Recent experimental advances have made it possible to study excited structure in superheavy nuclei. The observed states have often been interpreted as quasiparticle excitations. We show that in superheavy nuclei collective vibrations systematically appear as low-energy excitation modes. By using the microscopic Triaxial Projected Shell Model, we make a detailed prediction on γ-vibrational states and their $E2$ transition probabilities to the ground state band in fermium and nobelium isotopes where active structure research is going on, and in ${}^{270}\mathrm{Ds}$, the heaviest isotope where decay data have been obtained for the ground-state and for an isomeric state.

Electric-dipole-forbidden transitions of nuclei interacting with super-intense laser fields are investigated by considering stable isotopes with suitable low-lying first excited states. Different classes of transitions are identified, and all magnetic sublevels corresponding to the near-resonantly driven nuclear transition are included in the description of the nuclear quantum system. We find that large transition matrix elements and convenient resonance energies qualify nuclear $M1$ transitions as good candidates for the coherent driving of nuclei. We discuss the implications of resonant interaction of intense laser fields with nuclei beyond the dipole approximation for the controlled preparation of excited nuclear states and important aspects of possible experiments aimed at observing these effects.

The ${}^{13}\mathrm{N}$$+p$ elastic resonance scattering has been studied in inverse kinematics via a thick-target method. A ${}^{13}\mathrm{N}$ secondary beam of $47.8\pm 1.5$ MeV produced by the ${}^2\mathrm{H}$(${}^{12}\mathrm{C}$,${}^{13}\mathrm{N}$)$n$ reaction was used to bombard a 9.33 mg/cm${}^2$ (${\mathrm{CH}}_2){}_n$ target. The recoil protons were detected by a $\Delta E\text{−}E$ silicon counter telescope at ${\theta }_{\mathrm{lab}}={15}^{°}$. The performance of the setup was checked by ${}^{12}\mathrm{C}$$+p$ elastic resonance scattering with the same (${\mathrm{CH}}_2$)${}_n$ target. The excitation function for the ${}^{13}\mathrm{N}$($p,p$) elastic scattering was obtained in the energy interval of $E_{\mathrm{c}.\mathrm{m}.}~0.5\text{−}3.2$ MeV and was analyzed by using a multilevel $R$-matrix code MULTI7. Several low-lying excited states in ${}^{14}\mathrm{O}$ were surveyed. Our results confirm a very recent $2^{-}$ assignment to the 6.8 MeV level and agree with the observation of a new $0^{-}$ level at 5.7 MeV with a width of 400(45) keV.

The decay of the isoscalar giant monopole resonance (ISGMR) in nuclei is studied by means of a nonlinear classical model consisting of several noninteracting nucleons (particles) moving in a potential well with an oscillating nuclear surface (wall). The motion of the nuclear surface is described by means of a collective variable that appears explicitly in the Hamiltonian as an additional degree of freedom. The total energy of the system is therefore conserved. Although the particles do not directly interact with each other, their motions are indirectly coupled by means of their interaction with the moving nuclear surface. We consider as free parameters in this model the degree of collectivity and the fraction of nucleons that participate to the decay of the collective excitation. Specifically, we have calculated the decay width of the ISGMR in the spherical nuclei ${}^{208}\mathrm{Pb}$, ${}^{144}\mathrm{Sm}$, ${}^{116}\mathrm{Sn}$, and ${}^{90}\mathrm{Zr}$. Despite its simplicity and its purely classical nature, the model reproduces the trend of the experimental data that show that with increasing mass number the decay width decreases. Moreover the experimental results (with the exception of ${}^{90}\mathrm{Zr}$) can be well fitted using appropriate values for the free parameters mentioned above. It is also found that these values allow for a good description of the experimentally measured ${}^{112}\mathrm{Sn}$ and ${}^{124}\mathrm{Sn}$ decay widths. In addition, we give a prediction for the decay width of the exotic isotope ${}^{132}\mathrm{Sn}$ for which there is experimental interest. The agreement of our results with the corresponding experimental data for medium-heavy nuclei is dictated by the underlying classical mechanics, i.e., the behavior of the maximum Lyapunov exponent as a function of the system size.

