The stellar $\left(n,\gamma \right)$ cross sections of the Ne isotopes are important for a number of astrophysical quests, i.e., for the interpretation of abundance patterns in presolar material or with respect to the $s$-process neutron balance in red giant stars. This paper presents resonance studies of experimental data in the keV range, which had not been fully analyzed before. The analyses were carried out with the $\mathcal{R}$-matrix code sammy. With these results for the resonant part and by adding the components due to direct radiative capture, improved Maxwellian-averaged cross sections (MACS) could be determined. At $kT=30\mathrm{keV}$ thermal energy we obtain MACS values of $240\pm 29,1263\pm 160$, and $53.2\pm 2.7 \mu \mathrm{barn}$ for ${}^{20}\mathrm{Ne},{}^{21}\mathrm{Ne}$, and ${}^{22}\mathrm{Ne}$, respectively. In earlier work the stellar rates of ${}^{20}\mathrm{Ne}$ and ${}^{21}\mathrm{Ne}$ had been grossly overestimated. ${}^{22}\mathrm{Ne}$ and ${}^{20}\mathrm{Ne}$ are significant neutron poisons for the $s$ process in stars because their very small MACS values are compensated by their large abundances.

The transverse analyzing powers ${}^{T}T_{20}$ were obtained from a polarized beam study of the reaction ${}^{12}\mathrm{C}({}^7\mathrm{Li},\alpha ){}^{15}\mathrm{N}$ at $E_{\text{lab}}\left({}^7\text{Li}\right)=34$ MeV for several well known, strongly populated and isolated states in ${}^{15}\mathrm{N}$ to determine if they contained a sufficiently distinctive signature to be used to provide a test against which selectively populated and strong, but not well understood states, such as the one at $13.17$ MeV could be used to determine their spins and parities. Unfortunately, current finite range distorted wave Born approximation and coupled channels Born approximation calculations were not able to describe the data to the well-known states. The current work presents these experimental analyzing powers with the expectation that they can be used as a test of future detailed reaction model calculations.

We use the newly developed multireference in-medium similarity renormalization group to study all even isotopes of the calcium and nickel isotopic chains, based on two- plus three-nucleon interactions derived from chiral effective field theory. We present results for ground-state and two-neutron separation energies and quantify their theoretical uncertainties. At shell closures, we find excellent agreement with coupled-cluster results obtained with the same Hamiltonians. Our results confirm the importance of chiral $3N$ interactions to obtain a correct reproduction of experimental energy trends, and their subtle impact in neutron-rich Ca and Ni isotopes. At the same time, we uncover and discuss deficiencies of the input Hamiltonians which need to be addressed by the next generation of chiral interactions.

We derive the form of the viscous corrections to the phase-space distribution function due to bulk viscous pressure and shear stress tensor using the iterative Chapman-Enskog method. We then calculate the transport coefficients necessary for the second-order hydrodynamic evolution of the bulk viscous pressure and the shear stress tensor. We demonstrate that the transport coefficients obtained using the Chapman-Enskog method are different than those obtained previously using the 14-moment approximation for a finite particle mass. Specializing to the case of boost-invariant and transversally homogeneous longitudinal expansion, we show that the transport coefficients obtained using the Chapman-Enskog method result in better agreement with the exact solution of the Boltzmann equation in the relaxation-time approximation compared to results obtained in the 14-moment approximation. Finally, we explicitly confirm that the time evolution of the bulk viscous pressure is significantly affected by its coupling to the shear stress tensor.

Level lifetimes in the ${}^{32}\mathrm{P}$ nucleus have been determined using the Doppler-shift attenuation method (DSAM). Conventional DSAM measurements employ a thin target on a thick, high-$Z$ backing. An extension of the technique to thick molecular targets is presented. The necessary modifications in the standard analysis procedures, pertaining to the incorporation of stopping power estimations for molecular media and evolution of residue cross section in a thick target, have been implemented. Further, x-ray powder diffraction (XRD) and scanning electron microscopy (SEM) have also been carried out to probe the structural composition of the target. The lifetime results have been validated with respect to the previous measurements and upper limits on lifetimes of seven levels have been determined for the first time. Large-basis shell model calculations have been carried out and compared with the experimental measurements.

