We develop an extension of eigenvector continuation (EC) that makes it possible to extrapolate simulations of quantum systems in finite periodic boxes across large ranges of box sizes. The formal justification for this approach, which we call finite-volume eigenvector continuation (FVEC), is provided by matching periodic functions at different box sizes. As concrete FVEC implementation we use a discrete variable representation based on plane-wave states and present several applications calculated within this framework.

The effect of Coriolis $K$ mixing on the $\gamma$ decay of one-quasiparticle isomeric states is examined in transfermium nuclei with neutron number $N=153$. We consider a core-plus-quasiparticle coupling in which the $K$ mixing sharply increases if the isomeric quasiparticle state closely approaches the rotational state with the same angular momentum $I$, but built on another quasiparticle state which is either directly coupled to the isomeric ($\mathrm{\Delta }K=1$) or connected with it through the intermediate mixing quasiparticle orbitals ($\mathrm{\Delta }K>1$). This mechanism is likely to explain the 38-ns $K^{\pi }=7/2^{+}$ isomer in ${}^{251}\mathrm{Cf}$ which is quasidegenerated with an $I^{\pi }=7/2^{+}$ rotation state built on $K^{\pi }=1/2^{+}$. Our model explains the enhancement of its decay by three orders of magnitude compared to the $K^{\pi }=7/2^{+}$ isomer in ${}^{249}\mathrm{Cm}$. We suggest that the same mechanism could be of general importance for the isomer decay properties in a wide range of heavy odd-mass nuclei.

A quadrupole-octupole axially symmetric model is constructed for the unified description of alternate parity bands corresponding to octupole vibration or a stable deformation. The model depends on two parameters whose clear physical meaning allows a systematic description of the rotation-vibration dynamics of alternate parity bands analyzed for isotopic sequences of Ra, Th, U, and Pu nuclei. A critical point is identified in the $A=224–228$ mass region of the Ra and Th nuclei marking different stages of the transition between static and dynamic octupole deformation. Model predictions are performed for energies of unobserved states of the yrast sequence and of the excited bands as well as for the $E1, E2$, and $E3$ transition rates, which reproduce the available experimental data and exhibit a specific spin dependence for the transitional nuclei.

We discuss how the measurement of photon angular correlations can reveal information about the orientation of the fission fragment angular momenta. Photons from identified stretched $E2$ collective transitions in even-even fission product nuclei are particularly suitable because they do not affect the orientation of the nuclear spin. Their angular distribution relative to the direction of a fission fragment may reveal the orientation of the fragment spins relative to the fission axis. A novel means of probing the correlated fission fragment spins is the distribution of the opening angle between $E2$ photons from even-even partner fragments which reveals the mutual correlation of the fragment spins, if the photon helicities can be determined, demonstrating the potential power of helicity measurements in fission.

The composite nature of a shallow bound state is studied by using the weak-binding relation, which connects the compositeness of the bound state with observables. We first show that the previous weak-binding relation cannot be applied to the system with a large effective range. To overcome this difficulty, we introduce the finite-range correction by redefining the typical length scale in the weak-binding relation. A method to estimate the uncertainty of the compositeness is proposed. It is numerically demonstrated that the range correction enlarges the applicable region of the weak-binding relation. Finally, we apply the improved weak-binding relation to the actual hadrons, nuclei, and atomic systems [deuteron, $X\left(3872\right), D_{s0}^{*}\left(2317\right), D_{s1}\left(2460\right), N\mathrm{\Omega }$ dibaryon, $\mathrm{\Omega }\mathrm{\Omega }$ dibaryon, ${}_{\mathrm{\Lambda }}{}^3\mathrm{H}$, and ${}^4\mathrm{He}$ dimer] to discuss their internal structure from the compositeness. We present a reasonable estimation of the compositeness of the deuteron by properly taking into account the uncertainty. The results of $X\left(3872\right)$ and the $N\mathrm{\Omega }$ dibaryon show that the range correction is important to estimate the compositeness of physical states.

The synthesis of hyper-heavy elements is investigated under conditions simulating neutron star environment. The constrained molecular dynamics approach is used to simulate low energy collisions of extremely $n$-rich nuclei. A new type of the fusion barrier due to a “neutron wind” is observed when the effect of neutron star environment (screening of Coulomb interaction) is introduced implicitly. When introducing also a background of surrounding nuclei, the nuclear fusion becomes possible down to temperatures of ${10}^8$ K and synthesis of extremely heavy and $n$-rich nuclei appears feasible. A possible existence of hyper-heavy nuclei in a neutron star environment could provide a mechanism of extra coherent neutrino scattering or an additional mechanism, resulting in x-ray burst or a gravitational wave signal and, thus, becoming another crucial process adding new information to the suggested models on neutron star evolution.

