Exotic, neutron-rich nuclei of mass $A=115$ produced in proton-induced fission of ${}^{238}\mathrm{U}$ were extracted using the IGISOL mass separator. The beam of isobars was transferred to the JYFLTRAP Penning trap system for further separation to the isotopic level. Monoisotopic samples of ${}^{115}\mathrm{Ru}$ nuclei were used for $\gamma$and $\beta$ coincidence spectroscopy. In ${}^{115}\mathrm{Ru}$ we have observed excited levels, including an isomer with a half-life of 76(6) ms and ($7/2^{-}$) spin and parity. The first excited 61.7-keV level in ${}^{115}\mathrm{Ru}$ with spins and parity ($3/2^{+}$) may correspond to an $\mathit{oblate}$ $3/2^{+}$[431] Nilsson orbital. A half-life of 318(19) ms for the ${\beta }^{-}$ decay of the ($1/2^{+}$) ground state in ${}^{115}\mathrm{Ru}$ has been firmly established in two independent measurements, a value which is significantly shorter than that previously reported.

We use linear response analysis and the fluctuation-dissipation theorem to derive the energy loss of a heavy quark in the SU($2$) classical Coulomb plasma in terms of the $l=1$ monopole and nonstatic structure factor. The result is valid for all Coulomb couplings $\Gamma =V/K$, the ratio of the mean potential to kinetic energy. We use the Liouville equation in the collisionless limit to assess the SU($2$) nonstatic structure factor. We find the energy loss to be strongly dependent on $\Gamma$. In the liquid phase with $\Gamma \approx 4$, the energy loss is mostly metallic and soundless with neither a Cerenkov nor a Mach cone. Our analytical results compare favorably with the SU($2$) molecular dynamics simulations at large momentum and for heavy quark masses.

The corrections of two-photon exchange to the polarization $P_y$ of the deuteron are studied based on an effective Lagrangian approach. In addition, the two-photon exchange effect on the imaginary part of the deuteron electromagnetic form factors is also discussed.

The structure of $3/2^{-}$ and $1/2^{+}$ states in ${}^{11}\mathrm{B}$ is investigated with an $\alpha +\alpha +t$ orthogonality condition model (OCM) based on the Gaussian expansion method. Full levels up to the $3/2_3^{-}$ and $1/2_2^{+}$ states around the $\alpha +\alpha +t$ threshold ($E_x=11.1$ MeV) are reproduced consistently with the experimental energy levels. It is shown that the $3/2_3^{-}$ state located around the ${}^7\mathrm{Li}+\mathrm{\alpha }$ threshold has an $\alpha +\alpha +t$ cluster structure, whereas the $3/2_1^{-}$ and $3/2_2^{-}$ states have a shell-model-like compact structure. We found that the $3/2_3^{-}$ state does not possess an $\alpha$-condensate-like nature analogous to the $0_2^{+}$ state of ${}^{12}\mathrm{C}$ (Hoyle state) which has a dilute $3\alpha$-condensate structure described by a $(0S_{\alpha }){}^3$ configuration with about $70\%$ probability, although the monopole transition strength of the former is as large as that of the latter. We discuss the reasons why the $3/2_3^{-}$ state does not have the condensate character. On the other hand, the $1/2_1^{+}$ state just below the ${}^7\mathrm{Li}+\mathrm{\alpha }$ threshold has a cluster structure that can be interpreted as a parity-doublet partner of the $3/2_3^{-}$ state. We indicate that the $12.56$-MeV state ($J^{\pi }=1/2_2^{+}$) just above the $\alpha +\alpha +t$ threshold observed in the ${}^7\mathrm{Li}$(${}^7\mathrm{Li}$,${}^{11}\mathrm{B}$${}^{*}$)$t$ reaction, etc., is of the dilute cluster-gas-like configuration and is a strong candidate for the product states of clusters, having a configuration of $(0S_{\alpha }){}^2(0S_t)$ with about $65\%$ probability, from the analyses of the single-cluster motions in ${}^{11}\mathrm{B}$. The structure property of the $1/2^{+}$ resonant state is analyzed with the complex scaling method.