Background: An accurate description of nuclear pairing gaps is extremely important for understanding static and dynamic properties of the inner crusts of neutron stars and to explain their cooling process.

Purpose: We plan to study the behavior of the pairing gaps ${\Delta }_F$ as a function of the Fermi momentum $k_F$ for neutron and nuclear matter in all relevant angular momentum channels where superfluidity is believed to naturally emerge. The calculations will employ realistic chiral nucleon-nucleon potentials with the inclusion of three-body forces and self-energy effects.

Methods: The superfluid states of neutron and nuclear matter are studied by solving the BCS gap equation for chiral nuclear potentials using the method suggested by Khodel et al., where the original gap equation is replaced by a coupled set of equations for the dimensionless gap function $\chi \left(k\right)$ defined by $\Delta \left(k\right)={\Delta }_F\chi \left(k\right)$ and a nonlinear algebraic equation for the gap magnitude ${\Delta }_F=\Delta \left(k_F\right)$ at the Fermi surface. This method is numerically stable even for small pairing gaps, such as that encountered in the coupled ${}^{3}P{F}_2$ partial wave.

Results: We have successfully applied Khodel's method to singlet ($S$) and coupled channel ($SD$ and $PF$) cases in neutron and nuclear matter. Our calculations agree with other ab initio approaches, where available, and provide crucial inputs for future applications in superfluid systems.

Excited states in ${}^{160}\mathrm{Er}$ and ${}^{156}\mathrm{Dy}$ were populated via ${\beta }^{+}/\mathrm{EC}$ decay and were studied via conversion electrons and $\gamma$-ray spectroscopy at the Tandem Accelerator in the INFN Laboratori Nazionali del Sud in Catania, Italy. Conversion electrons were detected by a mini-orange spectrometer with a transmission energy window that ranged from 500 to 1000 keV for ${}^{160}\mathrm{Er}$ and from 350 keV to 750 keV for ${}^{156}\mathrm{Dy}$. The $E0$ decays of the first excited state at 893 keV in ${}^{160}\mathrm{Er}$ and at 676 keV in ${}^{156}\mathrm{Dy}$ were observed, and $X(E0/E2)$ ratios of reduced transition probabilities were deduced. Furthermore, for both nuclei $E0$ admixtures in transitions from the lower members of the $\beta$ and $\gamma$ bands to the ground-state band were observed, and $X(E0/E2)$ values were deduced. The values of the $X(E0/E2)$ for the $0_2^{+}$ decays are compared to IBA-1 calculations that use the full Hamiltonian in multipole expansion. Properties related to the nuclear shape seem to be sensitive to higher-order terms of the expansion.

A detailed level scheme for ${}^{221}\mathrm{Th}$ has been established in an experiment using the ${}^{18}\mathrm{O}+{}^{207}\mathrm{Pb}$ reaction at 96 MeV. The evaporation residues from this fissile system were selected with the HERCULES detector array and residue-gated $\gamma$ rays were measured with Gammasphere. Three band structures of interlinked, alternating-parity levels are observed, two of which are non-yrast. In addition, several high-lying excitations are found. The yrast band is seen up to spin-parity $37/2^{-}$ and $39/2^{+}$, beyond which a high-spin feeding transition is observed. The non-yrast sequences are interpreted as parity-doublet structures, based on a configuration similar to that of the yrast band in ${}^{223}\mathrm{Th}$ $(K=5/2)$. The key properties of even-odd nuclei in this mass region $\left[B\right(E1)/B(E2)$ and $B\left(M1\right)/B\left(E2\right)$ ratios, spin alignments, parity splittings] are reviewed.

We investigate the one-body dissipation dynamics in heavy-ion collisions of ${}^{16}\mathrm{O}+{}^{16}\mathrm{O}$ using a fully three-dimensional time-dependent Hartree-Fock (TDHF) theory with the modern Skyrme energy functional and without any symmetry restrictions. The energy dissipation is revealed to decrease in deep-inelastic collisions of the light systems as the bombarding energy increases owing to the competition between collective motion and single-particle degrees of freedom. The role of spin-orbit force is given particular emphasis in deep-inelastic collisions. The spin-orbit force causes a significant enhancement of the dissipation. The time-even coupling of spin-orbit force plays a dominant role at low energies, while the influence of time-odd terms is notable at high energies. About 40–65% of the total dissipation depending on the different parameter sets is predicted to arise from the spin-orbit force. The theoretical fusion cross section has a reasonably good agreement with the experimental data, considering that no free parameters are adjusted to reaction dynamics in the TDHF approach.