This work investigated the first-chance survival probabilities of highly excited compound superheavy nuclei in the prospect of synthesizing new superheavy elements. The main feature of our modelings is the adoption of microscopic temperature dependent fission barriers in calculations of fission rates. A simple derivation is demonstrated to elucidate the connection between the Bohr-Wheeler statistical model and the imaginary free energy method, obtaining a new formula for fission rates. Various models are examined to reproduce the experimental fission probability of ${}^{210}\mathrm{Po}$. Systematic studies of fission and survival probabilities of No, Fl, Og, and $Z=120$ compound nuclei are performed. Results show that $Z=120$ compound nuclei still have considerable first-chance survival probabilities at high excitations, which are very similar to that of Fl and Og nuclei.

Impacts of nuclear structure on multiplicity $\left(N_{\mathrm{ch}}\right)$ and anisotropic flows $(v_2$ and $v_3)$ in the isobaric collisions of ${}_{44}{}^{96}\mathrm{Ru}+{}_{44}{}^{96}\mathrm{Ru}$ and ${}_{40}{}^{96}\mathrm{Zr}+{}_{40}{}^{96}\mathrm{Zr}$ at $\sqrt{s_{NN}}$ = 7.7, 27, 62.4, and 200 GeV are investigated by using the string melting version of a multiphase transport (AMPT) model. In comparison with the experimental data released recently by the STAR Collaboration, it is found that the impact of quadrupole deformation ${\beta }_2$ on the $v_2$ difference is mainly manifested in the most central collisions, while the octupole deformation ${\beta }_3$ is in the near-central collisions, and the neutron skin effect dominates in the mid-central collisions. Viewing from the energy dependence, these effects are magnified at lower energies.

In this paper, the two-photon-exchange (TPE) effect in $ep\to en{\pi }^{+}$ at small $-t$ is discussed. In the previous work, the TPE contribution with one $\pi$ intermediate state is estimated numerically within a hadronic model under the pion-dominance approximation. Here we extend the discussion to include one $\rho$ intermediate state. The TPE contribution can be described by one scalar function in the limit $m_e\to 0$, the dispersion relation (DR) satisfied by this scalar function is analyzed. The analytic expressions for the imaginary parts of the TPE contributions from one $\pi$ or one $\rho$ intermediate state are given within the hadronic model. Combining these analytic expressions and the DR, the corresponding real parts of the TPE contributions can be estimated easily at any available region. This can help the further experimental analysis to include the TPE contributions in a convenient way. The numeric results show that the TPE correction with one $\rho$ intermediate state is much smaller than that with one $\pi$ intermediate state in the current energy region. These results suggest that the TPE contribution with an elastic state is the main TPE contribution in $ep\to en{\pi }^{+}$ at small $-t$.

In backward photoproduction of mesons, the produced vector meson takes most of the struck nucleon momentum. The nucleon loses most of its momentum, and so is shifted several units of rapidity. Thus the Mandelstam $u$ is small, while the squared momentum transfer $t$ is typically large, near the kinematic limit. In a collider geometry, backward production transfers the struck baryon by many units of rapidity, in a striking similarity to baryon stopping. We explore this similarity, and point out the similarities between the Regge theories used to model baryon stopping with those that are used for backward production. We then explore how backward production can be explored at higher energies than are available at fixed target experiments, by studying production at an electron-ion collider. We calculate the expected $ep$ cross sections and rates, finding that the rate for backward $\omega$ production is about 1/300 that of forward $\omega \mathrm{s}$. We discuss the kinematics of backward production and consider the detector requirements for experimental study. We demonstrate that an experiment at the proposed U.S. Electron-Ion Collider will have the capability to detect backward-production events and may provide a test for models of stopping in high-energy $ep$ collisions including the baryon-junction model.

We report on the measurement of ${}^{11}\mathrm{B}$ and ${}^{40}\mathrm{Ca}$ levels between excitation energies of 8 and 9 MeV using nuclear resonance fluorescence (NRF). The experiment was carried out with nearly monoenergetic and linearly polarized photon beams provided by the High-Intensity $\gamma$-ray Source ($\mathrm{HI}\gamma \mathrm{S}$) facility at the Triangle Universities Nuclear Laboratory (TUNL). States in ${}^{11}\mathrm{B}$ are important for calibrations of NRF measurements, while the properties of ${}^{40}\mathrm{Ca}$ levels impact potassium nucleosynthesis in globular clusters. For ${}^{40}\mathrm{Ca}$, we report on improved excitation energies and an unambiguous $2^{-}$ assignment for the state at 8425 keV. For ${}^{11}\mathrm{B}$, we obtained improved values for $\gamma$-ray multipolarity mixing ratios and branching ratios of the 8920-keV level.