Two-$\alpha$ emission from high-lying excited states of ${}^{18}\mathrm{Ne}$ was studied by complete-kinematics measurements. The ${}^{18}\mathrm{Ne}$ beam at the energy of 51.8 MeV/$u$ was bombarding a ${}^{197}\mathrm{Au}$ target to populate the excited states via Coulomb excitation. Products of two-$\alpha$ emission, ${}^{10}\mathrm{C}$$-\alpha -\alpha$, were measured by an array of silicon strip detectors and a CsI $+$ PIN telescope. With the help of Monte Carlo simulations, the experimental results show the characteristics of sequential two-$\alpha$ emission via ${}^{14}\mathrm{O}$ excited states. Sequential two-$\alpha$ and two-proton emissions from ${}^{18}\mathrm{Ne}$ via one-particle daughter states are compared and the distinction of the opening angles of these two modes originates from the difference of the mass ratio of emitted particles to daughter nuclei.

The half-life of the $\alpha$-decaying nucleus ${}^{221}\mathrm{Fr}$ was determined in different environments, that is, embedded in Si at 4 K, and embedded in Au at 4 K and about 20 mK. No differences in half-life for these different conditions were observed within $0.1\%$. Furthermore, we quote a value for the absolute half-life of ${}^{221}\mathrm{Fr}$ of $t_{1/2}=286.1(10)$ s that is of comparable precision to the most precise value available in the literature.

The $\gamma$-ray strength function method is devised to indirectly determine radiative neutron capture cross sections for radioactive nuclei. This method is applied here to the ${}^{107}\mathrm{Pd}$ ($T_{1/2}=6.5\times {10}^6$ yr) case. Photoneutron cross sections were measured for ${}^{105,106,108}\mathrm{Pd}$ near neutron threshold with quasimonochromatic laser-Compton-scattering $\gamma$-ray beams. These photoneutron cross sections as well as the reverse radiative neutron capture cross sections for ${}^{104,105}\mathrm{Pd}$ are used to provide constraints on the ${}^{107}\mathrm{Pd}$($n,\gamma$)${}^{108}\mathrm{Pd}$ cross section.

The production cross sections of neutron-rich isotopes ${}^{52,54,56,58,60}\mathrm{Ca}$, ${}^{136,138,140,142}\mathrm{Sn}$, and ${}^{146,148,150,152}\mathrm{Xe}$ are predicted for future experiments in the diffusive multinucleon transfer reactions ${}^{86,90,92,94}\mathrm{Kr}$, ${}^{124,130,132,134}\mathrm{Sn}$, ${}^{136,140,142,146}\mathrm{Xe}$, and ${}^{138,144,146}\mathrm{Ba}$$+$${}^{48}\mathrm{Ca}$ with stable and radioactive beams at incident energies close to the Coulomb barrier. Because of the small cross sections, the production of neutron-rich isotopes requires the optimal choice of projectile-target combinations and bombarding energies.

We show that parity-violating deep-inelastic scattering (PVDIS) of longitudinally polarized electrons from deuterium can in principle be a relatively clean probe of higher twist quark-quark correlations beyond the parton model. As first observed by Bjorken and Wolfenstein, the dominant contribution to the electron polarization asymmetry, proportional to the axial vector electron coupling, receives corrections at twist four from the matrix element of a single four-quark operator. We reformulate the Bjorken-Wolfenstein argument in a matter suitable for the interpretation of experiments planned at the Thomas Jefferson National Accelerator Facility (JLab). In particular, we observe that because the contribution of the relevant twist-four operator satisfies the Callan-Gross relation, the ratio of parity-violating longitudinal and transverse cross sections, $R^{\gamma Z}$, is identical to that for purely electromagnetic scattering, $R^{\gamma }$, up to perturbative and power-suppressed contributions. This result simplifies the interpretation of the asymmetry in terms of other possible novel hadronic and electroweak contributions. We use the results of MIT Bag Model calculations to estimate contributions of the relevant twist-four operator to the leading term in the asymmetry as a function of Bjorken $x$ and $Q^2$. We compare these estimates with possible leading twist corrections from violation of charge symmetry in the parton distribution functions.