Background: The nuclear structure of colliding nuclei is known to influence the fusion process. Couplings of the relative motion to nuclear shape deformations and vibrations lead to an enhancement of the sub-barrier fusion cross section in comparison with the predictions of one-dimensional barrier penetration models. This enhancement is explained by coupled-channels calculations including these couplings. The sub-barrier fusion cross section is also affected by nucleon transfer channels between the colliding nuclei.

Purpose: The aim of the present experiment is to investigate the influence of the projectile and target nuclear structures on the fusion cross sections in the ${}^{40}\mathrm{Ca}+{}^{58}\mathrm{Ni}$ and ${}^{40}\mathrm{Ca}+{}^{64}\mathrm{Ni}$ systems.

Methods: The experimental and theoretical fusion excitation functions as well as the barrier distributions were compared for these two systems. Coupled-channels calculations were performed using the ccfull code.

Results: Good agreement was found between the measured and calculated fusion cross sections for the ${}^{40}\mathrm{Ca}+{}^{58}\mathrm{Ni}$ system. The situation is different for the ${}^{40}\mathrm{Ca}+{}^{64}\mathrm{Ni}$ system where the coupled-channels calculations with no nucleon transfer clearly underestimate the fusion cross sections below the Coulomb barrier. The fusion excitation function was, however, well reproduced at low and high energies by including the coupling to the neutron pair-transfer channel in the calculations.

Conclusions: The nuclear structure of the colliding nuclei influences the fusion cross sections below the Coulomb barrier for both ${}^{40}\mathrm{Ca}+{}^{\mathrm{58,64}}\mathrm{Ni}$ systems. Moreover, we highlighted the effect of the neutron pair-transfer channel on the fusion cross sections in ${}^{40}\mathrm{Ca}+{}^{64}\mathrm{Ni}$.

We present the analysis of three deuteron stripping reactions, ${}^{14}\mathrm{C}(d,p){}^{15}\mathrm{C},{}^{58}\mathrm{Ni}(d,p){}^{59}\mathrm{Ni}$, and ${}^{116}\mathrm{Sn}(d,p){}^{117}\mathrm{Sn}$ using the combined method [A. M. Mukhamedzhanov and F. M. Nunes, Phys. Rev. C 72, 017602 (2005)], in which each reaction is analyzed at low and significantly higher energies. At low energies all these reactions are peripheral and the experimental asymptotic normalization coefficients (ANCs) are determined with accuracy about $10\%$. At higher energies we determine the spectroscopic factors (SFs) by fixing the normalization of the peripheral parts of the reaction amplitudes governed by the ANCs found from the low-energy data. The combined method imposes a strict limitation on the variation of the geometrical parameters of the single-particle potential, which can be arbitrarily taken in the standard approach. By checking the compatibility of the ANCs and SFs using the combined method we reveal the flaw in the contemporary nuclear reaction theory in treating the nuclear interior, which is the most crucial part in the determination of the SFs.

The process of formation of the participant system in heavy-ion collisions is investigated in the framework of a simplified analytic Glauber-like model, which is based on the relativistic Boltzmann transport equation. The key point lies in the time-dependent partition of the nucleon system into two groups: nucleons, which did not take part in any interaction before a given time, and nucleons, which already have interacted. In the framework of the proposed model we introduce a natural energy-dependent temporal scale $t_c$, which allows us to remove all dependencies of the model on the collision energy except for the energy dependence of the nucleon-nucleon cross section. By investigating the time dependence of the total number of participants we conclude that the formation process of the participant system becomes complete at $t\simeq 1.5t_c$. Time dependencies of participant total angular momentum and vorticity are also considered and used to describe the emergence of rotation in the reaction plane.

