Some general features of the eigenenergies and the eigenwave functions of a chaotic quantum system are investigated by level dynamics in connection with nuclear physics. It is shown that the chaotic property of the eigensolutions is due to a large number of avoided level crossings. The critical strength of the perturbation for onset of quantum chaos is that the average value of the matrix elements of the perturbation equals the average level spacing of the unperturbed Hamiltonian (in the so-called strong mixing limit in nuclear physics). This kind of critical perturbation makes each level experience 4–5 avoided level crossings, and produces a spreading width of 16–32 on average. The extreme sensitivity of eigenenergies and eigenwave functions to a small change of the perturbation also originates from the avoided level crossings. The analytical expressions for a measured sensitivity are derived. More general expressions for the probability distribution (or strength function) and the spreading width of a perturbed state over a regular basis are obtained, which generalize the previous results: the strength function is still in the form of a Lorentzian function but with a spreading width consisting of the regular level contribution (the width being given by the so-called picket-fence model) and the avoided-level crossing contribution (width from level fluctuations). The relation between two chaotic bases is peculiar and the corresponding strength function shows a remarkable discontinuity, which is new and due to the statistical independence of different chaotic bases. The decay properties of nuclear ergodic collective states are discussed and explained in terms of the above results. Extensive results of computer simulations are presented to verify the level dynamical predictions.

Cross sections have been measured for the ${}^{209}\mathrm{Bi}{(e,e}^{\prime }{p)}^{208}\mathrm{Pb}$ and ${}^{209}\mathrm{Bi}(\gamma {,p)}^{208}\mathrm{Pb}$ reactions using electrons at $E_e=293\mathrm{}$ and 412 MeV, and tagged photons at mean $E_{\gamma }\sim 43.7$ and $\sim 52.0$ MeV, respectively. The ${}^{209}\mathrm{Bi}{(e,e}^{\prime }{p)}^{208}\mathrm{Pb}$ results are compared to complete distorted wave impulse approximation calculations, from which it is deduced that a model of ${}^{209}\mathrm{Bi}$ based on a ${1h}_{9/2}$ proton orbiting an inert ${}^{208}\mathrm{Pb}$ core has a high degree of validity. The interpretation of the ${}^{209}\mathrm{Bi}(\gamma {,p)}^{208}\mathrm{Pb}$ results makes use of the ${(e,e}^{\prime }p)$ results to constrain the calculation of the direct knockout contribution. Using this approach, a comparison of the ${}^{209}\mathrm{Bi}(\gamma {,p)}^{208}\mathrm{Pb}$ data to various calculations with and without meson exchange contributions shows that the enhancement of the $(\gamma ,p)$ cross section due to meson exchange is small. This is in contrast to results obtained for light nuclei, but in agreement with results for heavier nuclei.

Energy levels and wave functions, obtained in realistic shell-model calculations for Ca and Sc isotopes up to $A=52\mathrm{}$ and ${}^{46}\mathrm{Ti},$ are analyzed using standard statistics such as the nearest level spacing distribution, the Dyson-Mehta ${\Delta }_3,$ and the mean localization length. These statistics are calculated for different energy regions of the spectrum. For all the Ca isotopes, in the ground state region the energy levels show strong deviations from Gaussian orthogonal ensemble predictions. It is shown that a transition to a more chaotic regime takes place as excitation energy increases. However, even when the full spectrum is taken into account, the ${\Delta }_3$ and the degree of localization of the eigenfunctions in the mean-field basis prove that Ca isotopes are less chaotic than Sc isotopes. A comparison with ${}^{46}\mathrm{Ti}$ shows that this nucleus is still more chaotic. Thus we find a clear isospin dependence in the degree of nuclear chaoticity.

We examine a broad resonance in the $0°$ ${}^{208}\mathrm{Pb}{\mathrm{}(p,n)\mathrm{}}^{208}\mathrm{Bi}$ and ${}^{90}\mathrm{Zr}{\mathrm{}(p,n)\mathrm{}}^{90}\mathrm{Nb}$ cross section spectra obtained at 795 MeV incident energy that appears at 32 MeV excitation energy in ${}^{208}\mathrm{Bi}$ and ${}^{90}\mathrm{Nb}.$ Earlier data taken at 200 MeV incident energy using the same reactions show no evidence for this resonance. We present theoretical results indicating that the spin isovector monopole predicted at this excitation energy is barely excited at 200 MeV while it is strongly excited at the higher energy. To further investigate this structure we have measured the first complete set of polarization-transfer observables for ${}^{\mathrm{nat}}\mathrm{Pb}$ at $0°$ using the $(\overrightarrow{p},\overrightarrow{n})$ reaction at 795 MeV. The data show this resonance is predominantly a spin flip $\Delta S=1\mathrm{}$ excitation giving strong supporting evidence for assigning this resonance as the spin isovector monopole.

Elastic and inelastic proton scattering to the $2_1^{+}$ states of the neutron-rich argon isotopes ${}^{42}\mathrm{Ar}$ and ${}^{44}\mathrm{Ar}$ have been measured in inverse kinematics with a beam energy of 33 MeV/nucleon. Phenomenological distorted wave Born approximation calculations are compared with the data and quadrupole deformation parameters of $|{\beta }_2|=0.32\mathrm{}\pm 0.05$ and $|{\beta }_2|=0.31\mathrm{}\pm 0.05$ are extracted for the $2_1^{+}$ states in ${}^{42}\mathrm{Ar}$ and ${}^{44}\mathrm{Ar},$ respectively. A consistent microscopic proton scattering analysis has been applied to all even-even argon isotopes from $A=36\mathrm{}$ to $A=44.\mathrm{}$ This analysis used microscopic collective model densities and a modified Jeukenne-Lejeune-Mahaux nucleon-nucleon effective interaction. The predicted cross sections agree very well with the experimental data, suggesting this microscopic analysis as a tool to test the structure of nuclei far from stability.

