We investigated the nuclear structure of ${}^{31}\mathrm{P}$ near the proton threshold using nuclear resonance fluorescence (NRF) to refine the properties of key resonances in the ${}^{30}\mathrm{Si}(p,\gamma ){}^{31}\mathrm{P}$ reaction, which is critical for nucleosynthesis in stellar environments. Excitation energies and spin-parities were determined for several states, including two unobserved resonances at $E_r=18.7\mathrm{keV}$ and $E_r=50.5\mathrm{keV}$. The angular correlation analysis enabled the first unambiguous determination of the orbital angular momentum transfer for these states. These results provide a significant update to the ${}^{30}\mathrm{Si}(p,\gamma ){}^{31}\mathrm{P}$ thermonuclear reaction rate, with direct implications for models of nucleosynthesis in globular clusters and other astrophysical sites. The revised rate is substantially lower than previous estimates at temperatures below 200 MK, affecting predictions for silicon isotopic abundances in stellar environments. Our work demonstrates the power of NRF in constraining nuclear properties, and provides a framework for future studies of low-energy resonances relevant to astrophysical reaction rates.

Accurately determining the size of the atomic nucleus with realistic nuclear forces is a long-outstanding issue of nuclear physics. The no-core shell model (NCSM), one of the powerful ab initio methods for nuclear structure, can achieve accurate energies of light nuclei. The extraction of converged radii is more difficult. In this work, we present a novel method to effectively extract the radius of light nuclei by restoring the long-range behavior of densities from NCSM calculations. The correct large distance asymptotics of two-body relative densities are deduced based on the NCSM densities in limited basis size. The resulting radii using the corrected densities show a nice convergence. The root-mean-square matter and charge radii of ${}^{4,6,8}\mathrm{He}$ and ${}^{6,7,8}\mathrm{Li}$ can be accurately obtained based on Jacobi-NCSM calculations with the high-precision chiral two-nucleon and three-nucleon forces combined with this new method. Our method can be straightforwardly extended to other ab initio calculations, potentially providing a better description of nuclear sizes with realistic nuclear forces.

The nuclear lattice effective field theory (NLEFT) is an efficient tool for solving nuclear many-body problems, which takes high-fidelity lattice chiral interactions as input and computes nuclear low-energy observables via quantum Monte Carlo techniques. In this work, we present the first next-to-next-to-next-to-leading order chiral forces on the lattice with the isospin-breaking effects fully taken into account. We focus on both the charge-independence breaking and charge-symmetry breaking effects. Specifically, we include the isospin-breaking effect from the mass difference between the charged and neutral pions in the one-pion-exchange potential, the Coulomb force for the $pp$ interaction, and the contribution of two additional charge-dependent contact operators. We also explicitly incorporate the two-pion-exchange potential, which was mostly neglected in previous NLEFT calculations. With these improvements, we are able to accurately reproduce the $np$ and $pp$ scattering phase shifts up to relative momentum $p\approx 200$ MeV as well as the deuteron properties. The construction of these charge-dependent lattice nuclear forces establishes a solid foundation for future high-precision nuclear ab initio calculations within the NLEFT framework.

We investigate the effect of temperature on $\alpha$-particle clustering in the diluted nucleus ${}^{16}\mathrm{O}$ using the multi-constrained finite-temperature relativistic Hartree-Bogoliubov model with the DD-ME2 interaction. At a critical density, the nucleus undergoes a Mott-like transition from a homogeneous to a localized configuration characterized by $\alpha$-particle clustering and the emergence of a finite nonaxial octupole deformation. We study the interplay between the onset of localization under nuclear dilution and the suppression of deformation and $\alpha$-particle clustering due to increasing temperature. Investigating the temperature-density plane, our findings indicate that temperature delays the formation of nonaxial octupole deformation and $\alpha$-particle clustering in dilute environments. Following the transition from homogeneous to clustered configurations, the nonaxial octupole deformation continues to increase with further dilution of the system and becomes nearly independent of temperature. We found that $\alpha$-particle clusters appear at temperatures up to $T=4.10$ MeV and at a corresponding normalized density ${\rho }_{\text{Mott}}/{\rho }_0\approx 0.09$.

