Fragment mass distributions from the fission of U and Pu isotopes at low excitation energies are studied using a dynamical model based on the fluctuation-dissipation theorem formulated as Langevin equations. The present calculations reproduced the overall trend of the asymmetric mass distribution without parameter adjustment for the first time using the Langevin approach. The Langevin trajectories show a complicated time evolution on the potential surface, which causes the time delay of fission, showing that dynamical treatment is vital. It was found that the shell effect of the potential energy landscape has a dominant role in determining the mass distribution, although it is rather insensitive to the strength of dissipation. Nevertheless, it is essential to include the effect of dissipation, because it has a crucial role in giving “fluctuation” to Langevin trajectories as well as for explaining the multiplicities of pre-scission neutrons as the excitation energy increases. Therefore, the present approach can serve as a basis for more refined analysis.

We investigate the effect of final state interaction (FSI) on the neutrino (antineutrino) scattering via neutral current from a ${}^{12}$C target in the quasielastic region within the framework of a relativistic single-particle model. Three different descriptions of the FSI, which are a relativistic mean field, a complex optical potential, and its real potential, are taken into account for two incident neutrino energies of 500 MeV and 1 GeV. The effects of the FSI are studied not only on the differential cross sections but also on each longitudinal, transverse, and transverse interference cross section. We found that the FSI description may play a vital role for the estimation of those cross sections, and the FSI effects on each response cross section may differ from those on the differential cross section. However, the asymmetry between neutrino and antineutrino scattering cross sections turns out to be nearly independent of the FSI descriptions. Finally, possible FSI effects on the MiniBooNE data are studied in detail.

We present the results of a high-precision quasi-elastic excitation function measurement for the ${}^{48}$Ca + ${}^{120}$Sn system at ${\theta }_{\mathrm{LAB}}$ = 160° at near-barrier energies in steps of 1.0 MeV. The corresponding quasi-elastic barrier distribution is derived. A large-scale coupled-channel calculation was performed to investigate the role of several reaction channels in the reaction mechanism. An excellent agreement between theory and data was obtained for the barrier distribution. The first quadrupole vibrations of the ${}^{48}$Ca and ${}^{120}$Sn, the 2$n$, and the ${}^4$He transfers have a strong influence on the reaction mechanism and are responsible for the good agreement achieved. The 1$n$ transfer has a minor importance in the result when compared with the 2$n$ transfer, which suggests that the pairing correlation might play an important role in the 2$n$-neutron transfer process. However, if the octupole vibration of the projectile is included in the coupling scheme, the agreement with the data gets worse. The comparison of the coupled-channel calculations with experimental data leads to the conclusion that the nuclear matter diffuseness of the ${}^{48}$Ca nucleus is 0.56 fm in agreement with most of the double-magic nuclei.

We have performed shell-model calculations of binding energies of nuclei around ${}^{132}$Sn. The main aim of our study has been to find out if the behavior of odd-even staggering across $N=82$ is explainable in terms of the shell model. In our calculations, we have employed realistic low-momentum two-body effective interactions derived from the charge-dependent Bonn nucleon-nucleon potential that have already proved quite successful in describing the spectroscopic properties of nuclei in the ${}^{132}$Sn region. Comparison shows that our results fully explain the trend of the experimental staggering.

Inclusive multineutron and multiproton removal cross sections from ${}^{112}\mathrm{Sn}$ and ${}^{104}\mathrm{Sn}$ at relativistic energies have been measured. The data show two distinct regimes of the reaction process that depend on the nucleon evaporation cost of the final nucleus. This behavior is universal by regarding the mass or asymmetry of the initial system or target composition. A state-of-the-art cascade and deexcitation model reproduces the observed trend but systematically fails in reproducing cross sections for the removal of the more bound nucleon species.

Lifetimes of the low-lying $(11/2^{-})$ states in ${}^{63,65}$Co have been measured employing the recoil distance doppler shift method (RDDS) with the AGATA $\gamma$-ray array and the PRISMA mass spectrometer. These nuclei were populated via a multinucleon transfer reaction by bombarding a ${}^{238}$U target with a beam of ${}^{64}$Ni. The experimental $B\left(E2\right)$ reduced transition probabilities for ${}^{63,65}$Co are well reproduced by large-scale shell-model calculations that predict a constant trend of the $B\left(E2\right)$ values up to the $N=40$ ${}^{67}$Co isotope.

