Recent models of the decay out of superdeformed (SD) bands can broadly be divided into two categories. One approach is based on the similarity between the tunneling process involved in the decay and that involved in the fusion of heavy ions, and it builds on the formalism of nuclear reaction theory. The other arises from an analogy between the superdeformed decay and transport between coupled quantum dots. These models suggest conflicting values for the spreading width of the decaying superdeformed states. In this paper, the decay of superdeformed bands in the five even-even nuclei in which the SD excitation energies have been determined experimentally is considered in the framework of both approaches, and the significance of the difference in the resulting spreading widths is considered. The results of the two models are also compared to tunneling widths estimated from previous barrier height predictions and a parabolic approximation to the barrier shape.

We consider the reaction $\gamma d\to {\pi }^{0}d$ in a wide energy range around and above the $\eta$-meson photoproduction threshold at backward c.m. angles of the outgoing pions. Our theoretical analysis is motivated by the recent measurements of the CLAS Collaboration at Jefferson Lab, where this kinematical region of the reaction has been thoroughly studied for the first time and an enhancement in the energy dependence of the differential cross section in the region of $E_{\gamma }~600\text{−}800\text{MeV}$ has been observed. Our preliminary and qualitative analysis, based on single- and double-scattering diagrams, shows that the observed structure can be explained by the contribution of the double-scattering diagram with intermediate production of the $\eta$ meson. The effect, to a considerable extent, is due to the contribution of the $N(1535)$ resonance to the amplitudes of subprocesses on the nucleons.

We have measured cross sections for the ${}^{63}\mathrm{Cu}(\alpha ,\gamma ){}^{67}\mathrm{Ga}$ reaction in the $5.9-$ to $8.7-\text{MeV}$ energy range using an activation technique. Natural Cu foils were bombarded with α beams from the ${88}^{\text{'}\text{'}}$ Cyclotron at Lawrence Berkeley National Laboratory (LBNL). Activated foils were counted using a γ-spectrometry system at LBNL's Low Background Facility. The ${}^{63}\mathrm{Cu}(\alpha ,\gamma ){}^{67}\mathrm{Ga}$ cross sections were determined and compared with the latest NON-SMOKER theoretical values. Experimental cross sections were found to be in agreement with theoretical values.

We count the number of pairs in the single-j-shell model of ${}^{44}\mathrm{Ti}$ for various interactions. For a state of total angular momentum I, the wave function can be written as $\Psi =\sum _{J_P{J}_N}D(J_P{J}_N)[(j^2){}_{J_P}(j^2){}_{J_N}]{}_I$, where $D(J_P{J}_N)$ is the probability amplitude that the protons couple to $J_P$ and the neutrons to $J_N$. For $I=0$ there are three states with ($I=0,T=0$) and one with ($I=0,T=2$). The latter is the double analog of ${}^{44}\mathrm{Ca}$. In that case ($T=2$), the magnitude of $D(\mathit{JJ})$ is the same as that of a corresponding two-particle coefficient of fractional parentage. In counting the number of pairs with an even angular momentum J, we find a new relationship is obtained by diagonalizing a unitary nine-j symbol. We are also able to get results for the “no-interaction” case for $T=0$ states, for which it is found, e.g., that there are fewer ($J=1,T=0$) pairs than on the average. Relative to this no-interaction case, we find that for the most realistic interaction used there is an enhancement of pairs with angular momentum $J=0,2,1$, and 7, and a depletion for the others. Also considered are interactions in which only the ($J=0,T=1$) pair state is at lower energy, interactions where only the ($J=1,T=0$) pair state is lowered, interactions where both are equally lowered, and the $Q·Q$ interaction. We are also able to obtain simplified formulas for the number of $J=0$ pairs for the $I=0$ states in ${}^{46}\mathrm{Ti}$ and ${}^{48}\mathrm{Ti}$ by noting that the unique state with isospin $\left|T_z\right|+2$ is orthogonal to all the states with isospin $\left|T_z\right|$.

Excited states of the nucleus ${}^{102}\mathrm{Ru}$ have been studied using the ${}^{96}\mathrm{Zr}$(${}^{10}\mathrm{B}$,$p3n$) reaction at a beam energy of $42\text{MeV}$. The emitted γ rays were detected with the Gammasphere spectrometer. The known positive-parity structure built on the second $2^{+}$ state was extended up to the ${10}^{+}$ and ${11}^{+}$ states. This structure has been interpreted as a quasi-γ band. Its energy staggering as a function of spin has been analyzed in order to derive information on the type of triaxiality present in ${}^{102}\mathrm{Ru}$, a nucleus that serves as one of the cores for chiral structures in the mass $A\approx 100$ region.