Both one-proton and one-neutron knockout reactions were performed with fast beams of two asymmetric, neutron-deficient rare isotopes produced by projectile fragmentation. The reactions are used to probe the nucleon spectroscopic strengths at both the weakly and strongly bound nucleon Fermi surfaces. The one-proton knockout reactions ${}^9\mathrm{Be}$(${}^{28}\mathrm{S}$,${}^{27}\mathrm{P}$)X and ${}^9\mathrm{Be}$(${}^{24}\mathrm{Si}$,${}^{23}\mathrm{Al}$)X probe the weakly bound valence proton states and the one-neutron knockout reactions and ${}^9\mathrm{Be}$(${}^{28}\mathrm{S}$, ${}^{27}\mathrm{S}$)X and ${}^9\mathrm{Be}$(${}^{24}\mathrm{Si}$, ${}^{23}\mathrm{Si}$)X the strongly bound neutron states in the two systems. The spectroscopic strengths are extracted from the measured cross sections by comparisons with an eikonal reaction theory. The reduction of the experimentally deduced spectroscopic strengths, relative to the predictions of shell-model calculations, is of order 0.8–0.9 in the removal of weakly bound protons and 0.3–0.4 in the knockout of the strongly bound neutrons. These results support previous studies at the extremes of nuclear binding and provide further evidence that in asymmetric nuclear systems the nucleons of the deficient species, at the more-bound Fermi surface are more strongly correlated than those of the more weakly bound excess species.

The nonextensive one-dimensional version of a hydrodynamic model for multiparticle production processes is proposed and discussed. It is based on nonextensive statistics assumed in the form proposed by Tsallis and characterized by a nonextensivity parameter $q$. In this formulation, the parameter $q$ describes some specific form of local equilibrium that is characteristic of the nonextensive thermodynamics and replaces the local thermal equilibrium assumption of the usual hydrodynamic models. We argue that there is correspondence between the perfect nonextensive hydrodynamics and the usual dissipative hydrodynamics. It leads to a simple expression for dissipative entropy current and allows predictions of the ratio of bulk and shear viscosities to entropy density, $\zeta /s$ and $\eta /s$, to be made.

The structure of ${}^{19-22}\mathrm{N}$ nuclei was investigated by means of in-beam γ-ray spectroscopic technique using fragmentation reactions of both stable and radioactive beams. Based on particle-γ and particle-$\gamma \gamma$ coincidence data, level schemes are constructed for the neutron-rich nitrogen nuclei. The experimental results are compared with shell model calculations. The strength of the $N=14$ and $Z=8$ shell closures and the weakening of the shell model interaction WBT are discussed.

Partons produced in the early stage of noncentral heavy-ion collisions can develop a longitudinal fluid shear because of the unequal local number densities of participant target and projectile nucleons. Under such fluid shear, local parton pairs with nonvanishing impact parameters have finite local relative orbital angular momentum along the direction opposite to the reaction plane. Such a finite relative orbital angular momentum among locally interacting quark pairs can lead to global quark polarization along the same direction because of spin-orbital coupling. Local longitudinal fluid shear is estimated within both the Landau fireball and the Bjorken scaling model of initial parton production. Quark polarization through quark-quark scatterings with the exchange of a thermal gluon is calculated beyond the small-angle scattering approximation in a quark-gluon plasma. The polarization is shown to have a nonmonotonic dependence on the local relative orbital angular momentum dictated by the interplay between electric and magnetic interactions. It peaks at a value of relative orbital angular momentum which scales with the magnetic mass of the exchanged gluons. With the estimated small longitudinal fluid shear in semiperipheral Au+Au collisions at energies currently available at the BNL Relativistic Heavy Ion Collider (RHIC), the final quark polarization is found to be small $\left|P_q\right|<0.04$ in the weak coupling limit. Possible behavior of the quark polarization in the strong coupling limit and implications on the experimental detection of such global quark polarization at RHIC and CERN Large Hadron Collider (LHC) are also discussed.

