Direct and sequential breakups of the projectile in the ${}^7\mathrm{Li}+{}^{112}\mathrm{Sn}$ reaction have been measured at a beam energy of 30 MeV. Cross sections for sequential breakup of ${}^7\mathrm{Li}$ into $\alpha$ and $t$ cluster fragments via its second resonant state of $5/2^{-}$ (6.68 MeV) in the continuum have been measured for the first time along with the first resonant state ($7/2^{-}$, 4.63 MeV). Probabilities of sequential breakup proceeding through $-1n$ and $-2n$ transfer channels, i.e., (${}^7\mathrm{Li},{}^6\mathrm{Li}$) and (${}^7\mathrm{Li},{}^5\mathrm{Li}$) reactions followed by breakup, into $\alpha +d$ and $\alpha +p$, respectively, were found to dominate over $\alpha +t$ breakup. Measured cross sections for the above breakup channels and elastic scattering have been compared with coupled-channel calculations to understand the reaction mechanism involving the weakly bound projectile ${}^7\mathrm{Li}$. Significant cross section for direct breakup of ${}^7\mathrm{Li}\to {}^6\mathrm{He}+p$ has also been measured for the first time, indicating the importance of the new (${}^6\mathrm{He}+p$) cluster configuration that may be necessary to understand the complete structure of ${}^7\mathrm{Li}$ and its energy levels.

We have examined the dependence of the shell correction to the nuclear liquid drop energy at finite excitations on the excitation energy (temperature). For this we have calculated the shell correction to the energy and free energy in a very broad region of nuclei and deformations starting directly from their formal definitions. We have found that the dependence of the shell corrections on the excitation energy differ substantially from the widely used approximation $\delta E\left(E^{*}\right)=\delta E\left(0\right)exp(-E^{*}/E_d)$, both at small and large excitations. In particular, below the critical temperature at which the pairing effects vanish, the shell correction to the free energy is rather insensitive to the excitation energy. We suggest a more accurate approximation for the temperature dependence of the shell correction to the energy and free energy that is expressed in terms of the shell correction to the energy of independent particles and the shell correction to the pairing energy at $T=0$ and few fitted constants.

The structure of low-lying excited states in ${}^{251}\mathrm{Fm}$, populated by the $\alpha$ decay of ${}^{255}\mathrm{No}$, has been investigated by means of combined $\gamma$ and internal conversion electron spectroscopy. The values for the internal conversion coefficients for the $1/2^{+}\to 5/2^{+}$ and $5/2^{+}\to 9/2^{-}$ transitions have been measured. The determined $M2/E3$ mixing ratio and lifetime for the $5/2^{+}$ decay to the ground state allowed to determine the corresponding reduced transitions strengths of $B\left(E3\right)=18\left(6\right)$ W.u. and $B\left(M2\right)=3.0\left(6\right)\times {10}^{-3}$ W.u. These results, as well as the results of previous studies in $N=151$ isotopes, are compared to theoretical calculations beyond the mean-field approach, including the first QRPA calculations using the Gogny D1M parametrization for such heavy odd-$N$ nuclei. The comparison points to the importance of accounting for the octupole vibrations for a proper understanding of the low-lying nuclear structure of some of the heaviest elements.

The spin magnetic-dipole transitions and the neutron-proton spin-spin correlations in $sd$-shell even-even nuclei with $N=Z$ are investigated by using shell-model wave functions taking into account enhanced isoscalar (IS) spin-triplet pairing as well as the effective spin operators. It was shown that the IS pairing and the effective spin operators gives a large quenching effect on the isovector (IV) spin transitions to be consistent with data observed by $(p,p^{\prime })$ experiments. On the other hand, the observed IS spin strengths show much smaller quenching effect than expected by the calculated results. The IS pairing gives a substantial quenching effect on the spin magnetic-dipole transitions, especially on the IV transitions. Consequently, an enhanced IS spin-triplet pairing interaction enlarges the proton-neutron spin-spin correlation deduced from the difference between the IS and the IV sum-rule strengths. The $\beta$-decay rates and the IS magnetic moments of the $sd$ shell are also studied in terms of the IS pairing as well as the effective spin operators.

