Reliable and precise lifetimes of excited states in ${}^{156}\mathrm{Dy}$ were measured by means of the recoil distance Doppler-shift technique in the coincidence mode. The experiment was performed at the Laboratori Nazionali di Legnaro with the GASP array and the Cologne coincidence plunger apparatus using the reaction ${}^{124}\mathrm{Sn}$(${}^{36}\mathrm{S}$,$4n$)${}^{156}\mathrm{Dy}$ at a beam energy of 155 MeV. New values of the branching ratios of transitions depopulating the levels of the first excited band have been derived. The measured transition probabilities of ${}^{156}\mathrm{Dy}$ in the ground-state band and the first excited band as well as the energy spectra are compared to the predictions of the recently proposed X(5) model and to an interacting boson approximation fit. The comparison reveals a different behavior of the intraband transition strengths and indicates a possible coexistence of a normal deformed ground-state band and an X(5)-like first excited band. It also reveals that in ${}^{156}\mathrm{Dy}$, the γ degree of freedom plays a more important role than it does in the well-established X(5) nuclei with $N=90$. A fit of the data using the general collective model suggests that a deeper collective potential $V(\beta ,\gamma )$ may also be a reason for the differences in the spectroscopic properties of ${}^{156}\mathrm{Dy}$ and those nuclei.

We describe a class of exactly-solvable models of interacting bosons based on the algebra SO(3, 2). Each copy of the algebra represents a system of neutron and proton bosons in a given bosonic level interacting via a pairing interaction. The model that includes $s$ and $d$ bosons is a specific realization of the IBM2, restricted to the transition regime between vibrational and γ-soft nuclei. By including additional copies of the algebra, we can generate proton-neutron boson models involving other boson degrees of freedom, while still maintaining exact solvability. In each of these models, we can study not only the states of maximal symmetry, but also those of mixed symmetry, albeit still in the vibrational to γ-soft transition regime. Furthermore, in each of these models we can study some features of $F$-spin symmetry breaking. We report systematic calculations as a function of the pairing strength for models based on $s,d$, and $g$ bosons and on $s,d$, and $f$ bosons. The formalism of exactly-solvable models based on the SO(3, 2) algebra is not limited to systems of proton and neutron bosons, however, but can also be applied to other scenarios that involve two species of interacting bosons.

The ${}^{14}\mathrm{N}$$(n,\gamma )$${}^{15}\mathrm{N}$ reaction is a primary source of high-energy $\gamma$ rays for use in the calibration of detectors for other neutron-capture reactions. The $\gamma$-ray intensities of ${}^{15}\mathrm{N}$ produced by thermal neutron capture and the $\gamma$-ray detection efficiency function have been simultaneously determined from $\gamma$-peak areas alone using the basic principle of intensity balance. A least-squares fit was made to a new type of intensity balance calculation, combined with traditional efficiency fitting of radioactive sources. This latter ensures the compatibility with low-energy efficiencies, while providing an unbiased efficiency function for higher (up to 10 MeV) $\gamma$-ray energies. The calculation is based on the assumption that the ${}^{15}\mathrm{N}$ decay scheme is complete. From the internal consistency of the resulting intensities, it is believed that they are more accurate than previously published values. The same is true for the derived efficiency function.

Cross sections of the ${}^{139}\mathrm{La}$$(\gamma ,n)$ and ${}^{141}\mathrm{Pr}$($\gamma ,n$) reactions were measured using quasi-monochromatic γ-ray beams from laser Compton scattering. The results are compared to the predictions of Hauser-Feshbach statistical calculations using different models for the γ-ray strength function. The model parameters are constrained by the present experimental data and used to estimate the stellar photoneutron rates and their associated uncertainties and to study the implication for the production of the rare odd-odd nuclide ${}^{138}\mathrm{La}$ by the p process. No evidence for a large thermonuclear p-process contribution to the solar ${}^{138}\mathrm{La}$ is found. The need to further explore the photodestruction rate of ${}^{138}\mathrm{La}$ is emphasized.

