Background: Knowing the difference between the neutron and proton densities of nuclei is a significant topic because of its importance for understanding neutron star structures and cooling mechanisms. The coherent-nuclear photoproduction of pions, $\left(\gamma ,{\pi }^0\right)$, combined with elastic electron scattering, has been suggested to be a very accurate probe of density differences.

Purpose: Study the $(\gamma ,{\pi }^0)$ reaction mechanism so as to better access the uncertainties involved in extracting the neutron density.

Methods: Include the effects of final-state pion-nucleus charge-exchange reactions on the cross section and study the influence of the nonzero spatial extent of the proton.

Results: The effects of final-state charge-exchange increase the cross section between 6% and 5%, generally decreasing as the momentum transfer increases. This leads to an increase of the extracted neutron skin distance by about 50%. The validity of the previous treatments of the proton size is confirmed.

Conclusion: The model dependence of the theoretically computed cross section increases the total systematic uncertainty (experiment plus theory) in extracting the neutron skin from the $(\gamma ,{\pi }^0)$ cross section by at least a factor of three.

Using a hybrid Gammasphere array coupled to 25 ${\mathrm{LaBr}}_3\left(\text{Ce}\right)$ detectors, the lifetimes of the first three levels of the yrast band in ${}^{114}\mathrm{Pd}$, populated via ${}^{252}\mathrm{Cf}$ decay, have been measured. The measured lifetimes are ${\tau }_{2^{+}}=103\left(10\right)\mathrm{ps}, {\tau }_{4^{+}}=22\left(13\right)\mathrm{ps}$, and ${\tau }_{6^{+}}\le 10\mathrm{ps}$ for the $2_1^{+}, 4_1^{+}$, and $6_1^{+}$ levels, respectively. Palladium-114 was predicted to be the most deformed isotope of its isotopic chain, and spectroscopic studies have suggested it might also be a candidate nucleus for low-spin stable triaxiality. From the lifetimes measured in this work, reduced transition probabilities $B(E2;J\to J-2)$ are calculated and compared with interacting boson model, projected shell model, and collective model calculations from the literature. The experimental ratio $R_{B\left(E2\right)}=B(E2;4_1^{+}\to 2_1^{+})/B(E2;2_1^{+}\to 0_1^{+})=0.80\left(42\right)$ is measured for the first time in ${}^{114}\mathrm{Pd}$ and compared with the known values $R_{B\left(E2\right)}$ in the palladium isotopic chain: the systematics suggest that, for $N=68$, a transition from $\gamma$-unstable to a more rigid $\gamma$-deformed nuclear shape occurs.

An outstanding problem in the theory of nuclear fission is understanding the Hamiltonian dynamics at the scission point. Here we apply the generator coordinate method to calculate decay widths for prescission configurations into the two-fragment continuum. Transitions that are allowed under diabatic dynamics can have widths up to several MeV. For nondiabatic decays through the pairing interaction, typical widths to a specific final-state channel are two to three orders of magnitude smaller. The nucleus ${}^{236}\mathrm{U}$ is taken as a representative example in the calculations.

We present a microscopic description of neutron and proton elastic and inelastic scattering off ${}^{206,207,208}\mathrm{Pb}$ and ${}^{209}\mathrm{Bi}$ together with new medium-energy (7.5–15.5 MeV) neutron elastic and inelastic scattering measurements for various low-energy levels. The Jeukenne, Lejeune, Mahaux (JLM) semimicroscopic folding model provides the relevant optical and transition potentials used to calculate the elastic and inelastic cross sections. Rearrangement corrections that account for proton and neutron density variations during the transition are considered. The nuclear diagonal and transition densities are calculated from a (quasiparticle) random phase approximation [(Q)RPA] structure model implemented with the Gogny D1S interaction. Calculated differential elastic and inelastic cross sections are mostly in very good agreement with available data. Predicted nuclear structure properties as well as scattering calculations and measurements for the yrast quadrupole excitation in ${}^{206}\mathrm{Pb}$ are carefully discussed. The rearrangement corrections to inelastic scattering form factors are shown to reduce medium energy nucleon inelastic cross section by up to 55%. The magnitude of these corrections changes depending on the probe, incident energy, multipolarity, and nature of the transitions considered. The combined analysis of nuclear structure properties and those for nucleon scattering cross sections measured previously over a range of incident energies provides stringent tests of present microscopic models and helps distinguish those scattering data which most likely call for revision.