We present a systematic study of $\mathrm{\Lambda }$ hyperon's polarization observables using event-by-event ($3+1$) dimensional relativistic hydrodynamics. The effects of initial hot spot size and quark gluon plasma's specific shear viscosity on the polarization observables are quantified. We examine the effects of the two formulations of the thermal shear tensor on the polarization observables using the same hydrodynamic background. With event-by-event simulations, we make predictions for the Fourier coefficients of ${\mathrm{\Lambda }}^{\prime }\mathrm{s}$ longitudinal polarization $P^z$ with respect to the event planes of different orders of anisotropic flow. We propose new correlations among the Fourier coefficients of $P^z$ and charged hadron anisotropic flow coefficients to further test the mapping from fluid velocity gradients to hyperon's polarization. Finally, we present a system size scan with $\mathrm{Au}+\mathrm{Au}$, $\mathrm{Ru}+\mathrm{Ru}$, and $\mathrm{O}+\mathrm{O}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$ to study the system size dependence of polarization observables at the BNL Relativistic Heavy-ion Collider.

The $\beta$ decays of the ground state (gs) and isomeric state $\left(m\right)$ of ${}^{96}\mathrm{Y}$ have been studied with the total absorption $\gamma$-ray spectroscopy technique at the Ion Guide Isotope Separator On-Line facility. The separation of the $8^{+}$ isomeric state from the $0^{-}$ ground state was achieved thanks to the purification capabilities of the JYFLTRAP double Penning trap system. The $\beta$-intensity distributions of both decays have been independently determined. In the analyses the deexcitation of the 1581.6 keV level in ${}^{96}\mathrm{Zr}$, in which conversion electron emission competes with pair production, has been carefully considered and found to have significant impact on the $\beta$-detector efficiency, influencing the $\beta$-intensity distribution obtained. Our results for ${}^{96\text{gs}}\mathrm{Y}$ $\left(0^{-}\right)$ confirm the large ground state to ground state $\beta$-intensity probability, although a slightly larger value than reported in previous studies was obtained, amounting to $96.6_{-2.1}^{+0.3}\%$ of the total $\beta$ intensity. Given that the decay of ${}^{96\text{gs}}\mathrm{Y}$ is the second most important contributor to the reactor antineutrino spectrum between 5 and 7 MeV, the impact of the present results on reactor antineutrino summation calculations has been evaluated. In the decay of ${}^{96m}\mathrm{Y}$ $\left(8^{+}\right)$, previously undetected $\beta$ intensity in transitions to states above 6 MeV has been observed. This shows the importance of total absorption $\gamma$-ray spectroscopy measurements of $\beta$ decays with highly fragmented deexcitation patterns. ${}^{96m}\mathrm{Y}$ $\left(8^{+}\right)$ is a major contributor to reactor decay heat in uranium-plutonium and thorium-uranium fuels around 10 s after fission pulses, and the newly measured average $\beta$ and $\gamma$ energies differ significantly from the previous values in evaluated databases. The discrepancy is far above the previously quoted uncertainties. Finally, we also report on the successful implementation of an innovative total absorption $\gamma$-ray spectroscopy analysis of the module-multiplicity gated spectra, as a first proof of principle to distinguish between decaying states with very different spin-parity values.

A method to visualize many-body correlations using the information of the full wave function is presented. The set of nucleon coordinates which maximizes the square of the wave function, that is, the most probable spatial configuration of nucleons, is visualized. The method is applied to Hartree-Fock (HF) and $\mathrm{HF}+\mathrm{BCS}$ wave functions of $p$- and $sd$-shell $N=Z$ even-even nuclei to analyze the many-body correlations in those systems. It is found that there are $\alpha$-cluster-like four-body correlations already at the HF level in some of the nuclei. The effects of pairing on the most probable configuration are also investigated. The method is useful to analyze the nuclear many-body correlations, and it suggests a new viewpoint to microscopic nuclear wave functions.