We look for signals of criticality in multifragment production in heavy-ion collisions using model-independent universal fluctuations theory. The phenomenon is studied as a function of system size, bombarding energy, and impact parameter over a wide range of INDRA data. For very central collisions $(b/b_{\max }<0.1)$ we find evidence that the largest fragment in each event, $Z_{\max }$, plays the role of an order parameter, defining two different regimes at low and high incident energy, respectively, according to the scaling properties of its fluctuations. Data for a wide range of system masses and incident energies collapse on to an approximately universal scaling function in each regime for the most central collisions. The forms of the scaling functions for the two regimes are established, and their dependence on the total mass and the bombarding energy is mapped out. Data suggest that these regimes are linked to the disappearance of heavy residues in central collisions.

The dense medium created in $\mathrm{Au}+\mathrm{Au}$ collisions at the Relativistic Heavy-Ion Collider significantly suppresses particle production from hard-scattering processes and their characteristic back-to-back angular correlation. We present a simple model of jet absorption in dense matter that incorporates a realistic nuclear geometry. Our calculations are performed at the jet level and assume independent jet fragmentation in the vacuum. This model describes quantitatively the centrality dependence of the observed suppression of the high $p_T$ hadron yield and of the back-to-back angular correlations. The azimuthal anisotropy of high $p_T$ particle production cannot be accounted for using a realistic nuclear geometry.

Charm- and bottom-quark rescattering in a quark-gluon plasma (QGP) is investigated with the objective of assessing the approach toward thermalization. Employing a Fokker-Planck equation to approximate the collision integral of the Boltzmann equation we augment earlier studies based on perturbative parton cross sections by introducing resonant heavy-light quark interactions. The latter are motivated by recent QCD lattice calculations that indicate the presence of “hadronic” states in the QGP. We model these states by colorless (pseudo-) scalar and (axial-) vector D and B mesons within a heavy-quark effective theory framework. We find that the presence of these resonances at moderate QGP temperatures substantially accelerates the kinetic equilibration of c quarks as compared to using perturbative interactions. We also comment on consequences for D-meson observables in ultrarelativistic heavy-ion collisions.

The PHENIX experiment at the relativistic heavy ion collider (RHIC) has measured transverse energy and charged particle multiplicity at midrapidity in $\mathrm{Au}+\mathrm{Au}$ collisions at center-of-mass energies $\sqrt{s_{\mathrm{NN}}}=19.6,130$, and $200\text{GeV}$ as a function of centrality. The presented results are compared to measurements from other RHIC experiments and experiments at lower energies. The $\sqrt{s_{\mathrm{NN}}}$ dependence of $dE{}_T/d\eta$ and $dN{}_{\mathrm{ch}}/d\eta$ per pair of participants is consistent with logarithmic scaling for the most central events. The centrality dependence of $dE{}_T/d\eta$ and $dN{}_{\mathrm{ch}}/d\eta$ is similar at all measured incident energies. At RHIC energies, the ratio of transverse energy per charged particle was found to be independent of centrality and growing slowly with $\sqrt{s_{\mathrm{NN}}}$. A survey of comparisons between the data and available theoretical models is also presented.

The signature of a possible dibaryon state is studied in two-photon production in proton-proton scattering, that is, in the process $\mathit{pp}\to D\gamma \to 2\gamma \mathit{NN}$. We have investigated the effects on the cross section for cases in which the dibaryon has spin $0^{\pm }$. Special attention is paid to interference of the dibaryon signal with that of the two-photon bremsstrahlung process.

Cross-section measurements of seven exit-channel configurations in the neutron-deuteron breakup at 13.0 MeV are reported and compared to rigorous calculations. Our data are consistent with those of previous measurements in four of six configurations. The present data for five configurations are in good agreement with theoretical predictions. The cross-section data for the space-star and another out-of-plane configuration are larger than the theoretical predictions by more than three standard deviations. The previously observed 20% discrepancy between theory and data for the space-star configuration is confirmed in the present work. The inclusion of the Tucson-Melbourne $2\pi$-exchange three-nucleon force changes the predicted cross section by only 2% and in the wrong direction needed to bring theory into agreement with data.

Extensions to the yrast and near-yrast decay sequences of the neutron-rich nucleus ${}_{15}^{34}{P}_{19}$ have been established through an analysis of the $\gamma$ deexcitation of fragments produced in deep-inelastic processes which occur when $230-\mathrm{MeV}{}^{36}\mathrm{S}$ ions interact with a thick target of ${}^{176}\mathrm{Yb}$. The highly sensitive GASP array of escape-suppressed Ge detectors was used to measure the resulting $\gamma$-ray deexcitations of both projectilelike and targetlike fragments. Previously unobserved excited states in ${}^{34}\mathrm{P}$ were observed at 3351, 6236, 2320, and (4723) keV. Several states above an excitation energy of 2.3 MeV involve intruder configurations from the $f_{7/2}$ shell. The investigation of negative parity intruder states on the periphery of the “island of inversion” has an important role to play in our understanding of the evolution of nuclear structure as the island of inversion is approached.