Effective field theories (EFTs) organize the description of complex systems into an infinite sequence of decreasing importance. Predictions are made with a finite number of terms, which induces a truncation error that is often left unquantified. We formalize the notion of EFT convergence and propose a Bayesian truncation error model for predictions that are correlated across the independent variables, e.g., energy or scattering angle. Central to our approach are Gaussian processes that encode both the naturalness and correlation structure of EFT coefficients. Our use of Gaussian processes permits efficient and accurate assessment of credible intervals, allows EFT fits to easily include correlated theory errors, and provides analytic posteriors for physical EFT-related quantities such as the expansion parameter. We demonstrate that model-checking diagnostics—applied to the case of multiple curves—are powerful tools for EFT validation. As an example, we assess a set of nucleon-nucleon scattering observables in chiral EFT. In an effort to be self-contained, appendices include thorough derivations of our statistical results. Our methods are packaged in Python code, called gsum, that is available for download on GitHub.

The paper studies the excitation of the ${}^{229}\mathrm{Th}$ nucleus to the anomalously low-lying isomeric state $3/2^{+}(8.28\pm 0.17$ eV) in the electron bridge process via the continuum of the electron spectrum. Resonant excitation of the nucleus was found to be always possible in the scheme, no matter where the electron levels of an atom or ion were located. Formulas for the excitation cross section by narrow and wide laser lines are obtained. In the resonance, where the process under consideration turns into laser photoionization followed by nuclear excitation in electron capture, the cross section of the process was shown to be comparable in magnitude with that of the photoionization of the thorium atom. Experimental schemes for testing the effect were proposed, which would allow measuring the frequency of the nuclear isomeric transition $3/2^{+}\to 5/2^{+}$ to a high precision, which is the first-priority (and still unresolved) task for creating a nuclear clock.

Low-spin natural-parity states in ${}^{20}\mathrm{Ne}$ at excitation energies larger than the proton separation energy can be fruitfully explored by analyzing the behavior of the ${}^{19}\mathrm{F}(p,{\alpha }_0){}^{16}\mathrm{O}$ and ${}^{19}\mathrm{F}(p,{\alpha }_{\pi }){}^{16}\mathrm{O}$ reactions. Previous analyses were affected by the presence of fragmentary data, often limited to small bombarding energy ranges and to just one reaction channel, preventing any firm conclusion on the spectroscopy of such states. We propose a critical analysis of all data sets published in the literature, especially concerning angular distribution and cross-section data of the ${}^{19}\mathrm{F}(p,{\alpha }_0){}^{16}\mathrm{O}$ and ${}^{19}\mathrm{F}(p,{\alpha }_{\pi }){}^{16}\mathrm{O}$ reactions at low bombarding energies ($E_p\approx 0.2$–10 MeV). For the first time, we perform a comprehensive $R$-matrix analysis of all such data, including also $p +{}^{19}\mathrm{F}$ elastic scattering data to better determine the partial widths associated to each decay channel. The obtained results help to remove uncertainties on several $J^{\pi }$ assignments for known states and point out the possible non-negligible role played by low-energy resonances in the determination of the ${}^{19}\mathrm{F}(p,{\alpha }_{\pi }){}^{16}\mathrm{O}$ reaction rate at temperatures relevant for Asimptotic Giant Branch (AGB) stars.

We study the performance of self-consistent mean-field and beyond-mean-field approximations in shell-model valence spaces. In particular, Hartree-Fock-Bogolyubov, particle-number variation after projection and projected generator coordinate methods are applied to obtain ground-state and excitation energies for even-even and odd-even Calcium isotopes in the $pf$ shell. The standard (and nontrivial) KB3G nuclear effective interaction was used. The comparison with the exact solutions—provided by the full diagonalization of the Hamiltonian—shows an outstanding agreement when particle-number and angular-momentum restorations are performed and both quadrupole and neutron-neutron pairing degrees of freedom are explicitly explored as collective coordinates.