We estimate how accurate the phase relaxation time of quantum many-body systems can be determined from data on forward peaking of evaporating protons from a compound nucleus. The angular range and accuracy of the data needed for a reliable determination of the phase relaxation time are evaluated. The general method is applied to analyze the inelastic scattering of 18 MeV protons from Pt for which previously measured double differential cross sections for two angles in the evaporating domain of the spectra show a strong forward peaking. A new experiment for an improved determination of the phase relaxation time is proposed. The experiment is also highly desirable for an accurate test of a formation of thermalized non-equilibrated matter in quantum many-body systems.

The high-spin nuclear structure of Tc isotopes is extended to more neutron-rich regions based on the measurements of prompt γ rays from the spontaneous fission of ${}^{252}\mathrm{Cf}$ at the Gammasphere. The high-spin level scheme of $N=67$ neutron-rich ${}^{110}\mathrm{Tc}$ ($Z=43$) is established for the first time, and that of ${}^{111}\mathrm{Tc}$ is extended and expanded. The ground band of ${}^{111}\mathrm{Tc}$ reaches the band-crossing region, and the new observation of the weakly populated $\alpha =-1/2$ member of the band provides important information on signature splitting. The systematics of band crossings in the isotopic and isotonic chains and a CSM calculation suggest that the band crossing of the ground band of ${}^{111}\mathrm{Tc}$ is due to alignment of a pair of $h_{11/2}$ neutrons. The best fit to signature splitting, branching ratios, and excitations of the ground band of ${}^{111}\mathrm{Tc}$ by the rigid triaxial rotor plus particle model calculations result in a shape of ${\varepsilon }_2=0.32$ and $\gamma =-{26}^{°}$ for this nucleus. Its triaxiality is larger than that of ${}^{107,109}\mathrm{Tc}$, which indicates increasing triaxiality in Tc isotopes with increasing neutron number. The identification of the weakly populated $K+2$ satellite band provides strong evidence for the large triaxiality of ${}^{111}\mathrm{Tc}$. In ${}^{110}\mathrm{Tc}$, the four lowest-lying levels observed are very similar to those in ${}^{108}\mathrm{Tc}$. At an excitation of 478.9 keV above the lowest state observed, ten states of a $\Delta I=1$ band are observed. This band of ${}^{110}\mathrm{Tc}$ is very analogous to the $\Delta I=1$ bands in ${}^{106,108}\mathrm{Tc}$, but it has greater and reversal signature splitting at higher spins.

It is shown via a study on a ${}^{26}\mathrm{Mg}$ target that the ($t$,${}^3\mathrm{He}$) reaction at 115 MeV/nucleon reaction is an accurate probe for extracting Gamow-Teller transition strengths. To do so, the data are complemented by results from the ${}^{26}\mathrm{Mg}$(${}^3\mathrm{He}$, $t$) reaction at 140 MeV/nucleon that allows for a comparison of $T=2$ analog states excited via the mirror reactions. Extracted Gamow-Teller strengths from ${}^{26}\mathrm{Mg}$($t$,${}^3\mathrm{He}$) and ${}^{26}\mathrm{Mg}$(${}^3\mathrm{He}$, $t$) are compared with those from ${}^{26}\mathrm{Mg}$($d$,${}^2\mathrm{He}$) and ${}^{26}\mathrm{Mg}$($p,n$) studies, respectively. A good correspondence is found, indicating probe independence of the strength extraction. Furthermore, we test shell-model calculations using the new USD-05B interaction in the $\mathit{sd}$-model space and show that it reproduces the experimental Gamow-Teller strength distributions well. In anticipation of further ($t$,${}^3\mathrm{He}$) experiments on medium-heavy nuclei aimed at determining weak-interaction rates of relevance for stellar evolution, a second goal of this work is to improve the understanding of the ($t$,${}^3\mathrm{He}$) and (${}^3\mathrm{He}$, $t$) reaction mechanisms at intermediate energies because detailed studies are scarce. The distorted-wave Born approximation is employed, taking into account the composite structures of the ${}^3\mathrm{He}$ and triton particles. The reaction model provides the means to explain systematic uncertainties at the 10%–20% level in the extraction of Gamow-Teller strengths as being because of interference between Gamow-Teller $\Delta L=0,\Delta S=1$ and $\Delta L=2,\Delta S=1$ amplitudes that both contribute to transitions from $0^{+}$ to $1^{+}$ states.