Pioneering electroweak measurements of the neutron skin thickness in lead-208 and calcium-48 are challenging our understanding of nuclear dynamics. Many theoretical models suggest that the slope of the symmetry energy controls the development of a neutron skin in neutron-rich nuclei. This led to the expectation that if lead-208 exhibits a large neutron skin, calcium-48 should as well. Given that the PREX Collaboration reported a relatively thick neutron skin in lead, we anticipated that calcium would also have a significant neutron skin. Instead, the CREX Collaboration reported a thin neutron skin in calcium. Although many suggestions have been proposed, the “CREX-PREX dilemma” remains unsolved. Recently, an intriguing scenario has emerged, suggesting that an enhanced isovector spin-orbit interaction could simultaneously account for both results. Following this approach, we performed relativistic mean-field calculations with an increased isovector spin-orbit potential. Our findings indicate that, while this modification significantly affects the structure of calcium-48, it has only a marginal impact on lead-208, thereby bringing the results into better agreement with experiment. However, the strong enhancement required to mitigate the CREX-PREX dilemma destroys the agreement with a successful spin-orbit phenomenology, primarily by modifying the well-known ordering of spin-orbit partners.

Background: A variety of phases in the inner crust of neutron stars are crucial for understanding the pulsar phenomena. However, the three-dimensional coordinate-space calculation of the phases is computationally demanding.

Purpose: We aim to generalize the Fermi operator expansion (FOE) method that is effective for finite-temperature coordinate-space simulation, from the Hartree-Fock theory to Hartree-Fock-Bogoliubov (HFB) theory including the pairing effects. Furthermore, the periodic structure with free neutrons in the inner crust requires us to treat the system with the band theory.

Method: We give a concise proof that the generalized density matrix in the HFB theory can be obtained with the FOE. The Chebyshev polynomial expansion is used for calculations of the HFB band theory.

Results: Using a model for a slab phase of the inner crust, the FOE method produces results in good agreement with those based on the diagonalization of the HFB Hamiltonian.

Conclusions: The FOE method for the HFB band theory is a powerful tool for studying the nontrivial exotic structures in neutron stars. The FOE method is suitable for parallelization and further acceleration is possible with nearsightedness.

The Ichimura-Austern-Vincent (IAV) model provides a powerful theoretical framework for describing inclusive breakup reactions. However, its post-form representation presents significant numerical challenges due to the absence of a natural cutoff in the transition matrix integration. This work presents a systematic assessment of convergence methods for post-form IAV calculations, comparing the bin method and the Vincent-Fortune approach. I demonstrate that while the bin method offers implementation simplicity, it exhibits strong parameter dependence that compromises numerical stability. In contrast, the Vincent-Fortune method, which employs complex contour integration, achieves reliable convergence without arbitrary parameters. I further introduce a novel hybrid approach that integrates finite-range distorted wave Born approximation (DWBA) with the Vincent-Fortune technique, combining the accuracy of finite-range treatment at short distances with the numerical stability of zero-range approximations in the asymptotic region. Numerical results for deuteron and ${}^6\mathrm{Li}$-induced reactions confirm the efficacy of this hybrid method, achieving reliable outcomes while resolving the convergence problems associated with the bin approach. This advancement enables more reliable calculations of nonelastic breakup cross sections and facilitates the extension of the IAV formalism beyond DWBA to incorporate continuum-discretized coupled-channels wave functions for a more comprehensive treatment of breakup processes.

