Background: The $\beta$ decays of fission products produced in nuclear fuel are important for nuclear energy applications and fundamental science of reactor antineutrinos. In particular, nuclear reactor safety is related to the decay modes of radioactive neutron-rich nuclei, primarily via the emission of $\gamma$ rays, neutrons, and electrons. Additionally nuclear reactors are the most powerful man-made source of antineutrinos emitted during the $\beta$ decay of fission products. These antineutrinos are used to inspect fundamental properties of leptons as well as informing reactor operation. However, the majority of data on complex decays of fission products collected in the evaluated nuclear data repositories like Evaluated Nuclear Structure Data File (ENSDF) and Evaluated Nuclear Data Files (ENDF) are based on low-efficiency and often incomplete measurements resulting in questionable reference reactor antineutrino flux predictions, see the analysis by [Nichols, J. Nucl. Sci. Technol. 52, 17 (2015)]. Various assessments like the one done under the auspices of the [Yoshida et al., Assessment of Fission Product Decay Data for Decay Heat Calculations: A report by the Working Party on International Evaluation Co-operation of the Nuclear Energy Agency Nuclear Science Committee (Nuclear Energy Agency, Organization for Economic Co-operation and Development, Paris, France, 2007), Vol. 25], as well as by [Sonzogni, Johnson, and McCutchan, Phys. Rev. C 91, 011301(R) (2015)] and [Dwyer and Langford, Phys. Rev. Lett. 114, 012502 (2015)], list the $A=142$ isobars with high cumulative fission yield among the important nuclei where data for reactor decay heat and/or antineutrino production should be verified and/or improved.

Purpose: Our goal is to improve the quality of $\beta$-decay measurements and evaluate the impact of modified decay schemes on reactor decay heat and antineutrino energy spectra, for fission products along the $A=142$ isobaric chain. This work is an in depth follow-up on [Rasco et al., Phys. Rev. Lett. 117, 092501 (2016)]. which presented briefly the impact of the corrected decay scheme of ${}^{142}\mathrm{Cs}$. Here, we extend the data to full isobaric decay chain including the daughter nuclei, ${}^{142}\mathrm{Ba}$ and ${}^{142}\mathrm{La}$, and present more details on the ${}^{142}\mathrm{Cs}$ results.

Method: The decays of neutron-rich isobars of mass $A=142$ produced by means of proton-induced fission of ${}^{238}\mathrm{U}$ were measured using the Modular Total Absorption Spectrometer (MTAS) array on-line at the mass separator and Tandem accelerator at Oak Ridge National Laboratory.

Results: The $\beta$-decay schemes for ${}^{142}\mathrm{Cs}$ and ${}^{142}\mathrm{La}$ were modified with respect to the nuclear data repositories. A small $\beta$-delayed neutron branching ratio for ${}^{142}\mathrm{Cs}$ emitter was remeasured as $0.{10}_{-3}^{+5}$ %. Improved precision on the measured half-lives is reported. Small corrections to the low-energy decay of ${}^{142}\mathrm{Ba}$ are made. The $\beta$-decay patterns for ${}^{142}\mathrm{La}$ and ${}^{142}\mathrm{Cs}$ are presented. The decay heat release and cross section for the detection of reactor antineutrinos are deduced and compared to earlier results.

Conclusions: The $\beta$-feeding pattern for ${}^{142}\mathrm{Cs}$ having decay energy value $Q_{\beta }$ of over 7 MeV was substantially modified with respect to the current ENSDF entry. Smaller changes were encountered for ${}^{142}\mathrm{La}$, but since this $A=142$ isobar also has a large cumulative yield in fission, the changes influence both decay heat and the antineutrino spectra. The previously known $\beta$ intensities for ${}^{142}\mathrm{Ba}$ decay ($Q_{\beta }$ value of 2.2 MeV) were verified and slightly modified. Overall, increased decay heat values and lower flux of antineutrinos interacting with matter are presented.

The framework of nuclear energy density functionals has been employed to describe nuclear structure phenomena for a wide range of nuclei. Recently, statistical properties of a given nuclear model, such as parameter confidence intervals and correlations, have received much attention, particularly when one tries to fit complex models. We apply information-theoretic methods to investigate stability of model reductions by the manifold boundary approximation method (MBAM). In an illustrative example of the density-dependent point-coupling model of the relativistic energy density functional, utilizing Monte Carlo simulations, it is found that main conclusions obtained from the MBAM procedure are stable under variation of the model parameters. Furthermore, we find that the end of the geodesic occurs when the determinant of the Fisher information metric vanishes, thus effectively separating the parameter space into two disconnected regions.

