ${}^{102}\mathrm{Rb}$ and ${}^{102}\mathrm{Sr}$ have been reduced by a factor of 2 relative to a previous measurement. The deviations from the AME extrapolated mass values by more the 0.5 MeV have been found.

Conclusions: The metrics obtained from the derivatives of the mass surface demonstrate no existence of a subshell gap or onset of deformation in the $N=66$ region in Rb and Sr isotopes. The neutron pairing gaps studied in this work are lower than the predictions by several mass models. The abundances calculated using the waiting-point approximation for the $r$ process are affected by these new masses in comparison with AME2016 mass values.

In this paper, we present a computation of the rates of strangeness-changing processes and the resultant bulk viscosity in matter at the densities and temperatures typical of neutron star mergers. To deal with the high temperature in this environment, we go beyond the Fermi surface approximation in our rate calculations and numerically evaluate the full phase space integral. We include processes where quarks move between baryons via meson exchange: These have generally been omitted in previous analyses but provide the dominant contribution to the rates of strangeness-changing processes and the bulk viscosity. The calculation of these rates is an essential step toward any calculation of dissipation mechanisms in hyperonic matter in mergers. As one application, we calculate the dissipation times for density oscillations at the frequencies seen in merger simulations. We find that hyperon bulk viscosity for temperatures in the MeV regime can probably be neglected in this context but becomes highly relevant for keV-range temperatures.

We combine the equation of state of dense matter up to twice nuclear saturation density $n_{\mathrm{sat}}$ obtained using chiral effective field theory $\left(\chi \mathrm{EFT}\right)$ and recent observations of neutron stars to gain insights about the high-density matter encountered in their cores. A key element in our study is the recent Bayesian analysis of correlated EFT truncation errors based on order-by-order calculations up to next-to-next-to-next-to-leading order in the $\chi \mathrm{EFT}$ expansion. We refine the bounds on the maximum mass imposed by causality at high densities and provide stringent limits on the maximum and minimum radii of $\sim 1.4{\mathrm{M}}_{\odot }$ and $\sim 2.0{\mathrm{M}}_{\odot }$ stars. Including $\chi \mathrm{EFT}$ predictions from $n_{\mathrm{sat}}$ to $2n_{\mathrm{sat}}$ reduces the permitted ranges of the radius of a $1.4{\mathrm{M}}_{\odot }$ star, $R_{1.4}$, by $\sim 3.5\text{km}$. If observations indicate $R_{1.4}<11.2\text{km}$, then our study implies that either the squared speed of sound $c_s^2>1/2$ for densities above $2n_{\mathrm{sat}}$ or that $\chi \mathrm{EFT}$ breaks down below $2n_{\mathrm{sat}}$. We also comment on the nature of the secondary compact object in GW190814 with mass $\simeq 2.6{\mathrm{M}}_{\odot }$ and discuss the implications of massive neutron stars $>2.1{\mathrm{M}}_{\odot }\left(2.6{\mathrm{M}}_{\odot }\right)$ in future radio and gravitational-wave searches. Some form of strongly interacting matter with $c_s^2>0.35\left(0.55\right)$ must be realized in the cores of such massive neutron stars. In the absence of phase transitions below $2n_{\mathrm{sat}}$, the small tidal deformability inferred from GW170817 lends support for the relatively small pressure predicted by $\chi \mathrm{EFT}$ for the baryon density $n_{\mathrm{B}}$ in the range $1\text{–}2n_{\mathrm{sat}}$. Together they imply that the rapid stiffening required to support a high maximum mass should occur only when $n_{\mathrm{B}}\gtrsim 1.5\text{–}1.8n_{\mathrm{sat}}$.

The ${}^{72}\mathrm{Ge}(n,\gamma )$ cross section was measured for neutron energies up to $300\mathrm{keV}$ at the neutron time-of-flight facility $\mathrm{n}\_\mathrm{TOF}$ (CERN), Geneva, for the first time covering energies relevant to heavy-element synthesis in stars. The measurement was performed at the high-resolution beamline EAR-1, using an isotopically enriched ${}^{72}\mathrm{Ge}\mathrm{O}_2$ sample. The prompt capture $\gamma$ rays were detected with four liquid scintillation detectors, optimized for low neutron sensitivity. We determined resonance capture kernels up to a neutron energy of $43\mathrm{keV}$, and averaged cross sections from 43 to $300\mathrm{keV}$. Maxwellian-averaged cross section values were calculated from $kT=5$ to $100\mathrm{keV}$, with uncertainties between $3.2\%$ and $7.1\%$. The new results significantly reduce uncertainties of abundances produced in the slow neutron capture process in massive stars.

