A high-precision measurement of the electron-capture (EC) decay $Q$ value for the ground-state-to-ground-state (gs-to-gs) transition of ${}^{113}\mathrm{Sn}$ to ${}^{113}\mathrm{In}$ has been performed using the JYFLTRAP double Penning trap mass spectrometer. Employing the phase-imaging ion-cyclotron-resonance technique, the isomeric state of ${}^{113}\mathrm{Sn}$ at 77.389(19) keV was resolved, and the cyclotron frequency ratio was measured between the isomer ${}^{113m}\mathrm{Sn}$ and the daughter nucleus ${}^{113}\mathrm{In}$. This yielded an isomer-to-ground-state $Q$ value of 1116.64(19) keV and gs-to-gs $Q$ value of 1039.25(19) keV. The atomic mass excess of ${}^{113}\mathrm{Sn}$ was determined as $-88327.87\left(27\right)\mathrm{keV}/c^2$, in excellent agreement with the Atomic Mass Evaluation 2020 (AME2020) but with a sixfold precision improvement. Using nuclear energy-level data for ${}^{113}\mathrm{In}$, we identified two low $Q$-value transitions of the ground state of ${}^{113}\mathrm{Sn}$ to excited states of ${}^{113}\mathrm{In}$ at 1024.280(50) keV ($Q_{\mathrm{EC}}^{*}=14.97\left(20\right)$ keV, second forbidden non-unique) and 1029.650(50) keV ($Q_{\mathrm{EC}}^{*}=9.60\left(20\right)$ keV, allowed). The allowed transition exhibits small energy differences [${\mathrm{\Delta }}_{\mathrm{L}1}=5.58\left(20\right)$ keV, ${\mathrm{\Delta }}_{\mathrm{L}2}=5.87\left(20\right)$ keV] from L1 and L2 shell binding energies, enhancing endpoint events. Partial half-lives and energy-release spectra were calculated using the self-consistent Dirac-Hartree-Fock-Slater method (including exchange, overlap, shake-up, and shake-off corrections) together with the nuclear shell model and showed enhanced endpoint sensitivity for the allowed transition to the state at 1029.650 keV. Including subthreshold atomic states in the spectral function enhances the EC rate near the zero-neutrino-momentum region by a factor of 5, enabling new approaches for low-$Q$-value EC decays in neutrino mass studies.

We perform a study of electromagnetic radiation in heavy-ion collisions at energies available at the Relativistic Heavy Ion Collider (RHIC) Beam Energy Scan (BES) and the CERN Super Proton Synchrotron (SPS) using the iEBE-MUSIC framework, which includes three-dimensional (3D) dynamical Monte Carlo Glauber initial conditions, MUSIC $(3+1)\mathrm{D}$ viscous relativistic hydrodynamics, and the UrQMD hadronic afterburner. The multistage modeling has been calibrated to hadronic data at RHIC-BES energies using a Bayesian analysis. Integrating the thermal photon emission rates with the medium evolution, we study the direct photon yield and elliptic flow and how they vary with collision energy and emission source. We compare with results obtained by the STAR and PHENIX Collaborations. We employ next-to-leading order thermal QCD dilepton emission rates to compute dilepton invariant mass spectra and extract the effective temperature of the quark-gluon plasma at different collision energies.

We include the small components of valence states of actinides in the calculation scheme within the linear augmented plane wave method for solids and study their influence on the electron density at the actinide nuclear region, which is important for such processes as electron capture, beta decay, internal conversion, and others. The method was applied to Ac, Th, ${\mathrm{ThO}}_2$, and ${\mathrm{UO}}_2$. We find that, depending on the material, the electron density of valence electrons at the nucleus increases by a factor of $2.4–4.3$, and this increase is due to the electron density from the small components of the $6p_{1/2}$ semicore states. Although accounting for the electron density of small components typically results in very small changes in the equilibrium lattice constant and bulk modulus, in some cases it reaches 0.007 Å for the lattice constant and 8 GPa for the bulk modulus. A refined electron density distribution in nucleus can be important for accurately describing electron-nuclear phenomena and for calculating characteristics measured in nuclear spectroscopy, especially for the low-energy clock transition in the ${}^{229}\mathrm{Th}$ nucleus.