Nilsson parameters $\kappa$ and $\mu$ have been studied in the framework of relativistic mean field (RMF) models. They are used to investigate the reason why RMF models give a relatively good prediction of the spin-orbit splitting but fail to reproduce the placement of the states with different orbital angular momenta. Instead of the relatively small effective mass $M^{*}$, the independence of $M^{*}$ from the angular momentum $l$ is found to be the reason.

In this work we study the contribution of the isoscalar tensor coupling to the realization of pseudospin symmetry in nuclei. Using realistic values for the tensor coupling strength, we show that this coupling reduces noticeably the pseudospin splittings, especially for single-particle levels near the Fermi surface. By using an energy decomposition of the pseudospin energy splittings, we show that the changes in these splittings come mainly through the changes induced in the lower radial wave function for the low-lying pseudospin partners and through changes in the expectation value of the pseudospin-orbit coupling term for surface partners. This allows us to confirm the conclusion already reached in previous studies, namely that the pseudospin symmetry in nuclei is of a dynamical nature.

A new alternative method for evaluating linear response theory is formally developed, and results are presented. This method involves the time evolution of the system using the time-dependent Hartree-Fock calculation and is constructed directly on top of a static Hartree-Fock calculation. By Fourier transforming the time-dependent result, the method extracts the response function and the total probability amplitude. This method allows for a coherent description of static properties of nuclei, such as binding energies and deformations, while also providing a method for calculating collective modes and reaction rates. A full three-dimensional cartesian basis-spline collocation representation is used with several Skyrme interactions. Sample results are presented for the giant multipole resonances of ${}^{16}\mathrm{O}$, ${}^{40}\mathrm{Ca}$, and ${}^{32}\mathrm{S}$ and compared to other calculations.

The positive-parity yrast states in the ${}^{91}\mathrm{Y}$ and ${}^{95}\mathrm{Nb}$ nuclei have been studied by γ-ray spectroscopy following heavy-ion-induced fusion-evaporation reactions. The lowest-lying transitions in these structures have been assigned via the $p2n$ channel of the reactions of ${}^{12}\mathrm{C}$ (38 MeV) and ${}^{16}\mathrm{O}$ (48 MeV) beams with a ${}^{82}\mathrm{Se}$ target, studied at the Bucharest Tandem accelerator. More detailed level schemes have been determined subsequently in a study performed with the GASP array of the inverse reactions produced by a ${}^{82}\mathrm{Se}$ (470 MeV) beam from the Legnaro Tandem-LINAC accelerator with oxygen and possibly carbon contaminants of a ${}^{192}\mathrm{Os}$ target. The observed level schemes are compared with local systematics and shell-model calculations.

The ${}^{114}\mathrm{Cd}(\alpha ,\mathit{xn})$ reaction has been studied for $E_{\alpha }=35\text{−}55\mathrm{MeV}$ following neutron emission and $\gamma$-ray deexcitation. Excitation functions of various $(\alpha ,\mathit{xn})$ channels measured from $\gamma$-ray yields have been compared with theoretical calculations based on ALICE-91 and CASCADE codes. Neutron energy spectra were generated from $\gamma$-gated neutron time of flight spectra. Neutron energy spectra corresponding to $(\alpha ,3n)$ and $(\alpha ,4n)$ reactions at $E_{\alpha }=50\mathrm{MeV}$ have been theoretically reproduced taking into account the contributions of equilibrated source with level density parameter $a=A/11$, along with the contributions from the pre-equilbrium process.

Investigations of nucleon induced reactions at incident energies of $14–90\text{MeV}$ resulting in the emission of complex particles ($A=2–4$) have provided insights which complement those previously obtained from ($N,\mathit{xN}$) reactions. The description of the preequilibrium energy spectra required modifications to an earlier phenomenological model for direct pickup reactions. This model supplements the usual exciton preequilibrium model. Work on complex particle induced reactions confirms some of these results, extends them to include stripping and exchange reactions, and provides evidence for a projectile dependence of the average effective matrix elements for the residual interactions in the exciton model. A full description of reactions with complex projectiles will require the inclusion of a realistic breakup component and the resulting reduction of the cross section available for the exciton model calculations. Reactions with complex particles in the entrance and/or exit channels have provided indirect evidence for the amount of surface peaking of the initial target-projectile interaction. A summary of additional data needed to help resolve remaining questions is presented.