The detailed analysis of the $\beta$-delayed fission data of ${}^{180}$Tl is presented. The experiment was performed by producing a pure beam of ${}^{180}$Tl by means of highly selective resonance laser ionization followed by mass separation with the ISOLDE (CERN, Geneva) isotope separator. A surprising asymmetric mass distribution of fission fragments from ${}^{180}$Hg, the daughter of ${}^{180}$Tl $\beta$ decays, was observed. Here, the energy calibration of the silicon detectors, which is crucial for a proper determination of the fission fragments’ energy and mass split, is presented and the total kinetic energy and its dependence on the mass split ratio is discussed. A more precise $\beta$-delayed fission probability $P_{\beta \text{DF}}{(}^{180}\text{Tl})=3.2\left(2\right)\times {10}^{-3}\%$ was deduced.

A detailed nuclear-decay spectroscopy study of the neutron-deficient isotope ${}^{178}$Tl has been performed using the highly selective Resonance Ionization Laser Ion Source and ISOLDE mass separator (CERN), which allowed a unique isobarically pure beam of ${}^{178}$Tl to be produced. The first identification of the $\beta$-delayed fission of this isotope was made and its probability $P_{\beta \text{DF}}{(}^{178}\text{Tl})=0.15\left(6\right)\%$ was determined. An asymmetric fission fragment mass distribution of the daughter isotope ${}^{178}$Hg (populated by the $\beta$ decay of ${}^{178}$Tl) was deduced based on the measured fission fragment energies. The fine-structure $\alpha$-decay pattern of ${}^{178}$Tl allowed the low-energy states in the daughter nucleus ${}^{174}$Au to be studied.

The phenomenon of wobbling can only occur for a nuclear shape with stable triaxial deformation. To date, only a few examples of this exotic collective mode have been observed in lutetium and tantalum isotopes. A search for a wobbling sequence was performed in ${}^{171}$Re to determine if this feature can be observed in $Z>73$ nuclei. No evidence was found for wobbling; however, an interaction between the $\pi i_{13/2}$ sequence and another positive-parity band may give an indication on why wobbling may not occur in this nucleus. The level scheme for ${}^{171}$Re was significantly extended and interpretations for the decay sequences are proposed within the context of the cranked shell model.

A microscopic theoretical framework based on relativistic energy density functionals (REDFs) is applied to studies of shape evolution, excitation spectra, and decay properties of transactinide nuclei. Axially symmetric and triaxial relativistic Hartree-Bogoliubov (RHB) calculations, based on the functional DD-PC1 and with a separable pairing interaction, are performed for the even-even isotopic chains between Fm and Fl. The occurrence of a deformed shell gap at neutron number $N=162$ and its role on the stability of nuclei in the region around $Z=108$ is investigated. A quadrupole collective Hamiltonian, with parameters determined by self-consistent constrained triaxial RHB calculations, is used to examine low-energy spectra of No, Rf, Sg, Hs, and Ds with neutron number in the interval $158\le N\le 170$. In particular, we analyze the isotopic dependence of several observables that characterize the transitions between axially symmetric rotors, $\gamma$-soft rotors, and spherical vibrators. An interesting example of a possible occurrence of shape-phase transitions and critical-point phenomena in this mass region is explored.

The effect of pairing correlations on the spectral statistical behavior of the spherical mean-field plus standard pairing model is investigated based on the exact solutions obtained from the extended Heine-Stieltjes correspondence. It is found that varying the pairing interaction strength $G$ in the model alters the statistical properties of the spectrum of the model. The spectrum is regular when $G$ is nonzero and either well below or well beyond the critical region of normal (localized) to superconducting (pair condensate) phase transition of the model, through which it is likely to display features of chaotic behavior. It is verified that the level statistics governed by the interplay between the single-particle energies and the pairing interaction for ${}^{48–53}$Ca calculated from the model with single-particle energies and a pairing strength extracted from experimental data indeed exhibits, for two of the Ca isotopes, spectral behaviors that deviate from the Poisson statistics within the phase transitional region, while most isotopes display regular spectra.