We measure event-by-event discrete changes in the net electric charge of an optically levitated silica microsphere arising from individual radioactive decays within the sphere, in coincidence with energy depositions in a nearby scintillation detector. The net charge of the levitated sphere is continuously monitored by measuring its driven response to an oscillating electric field, allowing individual charge-change events to be resolved on millisecond timescales with precision below an elementary charge. Simultaneously, $\alpha$ and $\beta$ particles emitted during decays of implanted ${}^{212}\mathrm{Pb}$ and its daughters are detected using a scintillator read out with an array of silicon photomultipliers. By correlating reconstructed charge-change times with the scintillator response, we can directly attribute abrupt changes in the sphere's net charge to individual nuclear decays, and identify differences in the distribution of charges ejected for $\alpha$ and $\beta$ decays. These results establish a new approach for studying low-energy charged particles emitted by radioactive decays at the single-decay level, and identify showers of radiogenically produced low-energy electrons emitted by $\alpha$-decaying radon daughters implanted near solid surfaces.

In this work, we study the longitudinal response function of the deuteron up to next-to-next-to-leading order in chiral effective field theory (chiral EFT). We use an approach that maintains exact renormalization group (RG) invariance at each order of the EFT expansion by treating all subleading corrections in perturbation theory. To that end, we extend the Lorentz integral transform method to allow for such a perturbative treatment. In doing so, we further develop the existing work on strictly RG-invariant chiral EFT, which has so far focused primarily on binding energies and static properties, to inelastic processes. We carefully analyze the convergence properties of the theory and find good agreement with available experimental data. Our findings provide the foundation for similar studies of inelastic processes in a range of nuclei, based on perturbatively renormalized EFT schemes.

Accurate prediction of fragmentation cross sections is essential for rare-isotope beam production, planning new-isotope searches, and designing experiments to study the most exotic regions of the nuclear chart. However, existing reaction models and phenomenological cross-section parametrizations often exhibit significant deviations over broad regions of mass and charge. In this work, a Bayesian-inspired model-averaging framework is developed to combine abrasion-ablation (AA) calculations based on multiple nuclear mass tables into a single statistically weighted estimate. For the calibrated systems, the model weights are assigned empirically according to the relative quality of fit to measured cross sections, thereby reducing systematic model bias while preserving the underlying physics content of the AA description. The weights are constrained using proton-rich fragmentation data for the ${}^{78}\mathrm{Kr}$ and ${}^{124}\mathrm{Xe}$ projectiles. The resulting parameter trends are then propagated to the ${}^{92}\mathrm{Mo}$ and ${}^{144}\mathrm{Sm}$ systems through a controlled scaling procedure. In the present implementation, the excitation-energy prescription is fixed, while the averaging is performed across nuclear-mass inputs; the framework provides both weighted cross sections and associated uncertainty estimates. Applied to proton-rich fragmentation, the present approach provides a practical basis for interpolation and limited extrapolation in regions relevant to rare-isotope production. The resulting predictions are used to assess the production of very proton-rich nuclei, and candidate new isotopes are discussed.

We investigate the capacity of nonorthogonal many-body expansions in the resolution of the nuclear shell-model secular problem. Exact shell-model solutions are obtained within the variational principle using nonorthogonal Slater determinants as the variational ansatz. These results numerically prove the realization of the Broeckhove-Deumens theorem on the existence of a discrete set of nonorthogonal wave functions that exactly span the full shell-model space for low-lying states of interest. With the angular-momentum variation after projection, pairing correlations are shown to be fully captured by Slater determinants as exemplified in the backbending phenomenon occurred in ${}^{48}\mathrm{Cr}$. The resulting discrete nonorthogonal shell model developed in such a variation-after-projection method is further examined in the case of ${}^{78}\mathrm{Ni}$, an exotic doubly magic nucleus at the edge of currently feasible diagonalization limits. Its ground state binding energy is shown to converge to a lower value than the largest large-scale shell-model diagonalization ever done by the conventional tridiagonal Lanczos method, revealing an outstanding performance of nonorthogonal Slater determinantal wave functions to describe the eigensolutions of shell-model Hamiltonians.