We study the ground and low-lying excited states of ${}^{15}\mathrm{O}$, ${}^{17}\mathrm{O}$, ${}^{15}\mathrm{N}$, and ${}^{17}\mathrm{F}$ using modern two-body nucleon-nucleon interactions and the suitably designed variants of the ab initio equation-of-motion coupled-cluster theory aimed at an accurate description of systems with valence particles and holes. A number of properties of ${}^{15}\mathrm{O}$, ${}^{17}\mathrm{O}$, ${}^{15}\mathrm{N}$, and ${}^{17}\mathrm{F}$, including ways the energies of ground and excited states of valence systems around ${}^{16}\mathrm{O}$ change as functions of the number of nucleons, are correctly reproduced by the equation-of-motion coupled-cluster calculations performed in up to eight major-oscillator shells. Certain disagreements with experiment are in part because of the degrees of freedom such as three-body interactions not accounted for in our effective two-body Hamiltonians. In particular, the calculated binding energies of ${}^{15}\mathrm{O}$/${}^{15}\mathrm{N}$ and ${}^{17}\mathrm{O}$/${}^{17}\mathrm{F}$ enable us to rationalize the discrepancy between the experimental and recently published [Phys. Rev. Lett. 94, 212501 (2005)] equation-of-motion coupled-cluster excitation energies for the $J^{\pi }=3^{-}$ state of ${}^{16}\mathrm{O}$. Our calculations demonstrate the feasibility of the equation-of-motion coupled-cluster methods to deal with valence systems around closed-shell nuclei and to provide results for systems beyond $A=16$.

We compare the generator coordinate method (GCM) and the random-phase approximation (RPA) in the framework of the exactly solvable Lipkin-Meshkov-Glick model. We show that the discretized GCM works quite well and permits to obtain results close to the exact results with a small number of discretization points.

We study the photoproduction of the exotic pentaquark ${\Theta }^{+}$ baryon with the vector kaon, assuming that the quantum numbers of the ${\Theta }^{+}$ to be $J^P=3/2^{\pm }$ and $J^P=1/2^{+}$. Scalar meson $\kappa (800)$ exchange is also taken into account. In contrast with the $\gamma N\to \overline{K}{\Theta }^{+}(3/2^{\pm })$ process, the large suppression from the proton target is not observed in the total cross sections. We also suggest a method to determine which meson exchange is the most dominant by analyzing the polarizations of incident photon and outgoing $K^{*}$. We find that κ exchange turns out to be prominent when the polarizations of the photon and $K^{*}$ are aligned to be parallel, whereas $K$ exchange predominates when they are perpendicular to each other.

Chiral perturbation theory supplemented by the Omnes function is employed to study the strength of the isoscalar central nuclear interaction, $G_S$, in the chiral limit vs the physical case. A very large modification is seen, i.e., ${\eta }_s=G_{S\text{chiral}}/G_{S\text{physical}}=1.37\pm 0.10$. This large effect is seen to arise dominantly at low energy from the extra contributions made by massless pions at energies near the physical threshold where the physical spectral function must vanish kinematically. The slope away from the chiral limit, $d_S$, is also calculated and is correspondingly large. I also explain why this large variation is to be expected.

The time-odd triaxial relativistic mean field approach is developed and applied to the investigation of the ground-state properties of light odd-mass nuclei near the double-closed shells. The nuclear magnetic moments including the isoscalar and isovector ones are calculated, and good agreement with Schmidt values is obtained. Taking ${}^{17}\mathrm{F}$ as an example, the splitting of the single-particle levels (around $0.7$ MeV near the Fermi level), the nuclear current, the core polarizations, and the nuclear magnetic potential, i.e., the spatial part of the vector potential due to the violation of the time reversal invariance, are investigated in detail.

The semiclassical model of relativistic Coulomb excitation is studied in situations in which the impact parameter is small enough so that projectile and target charge distributions overlap. The electromagnetic effects of this overlap are shown to be small. Realistic nucleon-nucleon reaction cross sections and realistic nuclear radial charge and matter distributions are used to determine a formula for the lower impact parameter limit to be used in the calculation of the Coulomb excitation cross section. A wide selection of projectile-target pairs is explored, in the bombarding energy range of 1 to 5 GeV per nucleon.