We present measurements of two-particle differential number correlation functions $R_2$ and transverse momentum correlation functions $P_2$, obtained from $p$-Pb collisions at 5.02 TeV and Pb-Pb collisions at 2.76 TeV. The results are obtained by using charged particles in the pseudorapidity range $\left|\eta \right|<1.0$ and transverse momentum range $0.2<p_{\mathrm{T}}<2.0$ GeV/$c$ as a function of pair separation in pseudorapidity, $\left|\mathrm{\Delta }\eta \right|$, azimuthal angle $\mathrm{\Delta }\phi$, and for several charged-particle multiplicity classes. Measurements are carried out for like-sign and unlike-sign charged-particle pairs separately and combined to obtain charge-independent and charge-dependent correlation functions. We study the evolution of the width of the near-side peak of these correlation functions with collision centrality. Additionally, we study Fourier decompositions of the correlators in $\mathrm{\Delta }\phi$ as a function of pair separation $\left|\mathrm{\Delta }\eta \right|$. Significant differences in the dependence of their harmonic coefficients on multiplicity classes are found. These differences can be exploited, in theoretical models, to obtain further insight into charged-particle production and transport in heavy-ion collisions. Moreover, an upper limit of nonflow contributions to flow coefficients $v_n$ measured in Pb-Pb collisions based on the relative strength of Fourier coefficients measured in $p$-Pb interactions is estimated.

I calculate the energy per particle of symmetric nuclear matter and pure neutron matter in the framework of the microscopic Brueckner-Hartree-Fock approach using some recent interactions derived in chiral perturbation theory at next-to-next-to-next-to-leading order (N3LO) for the nucleon-nucleon ($NN$) force, and next-to-next-to-leading order (N2LO) for the nucleon-nucleon-nucleon ($NNN$) one. The interactions considered in the present work have been adjusted to properties of light nuclei with $A=3$, adopting local regulators for the $NNN$ interaction. I performed several calculations using an effective density dependent two-body force obtained from the original $NNN$ one keeping the same parameters and the same regularization scheme employed in finite light nuclei calculations; I then compared these results with other calculations obtained, retaining the same parameters of the $NNN$ force fixed on light nuclei but using a nonlocal regulator. This second strategy has been often used in the literature due to the easier derivation of the effective $NN$ force in this case. I found that in pure neutron matter the use of local or nonlocal regulators does not sensibly affect the calculation of the energy per particle while in symmetric nuclear matter the use of local or nonlocal regulators produces appreciable differences. Saturation properties of nuclear matter are discussed for the various models considered; the uncertainties on the reported calculations are also estimated.

The decays of the $\beta$-delayed neutron emitters ${}^{137}\mathrm{I}$ and ${}^{95}\mathrm{Rb}$ have been studied with the total absorption $\gamma$-ray spectroscopy technique. The purity of the beams provided by the JYFLTRAP Penning trap at the ion guide isotope separator on-line facility in Jyväskylä allowed us to carry out a campaign of isotopically pure measurements with the decay total absorption $\gamma$-ray spectrometer, a segmented detector composed of 18 NaI(Tl) modules. The contamination coming from the interaction of neutrons with the spectrometer has been carefully studied, and we have tested the use of time differences between prompt $\gamma$ rays and delayed neutron interactions to eliminate this source of contamination. Due to the sensitivity of our spectrometer, we have found a significant amount of $\beta$ intensity to states above the neutron separation energy that deexcite by $\gamma$ rays, comparable to the neutron emission probability. The competition between $\gamma$ deexcitation and neutron emission has been compared with Hauser-Feshbach calculations, and it can be understood as a nuclear structure effect. In addition, we have studied the impact of the $\beta$-intensity distributions determined in this work on reactor decay heat and reactor antineutrino spectrum summation calculations. The robustness of our results is demonstrated by a thorough study of uncertainties and with the reproduction of the spectra of the individual modules and the module-multiplicity gated spectra. This work represents the state-of-the-art of our analysis methodology for segmented total absorption spectrometers.

We study the effects of nuclear symmetry energy on the mass-radius relation and tidal deformability of neutron stars, considering the self-consistency of the equation of state (EOS). We first construct a set of unified EOSs based on relativistic mean-field models with different density dependence of the symmetry energy. For the description of pasta phases appearing in the inner crust of neutron stars, we perform a self-consistent Thomas-Fermi calculation using the same nuclear interaction as that for the uniform matter in the core. To examine possible effects from the self-consistency of the EOS on neutron star properties, we separately investigate the impacts of crust and core segments. By matching the same core EOS to different crust EOSs, it is found that neutron-star radii are significantly affected by the crust segment. On the other hand, the neutron-star radii are also strongly dependent on the core EOS. However, the correlation between the radius and the symmetry energy slope of the core EOS is opposite to that of the crust EOS. It is likely that the nuclear model with a small slope parameter is favored by recent astrophysical observations.