We report on microscopic calculations for the ${}^4\mathrm{He}$ compound system in the framework of the resonating group model employing realistic nucleon-nucleon and three-nucleon forces. The resulting scattering phase shifts are compared with those of a comprehensive $R$-matrix analysis of all data in this system, which are available in numerical form. The agreement between calculation and analysis is very good in most cases. Adding three-nucleon forces yields large effects in many cases. For a few cases, the new agreement is striking. We relate some differences between calculation and analysis to specific data and discuss experiments necessary to clarify the situation. From the results, we conclude that the data of the ${}^4\mathrm{He}$ system might be well suited to determining the structure of the three-nucleon force.

Analytical solutions of the Bohr Hamiltonian are obtained in the γ-unstable case, as well as in an exactly separable rotational case with $\gamma \approx 0$, called the exactly separable Morse (ES-M) solution. Closed expressions for the energy eigenvalues are obtained through the asymptotic iteration method (AIM), the effectiveness of which is demonstrated by solving the relevant Bohr equations for the Davidson and Kratzer potentials. All medium mass and heavy nuclei with known ${\beta }_1$ and ${\gamma }_1$ bandheads have been fitted by using the two-parameter γ-unstable solution for transitional nuclei and the three-parameter ES-M for rotational ones. It is shown that bandheads and energy spacings within the bands are well reproduced for more than 50 nuclei in each case.

The half-life of ${}^{10}\mathrm{C}$ has been measured to be 19.310(4) s, a result with 0.02% precision, which is a factor of three improvement over the best previous result. Since ${}^{10}\mathrm{C}$ is the lightest superallowed $0^{+}\to 0^{+}$ ${\beta }^{+}$ emitter, its $\mathit{ft}$ value has the greatest weight in setting an upper limit on the possible presence of scalar currents.

For Be and C isotopes with $N>8$, the shell-model study with $2\hslash \omega$ basis states shows the enhancement of neutron quadrupole matrix elements. The neutron-rich nuclei such as ${}^{14}\mathrm{Be}$ and ${}^{16}\mathrm{C}$ have a few neutrons in the $1s_{1/2}$ and $0d_{5/2}$ orbits, and the neutrons in these orbits give the large neutron quadrupole motion because these orbits have almost the same single-particle energies. A large ratio of proton and neutron quadrupole matrix elements in these nuclei indicates decoupled motions of proton and neutron, which are suggested in the measurements of the $B(E2)$ values.

An experimental study of nuclear reactions between ${}^{28}\mathrm{Si}$ nuclei at 200 and 300 MeV/nucleon and hydrogen or deuterium target nuclei was performed at the CELSIUS storage ring in Uppsala, Sweden, to collect information about the reactions responsible for single-event effects in microelectronics. Inclusive data on ${}^{28}\mathrm{Si}$ fragmentation, as well as data on correlations between recoils and spectator protons or $\alpha$ particles are compared to predictions from the Dubna cascade model and the Japan Atomic Energy Research Institute version of the quantum molecular dynamics model. The comparison shows satisfactory agreement for inclusive data except for He fragments where low-energy sub-barrier fragments and recoiling fragments with very large momenta are produced much more frequently than predicted. The yield of exclusive data are also severely underestimated by the models whereas the charge distributions of recoils in these correlations compare well. The observed enhancement in He emission, which may well be important for the description of single-event effects, is most likely to be attributed to α clustering in ${}^{28}\mathrm{Si}$ nuclei.

We study quark thermal recombination as a function of energy density during the evolution of a heavy-ion collision in a numerical model that reproduces aspects of quantum chromodynamics phenomenology. We show that starting with a set of free quarks (or quarks and antiquarks) the probability to form colorless clusters of three quarks differs from that to form colorless clusters of quark-antiquark and that the former has a sharp jump at a critical energy density, whereas the latter transits smoothly from the low to the high-energy-density domains. We interpret this as a quantitative difference in the production of baryons and mesons with energy density. We use this approach to compute the proton and pion spectra in a Bjorken scenario that incorporates the evolution of these probabilities with energy density and therefore with proper time. From the spectra, we compute the proton-to-pion ratio and compare to data at the highest Relativistic Heavy Ion Collider energies. We show that for a standard choice of parameters, this ratio reaches 1, though the maximum is very sensitive to the initial evolution proper time.