The problem of the divergences which arise in beyond mean-field calculations, when a zero-range effective interaction is employed, has not been much considered so far. Some of us have proposed, quite recently, a scheme to regularize a zero-range Skyrme-type force when it is employed to calculate the total energy, at second-order perturbation theory level, in uniform matter. Although this scheme looked promising, the extension for finite nuclei is not straightforward. We introduce such a procedure in the current paper, by proposing a regularization procedure that is similar, in spirit, to the one employed to extract the so-called $V_{\text{low-}k}$ from the bare force. Although this has been suggested already by B. G. Carlsson and collaborators, the novelty of our work consists of setting on equal footing uniform matter and finite nuclei; in particular, we show how the interactions that have been regularized in uniform matter behave when they are used in a finite nucleus with the corresponding cutoff. We also address the problem of the validity of the perturbative approach in finite nuclei for the total energy.

Background: The fusion excitation function of the system ${}^{28}\mathrm{Si}+{}^{28}\mathrm{Si}$ at energies near and below the Coulomb barrier is known only down to $\simeq 15$ mb. This precludes any information on both coupling effects on sub-barrier cross sections and the possible appearance of hindrance. For ${}^{28}\mathrm{Si}+{}^{30}\mathrm{Si}$ even if the fusion cross section is measured down to $\simeq 50$ $\mu \mathrm{b}$, the evidence of hindrance is marginal. Both systems have positive fusion $Q$ values. While ${}^{28}\mathrm{Si}$ has a deformed oblate shape, ${}^{30}\mathrm{Si}$ is spherical.

Purpose: We investigate 1. the possible influence of the different structure of the two Si isotopes on the fusion excitation functions in the deep sub-barrier region and 2. whether hindrance exists in the $\text{Si}+\text{Si}$ systems and whether it is strong enough to generate an $S$-factor maximum, thus allowing a comparison with lighter heavy-ion systems of astrophysical interest.

Methods: ${}^{28}\mathrm{Si}$ beams from the XTU Tandem accelerator of the INFN Laboratori Nazionali di Legnaro were used. The setup was based on an electrostatic beam separator, and fusion evaporation residues (ER) were detected at very forward angles. Angular distributions of ER were measured.

Results: Fusion cross sections of ${}^{28}\mathrm{Si}+{}^{28}\mathrm{Si}$ have been obtained down to $\simeq 600$ nb. The slope of the excitation function has a clear irregularity below the barrier, but no indication of a $S$-factor maximum is found. For ${}^{28}\mathrm{Si}+{}^{30}\mathrm{Si}$ the previous data have been confirmed and two smaller cross sections have been measured down to $\simeq 4$ $\mu \mathrm{b}$. The trend of the $S$-factor reinforces the previous weak evidence of hindrance.

Conclusions: The sub-barrier cross sections for ${}^{28}\mathrm{Si}+{}^{28}\mathrm{Si}$ are overestimated by coupled-channels calculations based on a standard Woods-Saxon potential, except for the lowest energies. Calculations using the M3Y+repulsion potential are adjusted to fit the ${}^{28}\mathrm{Si}+{}^{28}\mathrm{Si}$ and the existing ${}^{30}\mathrm{Si}+{}^{30}\mathrm{Si}$ data. An additional weak imaginary potential (probably simulating the effect of the oblate ${}^{28}\mathrm{Si}$ deformation) is required to fit the low-energy trend of ${}^{28}\mathrm{Si}+{}^{28}\mathrm{Si}$. The parameters of these calculations are applied to predict the ion-ion potential for ${}^{28}\mathrm{Si}+{}^{30}\mathrm{Si}$. Its cross sections are well reproduced by also including one- and successive two-neutron transfer channels, besides the low-lying surface excitations.