Neutrino nuclear scattering in hot and dense matter relevant for supernovae, neutron star mergers, and proto-neutron stars is considered. At finite temperature, neutrinos exhibit exo- and endoenergetic scattering on nuclear species due to the neutral-current Gamow-Teller interaction component. From an analysis of energy transfer and straggling cross sections we demonstrate that additional noticeable mechanisms in equilibrating neutrinos with matter originate in magnetized nucleon gas. Average energy transfer, i.e., ratio of energy transfer and scattering cross sections, depends almost linearly on neutrino energy and changes from positive to negative value. For hot nuclear material such crossover between acceleration and stopping regimes occurs when neutrino energy is about a factor four of temperature. Similar features are displayed for neutrino scattering on hot atomic nuclei. For the ${}^{56}\mathrm{Fe}$ nucleus the stopping regime starts at energies slightly above than four times temperature. Possible effects in neutrino transport and spectra are discussed.

Isotope-production cross sections for $p$-, $d$-, and C-induced spallation reactions on ${}^{93}\mathrm{Nb}$ at 113 MeV/nucleon were measured using the inverse-kinematics method employing secondary targets of ${\mathrm{CH}}_2$, ${\mathrm{CD}}_2$, and C. The measured cross sections for ${}^{90}\mathrm{Mo}$, ${}^{90}\mathrm{Nb}$, ${}^{86,88}\mathrm{Y}$ produced by $p$-induced reactions were found to be consistent with those measured by the conventional activation method. We performed benchmark tests of the reaction models INCL-4.6, JQMD, and JQMD-2.0 implemented in the Particle and Heavy Ion Transport code System (PHITS) and of the nuclear data libraries JENDL-4.0/HE, TENDL-2017, and ENDF/B-VIII.0. The model calculations also showed generally good agreement with the measured isotope-production cross sections for $p$-, $d$-, and C-induced reactions. It also turns out that, among the three nuclear data libraries, JENDL-4.0/HE provides the best agreement with the measured data for the $p$-induced reactions. We compared the present ${}^{93}\mathrm{Nb}$ data with the ${}^{93}\mathrm{Zr}$ data, that were measured previously by the same inverse kinematics method (Kawase et al., Prog. Theor. Exp. Phys. 2017, 093D03 (2017)), with particular attention to the effect of neutron-shell closure on isotope production in $p$- and $d$-induced spallation reactions. The isotopic distributions of the measured production cross sections in the ${}^{93}\mathrm{Zr}$ data showed noticeable jumps at neutron number $N=50$ in the isotopic chains of $\mathrm{\Delta }Z=0$ and $-1$, whereas no such jump appeared in isotopic chain of $\mathrm{\Delta }Z=0$ in the ${}^{93}\mathrm{Nb}$ data. From INCL-4.6 $+$ GEM calculations, we found that the jump formed in the evaporation process is smeared out by the intranuclear cascade component in ${}^{91}\mathrm{Nb}$ produced by the ${}^{93}\mathrm{Nb}(p,p2n)$ and $(d,d2n)$ reactions on ${}^{93}\mathrm{Nb}$. Moreover, for ${}^{93}\mathrm{Nb}$, the distribution of the element-production cross sections as a function of the change in proton number $\mathrm{\Delta }Z$ is shifted to smaller $\mathrm{\Delta }Z$ than for ${}^{93}\mathrm{Zr}$, because the excited Nb prefragments generated by the cascade process are more likely to emit protons than the excited Zr prefragments, due to the smaller proton-separation energies of the Nb isotopes.

We argue that the analytical approach of [Phys. Rev. C 98, 014312 (2018)] is incorrect. The authors obtain a solution for a sextic potential through the truncation of the power series of the wave-function ansatz. We show that the procedure should be equivalent to that of the quasiexactly solvable versions of the sextic potential used previously and that the quantization of the total energy is not performed properly. Additionally, we question the reliability of the transition probabilities calculated between states described by different collective potentials and, respectively, belonging to distinct Hilbert spaces.