The ${}^{16}\mathrm{O}$($p,\gamma$)${}^{17}\mathrm{F}$ reaction rate is revisited with special emphasis on the stellar temperature range of $T=60\text{−}100$ MK, important for hot bottom burning in asymptotic giant branch (AGB) stars. We evaluate existing cross-section data that were obtained since 1958 and, if appropriate, correct published data for systematic errors that were not noticed previously, including the effects of coincidence summing and updated effective stopping powers. The data are interpreted by using two different models of nuclear reactions, that is, a potential model and R-matrix theory. A new astrophysical $S$ factor and recommended thermonuclear reaction rates are presented. As a result of our work, the ${}^{16}\mathrm{O}$($p,\gamma$)${}^{17}\mathrm{F}$ reaction has now the most precisely known rate involving any target nucleus in the mass $A⩾12$ range, with reaction rate errors of about 7% over the entire temperature region of astrophysical interest ($T=0.01\text{−}2.5$ GK). The impact of the present improved reaction rate with its significantly reduced uncertainties on the hot bottom burning in AGB stars is discussed. In contrast to earlier results we find now that there is not clear evidence to date for any stellar grain origin from massive AGB stars.

Background: The meson exchange current (MEC) contribution is important in the neutron-proton bremsstrahlung process ($\mathit{np}\gamma$) when the two nucleon-scattering angles are small. However, our understanding of such effects is limited, and the reason why meson exchange current effects dominate the $\mathit{np}\gamma$ cross section has not been thoroughly investigated. Purpose: The primary focus of this investigation is to understand the origin of the MEC contribution, to identify the leading MEC amplitudes, and to comprehend why these MEC amplitudes dominate the $\mathit{np}\gamma$ cross sections. Method: We used a new method that combines the one-boson-exchange (OBE) approach with the soft-photon approach to define 10 different $\mathit{np}\gamma$ amplitudes. These amplitudes are used to calculate $\mathit{np}\gamma$ cross sections at 225 MeV for nucleon laboratory scattering angles lying between ${12}^{°}$ and ${43}^{°}$. The results of these calculations are then compared to investigate the meson exchange current effect in $\mathit{np}\gamma$. Results: (i) The OBE amplitude $M_{\mathit{np}\gamma ,\mu }^{\mathrm{PS}}$ and the two-u-two-t special (TuTts) soft-photon amplitude $M_{\mathit{np}\gamma ,\mu }^{\mathrm{TuTts}}$ predict quantitatively similar $\mathit{np}\gamma$ cross sections. (ii) The MEC effect is found to be significant when the two nucleon-scattering angles are far from the elastic limit (${45}^{°}$), but the effect is insignificant when the nucleon angles approach the elastic limit. (iii) The origin of the MEC effect and the leading MEC amplitudes have been identified in this investigation. Furthermore, the reason is now clear why the leading MEC amplitudes dominate the $\mathit{np}\gamma$ cross section when the nucleon-scattering angles are small. (iv) The contribution from the anomalous magnetic moments of the proton and the neutron is confirmed to be negligibly small. (v) In general, the theoretical cross sections using the amplitude $M_{\mathit{np}\gamma ,\mu }^{\mathrm{PS}}$, or the amplitude $M_{\mathit{np}\gamma ,\mu }^{\mathrm{TuTts}}$, are consistent with the triple differential cross sections recently measured at the Los Alamos National Laboratory. However, there exists an unexplained discrepancy between theory and experiment in some cases. Conclusions: The findings of this investigation have enhanced our understanding of the meson exchange current effect in $\mathit{np}\gamma$. The comparative amplitude method introduced can be used for other bremsstrahlung investigations.

We study pion propagation in asymmetric nuclear matter (ANM). One of the interesting consequences of pion propagation in ANM is the mode splitting for the different charged states of pions. First we describe the pion-nucleon dynamics using the nonchiral model in which one starts with pseudoscalar $\pi N$ coupling, and the pseudovector representation is obtained via suitable nonlinear field transformations. For both of these cases, the effect of the Dirac sea is estimated. Subsequently, we present results using the chiral effective Lagrangian where the short-distance behavior (Dirac vacuum) is included by redefining the field parameters as done in the modern effective field theory approach developed recently. The results are compared with previous calculations for symmetric nuclear matter. Closed form analytical results are presented for the effective pion masses and dispersion relations by making a hard nucleon loop approximation and suitable density expansion.