We investigate fusion reactions in collisions of neutron-halo projectiles with heavy targets. For this purpose, we use a recently developed theoretical approach to calculate cross sections for fusion processes in ${}^{11}\mathrm{Be}+{}^{209}\mathrm{Bi}$, ${}^6\mathrm{He}+{}^{209}\mathrm{Bi}$, and ${}^6\mathrm{He}+{}^{238}\mathrm{U}$ collisions and compare the results with the available data. The overall agreement between theory and experiment is good. Comparing the cross sections with predictions of a barrier penetration model that ignores the cluster structure of the projectile, we conclude that the fusion cross sections are suppressed above the Coulomb barrier and enhanced below. Further, we find that the deviations from predictions of the barrier penetration model depend exclusively on the breakup threshold of the projectile, increasing as it decreases.

The excitation functions of proton elastic scattering on ${}^{12}\mathrm{C}$ and ${}^{14,15}\mathrm{O}$ nuclei at the energies near the proton-emission threshold are calculated using the Skyrme Hartree-Fock (SHF) in continuum approach. For each excitation function, the first resonance is identified as the $s$-state resonance of the mean-field theory. For ${}^{15}\mathrm{O}$, whose ground-state spin is nonzero, the $s$-state resonance splits into two resonances via the spin-spin component of the optical potential. With a slight adjustment of the strength of the central potential, which is obtained from the SHF in continuum approach, the excitation functions of proton elastic scattering for the three nuclei can be explained with high accuracy. The proposed framework can provide a practical method to explain nuclear scattering at the energies near the proton-emission threshold with minimal experimental input.

We determined the ultracold neutron (UCN) production rate by superthermal conversion in the solid deuterium $\left({\mathrm{sD}}_2\right)$ moderator of the UCN source at the Paul Scherrer Institute (PSI). In particular, we considered low amounts of less than 20 mol of ${\mathrm{D}}_2$, deposited on the cooled moderator vessel surfaces in thin films of a few mm in thickness. We measured the isotopic $(c_{\text{HD}}<0.2\%)$ and isomeric $(c_{\text{para}}\le 2.7\%)$ purity of the deuterium to conclude that absorption and up-scattering at 5 K have a negligible effect on the UCN yield from the thin films. We compared the calculated UCN yield based on the previously measured thermal neutron flux from the heavy water thermal moderator with measurements of the UCN count rates at the beamports. We confirmed our results and thus demonstrated an absolute characterization of the UCN production and transport in the source by simulations.

Relativistic Brueckner-Hartree-Fock (RBHF) theory in the full Dirac space allows one to determine uniquely the momentum dependence of scalar and vector components of the single-particle potentials. In order to extend this new method from nuclear matter to finite nuclei, as a first step, properties of ${}^{208}\mathrm{Pb}$ are explored by using the microscopic equation of state for asymmetric nuclear matter and a liquid droplet model. The neutron and proton density distributions, the binding energies, the neutron and proton radii, and the neutron skin thickness in ${}^{208}\mathrm{Pb}$ are calculated. In order to further compare the charge densities predicted from the RBHF theory in the full Dirac space with the experimental charge densities, the differential cross sections and the electric charge form factors in the elastic electron-nucleus scattering are obtained by using the phase-shift analysis method. The results from the RBHF theory are in good agreement with the experimental data. In addition, the uncertainty arising from variations of the surface term parameter $f_0$ in the liquid droplet model is also discussed.

We study the directed flow of identified particles in Au+Au collisions at $\sqrt{s_{NN}}=7.7$ to 62.4 GeV. The Glauber model is extended to include both a tilted deformation of the QGP fireball with respect to the longitudinal direction and a non-zero longitudinal flow velocity gradient in the initial state. By combining this improved initial condition with a (3+1)-dimensional viscous hydrodynamic model calculation, we obtain a satisfactory description of the transverse momentum spectra and the rapidity dependent directed flow coefficient of different hadron species. Our calculation indicates the sensitivity of the hadron directed flow, especially its splitting between protons and antiprotons, to both the initial geometry and the initial longitudinal flow velocity. Therefore, the combination of directed flow of different hadrons can provide a tight constraint on the initial condition of nuclear matter created in heavy-ion collisions. The initial condition extracted from the directed flow is further tested with the global polarization of $\mathrm{\Lambda }$ and $\overline{\mathrm{\Lambda }}$ within the same theoretical framework, where we obtain a reasonable description of these hyperon polarization observed at different collision energies at RHIC.