An extensive data set for the ${}^6\mathrm{Li}+{}^{15}\mathrm{N}$ system at an energy $E_{\mathrm{c}.\mathrm{m}.}=23.1$ MeV, consisting of elastic and inelastic scattering to excited states of ${}^{15}\mathrm{N}$ and the $3_1^{+}$, $2_1^{+}$, and $1_1^{+}$ spin-orbit triplet of $L=2$, $T=0$ resonances in ${}^6\mathrm{Li}$, was analyzed with a single calculation including the ${}^6\mathrm{Li}\to \alpha +d$ breakup, excitation of the ${}^{15}\mathrm{N}$ levels, and the ${}^{15}\mathrm{N}({}^6\mathrm{Li},{}^7\mathrm{Li}){}^{14}\mathrm{N}$ one-neutron pickup reaction employing the coupled discretized continuum channel, coupled channel, and coupled reaction channel techniques, respectively. Since the experiment was performed in inverse kinematics, and owing to the specific structure properties of ${}^{15}\mathrm{N}$, it was possible to measure an angular distribution for population of the $1_1^{+}$ resonance of ${}^6\mathrm{Li}$ for the first time, without the need for time-consuming and complicated coincidence measurements through detection of the scattered ${}^{15}\mathrm{N}$. A good description of the cross sections for populating all three ${}^6\mathrm{Li}$ resonances was obtained, confirming the validity of the $\alpha +d$ cluster model of ${}^6\mathrm{Li}$. In the methodology adopted the surface absorption was mostly generated by the included couplings, and while the ${}^6\mathrm{Li}$ breakup had the most important influence on the elastic scattering, coupling to the ${}^{15}\mathrm{N}$ inelastic excitations was also found to have a significant effect, particularly at midrange angles. By contrast, the one-neutron pickup coupling had a negligible effect on the other channels.

We evaluate the viscous damping of anisotropic flow in heavy-ion collisions for arbitrary temperature-dependent shear and bulk viscosities. We show that the damping is solely determined by effective shear and bulk viscosities, which are weighted averages over the temperature. We determine the relevant weights for nucleus-nucleus collisions at $\sqrt{s_{NN}}=5.02$ TeV and 200 GeV, corresponding to the maximum Large Hadron Collider (LHC) and Relativistic Heavy Ion Collider (RHIC) energies, by running ideal and viscous hydrodynamic simulations. The effective shear viscosity is driven by temperatures below 210 MeV at RHIC and below 280 MeV at the LHC, with the largest contributions coming from the lowest temperatures, just above freeze-out. The effective bulk viscosity is driven by somewhat higher temperatures, corresponding to earlier stages of the collision. We show that at a fixed collision energy, the effective viscosity is independent of centrality and system size, to the same extent as the mean transverse momentum of outgoing hadrons. The variation of viscous damping is determined by Reynolds number scaling.

The aCORN experiment measures the neutron-decay electron-antineutrino correlation ($a$ coefficient) using a novel method based on an asymmetry in proton time-of-flight for events where the beta electron and recoil proton are detected in delayed coincidence. We report the data analysis and result from the second run at the NIST Center for Neutron Research, using the high-flux cold neutron beam on the new NG-C neutron guide end position: $a=-0.10758\pm 0.00136\left(\text{stat}\right)\pm 0.00148\left(\text{sys}\right)$. This is consistent within uncertainties with the result from the first aCORN run on the NG-6 cold neutron beam. Combining the two aCORN runs, we obtain $a=-0.10782\pm 0.00124\left(\text{stat}\right)\pm 0.00133\left(\text{sys}\right)$, which has an overall relative standard uncertainty of 1.7%. The corresponding result for the ratio of weak coupling constants $\lambda =G_A/G_V$ is $\lambda =-1.2796\pm 0.0062$.

Over the past decade the in-medium similarity renormalization group (IMSRG) approach has proven to be a powerful and versatile ab initio many-body method for studying medium-mass nuclei. So far, the IMSRG was limited to the approximation in which only up to two-body operators are incorporated in the renormalization group flow, referred to as the IMSRG(2). In this work, we extend the IMSRG(2) approach to fully include three-body operators yielding the IMSRG(3) approximation. We use a perturbative scaling analysis to estimate the importance of individual terms in this approximation and introduce truncations that aim to approximate the IMSRG(3) at a lower computational cost. The IMSRG(3) is systematically benchmarked for different nuclear Hamiltonians for ${}^4\mathrm{He}$ and ${}^{16}\mathrm{O}$ in small model spaces. The IMSRG(3) systematically improves over the IMSRG(2) relative to exact results. Approximate IMSRG(3) truncations constructed based on computational cost are able to reproduce much of the systematic improvement offered by the full IMSRG(3). We also find that the approximate IMSRG(3) truncations behave consistently with expectations from our perturbative analysis, indicating that this strategy may also be used to systematically approximate the IMSRG(3).