Neutrino energy losses through neutral weak currents in the triplet-spin superfluid neutron liquid are studied for the case of condensate involving several magnetic quantum numbers. Low-energy excitations of the multicomponent condensate in the timelike domain of the energy and momentum are analyzed. Along with the well-known excitations in the form of broken Cooper pairs, the theoretical analysis predicts the existence of collective waves of spin density in the one-component condensate at very low energy. Because of a rather small excitation energy of spin waves, their decay leads to a substantial neutrino emission at the lowest temperatures when all other mechanisms of neutrino energy loss are killed by a superfluidity. Neutrino energy losses caused by the pair recombination and spin-wave decays are examined in all of the multicomponent phases that might represent the ground state of the condensate, according to modern theories, and for the case when a phase transition occurs in the condensate at some temperature. Our estimate predicts a sharp increase in the neutrino energy losses followed by a decrease, along with a decrease in the temperature that takes place more rapidly than it would without the phase transition. We demonstrate the important role of the neutrino radiation caused by the decay of spin waves in the cooling of neutron stars.

The recently claimed observations of non-negligible amounts of ${}^6\mathrm{Li}$ in old halo stars have renewed interest in the Big Bang nucleosynthesis (BBN) of ${}^6\mathrm{Li}$. One important ingredient in the predicted BBN abundance of ${}^6\mathrm{Li}$ is the low-energy ${}^2\mathrm{H}$($\alpha$,$\gamma$)${}^6\mathrm{Li}$ cross section. Up to now, the only available experimental result for this cross section showed an almost constant astrophysical $S$ factor below $400$ keV, contrary to theoretical expectations. We report on a new measurement of the ${}^2\mathrm{H}$($\alpha$,$\gamma$)${}^6\mathrm{Li}$ reaction using the breakup of ${}^6\mathrm{Li}$ at 150 $A\hspace{0.5em}$ MeV. Even though we cannot separate experimentally the Coulomb contribution from the nuclear one, we find clear evidence for Coulomb-nuclear interference by analyzing the scattering angular distributions. This is in line with our theoretical description, which indicates a drop of the $S_{24}$ factor at low energies as predicted also by most other models. Consequently, we find even lower upper limits for the calculated primordial ${}^6\mathrm{Li}$ abundance than before.

We discuss the thermalization process of the neutron star’s crust described by solving the heat-transport equation with a microscopic input for the specific heat of baryonic matter. The heat equation is solved with initial conditions specific to a rapid cooling of the core. To calculate the specific heat of inner-crust baryonic matter, that is, nuclear clusters and unbound neutrons, we use the quasiparticle spectrum provided by the Hartree-Fock-Bogoliubov approach at finite temperature. In this framework, we analyze the dependence of the crust thermalization on pairing properties and on cluster structure of inner-crust matter. It is shown that the pairing correlations reduce the crust thermalization time by a large fraction. The calculations show also that the nuclear clusters have a non-negligible influence on the time evolution of the surface temperature of the neutron star.

A many-body Hamiltonian involving the mean field for a projected spherical single-particle basis, the pairing interactions for alike nucleons, and the dipole-dipole proton-neutron interactions in the particle-hole (ph) channel and the ph dipole pairing potential is treated by the projected gauge fully renormalized proton-neutron quasiparticle random phase approximation approach. The resulting wave functions and energies for the mother and daughter nuclei are used to calculate the $2\nu \beta \beta$ decay rate and the process half-life. For illustration, the formalism is applied for the decay ${}^{100}\mathrm{Mo}\to {}^{100}$Ru. The calculated half-life is in agreement with the corresponding experimental data. The Ikeda sum rule is obeyed.

On the basis of the adiabatic self-consistent collective coordinate method, we develop an efficient microscopic method of deriving the five-dimensional quadrupole collective Hamiltonian and illustrate its usefulness by applying it to the oblate-prolate shape coexistence/mixing phenomena in proton-rich ${}^{68,70,72}\mathrm{Se}$. In this method, the vibrational and rotational collective masses (inertial functions) are determined by local normal modes built on constrained Hartree-Fock-Bogoliubov states. Numerical calculations are carried out using the pairing-plus-quadrupole Hamiltonian including the quadrupole-pairing interaction within the two major-shell active model spaces both for neutrons and protons. It is shown that the time-odd components of the moving mean-field significantly increase the vibrational and rotational collective masses in comparison with the Inglis-Belyaev cranking masses. Solving the collective Schrödinger equation, we evaluate excitation spectra, quadrupole transitions, and moments. The results of the numerical calculation are in excellent agreement with recent experimental data and indicate that the low-lying states of these nuclei are characterized as an intermediate situation between the oblate-prolate shape coexistence and the so-called $\gamma$ unstable situation where large-amplitude triaxial-shape fluctuations play a dominant role.