The determination of the electron neutrino mass by electron capture in ${}^{163}\mathrm{Ho}$ relies on a precise understanding of the deexcitation of a core hole after an electron-capture event. Here we present an ab initio calculation of the electron-capture spectrum of ${}^{163}\mathrm{Ho}$, i.e., the ${}^{163}\mathrm{Ho}$ decay rate as a function of the energy distribution between the ${}^{163}\mathrm{Dy}$ daughter atom and the neutrino. Our current level of theory includes all intra-atomic decay channels and many-body interactions on a basis of fully relativistic bound orbitals. We use theoretical methods developed and extensively used for the calculation of core level spectroscopy on correlated electron materials. Our comparison to experimental electron-capture data critically tests the accuracy of these theories. We find that relativistic interactions beyond the Dirac equation lead to only minor shifts of the spectral peaks. The electronic relaxation after an electron-capture event due to the modified nuclear potential leads to a mixing of different edges, but, due to conservation of angular momentum of each scattered electron, no additional structures emerge. Many-body Coulomb interactions lead to the formation of multiplets and to additional peaks corresponding to multiple core holes created via Auger decay. Multiplets crucially change the appearance of the resonances on a Rydberg energy scale. The additional structures due to Auger decay are, although clearly visible, relatively weak compared to the single core hole states and are incidentally far away from the end-point region of the spectrum. As the end point of the spectrum is affected most by the neutrino mass, these additional states do not directly influence the statistics for determining the neutrino mass. The multiplet broadening and Auger shake-up of the main core-level edges do, however, change the apparent linewidth and accompanying lifetime of these edges. Fitting core-level edges, either in electron-capture spectroscopy or in x-ray absorption spectroscopy, by a single resonance thus leads to an underestimation of the core hole lifetime.

In order to calculate the α-decay half-lives of a wide range of heavy and superheavy nuclei, we introduced a modified temperature-dependent surface energy coefficient in the proximity potential based on thermal properties of liquids and hot nuclei. An increase in the α-decay half-life was observed by decreasing the surface energy coefficient as a result of temperature incorporation of the parent nuclei. The introduced temperature-dependent surface energy coefficient evaluated the half-lives which were in good agreement with the experimental data. Moreover, the results of the present paper confirm the closed-shell effects.

Charge state distributions of the Ra recoil ions produced in the ${}^{12}\mathrm{C}+\text{Pb}$ fusion-evaporation reactions have been obtained by measuring their yields as a function of the high voltage applied to an electrostatic deflector. Well-defined two-humped yield curves for evaporation residues (ERs) were observed. Such observations can be explained by the different sets of charge states inherent in Ra recoil ions. These charge sets correspond to the equilibrated and nonequilibrated components, as earlier observed for evaporation residues produced in different reactions. The main parameters of the distributions (mean charge values, widths, and relative intensities) for both components have been estimated using Monte Carlo simulations of the transmission of the Ra recoil ions through the deflector. For the equilibrated component the values of the mean charge and width are close to those given by different empirical systematics. For the nonequilibrated component these parameters have been obtained for the first time. The additional nonequilibrated ionization is presumably due to the formation of inner shell vacancies produced by the internal conversion of nuclear isomeric transitions of ERs. Nonequilibrated charge parameters obtained for Ra recoil ions are compared to similar available experimental data and some theoretical predictions.

Anisotropic hydrodynamics improves upon standard dissipative fluid dynamics by treating certain large dissipative corrections nonperturbatively. Relativistic heavy-ion collisions feature two such large dissipative effects: (i) Strongly anisotropic expansion generates a large shear stress component which manifests itself in very different longitudinal and transverse pressures, especially at early times. (ii) Critical fluctuations near the quark-hadron phase transition lead to a large bulk viscous pressure on the conversion surface between hydrodynamics and a microscopic hadronic cascade description of the final collision stage. We present a new dissipative hydrodynamic formulation for nonconformal fluids where both of these effects are treated nonperturbatively. The evolution equations are derived from the Boltzmann equation in the 14-moment approximation, using an expansion around an anisotropic leading-order distribution function with two momentum-space deformation parameters, accounting for the longitudinal and transverse pressures. To obtain their evolution we impose generalized Landau matching conditions for the longitudinal and transverse pressures. We describe an approximate anisotropic equation of state that relates the anisotropy parameters with the macroscopic pressures. Residual shear stresses are smaller and are treated perturbatively, as in standard second-order dissipative fluid dynamics. The resulting optimized viscous anisotropic hydrodynamic evolution equations are derived in $3+1$ dimensions and tested in a ($0+1$)-dimensional Bjorken expansion, using a state-of-the-art lattice equation of state. Comparisons with other viscous hydrodynamical frameworks are presented.