We study the correlation between the neutron skin development and the low-energy dipole response associated with the pygmy dipole resonance (PDR) in connection with the properties of symmetry energy. We perform our investigation within a microscopic transport model based on the Landau-Vlasov kinetic equation by employing three different equations of state in the isovector sector. Together with the giant dipole resonance, for all studied systems, we identify a PDR collective mode whose energy centroid is very well described by the parametrization $E_{\mathrm{PDR}}=41A^{-1/3}$. A linear correlation between the energy-weighted sum rule (EWSR) associated to PDR and the neutron skin thickness is evidenced. An increase of 15 MeV fm${}^2$ of EWSR, in correspondence to a change of 0.1 fm of the neutron skin size, is obtained. We conjecture that different nuclei having close neutron skin sizes will exhaust the same EWSR in the pygmy region. This suggests that a precise experimental estimate of the total EWSR exhausted by the PDR allows the determination of the neutron skin size, constraining the slope parameter of the symmetry energy.

The dynamics of energy dissipation in head-on fusion reactions of mass-symmetric systems at low bombarding energies is studied by exploiting the improved quantum molecular dynamics model. The results indicate that the form and magnitude of the mass parameter and friction coefficient show strong dependence on system size, bombarding energy, and relative distance. The dynamical mass parameter has almost no effect on the friction coefficient. Two-body collisions play an important role in energy dissipation even when the incident energy is much lower than the Fermi energy. The nucleon-nucleon collisions not only attenuate the energy dissipation but also hinder the nucleon transfer process.

Background: The isobaric yield ratio for mirror nuclei [IYR(m)] in heavy-ion collisions, which is assumed to depend linearly on $x=2(Z-1)/A^{1/3}$ of a fragment, is applied to study some coefficients of the energy terms in the binding energy, as well as the difference between the chemical potentials of a neutron and proton. It is found that the IYR(m) has a systematic dependence on the reaction, which has been explained as the volume and/or the isospin effects in previous studies. However, neither the volume nor the isospin effects can fully interpret the data.

Purpose: We suppose that the IYR(m) depends on the neutron-skin thickness (${\delta }_{np}$) of the projectile, and check the idea of whether the neutron-skin thickness effects can fully explain the systematic dependence of the IYR(m).

Methods: A modified statistical abrasion-ablation model is used to calculate the reactions induced by projectiles of three series: (1) the calcium isotopes from ${}^{36}$Ca to ${}^{56}$Ca as projectiles with different limitations on the impact parameters ($b_{\text{max}}$) to show the volume effects according to $b_{\text{max}}$; (2) the $A=45$ isobars as the projectiles having different isospins and ${\delta }_{np}$; and (3) projectiles having similar ${\delta }_{np}$ to show whether the IYR(m) depends on the volume or the isospin of the projectile.

Results: The IYR(m) shows a distribution of a linear part in the small-$x$ fragments, and a nonlinear part in the large-$x$ fragments. The linear part of IYR(m) is fitted. (1) In the calcium isotopic reactions, the IYR(m) depends on the isospin or the volume of the projectile, but ${\delta }_{np}$ greatly influences the nonlinear part of the IYR(m). The IYR(m) does not depend on the colliding source in reactions of small $b_{\text{max}}$ for the nonneutron-rich projectiles, and does not depend on the collision sources in reactions by the neutron-rich projectiles. (2) In reactions of the $A=45$ isobars, though IYR(m) depends on the isospin of projectile, IYR(m) shows small dependence on isospin if ${\delta }_{np}>0$. (3) In the reactions of projectiles having similar ${\delta }_{np}$, the IYR(m) in the small mass fragments show no dependence on the volume and the isospin of the projectile when the mass of the projectile is relatively large. Specifically, the dependence of IYR(m) on the mass of the isospin of the projectile vanishes when ${\delta }_{np}\sim 0.02\text{fm}$.

Conclusions: The linear and nonlinear parts of the IYR(m) are governed by the core and the surface (skin) of the projectile, respectively. The neutron-skin effects can well explain the systematic dependence of the IYR(m).