A comprehensive Bayesian analysis of the three-dimensional (3D) dynamics of high-energy nuclear collisions is presented. We perform a systematic model-to-data comparison using simulations of large and small collision systems, and a broad range of measurements from the PHENIX, STAR, PHOBOS, and BRAHMS collaborations spanning nearly two decades of operations at the BNL Relativistic Heavy Ion Collider (RHIC). In particular, we perform fully 3D multistage simulations including rapidity-dependent energy deposition with global energy conservation using the 3D Glauber model, along with relativistic viscous hydrodynamics with music. We calibrate the model on rapidity- and $p_T$-differential observables and analyze the respective constraints on initial state and transport properties they provide. We emphasize the additional constraints provided by rapidity-dependent measurements, the differences in large and small system calibrations, and the tension exhibited by particular observables. We use our calibrated model to make predictions of observables in $p$-Au and ${}^3\mathrm{He}$-Au collisions. Furthermore, we facilitate direct comparison of experimental measurements by highlighting the dependence of flow measurements on the rapidity of the regions of interest and reference, as well as the importance of the centrality selection. In particular, we examine the apparent differences between the STAR and PHENIX $v_2$ and $v_3$ measurements in small systems.

In the most extended layer of the inner crust of neutron stars, nuclear matter is believed to form a crystal of clusters immersed in a superfluid neutron gas. Here we analyze this phase of matter within fully self-consistent Hartree-Fock-Bogoliubov calculations using Skyrme-type energy density functionals for the mean field and a separable interaction in the pairing channel. The periodicity of the lattice is taken into account using Bloch boundary conditions, in order to describe the interplay between band structure and superfluidity. A relative flow between the clusters and the surrounding neutron gas is introduced in a time-independent way. As a consequence, the complex order parameter develops a phase, and in the rest frame of the superfluid one finds a counterflow between neutrons inside and outside the clusters. The neutron superfluid fraction is computed from the resulting current. Our results indicate that, at densities above $0.03{\text{fm}}^{-3}$, more than $90\%$ of the neutrons are effectively superfluid, independently of the detailed choice of the interaction, cluster charge, and lattice geometry. This fraction is only slightly lower than the one obtained recently within linear response theory on top of the Bardeen-Cooper-Schrieffer approximation, and it approaches the hydrodynamic limit for strong pairing. As a consequence, it is likely that the inner crust alone can provide a sufficient superfluid angular momentum reservoir to explain pulsar glitches.

Recent astronomical observations indicate that additional nucleosynthesis pathways are required to understand some atypical elemental abundance patterns revealed by new observations. One such process that can help to explain these observations is the intermediate neutron-capture process ($i$ process). The nuclear properties of isotopes involved in this nucleosynthesis pathway are experimentally well constrained with the exception of the neutron-capture reaction rates, which are provided almost entirely by theory. In this paper, the first experimentally constrained reaction rate on the ${}^{87}\mathrm{Kr}(n,\gamma ){}^{88}\mathrm{Kr}$ reaction is provided by employing the $\beta$-Oslo method. The impact of this reaction on the abundance of rubidium within the $i$ process is investigated.

We present the results of a multimethodological study aimed at investigating the interaction between graphene and tritium during its $\beta$-decay to helium, under different levels of loading and geometrical configurations. We combine density-functional theory (DFT) to evaluate the interaction potentials, with calculations of the decay rate, in order to study the consequences that the presence of the substrate has on the $\beta$-decay spectrum of tritium. We determine the shape of the event rate, accounting for the effects of (part of) the corresponding condensed-matter degrees of freedom. In the context of future neutrino experiments, our results provide important information aimed at the optimization of hosting material. Furthermore, our work outlines a novel theoretical and computational scheme to account for the different timescales involved in the process and to address a question at the boundary between high- and low-energy physics. This requires nonconventional declinations of DFT combined with full quantum treatments of the nuclear configuration involved in the decay process. Our results pave the way for future studies aimed at determining the physics reach of upcoming neutrino mass experiments.