Neutron-capture reactions on very neutron-rich nuclei are essential for heavy-element nucleosynthesis through the rapid neutron-capture process, now shown to take place in neutron-star merger events. For these exotic nuclei, radiative neutron capture is extremely sensitive to their $\gamma$-emission probability at very low $\gamma$ energies. In this work, we present measurements of the $\gamma \text{-decay}$ strength of ${}^{70}\mathrm{Ni}$ over the wide range $1.3\le E_{\gamma }\le 8$ MeV. A significant enhancement is found in the $\gamma \text{-decay}$ strength for transitions with $E_{\gamma }<3$ MeV. At present, this is the most neutron-rich nucleus displaying this feature, proving that this phenomenon is not restricted to stable nuclei. We have performed $E1$-strength calculations within the quasiparticle time-blocking approximation, which describe our data above $E_{\gamma }\simeq 5$ MeV very well. Moreover, large-scale shell-model calculations indicate an $M1$ nature of the low-energy $\gamma$ strength. This turns out to be remarkably robust with respect to the choice of interaction, truncation, and model space, and we predict its presence in the whole isotopic chain, in particular the neutron-rich ${}^{72,74,76}\mathrm{Ni}$.

Low-energy dipole states in oxygen isotopes are investigated using a Hartree-Fock plus random-phase approximation calculation with Skyrme interactions. We obtain the lowest energy dipole state as isoscalar dominant on the spherical ground states of ${}^{16–22}\mathrm{O}$, while that in ${}^{24}\mathrm{O}$ couples to the continuum states. This suggests that the nature of low-energy dipole mode in light nuclei changes at $N=16$.

Neutron lifetime is one of the most important physical constants: it determines parameters of the weak interaction and predictions of primordial nucleosynthesis theory. There remains the unsolved problem of a 3.9σ discrepancy between measurements of this lifetime using neutrons in beams and those with stored ultracold neutrons (UCN). In our experiment we measure the lifetime of neutrons trapped by Earth's gravity in an open-topped vessel. Two configurations of the trap geometry are used to change the mean frequency of UCN collisions with the surfaces; this is achieved by plunging an additional surface into the trap without breaking the vacuum. The trap walls are coated with a hydrogen-less fluorine-containing polymer to reduce losses of UCN. The stability of this coating over multiple thermal cycles between 80 and 300 K was tested. At 80 K, the probability of UCN loss due to collisions with the trap walls is just 1.5% of the probability of β decay. The free neutron lifetime is determined by extrapolation to an infinitely large trap with zero collision frequency. The result of these measurements is ${\tau }_n=881.5\pm 0.7_{\mathrm{stat}}\pm 0.6_{\mathrm{syst}}\mathrm{s}$ which is consistent with the conventional value of 880.2 ± 1.0 s presented by the Particle Data Group. Future prospects for this experiment are in further cooling to 10 K, which will lead to an improved accuracy of measurement. In conclusion we present an analysis of currently available data on various measurements of the neutron lifetime.

We argue whether the physics of the general approach of Severyukhin et al. [Phys. Rev. C 95, 061305(R) (2017)] is appropriate.

We demonstrate that our approach [Phys. Rev. C 95, 061305(R) (2017)] serves as a useful tool to describe the gross structure of the spreading widths of the giant resonances of the doubly magic heavy nuclei. It reduces significantly the computational efforts implementing the ideas of random matrix distribution of the coupling between one-phonon and two-phonon states and generating the energies of the two-phonon states by means of the Gaussian orthogonal ensemble distribution. We show that the Comment misrepresents our paper and fails to provide plausible arguments against the description of the gross structure with the aid of the random matrix theory.

The isoscalar neutron-proton pairing is thought to be important for nuclei with equal number of protons and neutrons but its manifestation in structure properties remains to be understood. We investigate the Gamow-Teller (GT) transitions for the $f_{7/2}$-shell nuclei in large-scale shell-model calculations with the realistic Hamiltonian. We show that the isoscalar $T=0,J^{\pi }=1^{+}$ neutron-proton pairing interaction plays a decisive role for the concentration of GT strengths at the first-excited $1_1^{+}$ state in ${}^{42}\mathrm{Sc}$, and that the suppression of these strengths in ${}^{46}\mathrm{V}$, ${}^{50}\mathrm{Mn}$, and ${}^{54}\mathrm{Co}$ is mainly caused by the spin-orbit force supplemented by the quadrupole-quadrupole interaction. Based on the good reproduction of the charge-exchange reaction data, we further analyze the interplay between the isoscalar and isovector pairing correlations. We conclude that even for the most promising $A=42$ nuclei where the SU(4) isoscalar-isovector-pairing symmetry is less broken, the probability of forming an isoscalar neutron-proton pairing condensation is less than 60% as compared to the expectation at the SU(4)-symmetry limit.