Measurements of the $5p{}^{2}P_{3/2}\to 9s{}^{2}S_{1/2}$ and $5p{}^{2}P_{1/2}\to 8s{}^{2}S_{1/2}$ transitions in the indium atom, combined with new atomic physics calculations, were used to extract the changes in mean-square nuclear charge radii, $\delta \langle r^2\rangle$, of the indium ($Z=49$) isotopes ${}^{101–111}\mathrm{In}, {}^{113–123}\mathrm{In}$, and ${}^{125–131}\mathrm{In}$. With a proton hole in the closed nuclear shell of $Z=50$, indium provides a detailed study of the effect of unpaired nucleons adjacent to the proton-shell closure, allowing investigation into the charge radii for isotopes between the two major neutron-shell closures at $N=50$ and $N=82$. A study of the variations in charge radii between neighboring isotopes with neutron number (the ‘odd-even staggering') is presented and provides further insight and challenges for the theoretical description of the size of proton-hole nuclei. Two nuclear theories, density functional theory and the valence-space in-medium similarity renormalization group method, were employed to interpret the data. The new information obtained in this work provides valuable insights into the successes and shortcomings of the theoretical approaches employed.

Double deeply virtual Compton scattering (DDVCS) is a promising channel for generalized parton distribution (GPD) studies as it is a generalization of the deeply virtual Compton-scattering (DVCS) and timelike Compton-scattering (TCS) processes. In contrast to DVCS and TCS, the GPD phase space accessed through DDVCS is not constrained by on-shell conditions on the incoming and outgoing photons, thus allowing unrestricted GPD extraction from experimental observables. Considering polarized electron and positron beams directed to a polarized proton target, we study the sensitivity of the DDVCS cross-section asymmetries to the chiral-even proton GPDs from different model predictions. The feasibility of such measurements is further investigated in the context of the CLAS and SoLID spectrometers at the Thomas Jefferson National Accelerator Facility and the future Electron-Ion Collider at the Brookhaven National Laboratory.

Experiments are described, and results are provided, for the duplication of the first-ever triton-deuterium (colloquially referred to as DT) fusion experiment accidentally performed by A. J. Ruhlig in 1938, but forgotten in the published scientific literature. We find that Ruhlig overestimated the ratio of the triton-deuterium over deuteron-deuterium neutron yields in his secondary reaction (reaction-in-flight) experiment compared to modern theoretical calculations and our duplication of his experiment using modern neutron detection methods. Nevertheless, Ruhlig's observation provided the motivation for the application of DT fusion after World War II and its more recent importance in peaceful energy production at DT fusion facilities around the world. Additionally, the experimental technique used in the present work provides a novel approach for checking on low-energy triton stopping powers in deuterium containing compounds.

The ${}^{13}\mathrm{C}(p,\gamma ){}^{14}\mathrm{N}$ reaction is the second reaction of the CNO cycle. This cycle takes place in our Sun and fuels massive, red, and asymptotic giant branch stars. The ${}^{13}\mathrm{C}(p,\gamma ){}^{14}\mathrm{N}$ rate affects the final abundances of ${}^{12,13}\mathrm{C}$ and ${}^{19}\mathrm{F}$ nuclides, with impact on our understanding of the $i$ and $s$ process, giant star nucleosynthesis and mixing processes, and ultimately the chemical evolution of the galaxy. Here, we report on a new measurement of the ${}^{13}\mathrm{C}(p,\gamma ){}^{14}\mathrm{N}$ cross section, which has been performed at the Felsenkeller shallow underground laboratory in Dresden (Germany). The present $S$-factor results agree at low energy with LUNA data but are about 20% lower than previous literature data over the whole energy range explored, $E=310-680\mathrm{keV}$. The narrow resonance corresponding to the 7966.9(5) keV excited state has been investigated and we report a new resonance strength, $\omega \gamma =18\left(2\right)\mathrm{meV}$. In addition, a new $R$-matrix fit is presented, from which new parameters for the broad resonance corresponding to the 8062.0(10) keV excited state are derived and a new extrapolation for the total $S$ factor down to zero energy is obtained, $S_{\mathrm{tot}}\left(0\right)=6.4\left(4\right)\mathrm{keV}$ b. Finally a new reaction rate is calculated and reported here.