The development of advanced $\gamma$-ray tracking arrays allows for a sensitive new technique to investigate elusive states of exotic nuclei with fast rare-isotope beams. By taking advantage of the excellent energy and position resolution of the Gamma-Ray Energy Tracking In-beam Nuclear Array, we developed a novel technique to identify in-flight isomeric decays of the $0_2^{+}$ state in ${}^{32}\mathrm{Mg}$ populated in a two-proton removal reaction. We confirm the $0_2^{+}\to 2_1^{+}\gamma$-ray transition of ${}^{32}\mathrm{Mg}$ and constrain the $0_2^{+}$ decay lifetime, suggesting a large collectivity. The small partial cross section populating the $0_2^{+}$ state in this reaction provides experimental evidence for the reduced occupancy of the normal configuration of the $0_2^{+}$ state, indicating the intruder dominance of this state.

I have used a simple two-state mixing model to analyze $0\leftrightarrow 2$ transition matrix elements in ${}^{182,184}\mathrm{Hg}$. Fits provide $0^{+}$ and $2^{+}$ mixing in both nuclei, and values of basis-state $E2$ matrix elements. I agree with previous work that the ground state contains most of the less-collective basis state, but the converse is true for the $2^{+}$. It turns out that the potential mixing matrix elements are not independent of $J$, as is commonly assumed. I also include an analysis with newly revised matrix elements.

The first nuclear-excited state of ${}^{229}\mathrm{Th}, {}^{229\mathrm{m}}\mathrm{Th}$, is known to have extremely low excitation energy at 8.28 ± 0.17 eV, and the nuclear decay mode and half-life of ${}^{229\mathrm{m}}\mathrm{Th}$ are considered to depend on its chemical environment. Recently, internal-conversion (IC) electrons from ${}^{229\mathrm{m}}\mathrm{Th}$ produced from a ${}^{233}\mathrm{U}$ source were detected for the first time, and the half-life of ${}^{229\mathrm{m}}\mathrm{Th}$ on the nickel-alloy surface of a microchannel plate detector was determined. In this study, to determine the half-lives for other chemical environments, we produced ${}^{229\mathrm{m}}\mathrm{Th}$ through the β decay of ${}^{229}\mathrm{Ac}$ and measured low-energy IC electrons from ${}^{229\mathrm{m}}\mathrm{Th}$ using the coincidence measurement technique between high-energy electrons (mainly β particles and high-energy IC electrons) and all electrons (including IC electrons from ${}^{229\mathrm{m}}\mathrm{Th}$) emitted from an ${}^{229}\mathrm{Ac}$ electrodeposited source. The ${}^{229}\mathrm{Ac}$ nuclide was produced by the ${}^{232}\mathrm{Th}(p,\alpha ){}^{229}\mathrm{Ac}$ reaction and then was separated from a large amount of the reaction byproducts utilizing chemical separation techniques. Electron signals, which correspond to the IC electrons from ${}^{229\mathrm{m}}\mathrm{Th}$, were detected using the coincidence measurement technique. The half-life of ${}^{229\mathrm{m}}\mathrm{Th}$ in the Ac electrodeposited source was determined to be 10(8) μs, which is close to the previous experimental value. The method established in this study lays the foundations to study the IC-decay property of ${}^{229\mathrm{m}}\mathrm{Th}$ as a function of the chemical environment.

The incomplete fusion dynamics of ${}_{10}{}^{20}\mathrm{Ne}+{}_{82}{}^{208}\mathrm{Pb}$ collisions at energies above the Coulomb barrier are investigated using a novel semiclassical dynamical model, which combines a classical trajectory model with stochastic breakup, as implemented in the platypus code, with a dynamical fragmentation theory treatment of two-body clusterization and decay of a projectile. A finite-difference method solution to the time-independent Schrödinger equation in the charge asymmetry coordinate is employed by way of diagonalizing a tridiagonal Hamiltonian matrix with periodic boundary conditions. Results are compared with published experimental values to indicate the success of this new model, and next steps for its development are detailed.

We study the impact of the description of the knockout nucleon wave function on electron- and neutrino-induced quasielastic and single-pion production cross sections. We work in a fully relativistic and quantum mechanical framework, where the relativistic mean-field model is used to describe the target nucleus. The focus is on Pauli blocking and the distortion of the final nucleon; these two nuclear effects are separated and analyzed in detail. We find that a proper quantum mechanical treatment of these effects is crucial to provide the correct magnitude and shape of the inclusive cross section. Also, this seems to be key to predict the right ratio of muon-neutrino to electron-neutrino cross sections at very forward scattering angles.