We develop a statistical approach for the description of complex nuclei formation from dynamically produced baryons in high energy heavy-ion reactions. We consider a finite highly excited expanding nuclear system formed after central nucleus-nucleus collisions. This system is subdivided into primary equilibrated nucleon clusters. The final nuclei are produced after the decay of these excited clusters. By the successful comparison with the FOPI experimental data we prove the possibility of such a local equilibrium in nuclear matter with the temperature corresponding to the phase coexistence region. The regularities obtained in this new nuclei production mechanism are shown.

The first direct determination of the ground-state–to–ground-state $Q$ values of the ${\beta }^{-}$ decay ${}^{76}\mathrm{As}\to {}^{76}\mathrm{Se}$ and the electron-capture decay ${}^{155}\mathrm{Tb}\to {}^{155}\mathrm{Gd}$ was performed utilizing the double Penning trap mass spectrometer JYFLTRAP. By measuring the atomic mass difference of the decay pairs via the phase-imaging ion-cyclotron-resonance technique, the $Q$ values of ${}^{76}\mathrm{As}\to {}^{76}\mathrm{Se}$ and ${}^{155}\mathrm{Tb}\to {}^{155}\mathrm{Gd}$ were determined to be 2959.265(74) keV and 814.94(18) keV, respectively. The precision was increased relative to earlier measurements by factors of 12 and 57, respectively. The new $Q$ values are 1.33 keV and 5 keV lower compared to the values adopted in the most recent Atomic Mass Evaluation 2020. With the newly determined ground-state–to–ground-state $Q$ values combined with the excitation energy from $\gamma$-ray spectroscopy, the $Q$ values for ground-state–to–excited-state transitions ${}^{76}\mathrm{As}$ (ground state) $\to {}^{76}\mathrm{Se}^{*}$ (2968.4(7) keV) and ${}^{155}\mathrm{Tb}$ (ground state) $\to {}^{155}\mathrm{Gd}^{*}$ (815.731(3) keV) were derived to be $-9.13\left(70\right)$ keV and $-0.79\left(18\right)$ keV. Thus we have confirmed that both of the ${\beta }^{-}$-decay and EC-decay candidate transitions are energetically forbidden at a level of at least $4\sigma$, thus definitely excluding these two cases from the list of potential candidates for the search of low-$Q$-value ${\beta }^{-}$ or EC decays to determine the electron-(anti)neutrino mass.

The damping of isoscalar giant quadrupole resonance in ${}^{16}\mathrm{O}$ is studied using extended random-phase-approximation approaches derived from the time-dependent density-matrix theory. It is pointed out that the effects of ground-state correlations bring strong fragmentation of quadrupole strength even if the number of two-particle–two-hole configurations is strongly limited.

Evidence for the presence of short-lived radioactive isotopes when the Solar System formed is preserved in meteorites, providing insights into the conditions at the birth of our Sun. A low-mass core-collapse supernova had been postulated as a candidate for the origin of ${}^{10}\mathrm{Be}$, reinforcing the idea that a supernova triggered the formation of the Solar System. We present a detailed study of the production of ${}^{10}\mathrm{Be}$ by the $\nu$ process in supernovae, which is very sensitive to the reaction rate of the major destruction channel, ${}^{10}\mathrm{Be}{(p,\alpha )}^7\text{Li}$. With data from recent nuclear experiments that show the presence of a resonant state in ${}^{11}\mathrm{B}$ at $\approx 193$ keV, we derive new values for the ${}^{10}\mathrm{Be}{(p,\alpha )}^7\text{Li}$ reaction rate, which are significantly higher than previous estimates. We show that, with the new ${}^{10}\mathrm{Be}{(p,\alpha )}^7\text{Li}$ reaction rate, a low-mass CCSN is unlikely to produce enough ${}^{10}\mathrm{Be}$ to explain the observed ${}^{10}\mathrm{Be}/{}^9\mathrm{Be}$ ratio in meteorites, even for a wide range of neutrino spectra considered in our models.

The theoretical analysis of the ${}^2\mathrm{H}{\left(d,p\right)}^3\mathrm{H}$ reaction taking place in both metallic as well as gaseous targets at deuteron energies of several keV presented here indicates a strong contribution of the single-particle $0^{+}$ threshold resonance. Additional arguments based on the weak coupling between the 2 + 2 and 3 + 1 clustering states of the compound nucleus ${}^4\mathrm{He}$ support this resonance and suggest its large partial width for the internal electron-positron pair formation that overestimates the proton width. A detailed study of the interplay between the resonance transition and the electron screening effect enables estimation of the nuclear reaction rate of the deuteron-deuteron fusion reactions at room temperature.