In this work we survey the detectability of the ${\beta }^{-}$ channel of ${}_{23}^{50}\mathrm{V}$ leading to the first excited $2^{+}$ state in ${}_{24}^{50}\mathrm{Cr}$. The electron-capture (EC) half-life corresponding to the transition of ${}_{23}^{50}V$ to the first excited $2^{+}$ state in ${}_{22}^{50}\mathrm{Ti}$ had been measured earlier. Both of the mentioned transitions are 4th-forbidden non-unique. We have performed calculations of all the involved wave functions by using the nuclear shell model with the GXPF1A interaction in the full f-p shell. The computed half-life of the EC branch is in good agreement with the measured one. The predicted half-life for the ${\beta }^{-}$ branch is in the range $\approx 2\times {10}^{19}$ yr whereas the present experimental lower limit is $1.5\times {10}^{18}$ yr. We discuss also the experimental lay-out needed to detect the ${\beta }^{-}$-branch decay.

A new form of two-photon exchange (TPE) effect is studied to explain the discrepancy between unpolarized and polarized experimental data in elastic $ep$ scattering. The mechanism is based on a simple idea that apart from the usual TPE effects from box and crossed-box diagrams, the mesons may also be exchanged in elastic $ep$ scattering by two-photon coupling at loop level. The detailed study shows such contributions to reduced unpolarized cross section (${\sigma }_{\mathrm{un}}$) and polarized observables ($P_t,P_l$) at fixed $Q^2$ are only dependent on proton's electromagnetic form factors $G_{E,M}$ and a new unknown universal parameter $g$. After combining this contribution with the usual TPE contributions from box and crossed-box diagrams, the ratio ${\mu }_p{G}_E/G_M$ extracted from the recent precise unpolarized and polarized experimental data can be described consistently.

The proton radius puzzle refers to the $\approx 7\sigma$ discrepancy that exists between the proton charge radius determined from muonic hydrogen and that determined from electronic hydrogen spectroscopy and electron-proton scattering. One possible partial resolution to the puzzle includes errors in the extraction of the proton radius from $ep$ elastic scattering data. This possibility is made plausible by certain fits that extract a smaller proton radius from the scattering data consistent with that determined from muonic hydrogen. The reliability of some of these fits that yield a smaller proton radius was studied. We found that fits of form factor data with a truncated polynomial fit are unreliable and systematically give values for the proton radius that are too small. Additionally, a polynomial fit with a ${\chi }_{\text{reduced}}^2\approx 1$ is not a sufficient indication for a reliable result.

The cell structure of $\beta$-stable clusters in the inner crust of cold and warm neutron stars is studied within the Thomas–Fermi approach by using relativistic mean-field nuclear models. The relative size of the inner crust and the pasta phase of neutron stars is calculated, and the effect of the symmetry energy slope parameter $L$ on the profile of the neutron star crust is discussed. It is shown that, while the size of the total crust is mainly determined by the incompressibility modulus, the relative size of the inner crust depends on $L$. It is found that the inner crust represents a larger fraction of the total crust for smaller values of $L$. Finally, it is shown that, at finite temperature the pasta phase in $\beta$-equilibrium matter essentially melts above $5\text{to}6$ MeV, and that the onset density of the rod-like and slab-like structures does not depend on the temperature.

The upper limit of the neutron $i_{13/2}$ single-particle energy $\left({\varepsilon }_{i13/2}\right)$ is estimated in the random quasiparticle ensemble with single-particle energies. The ${\varepsilon }_{i13/2}$ distributions under constraints from ${}^{134,135}\mathrm{Te}$ and ${}^{136,137}\mathrm{Xe}$ spectra demonstrate that the $i_{13/2}$ single-particle state can be physically mixed with the $f_{7/2}\otimes 3^{-}$ configuration only if ${\varepsilon }_{i13/2}<3$ MeV. Thus, our ensemble calculation suggests a robust upper limit of 3 MeV.

The isotope ${}^{176}\mathrm{Au}$ has been studied in the complete fusion reaction ${}^{40}\mathrm{Ca}+{}^{141}\mathrm{Pr} \to {}^{176}\mathrm{Au}+5n$ at the velocity filter SHIP (GSI, Darmstadt). The complex fine-structure $\alpha$ decay of two isomeric states in ${}^{176}\mathrm{Au}$ feeding several previously unknown excited states in the daughter nucleus ${}^{172}\mathrm{Ir}$ is presented. An $\alpha$-decay branching ratio of $b_{\alpha }=9.5\left(11\right)\%$ was deduced for the high-spin isomer in ${}^{172}\mathrm{Ir}$.