${}^{15}\mathrm{N}{(\alpha ,\gamma )}^{19}\mathrm{F}$ is believed to be the primary means of stellar nucleosynthesis of fluorine. Here, we present the use of a single-fluid bubble chamber to measure the cross section of the time-inverse photodissociation reaction. The method benefits from a luminosity increase of several orders of magnitude due to the use of a thicker liquid target—when compared to thin films or gas targets—and from the reciprocity theorem. We discuss the results of an experiment at the Thomas Jefferson National Accelerator Facility, where the cross section of the photodisintegration process ${}^{19}\mathrm{F}(\gamma , \alpha ){}^{15}\mathrm{N}$ was measured by bombarding a superheated fluid of ${\mathrm{C}}_3{\mathrm{F}}_8$ with bremsstrahlung $\gamma$ rays produced by impinging a 4–5.5 MeV electron beam on a Cu radiator. From the photodissociation yield the cross section was extracted by performing a convolution with a Monte Carlo–generated $\gamma$-ray beam spectrum. The measurement produced a cross section that was then time inverted using the reciprocity theorem. The cross section for the ${}^{15}\mathrm{N}(\alpha ,\gamma ){}^{19}\mathrm{F}$ reaction was determined down to a value in the range of hundreds of picobarns. With further improvements of the experimental setup the technique could potentially push cross section measurements down to the single picobarn range.

Background: Well-established coupled channel and coupled reaction channel (CRC) processes make contributions to elastic scattering that are not included in standard folding models of the optical model potential (OMP). Such contributions have been established for ${}^3\mathrm{He}$ interacting with ${}^{208}\mathrm{Pb}$ but the corresponding contributions for ${}^3\mathrm{H}$ are expected to be different, particularly for pickup coupling.

Purpose: To establish and characterize the contribution to the interaction potential between ${}^3\mathrm{H}$ and ${}^{208}\mathrm{Pb}$ that is generated by coupling to proton pickup (outgoing ${}^4\mathrm{He}$) channels; also to study the contribution of collective states and identify effects of dynamical nonlocality due to these couplings.

Methods: CRC calculations, including coupling to collective states, will provide the elastic channel $S$-matrix $S_{lj}$ resulting from the included processes. Inversion of $S_{lj}$ will produce the local potential that yields, in a single channel calculation, the elastic scattering observables from the coupled channel calculation. Subtracting the bare potential from the inverted CRC potential yields a local and $l$-independent representation of the dynamical polarization potential (DPP). From the DPPs due to a range of combinations of channel couplings, the influence of dynamically generated nonlocality can be identified.

Results: Coupling to ${}^4\mathrm{He}$ channels makes a smaller contribution to the ${}^3\mathrm{H}$ interaction than it does for incident ${}^3\mathrm{He}$. On the other hand coupling to inelastic channels makes a greater contribution than it does for ${}^3\mathrm{He}$. The nonadditivity of the DPPs implies their dynamical nonlocality.

Conclusions: The DPPs established here challenge the notion that folding models, in particular local density models, provide a satisfactory description of elastic scattering of ${}^3\mathrm{H}$ from nuclei. Coupling to proton pickup channels induces dynamical nonlocality in the ${}^3\mathrm{H}$ OMP with implications for direct reactions involving ${}^3\mathrm{H}$. Departures from a smooth radial form for the ${}^3\mathrm{H}$ OMP should be apparent in high quality fits to suitable elastic scattering data. Future theories of the interaction of ${}^3\mathrm{H}$ with nuclei should include some representation of outgoing ${}^4\mathrm{He}$.

Based on the extended hadronic transport model of relativistic heavy-ion collisions, the incompressibility of dense hadronic matter created in relativistic $\mathrm{Au}+\mathrm{Au}$ heavy-ion collisions at $\sqrt{s_{NN}}=3$ GeV is studied. By comparing experimental proton directed flow, productions of strange hadrons $\varphi$, $K^{-}$ as well as their ratio $\varphi /K^{-}$, proton high-order cumulants to the model calculations, a large incompressibility of dense hadronic matter is obtained from nucleon observabels while a rather small incompressibility is needed to fit the data of strange hadrons. This may indicate hadronic matter possesses different incompressibilities in different density regions, i.e., the incompressibility may become stiffer from saturation density to a certain baryon density and then turn to soft before reaching hadron-quark phase transition. The study also shows that the incompressibility significantly affects the critical baryon density of hadron-quark phase transition.