The dinuclear system model incorporates several essential input physical quantities, including nuclear mass, fission barrier, shell correction energy, level density parameter, shell damping factor, etc., which are derived from diverse nuclear structure models. To achieve theoretical consistency, we try to generate these essential input physical quantities from the finite-temperature covariant density functional theory using the PC-PK1 energy density functional, with pairing correlations treated via the BCS approach. With microscopically determined input parameters, the dinuclear system model can successfully reproduce experimental results for (i) cold fusion reaction systems (${}^{48}\mathrm{Ca}+{}^{204,206–208}\mathrm{Pb}\to {}^{252,254–256}\mathrm{No}^{*}$) and (ii) hot fusion reaction systems (${}^{48}\mathrm{Ca} + {}^{239,240,242,244}\mathrm{Pu} \to {}^{287,288,290,292}\mathrm{Fl}^{*}$). Furthermore, we perform calculations for the fusion reactions ${}^{50}\mathrm{Ti}+{}^{249}\mathrm{Cf}, {}^{51}\mathrm{V}+{}^{249}\mathrm{Bk}, {}^{54}\mathrm{Cr}+{}^{248}\mathrm{Cm}$, and ${}^{55}\mathrm{Mn}+{}^{243}\mathrm{Am}$, targeting the synthesis of element 120. It is found that the maximum synthesis cross sections for these four reactions are 48.20, 12.33, 5.25, and 0.47 fb corresponding to ${}^{50}\mathrm{Ti}({}^{249}\mathrm{Cf},4n$)${}^{295}120$ at $E_{\mathrm{CN}}^{*}$ = 41 MeV, ${}^{51}\mathrm{V}({}^{249}\mathrm{Bk},3n$)${}^{297}120$ at $E_{\mathrm{CN}}^{*}$ = 34 MeV, ${}^{54}\mathrm{Cr}({}^{248}\mathrm{Cm},3n$)${}^{299}120$ at $E_{\mathrm{CN}}^{*}$ = 32 MeV, and ${}^{55}\mathrm{Mn}({}^{243}\mathrm{Am},5n$)${}^{293}120$ at $E_{\mathrm{CN}}^{*}$ = 53 MeV, respectively.

High-order perturbative ab initio calculations are challenging due to the rapidly growing configuration space and the difficulty of assessing convergence. In this letter, we introduce perturbation theory quantum Monte Carlo (PTQMC), a stochastic approach designed to compute high-order many-body perturbative corrections. By representing the perturbative wave function with random walkers in configuration space, PTQMC avoids the exponential scaling inherent to conventional constructions of high-rank excitation operators. Benchmark calculations for the Richardson pairing model demonstrate that PTQMC accurately reproduces exact many-body perturbation theory (MBPT) coefficients up to 16th order, even in strongly divergent regimes. We further show that combining PTQMC with series resummation techniques yields stable and precise energy estimates in cases where the straightforward perturbative series fails. Finally, we propose the effective number of configurations, $e^S$, as a global measure of perturbative wave-function complexity that can be directly extracted within PTQMC. We demonstrate that the saturation behavior of $e^S$ provides a more reliable indicator of the validity of perturbative expansions than energy convergence alone.

The cryogenic approach to the search for the neutron electric dipole moment—performing the experiment in superfluid liquid helium—holds promise for a substantial increase in sensitivity, potentially enabling a sensitivity level of ${10}^{-28}$ $e\mathrm{cm}$. A crucial component in realizing such an experiment is the high-voltage and electrode system capable of providing an electric field of 75 kV/cm. This, in turn, requires an electric potential of 635 kV to be applied to the high-voltage electrode, while simultaneously satisfying other experimental constraints, such as those on heat load and magnetic noise requirements. This paper describes the outcome of a comprehensive development program addressing these challenges. It outlines the system requirements, discusses new insights into relevant physical phenomena, and details selected technical solutions with their corresponding experimental demonstrations and expected performance. The results collectively demonstrate the successful development of the necessary technology for the high-voltage and electrode system for this approach.