The PHENIX Collaboration has reported third-order harmonic oscillations of the source radius parameters when measuring the Hanbury-Brown–Twiss (HBT) correlation function for charged hadrons relative to the triangular flow angle. We explore possible origins of such third-order oscillations with a simple Gaussian emission function featuring both a triangular geometric deformation and triangular flow. Third-order oscillations of the HBT radii can arise from a purely geometric triangular deformation superimposed on an azimuthally symmetric radial flow, or from a radially symmetry spatial distribution which expands anisotropically with a triangular component in the flow velocity profile. In both cases the final particle momentum distribution features triangular flow. We show that the two alternatives can be distinguished experimentally through the phase of the azimuthal oscillations of the HBT radii relative to the triangular flow plane.

Motivated by an experimental proposal for the measurement of the $\pi N\to \pi \pi N$ reactions at J-PARC, we examine the potential impact of the $\pi N\to \pi \pi N$ cross section data on the determination of the resonance parameters of the high-mass $N^{*}$ states. For this purpose, we make use of the ANL-Osaka dynamical coupled-channels model, which has been developed recently through a combined analysis of the unpolarized cross section as well as polarized observables from pion- and photon-induced $\pi N$, $\eta N$, $K\Lambda$, and $K\Sigma$ production reactions off a proton target. We present predictions for the $\pi N\to \pi \pi N$ total cross sections and invariant mass distributions, and demonstrate that the $\pi N\to \pi \pi N$ differential cross section data can indeed be a crucial source of information for understanding $N^{*}\to \pi \Delta ,\rho N,\sigma N\to \pi \pi N$ decay of the high-mass $N^{*}$ states.

Cross section measurements of the reactions ${}^{90,92}$Zr($p$,$\gamma$)${}^{91,93}$Nb were performed using the National Superconducting Cyclotron Laboratory Summing NaI(Tl) detector at the University of Notre Dame. These reactions are part of the nuclear reaction flow for the synthesis of the light $p$ nuclei. For the ${}^{90}$Zr($p$,$\gamma$)${}^{91}$Nb reaction the new measurement resolves the disagreement between previous results. For the ${}^{92}$Zr($p$,$\gamma$)${}^{93}$Nb reaction the present work reports the first measurement of this reaction cross section. Both reaction cross sections are compared to theoretical calculations and a very good agreement with the standard non-smoker model is observed.

$J^{\pi }=0^{+}$ states have been investigated in the actinide nucleus ${}^{240}$Pu up to an excitation energy of 3 MeV with a high-resolution ($p,t$) experiment at $E_p$ = 24 MeV. To test the recently proposed $J^{\pi }=0_2^{+}$ double-octupole structure, the phenomenological approach of the spdf-interacting boson model has been chosen. In addition, the total 0${}^{+}$ strength distribution and the $0^{+}$ strength fragmentation have been compared to the model predictions as well as to the previously studied ($p,t$) reactions in the actinides. The results suggest that the structure of the 0${}_2^{+}$ states in the actinides might be more complex than the usually discussed pairing isomers. Instead, the octupole degree of freedom might contribute significantly. The signature of two close-lying 0${}^{+}$ states below the 2-quasiparticle energy is presented as a possible manifestation of strong octupole correlations in the structure of the 0${}_2^{+}$ states in the actinides.

A two-phonon version of the relativistic quasiparticle time-blocking approximation introduces a new class of many-body models for nuclear structure calculations based on the covariant energy density functional. As a fully consistent extension of the relativistic quasiparticle random phase approximation, the relativistic two-phonon model implies fragmentation of nuclear states over two-quasiparticle and two-phonon configurations coupled to each other. In particular, we show how the lowest two-phonon $1^{-}$ state, identified as a member of the $[2^{+}\otimes 3^{-}]$ quintuplet, emerges from the coherent two-quasiparticle pygmy dipole mode in vibrational nuclei. The inclusion of the two-phonon configurations into the model space allows a quantitative description of the positions and the reduced transition probabilities of the lowest $1^{-}$ states in tin isotopes ${}^{112,116,120,124}$Sn as well as the low-energy fraction of the dipole strength below the giant dipole resonance without any adjustment procedures. The model is applied to the low-lying dipole strength in neutron-rich ${}^{68,70,72}$Ni isotopes. Recent experimental data for ${}^{68}$Ni are reproduced fairly well.