Electric charge transport of hadronic matter at finite temperature and magnetic field is studied within the linear $\sigma$ model. Anisotropic transport coefficients associated with the charge transport are estimated both in the weak and strong regimes of the magnetic field using the transport theory approach. In a weakly magnetized medium, the magnetic field effects are incorporated through the Lorentz force term in the Boltzmann equation. Strong magnetic field puts further constraints on the motion of charged particles through Landau quantization. Magnetic field-dependent thermal relaxation time is obtained from interaction rates of hadrons with the $S$-matrix approach by considering the Landau level kinematics of the charged hadrons. Mean-field effects are embedded in the analysis through the temperature-dependent hadron masses. Further, the hadronic medium response to a time-varying external electric field is studied in weak and strong magnetic field regimes. It is seen that electromagnetic responses of the hadronic matter have a strong dependence on the mean-field effects, $\sigma$ mass, the strength of the external fields, and its evolution in the medium.

Relativistic energy-density functional (REDF) theory has been developed and utilized for self-consistent mean-field calculations of atomic nuclei. The proton-emitting radioactivity can provide a suitable reference to improve the predicting ability of REDF especially on the proton-drip line. One needs to consider the quantum tunneling effect, which plays an essential role in nucleon-emitting radioactive processes. However, the relativistic quantum tunneling has been less investigated compared with the nonrelativistic case. This work is devoted to a theoretical evaluation of one-proton ($1p$) radioactivity based on the relativistic Dirac formalism. For this purpose, I develop the time-dependent (TD) Dirac-spinor calculation to simulate the $1p$ emission. By utilizing the relativistic Hartree-Bogoliubov (RHB) calculation with the DD-PCX parameters, single-proton potentials for the time-dependent Dirac spinor are determined. The TD-Dirac calculation is applied to the $1p$ emissions from the ${}^{37}\mathrm{Sc}$ and ${}^{39}\mathrm{Sc}$ nuclei, which can be well approximated as the valence proton and the proton-close-shell cores. The sensitivity of $1p$-emission energy and decaying width to the mass number is demonstrated. Remarkable sensitivity exists due to the size of the system, which affects the nuclear part of potentials and energy levels, whereas the Coulomb barrier is common with the same atomic number. The calculated $1p$ energy and decaying lifetime are roughly consistent to the experimental limitation. The present TD-Dirac calculation is expected as applicable widely to proton-rich nuclides in order to improve the REDF by utilizing the $1p$-emission data.

Based on Boltzmann-Uehling-Uhlenbeck simulations calibrated by previous efforts of the transport model evaluation project, we have studied the specific shear viscosity $\eta /s$ of nuclear matter in the spinodal region using the Green-Kubo method. With the momentum-independent mean-field potential which reproduces reasonably well empirical nuclear matter properties and the nuclear phase diagram, we have generated dynamically stable and thermalized nuclear cluster systems in a box with the periodic boundary condition. Extensive results of $\eta /s$ at different average densities and temperatures in uniform and nonuniform systems are compared, and we found that the shear viscosity is smaller with nuclear clusters due to the enhanced correlation of the energy-momentum tensor and the stronger collision effect. The temperature dependence of $\eta /s$ has a minimum only at low average densities of $\rho <0.3{\rho }_0$. The present study serves as a rigorous baseline calculation of $\eta /s$ in nuclear systems with clusters, and helps our understanding of the relation between the shear viscosity and the nuclear phase diagram.

The magnetic fields in heavy-ion collisions are important ingredients for many interesting phenomena, such as the chiral magnetic effect, the chiral magnetic wave, the directed flow $v_1$ of $D^0$ mesons, and the splitting of the spin polarization of the $\mathrm{\Lambda }/\overline{\mathrm{\Lambda }}$. Quantitative studies of these phenomena, however, suffer from limited understanding of the dynamical evolution of these fields in the medium created by the collisions, which remains a critical and challenging problem. The initial magnetic fields from the colliding nuclei decay very fast in the vacuum but their lifetime could be extended through medium response due to electrically conducting quarks and antiquarks. Here we perform a detailed analysis of such medium effect on the dynamical magnetic fields by numerically solving Maxwell's equations concurrently with the expanding medium described by viscous hydrodynamics, under the assumption of negligible back reaction of the fields on the fluid evolution. Our results suggest a considerable enhancement of late time magnetic fields, the magnitude of which depends sensitively on the fireball expansion as well as the medium electric conductivity both before and during hydrodynamic stage.