Radiative strength functions (RSFs) model the bulk electromagnetic response of highly excited nuclei and are critical inputs for statistical reaction codes. In this paper, we present a definition of the RSF that is consistent with Hauser-Feshbach reaction codes and that can be efficiently computed with the shell model using the Lanczos strength-function (LSF) method. We introduce a variant of the shell-model LSF method that exploits the energy-localized Brink-Axel hypothesis, which makes it possible to compute both electric and magnetic RSFs across all energies relevant to capture reactions. We verify agreement with the conventional definition of RSFs with benchmark calculations of ${}^{24}\mathrm{Mg}$ and then present novel results for ${}^{56}\mathrm{Fe}$. For ${}^{56}\mathrm{Fe}$ we find that (i) the $M1$ RSF shape evolves smoothly with excitation energy, consistent with the energy-localized Brink-Axel hypothesis; (ii) both $M1$ and $E1$ transitions contribute significantly to the radiative strength below the photoabsorption threshold; and (iii) within the sdpf model space, the strength below 3 MeV observed in Oslo-type experiments cannot be fully reproduced. These results pave the way for a coherent microscopic description of RSFs and further motivate the use of energy-dependent RSFs in modern reaction codes.

We present a microscopic triaxial quadrupole-octupole collective Hamiltonian (TQOCH) that unifies collective rotations, quadrupole-octupole vibrations, and their couplings to model low-lying nuclear states of both parities. The TQOCH's dynamics are governed by collective parameters derived from multidimensionally constrained covariant density functional theory. The model's validity is demonstrated through calculations of ${}^{152}\mathrm{Sm}$, including its deformation energy surfaces, excitation spectra, and transition probabilities. As a predictive tool, the TQOCH probes complex nuclear phenomena like shape coexistence and phase transitions, directly connecting their microscopic origins to spectroscopic observables.

We report on high-precision mass measurements of the ground and first isomeric state of ${}^{75}\mathrm{Zn}$, performed using the time-of-flight ion-cyclotron-resonance technique at the ISOLTRAP Penning-trap mass spectrometer at ISOLDE/CERN. The isomeric state was produced using in-trap decay of ${}^{75}\mathrm{Cu}$. This marks the first direct investigation of the isomeric state of ${}^{75}\mathrm{Zn}$ via mass spectrometry. The isomer was observed at an excitation energy of $123.7\left(20\right)\mathrm{keV}$, in $2\sigma$ agreement with the value previously determined through decay spectroscopy. In addition, our measurements correct a misassignment of the ground-state mass excess based on a previous measurement by Baruah et al., revising the value to $-62681.0\left(21\right)\mathrm{keV}$. To further investigate the earlier discrepancy, we explored the spin-parity assignments of the ground and isomeric states in ${}^{75}\mathrm{Zn}$ using Skyrme Hartree-Fock plus Bardeen-Cooper-Schrieffer theoretical calculations, given the absence of definitive experimental data. In light of the laser spectroscopy results from Wraith et al., our results add strong evidence for a spin-1/2 ground state, which would agree with large-scale shell-model predictions as well as explaining disagreements with the Monte Carlo shell model.

Motivated by recent findings on the separability of optical potentials that are derived from folding off-shell densities with off-shell nucleon-nucleon amplitudes, we study the off-shell character of one-body density matrices created within the no-core shell model. Concentrating on nuclei with a $0^{+}$ ground state from ${}^4\mathrm{He}$ through ${}^{48}\mathrm{Ca}$, we investigate the off-shell character of their one-body density matrices in momentum space when using the momentum transfer and the average momentum as variables. A singular value decomposition of the one-body density matrices reveals that they can be characterized by only very few terms, depending on the mass number of the nucleus. These findings are independent of the nucleon-nucleon interactions employed, as well as of computational specifics, such as grid spacing and size of the model space.