The ${}^{106}\mathrm{Cd}$($\alpha ,\gamma )$${}^{110}\mathrm{Sn}$ reaction cross section has been measured in the energy range of the Gamow window for the astrophysical $p$-process scenario. The cross sections for ${}^{106}\mathrm{Cd}$($\alpha ,n$)${}^{109}\mathrm{Sn}$ and for ${}^{106}\mathrm{Cd}$($\alpha ,p$)${}^{109}\mathrm{In}$ below the ($\alpha ,n$) threshold have also been determined. The results are compared with predictions of the statistical model code NON-SMOKER using different input parameters. The comparison shows that a discrepancy for ${}^{106}\mathrm{Cd}$($\alpha ,\gamma )$${}^{110}\mathrm{Sn}$ when using the standard optical potentials can be removed with a different α + ${}^{106}\mathrm{Cd}$ potential. Some astrophysical implications are discussed.

The two-proton knockout reaction ${}^9\mathrm{Be}$(${}^{54}\mathrm{Ti}$,${}^{52}\mathrm{Ca}+\gamma$) has been studied at 72 MeV/nucleon. Besides the strong feeding of the ${}^{52}\mathrm{Ca}$ ground state, the only other sizeable cross section proceeds to a $3^{-}$ level at 3.9 MeV. There is no measurable direct yield to the first excited $2^{+}$ state at 2.6 MeV. The results illustrate the potential of such direct reactions for exploring cross-shell proton excitations in neutron-rich nuclei and confirms the doubly-magic nature of ${}^{52}\mathrm{Ca}$.

The single-particle structure of ${}^{57}\mathrm{Ni}$ and level structure of ${}^{56}\mathrm{Ni}$ were investigated with the ${}^9\mathrm{Be}$ (${}^{57}\mathrm{Ni}$,${}^{56}\mathrm{Ni}+\gamma$)$X$ reaction at 73 MeV/nucleon. An inclusive cross section of 41.4(12) mb was obtained for the reaction, compared to a theoretical prediction of 85.4 mb, hence only 48(2)% of the theoretical cross section is exhausted. This reduction in the observed spectroscopic strength is consistent with that found for lighter well-bound nuclei. One-neutron removal spectroscopic factors of 0.58(11) to the ground state and 3.7(2) to all excited states of ${}^{56}\mathrm{Ni}$ were deduced.

There exist several effective interactions whose parameters are fitted to force mean field predictions to reproduce experimental findings of finite nuclei and calculated properties of infinite nuclear matter. By exploiting this technique, one can give a good description of nuclear binding energies. We present evidence that further progress can be made by taking into account medium polarization effects associated with surface and pairing vibrations.

The level structure of ${}^{12}\mathrm{N}$ has been investigated from 2.2 to 11.0 MeV in excitation energy using a ${}^{11}\mathrm{C}$+$p$ resonance interaction with thick targets and inverse kinematics. Excitation functions were fitted using an R-matrix approach. Sixteen levels in ${}^{12}\mathrm{N}$ were included in the analysis, several of them are new. Spin-parity assignments, excitation energies and widths are proposed for these levels.

PHENIX has measured the centrality dependence of midrapidity pion, kaon, and proton transverse momentum distributions in $d+\mathrm{Au}$ and $p+p$ collisions at $\sqrt{s_{{}_{\mathit{NN}}}}=200$ GeV. The $p+p$ data provide a reference for nuclear effects in $d+\mathrm{Au}$ and previously measured $\mathrm{Au}+\mathrm{Au}$ collisions. Hadron production is enhanced in $d+\mathrm{Au}$, relative to independent nucleon-nucleon scattering, as was observed in lower energy collisions. The nuclear modification factor for (anti)protons is larger than that for pions. The difference increases with centrality but is not sufficient to account for the abundance of baryon production observed in central $\mathrm{Au}+\mathrm{Au}$ collisions at the BNL Relativistic Heavy Ion Collider (RHIC). The centrality dependence in $d+\mathrm{Au}$ shows that the nuclear modification factor increases gradually with the number of collisions encountered by each participant nucleon. We also present comparisons with lower energy data as well as with parton recombination and other theoretical models of nuclear effects on particle production.