The representation on a Fock space of the group of Bogolyubov transformations is recognized as the spin representation of an orthogonal group. Derivations based on this observation of some known formulas for the overlap amplitude of two Bogolyubov quasifermion vacuum states that are in some cases more complete than those in the literature are shown. It is pointed out that the name of an “Onishi formula” is assigned in the literature to two different expressions which are related but have different scopes. One of them has what has been described as a sign problem; the other one, due to Onishi and Yoshida, has a more limited scope and no sign problem. I give a short proof of the latter, whose derivation is missing in the paper by Onishi and Yoshida, and a new, combinatoric, proof of an equivalent formula recently derived by Robledo.

Emission of the bremsstrahlung photons in the scattering of protons off nuclei in the $\mathrm{\Delta }$-resonance energy region is studied. Including properties of $\mathrm{\Delta }$ resonance in the target nucleus in the bremsstrahlung model, the following issues are found. (1) The ratio between incoherent emission and coherent emission is about ${10}^6–{10}^7$ for $p+{}^{197}\mathrm{Au}$ (without $\mathrm{\Delta }$ resonance) at the proton beam energy $E_p$ of 190 MeV, where the calculated full bremsstrahlung spectrum is in good agreement with experimental data. This confirms the importance of incoherent processes in the study of $\mathrm{\Delta }$ resonances in this reaction, which have not been studied yet. The coherent and incoherent contributions, electric and magnetic contributions, and full bremsstrahlung spectra for the scattering of protons on the ${}^{12}\mathrm{C}, {}^{40}\mathrm{Ca}, {}^{208}\mathrm{Pb}$ nuclei at $E_p=800\mathrm{MeV}$ are found, and conditions for the most intensive bremsstrahlung emission are found. (2) The transition $pN\to {\mathrm{\Delta }}^{+}N$ in the target nucleus reinforces emission of bremsstrahlung photons in that reaction at $E_p=800\mathrm{MeV}$. The difference between the spectra for normal nuclei and nuclei with included $\mathrm{\Delta }$ resonance is larger for lighter nuclei, but the spectra are larger for heavier nuclei. (3) Taking short-lived $\mathrm{\Delta }$ resonance into account, It is found that the spectrum for the target nucleus with $\mathrm{\Delta }$ resonance is essentially larger in the high energy photon region than the spectrum without this $\mathrm{\Delta }$ resonance (calculations for ${}_{\mathrm{\Delta }}{}^{12}\mathrm{C}, {}_{\mathrm{\Delta }}{}^{40}\mathrm{Ca}, {}_{\mathrm{\Delta }}{}^{208}\mathrm{Pb}$ in comparison with ${}^{12}\mathrm{C}, {}^{40}\mathrm{Ca}, {}^{208}\mathrm{Pb}$ are provided). Such an aspect is recommended for registration of $\mathrm{\Delta }$ resonances in nuclei in future experiments.

The CUPID-Mo experiment, located at the Laboratoire Souterrain de Modane (France), was a demonstrator experiment for CUPID. It consisted of an array of $20{\mathrm{Li}}_2{}^{100}\mathrm{Mo}{\mathrm{O}}_4$ (LMO) calorimeters, each equipped with a Ge light detector for particle identification. In this work, we present the result of a search for two-neutrino and neutrinoless double-$\beta$ decays of ${}^{100}\mathrm{Mo}$ to the first $0^{+}$ and $2^{+}$ excited states of ${}^{100}\mathrm{Ru}$ using the full CUPID-Mo exposure ($2.71\mathrm{kg}\mathrm{yr}$ of LMO). We measure the half-life of $2\nu \beta \beta$ decay to the $0_1^{+}$ state as $T_{1/2}^{2\nu \to 0_1^{+}}=(7.5\pm 0.8\text{(stat.)}{}_{-0.3}^{+0.4}\text{(syst.)})\times {10}^{20}\mathrm{yr}$. The bolometric technique enables measurement of the electron energies as well as the $\gamma$ rays from nuclear deexcitation and this allows us to set new limits on the two-neutrino decay to the $2_1^{+}$ state of $T_{1/2}^{2\nu \to 2_1^{+}}>4.4\times {10}^{21}\mathrm{yr}(90\% \text{c.i.})$ and on the neutrinoless modes of $T_{1/2}^{0\nu \to 2_1^{+}}>2.1\times {10}^{23}\mathrm{yr}(90\% \text{c.i.})$, $T_{1/2}^{0\nu \to 0_1^{+}}>1.2\times {10}^{23}\mathrm{yr}(90\% \text{c.i.})$. Information on the electrons' spectral shape is obtained, which allows us to make the first comparison of the single and higher state dominance $2\nu \beta \beta$ decay models for the $0_1^{+}$ excited state of ${}^{100}\mathrm{Ru}$.