Background: Physics-based emulators offer a fast and reliable replacement for an exact solution of the scattering problem in nuclear physics. Previous work developed a reduced-basis single channel emulator for nonaffine projectile-target interactions, such as optical potentials, to describe elastic scattering.

Purpose: Since many reactions of interest can be cast as a coupled-channel problem, the purpose of this work is to extend the reduced basis methods (RBM) to a coupled-channel framework.

Method: We generalize the reduced basis method to coupled-channel equations (CC-RBM) to describe inelastic scattering. Although our framework is general, in this work we apply it to reactions where the Hamiltonian coupling term comes from assuming a rotational structure model for the target. From a set of training coupled-channel wave functions, we perform a singular value decomposition to obtain a reduced set of basis wave functions, and then solve the extended (Petrov-)Galerkin equations in that basis. In addition, the empirical interpolation method is used to expand the nonaffine coupling potentials.

Results: We apply the CC-RBM method to elastic and inelastic scattering of neutrons on ${}^{48}\mathrm{Ca}$ including a quadrupole coupling to populate the first $2^{+}$ state, and neutrons on ${}^{208}\mathrm{Pb}$, including an octupole coupling to populate its first $3^{-}$ state. We demonstrate that the CC-RBM calculated elastic and inelastic cross sections match those obtained using traditional finite-difference (high-fidelity) methods. We show that the CC-RBM results can reliably reproduce the nuclear scattering cross sections at different energy regimes.

Conclusions: The computational accuracy versus time plots demonstrate that the CC-RBM method efficiently increases precision with increasing basis size. Most importantly, for the precisions required in reaction calculations (a percent on the cross section), we find the CC-RBM method offers roughly 1.5 orders of magnitude gain in computational speed compared to the traditional coupled-channels solver. However, we also discuss how this scaling becomes less favorable, the larger the number of channels included in the original coupled-channel set.

Exploring the reaction mechanisms responsible for the production of neutron-rich nuclides, we undertook a systematic study of the momentum distributions of projectile-like fragments from peripheral collisions of ${}^{86}\mathrm{Kr}$ at 15 MeV/nucleon with ${}^{64}\mathrm{Ni}$ and ${}^{124}\mathrm{Sn}$. For this purpose, our previous data collected with the momentum achromat recoil separator (MARS) at the Cyclotron Institute of Texas A&M were adopted. The momentum per nucleon ($p/A$) distributions of the ejectiles are characterized by a quasi-elastic peak just below the projectile velocity and a region at lower velocities corresponding to dissipative events. Two-body kinematics was employed to extract the total excitation energies of these regions. It was found that very neutron-rich isotopes can be probed in these reactions, especially with the heavier target via processes involving proton removal, neutron pickup, or a combination of these, up to a triple charge exchange process observed in the data. The experimental data were systematically compared with calculations employing the deep-inelastic transfer (DIT) model and the constrained molecular dynamics (CoMD) model followed by the GEMINI deexcitation code. The DIT model, phenomenologically treating the sequential exchange of nucleons, offered an overall qualitative description of the experimental momentum distributions, however underestimating the data in the quasielastic part of most of the channels. The CoMD model, based on a fully microscopic $N$-body approach, offered an overall better description of the majority of the data, whereas, in some cases, it led to overestimation of the quasielastic part of the momentum distributions. The detailed comparison of the model calculations with the experimental data provided valuable insight into the reaction mechanisms in this energy regime, suggesting, apart from independent nucleon exchange, the contribution of target inelastic excitation and direct reaction processes involving neutron and proton pair transfer, cluster transfer, and meson-mediated charge exchange. This work paves the way to a systematic investigation of the mechanisms of multinucleon transfer reactions involving medium-mass heavy ions below the Fermi energy and provides guidance for the production of exotic neutron-rich nuclei.