The $\beta$ decay of the $N=51$ nucleus ${}^{81}\mathrm{Zn}$ was studied by means of $\beta$-$\gamma$ spectroscopy and from isotopically pure beams produced at the Holifield Radioactive Ion Beam Facility (HRIBF). We observe several competing $\beta$ transitions populating ${}^{81}\mathrm{Ga}$ that are interpreted as allowed Gamow-Teller decays to positive parity, core excited states, and first-forbidden decays to negative parity states. The measured $\beta$-decay pattern suggests an assignment of $I^{\pi }=5/2^{+}$ for the ${}^{81}\mathrm{Zn}$ ground state. The systematics of core excited states in $N=50$ isotones indicate a strengthening of the $N=40$ subshell gap near ${}^{78}\mathrm{Ni}$.

This work presents an extensive exploration of scattering and tunneling involving composite objects with intrinsic degrees of freedom. We aim at exact solutions to such scattering problems. Along this path we demonstrate solutions to model Hamiltonians and develop different techniques for addressing these complex reaction-physics problems, discuss their applicability, and investigate the relevant convergence issues. As examples, we study the scattering of two-constituent deuteron-like systems either with an infinite set of intrinsic bound states or with a continuum of states that allows for breakup. We show that the internal degrees of freedom of the projectile and its virtual excitation in the course of reactions play an important role in shaping the $S$-matrix and related observables, giving rise to enhanced or reduced tunneling in various situations.

Proton and $\alpha$-particle spectra have been measured at backward angles in the ${}^{12}\mathrm{C}$ $+$ ${}^{93}\mathrm{Nb}$ reaction at $E({}^{12}\mathrm{C})=37.5$–$60$ MeV and in the ${}^{16}\mathrm{O}$$+$${}^{93}\mathrm{Nb}$ reaction at $E({}^{16}\mathrm{O})=54$–$75$ MeV. The inclusive particle spectra generally are in good agreement with the statistical model calculations except for the $\alpha$ spectra in the ${}^{12}\mathrm{C}$-induced reaction at beam energies of $37.5$–$42.5$ MeV which are close to the Coulomb barrier in the entrance channel. In these cases the evaporation peak is up to $2$ MeV lower than its expected position from the statistical model predictions. Gamma-multiplicity-gated $\alpha$ spectra, measured in the same reaction, also show the aforementioned discrepancy. These observations reveal that the conventional statistical model cannot explain the $\alpha$-particle spectra in the ${}^{12}\mathrm{C}$-induced reactions near the Coulomb barrier.

Sub-barrier fusion cross sections of ${}^{36}\mathrm{S}$ $+$ ${}^{64}\mathrm{Ni}$ have been measured down to $\simeq$$3$ $\mu$b. The logarithmic slope of the fusion excitation function has a steep rise in the barrier region with decreasing energy and saturates at lower energies. The data can be reproduced within the coupled-channels model using a Woods-Saxon potential with a large diffuseness. The slope saturation is analogous to what has been observed for ${}^{36}\mathrm{S}$, ${}^{48}\mathrm{Ca}$ $+$ ${}^{48}\mathrm{Ca}$, while for heavier systems the slope increases steadily below the barrier.

We have compared the results of dynamical modeling of the fission process with predictions of the Kramers formulas. For the case of large dissipation, there are two of them: the integral rate $R_I$ and its approximation $R_O$. As the ratio of the fission barrier height $B_f$ to the temperature $T$ reaches 4, any analytical rate is expected to agree with the dynamical quasistationary rate $R_D$ within $2\%$. The latter has been obtained using numerical modeling with six different potentials. It has been found that the difference between $R_O$ and $R_D$ sometimes exceeds $20\%$. The features of the potentials used that are responsible for this disagreement are identified and studied. It is demonstrated that it is $R_I$, not $R_O$, that meets this expectation regardless of the potential used.