The calculation of the spectrum of antineutrinos (${\overline{\mathrm{\nu }}}_{\mathrm{e}}$) from a reactor is a complicated problem requiring several nuclear data and physics inputs. Many of these have been investigated thoroughly to improve calculations and properly account for uncertainties. One input which has heretofore escaped consideration is the fission-yield distribution between ground and isomeric states. In this work, we explore the effect of incorporating newly evaluated isomeric yield ratios (IYR) for 43 fission products into summation calculations and identify the disproportionate importance of certain isotopes, particularly at higher energies. Our analysis indicates that updated IYRs contribute to a significant increase in the ${\overline{\mathrm{\nu }}}_{\mathrm{e}}$ spectrum around and above 7 MeV, with increases of more than 50% at higher energies. Through a detailed sensitivity study, we highlight a number of isotopes for which the IYR has a substantial effect on the ${\overline{\mathrm{\nu }}}_{\mathrm{e}}$ spectrum. This work stresses the critical role of isomeric yields in calculations of reactor ${\overline{\mathrm{\nu }}}_{\mathrm{e}}$ spectra and points to the necessity for their accurate experimental determination, especially for key fission products, in order to refine our understanding and address the observed anomalies between measured and calculated ${\overline{\mathrm{\nu }}}_{\mathrm{e}}$ spectra.

Within the recently developed five-dimensional Langevin approach for the description of fission of heavy nuclei, we have calculated the fission fragments mass and kinetic energy distributions for the fission of ${}^{180}\mathrm{Hg}$ and ${}^{190}\mathrm{Hg}$ formed in the reactions ${}^{36}\mathrm{Ar}+{}^{144}\mathrm{Sm}\Rightarrow {}^{180}\mathrm{Hg}$ and ${}^{36}\mathrm{Ar}+{}^{154}\mathrm{Sm}\Rightarrow {}^{190}\mathrm{Hg}$ at few excitation energies and found very good agreement between the calculated and experimental results. Special attention was paid to the accurate description of the dependence of shell effects on the excitation energy. It was shown that the effect of multichance fission on the mass distribution is noticeable only at small excitation energies. The kinetic energy distributions are more sensitive to pre-scission neutron emission.

Background: The probability per unit area for a radioactive ${}^{88}\mathrm{Zr}$ nucleus ($t_{1/2}=83.4$ d) to capture neutrons across resonance energies—the neutron-capture resonance integral ($I_{\gamma }$)—is the largest ever reported [Shusterman et al., Phys. Rev. C 103, 024614 (2021)] with a value of $2.53\left(28\right)\times {10}^6$ barns. This implies that the neutron-capture cross section is orders of magnitude larger than previously thought at energies relevant to explosive environments applications, such as nuclear astrophysics and radiochemical diagnostics of nuclear devices.

Purpose: These applications require the shape of the capture cross section across a wide energy range which has never been measured before. The unexpectedly large values of both the thermal capture cross section and resonance integral could have a large impact on applications. Thus, the determination of the ${}^{88}\mathrm{Zr}$ neutron capture cross sections over a wide energy range is important on both fundamental and applied levels.

Method: A neutron transmission experiment on ${}^{88}\mathrm{Zr}$ [Stamatopoulos et al., Phys. Rev. Lett. 134, 112702 (2025)] was performed at the Device for Indirect Capture Experiments on Radionuclides (DICER) at the Los Alamos Neutron Science CEnter (LANSCE), from $0.0253$ to 500 eV using the time of flight technique. Any resonances responsible for the large $(n,\gamma )$ cross section (${\sigma }_{\gamma }$), will be reflected in the ($n$,tot) cross section. The ($n$,tot) data were used to extract the capture cross section as a function of energy.