Hyperfine-structure parameters and isotope shifts of ${}^{195–211}\mathrm{At}$ have been measured for the first time at CERN-ISOLDE, using the in-source resonance-ionization spectroscopy method. The hyperfine structures of isotopes were recorded using a triad of experimental techniques for monitoring the photo-ion current. The Multi-Reflection Time-of-Flight Mass Spectrometer, in connection with a high-resolution electron multiplier, was used as an ion-counting setup for isotopes that either were affected by strong isobaric contamination or possessed a long half-life; the ISOLDE Faraday cups were used for cases with high-intensity beams; and the Windmill decay station was used for short-lived, predominantly $\alpha$-decaying nuclei. The electromagnetic moments and changes in the mean-square charge radii of the astatine nuclei have been extracted from the measured hyperfine-structure constants and isotope shifts. This was only made possible by dedicated state-of-the-art large-scale atomic computations of the electronic factors and the specific mass shift of atomic transitions in astatine that are needed for these extractions. By comparison with systematics, it was possible to assess the reliability of the results of these calculations and their ascribed uncertainties. A strong deviation in the ground-state mean-square charge radii of the lightest astatine isotopes, from the trend of the (spherical) lead isotopes, is interpreted as the result of an onset of deformation. This behavior bears a resemblance to the deviation observed in the isotonic polonium isotopes. Cases for shape coexistence have been identified in ${}^{197,199}\mathrm{At}$, for which a significant difference in the charge radii for ground ($9/2^{-}$) and isomeric ($1/2^{+}$) states has been observed.

The half-life of the ${}^{20}\mathrm{F}$ ground state was measured using a radioactive beam implanted in a plastic scintillator and recording $\beta \gamma$ coincidences together with four CsI(Na) detectors. The result, $T_{1/2}=11.0011{\left(69\right)}_{\mathrm{stat}}{\left(30\right)}_{\mathrm{sys}}$ s, is at variance by 17 combined standard deviations with the two most precise results. The present value revives the poor consistency of results for this half-life and calls for a new measurement, with a technique having different sources of systematic effects, to clarify the discrepancy.

Employing the stochastic mean-field (SMF) approach, we develop a quantal diffusion description of the multi-nucleon transfer in heavy-ion collisions at finite impact parameters. The quantal transport coefficients are determined by the occupied single-particle wave functions of the time-dependent Hartree-Fock equations. As a result, the primary fragment mass and charge distribution functions are determined entirely in terms of the mean-field properties. This powerful description does not involve any adjustable parameter, includes the effects of shell structure, and is consistent with the fluctuation-dissipation theorem of the nonequilibrium statistical mechanics. As a first application of the approach, we analyze the fragment mass distribution in ${}^{48}\mathrm{Ca}+{}^{238}\mathrm{U}$ collisions at the center-of-mass energy $E_{\text{c.m.}}=193$ MeV and compare the calculations with the experimental data.

The internal temperatures of fragments produced by an excited nuclear source are investigated by using the microcanonical version of the statistical multifragmentation model, with discrete energy. We focus on the fragments' properties at the breakup stage, before they have time to deexcite by particle emission. Since the adopted model provides the excitation energy distribution of these primordial fragments, it allows one to calculate the temperatures of different isotope families and to make inferences about the sensitivity to their isospin composition. It is found that, due to the functional form of the nuclear density of states and the excitation energy distribution of the fragments, proton-rich isotopes are hotter than neutron-rich isotopes. This property has been taken to be an indication of earlier emission of the former from a source that cools down as it expands and emits fragments. Although this scenario is incompatible with the prompt breakup of a thermally equilibrated source, our results reveal that the latter framework also provides the same qualitative features just mentioned. Therefore they suggest that this property cannot be taken as evidence for nonequilibrium emission. We also found that this sensitivity to the isotopic composition of the fragments depends on the isospin composition of the source, and that it is weakened as the excitation energy of the source increases.

Dihadron and jet-hadron correlationsare commonly used in relativistic heavy ion collisions to study the soft component of jets in a quark gluon plasma. There is a large correlated background which is described by the Fourier decomposition of the azimuthal anisotropy where $v_n$ is the $n\mathrm{th}$ order coefficient. The path length dependence of partonic energy loss can be studied by varying the angle of the high momentum trigger particle or jet relative to a reconstructed event plane. This modifies the shape of the background correlated with that event plane. The original derivation of the shape of this background only considered correlations relative to the second-order event plane, which is correlated to the initial participant plane. We derive the shape of this background for an event plane at an arbitrary order. There is a phase shift in the case of jets restricted to asymmetric regions relative to the event plane. For realistic correlations between event planes, the correlation between the second- and fourth-order event planes leads to a much smaller effect than the finite event plane resolution at each order. Finally, we assess the status of the rapidity even $v_1$ term due to flow, which has been measured to be comparable to $v_2$ and $v_3$ terms.