Gamma-ray production cross-section data have been obtained for the inelastic neutron scattering reactions ${}^{126,128,130}\mathrm{Te}(n,n^{\prime }\gamma )$ at five neutron energies between 3.6 and 10 MeV. We report data for the $\gamma$-ray energy region relevant to $0\nu \beta \beta$ decay of ${}^{130}\mathrm{Te}$ with a $Q_{\beta \beta }$ value of 2527.515 keV, assuming natural-abundance tellurium, as used at CUORE and $\mathrm{SNO}+$. The natural abundance of ${}^{130}\mathrm{Te}$, ${}^{128}\mathrm{Te}$, and ${}^{126}\mathrm{Te}$ is 34%, 32%, and 19%, respectively. For CUORE the $\gamma$-ray cascades from the excited state in ${}^{130}\mathrm{Te}$ at 2527.06 keV and in ${}^{126}\mathrm{Te}$ at 2533.85 keV are of concern. For $\mathrm{SNO}+$, accounting for its inferior energy resolution, an additional four levels are important in ${}^{130}\mathrm{Te}$, an additional nine levels in ${}^{128}\mathrm{Te}$, and an additional eight levels in ${}^{126}\mathrm{Te}$. Of these, we report neutron-induced $\gamma$-ray production cross sections for the strongest transitions: the 2581.15 keV level in ${}^{130}\mathrm{Te}$, the 2494.20, 2508.06, and 2630.14 keV levels in ${}^{128}\mathrm{Te}$, and the 2496.83 and 2585.46 keV level in ${}^{126}\mathrm{Te}$. The largest cross-section values were found for cascade $\gamma$-ray transitions to the ground state, while direct transitions to the ground state are very weak and were not observed in the present work. Both the CUORE and $\mathrm{SNO}+$ detectors, however, may not be able to distinguish between cascade transitions and direct transitions to the ground state, making the neutron-induced excitation of the 2527.06 keV state of ${}^{130}\mathrm{Te}$ in particular a potential problem for $0\nu \beta \beta$ decay searches of ${}^{130}\mathrm{Te}$, because it matches its $Q_{\beta \beta }$ value.

Background: The influence of halo structure of ${}^6\mathrm{He}$, ${}^8\mathrm{B}$, ${}^{11}\mathrm{Be}$, and ${}^{11}\mathrm{Li}$ nuclei in several mechanisms such as direct reactions and fusion is already established, although not completely understood. The influence of the ${}^{10}\mathrm{C}$ Brunnian structure is less known.

Purpose: To investigate the influence of the cluster configuration of ${}^{10}\mathrm{C}$ on the elastic scattering at an energy close to the Coulomb barrier.

Methods: We present experimental data for the elastic scattering of the ${}^{10}\mathrm{C}+{}^{208}\mathrm{Pb}$ system at $E_{\mathrm{lab}}=66$ MeV. The data are compared to the three- and the four-body continuum-discretized coupled-channels calculations assuming ${}^9\mathrm{B}+p$, ${}^6\mathrm{Be}+\alpha$, and ${}^8\mathrm{Be}+p+p$ configurations.

Results: The experimental angular distribution of the cross sections shows the suppression of the Fresnel peak that is reasonably well reproduced by the continuum-discretized coupled-channels calculations. However, the calculations underestimate the cross sections at backward angles. Couplings to continuum states represent a small effect.

Conclusions: The cluster configurations of ${}^{10}\mathrm{C}$ assumed in the present work are able to describe some of the features of the data. To explain the data at backward angles, experimental data for the breakup and an extension of theoretical formalism towards a four-body cluster seem to be in need to reproduce the measured angular distribution.

Background: Numerous studies of the ground-state decay of the pygmy dipole resonance (PDR) have been carried out in the past. However, data on the decay of the PDR to low-lying excited states is still very scarce due to limitations of the sensitivity to weak branching transitions of experimental setups.

Purpose: We present a detailed examination of the low-energy dipole response of ${}^{128}\mathrm{Te}$ and ${}^{130}\mathrm{Te}$ below their neutron separation thresholds of 8.8 and 8.5 MeV, respectively.

Methods: Photonuclear reactions with the subsequent $\gamma$-ray spectroscopy of the decay channel with continuous-energy bremsstrahlung at varying endpoint energies and linearly polarized quasimonochromatic $\gamma$-ray beams with energies ranging from 2.7 to 8.9 MeV in steps of roughly 250 keV were used for probing the decay behavior of the low-energy dipole response in ${}^{128}\mathrm{Te}$ and ${}^{130}\mathrm{Te}$. In addition, $(\vec{\gamma },{\gamma }^{\prime }{\gamma }^{\prime \prime })$ reactions were used to study the population of low-lying states of ${}^{128}\mathrm{Te}$.

Results: Spin-parity quantum numbers and reduced transition probabilities are determined for individual photo-excited states. The analysis of average decay properties for nuclear levels in narrow excitation-energy bins enable the extraction of photoabsorption cross sections, average branching ratios to the $2_1^{+}$ state, and the distinction between $E1$ and $M1$ transitions to the ground state and to the $2_1^{+}$ state accounting for resolved and unresolved transitions.

Conclusions: Above 5 MeV, the experimental data are in reasonable agreement to calculations within the quasiparticle phonon model. The major fraction of the ground-state decay channel is due to $E1$ transitions, while less than $5–10$% stem from $M1$ transitions. Furthermore, first direct experimental evidence is provided that the population of the $2_1^{+}$ state of ${}^{128}\mathrm{Te}$ via primary $\gamma$-ray transitions from excited states in the PDR region from 5 to 9 MeV is dominated by $E1$ transitions of $1^{-}$ states.