Results: The present work revealed a nuclear level in the $n+{}^{88}\mathrm{Zr}$ system at 171 meV above the neutron separation energy and a thermal neutron-capture cross section of 771(31) kb, which is in good agreement with the recently published value [Shusterman et al., Phys. Rev. C 103, 024614 (2021) and Shusterman et al., Nature (London) 565, 328 (2019)]. In contrast, the neutron-capture resonance integral extracted from the present data is 15.21(67) kb and is roughly a factor of 200 smaller than the literature value [Shusterman et al., Phys. Rev. C 103, 024614 (2021)].

Conclusions: The recently reported enormous thermal capture cross section was confirmed and is attributed to a resonance at 171 meV and bound state 174 eV below the neutron separation energy. Our obtained value of the resonance integral is 166 times smaller than reported and that can have a huge impact on applications.

High-spin isomers in very-neutron-rich $A\approx 190$ Hf-Ta-W nuclei were populated via the pioneering fragmentation of a ${}^{198}\mathrm{Pt}$ primary beam at the National Superconducting Cyclotron Laboratory. The nuclei were implanted in a Si detector stack surrounded by the Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA) to detect delayed $\gamma$ rays, providing first level schemes using $\gamma \text{−}\gamma$ coincidence data from isomeric decays in this previously inaccessible region of the nuclear chart. A sudden transition to a strong triaxial shape is observed in the very-neutron-rich ${}^{189}\mathrm{Ta}$ $(N=116)$ nucleus from axially prolate shapes in lighter Ta isotopes, providing a critical experimental benchmark for competing theoretical predictions of nuclear-shape evolution.

The probabilities for γ-ray and particle emission as a function of the excitation energy of a decaying nucleus are valuable observables for constraining the ingredients of the models that describe the deexcitation of nuclei near the particle emission threshold. These models are essential in nuclear astrophysics and applications. In this paper, we have for the first time simultaneously measured the γ-ray and neutron emission probabilities of ${}^{208}\mathrm{Pb}$. The measurement was performed in inverse kinematics at the Experimental Storage Ring (ESR) of the GSI/FAIR facility, where a ${}^{208}\mathrm{Pb}$ beam interacted through the ${}^{208}\mathrm{Pb}(p,p^{\prime })$ reaction with a hydrogen gas jet target. Instead of detecting the γ rays and neutrons emitted by ${}^{208}\mathrm{Pb}$, we detected the heavy beamlike residues produced after γ and neutron emission. These heavy residues were fully separated by a dipole magnet of the ESR and were detected with outstanding efficiencies. The comparison of the measured probabilities with model calculations has allowed us to test and select different descriptions of the γ-ray strength function and the nuclear level density available in the literature.

Mu2e and COMET will search for electrons produced via the neutrinoless conversion of stopped muons bound in 1s atomic orbits of ${}^{27}\mathrm{Al}$, improving existing limits on charged lepton flavor violation (CLFV) by roughly four orders of magnitude. Conventionally, $\mu \to e$ conversion experiments are optimized to detect electrons originating from transitions where the nucleus remains in the ground state, thereby maximizing the energy of the outgoing electron. Clearly, detection of a positive signal in forthcoming experiments would stimulate additional work—including subsequent conversion experiments using complementary nuclear targets—to further constrain the new physics responsible for CLFV. Here we argue that additional information can be extracted without the need for additional experiments, by considering inelastic conversion in ${}^{27}\mathrm{Al}$. Transitions to low-lying nuclear excited states can modify the near-endpoint spectrum of conversion electrons, with the ratio of the elastic and inelastic responses being sensitive to the underlying CLFV operator. We extend the nuclear effective theory of $\mu \to e$ conversion to the inelastic case, which adds five new response functions to the six that arise for the elastic process. We evaluate these nuclear response functions in ${}^{27}\mathrm{Al}$ and calculate the resulting conversion-electron signal, taking into account the resolution anticipated in Mu2e/COMET. We find that ${}^{27}\mathrm{Al}$ is an excellent target choice from the perspective of the new information that can be obtained from inelastic $\mu \to e$ conversion.

The low-energy octupole $3^{-}$ state of ${}^{208}\mathrm{Pb}$ is investigated within the framework of the nuclear shell model with realistic nucleon-nucleon interactions. It is shown that the large correlation energy of this state is essentially due to the scattering of fully-aligned nucleon pairs, with the dominant role played by the scattering of high angular momentum fully-aligned neutron-proton pairs. A large fragmentation of the one-particle one-hole wave function, together with the coherence of the wave function, leads to the collective character of the octupole state. This coherence is shown to be a generic property of yrast natural-parity eigenstates of the nuclear many-body Hamiltonian. It induces a constructive accumulation of interaction strength, which may lead to a significant fragmentation of the wave function and a large correlation energy. Electric transitions from the octupole state to the ground state also benefit from this coherence property, resulting in a large enhancement of the transition probability.

We propose two novel constraints for the theoretical corrections to Gamow-Teller transition rates. The first, derived from a two-level model, predicts forbidden regions within the plane defined by the isospin-mixing correction ${\delta }_{C1}$ and the ratio $\eta$ of the isospin-symmetry Gamow-Teller matrix elements between the upper and lower admixed states. It serves as a filter for the theoretical calculations, particularly effective for small values of $\left|\eta \right|$. The other employs experimental $ft$ values, incorporating the upper admixed states, and exploits mirror symmetry to eliminate isospin-invariant and nuclear structure-independent quantities presented in the master decay formula. Within the standard model, this approach offers an alternative means for collectively testing the theoretical corrections for isospin and radiative effects beyond tree level. Additionally, it enables an experimental extraction of ${\eta }^2$, yielding a sensitive test for the isospin-conserving component of the nuclear Hamiltonian. Our investigation also reveals a substantial cancellation among radiative correction contributions in these tests, suggesting that these corrections are largely invariant under mirror symmetry. Importantly, the remarkable consistency of the nuclear structure corrections achieved in this axial-vector process provides a robust validation for the underlying theoretical approach in the purely vector process, especially the superallowed $0^{+}\to 0^{+}$ nuclear $\beta$ decay—the most accurate tool for extracting the $V_{ud}$ matrix element.

As a step towards the ultimate goal of a high-precision mass measurement of doubly magic ${}^{100}\mathrm{Sn}$, the mass of ${}^{103}\mathrm{Sn}$ was measured at the Low Energy Beam and Ion Trap (LEBIT) located at the Facility for Rare Isotope Beams (FRIB). Utilizing the time-of-flight ion cyclotron resonance technique, a mass uncertainty of 3.7 keV was achieved, an improvement by more than an order of magnitude compared to a recent measurement performed in 2023 at the Cooler Storage Ring (CSRe) in Lanzhou. Although the LEBIT and CSRe mass measurements of ${}^{103}\mathrm{Sn}$ are in agreement, they diverge from the experimental mass value reported in the 2016 version of the Atomic Mass Evaluation (AME2016), which was derived from the measured $Q_{{\beta }^{+}}$ value and the mass of ${}^{103}\mathrm{In}$. In AME2020, this indirectly measured ${}^{103}\mathrm{Sn}$ mass was classified as a “seriously irregular mass” and replaced with an extrapolated value, which aligns with the most recent measured values from CSRe and LEBIT. As such, the smoothness of the mass surface is confidently reestablished for ${}^{103}\mathrm{Sn}$. Furthermore, LEBIT's mass measurement of ${}^{103}\mathrm{Sn}$ enabled a significant reduction in the mass uncertainties of five parent isotopes which are now dominated by uncertainties in their respective $Q$ values.