The first terms of the effective range expansion are accurately determined with a small number of evaluations of the potential. The method is based on the R matrix theory with a Lagrange basis which leads to a simple meshlike approximation. It is valid for both neutral and charged collisions for arbitrary partial waves. The accuracy of the algorithm is illustrated with an analytically solvable example, with different cases of potential scattering and in particular with the Paris and Bonn nucleon-nucleon potentials.

We study the density dependence of charge symmetry breaking by calculating the energy difference as a function of density between adding one neutron or one proton to uniform nuclear matter. Isospin violation from electromagnetic interactions are expected to increase with density as the average distance between quarks decreases. In contrast, isospin violation from the up-down quark mass difference should decrease with density as the contributions from the small quark masses are suppressed by the increasing Fermi momentum. The Okamoto-Nolen-Schiffer (ONS) anomaly in the binding energy of mirror nuclei was studied at high density by adding a single neutron or a proton to a quark-gluon plasma. In the limit of very high density we find an anomaly equal to two-thirds of the Coulomb exchange energy of a proton. This effect is dominated by quark electromagnetic interactions—rather than by the up-down quark mass difference, and has the same sign as that observed in normal nuclei.

We have measured two-fragment correlation functions of the intermediate mass fragments emitted from quasiprojectile sources and midrapidity component formed in ${}^{58}\mathrm{Ni}{+}^{197}\mathrm{Au}$ at 34.5 MeV/nucleon. The two-fragment correlation functions of midrapidity component show a stronger Coulomb suppression than the quasiprojectile source. This Coulomb suppression for midrapidity component changes very little with the excitation energy of the quasiprojectile source deduced event by event by calorimetry method. By comparing the experimental correlation functions with an N-body Coulomb trajectory code calculation, the emission time of quasiprojectile sources has been extracted as a function of the excitation energy. The emission time decreases monotonically with the excitation energy in the range of 2–6 A MeV from 550 $\mathrm{fm}/c$ to about 150 $\mathrm{fm}/c.\mathrm{}$ Above excitation energy of $6A$ MeV, the emission time becomes shorter and constant, suggesting that prompt multifragmentation occurs in these quasiprojectile sources.

In the plane wave one-body approximation the reaction of deuteron photodisintegration is considered in the framework of the Bethe-Salpeter formalism for the two-nucleon system. Results are obtained for deuteron vertex function, which is the solution of the homogeneous Bethe-Salpeter equation with a multirank separable interaction kernel, with a given analytical form. A comparison is presented with predictions of nonrelativistic, quasipotential approaches and the equal time approximation. It is shown that important contributions come from the boost in the arguments of the initial state vertex function and the boost on the relative energy in the one-particle propagator due to recoil.

The neutron-neutron final-state interaction (FSI) has been investigated in the ${}^2\mathrm{H}\mathrm{}(n,np)n$ reaction at 25.3 and 16.6 MeV, detecting neutrons and protons in coincidence in a geometry which should enable a practically model-independent determination of the ${}^1{S}_0$ neutron-neutron scattering length $a_{\mathrm{nn}}.$ The analysis was performed by means of detailed Monte Carlo simulations based on rigorous three-body calculations with realistic nucleon-nucleon potentials. At 25.3 MeV, the value of $a_{\mathrm{nn}}$ deduced from the absolute cross section in the FSI peak is $-16.3\pm 0.4\mathrm{fm}$ while the relative cross section, normalized in the region of neutron-proton quasifree scattering, gives $-16.1\pm 0.4\mathrm{fm}.$ The relative data obtained at 16.6 MeV yielded $a_{\mathrm{nn}}=-16.2\pm 0.3\mathrm{fm}.$ In addition, the ${}^1{S}_0$ neutron-proton scattering length was measured at 25.2 MeV in the same configuration for comparison. While our results for $a_{\mathrm{nn}}$ are incompatible with those of a similar investigation performed recently at 13 MeV where the two neutrons were detected, both results for $a_{\mathrm{np}}$ are in good agreement with the accurately known value from free n-p scattering.

We investigate the spin structure of many-fermion systems with a spin-conserving two-body random interaction. We find a strong dominance of spin-0 ground states and considerable correlations between energies and wave functions of low-lying states with different spin, but no indication of pairing. The spectral densities exhibit spin-dependent shapes and widths, and depend on the particle density as well as on the relative strengths of the spin-0 and spin-1 couplings in the two-body random matrix. The spin structure of low-lying states can largely be explained analytically.

The particle-unbound nucleus ${}^{13}\mathrm{Be}$ was populated in fragmentation reactions using the method of sequential-neutron-decay-spectroscopy at $0°.$ The observed central peak in the relative velocity spectrum is most likely first evidence for low lying s-wave strength with a scattering length of $a_s<-10\hspace{0.5em}\mathrm{fm}.$ This virtual state as the ground state of ${}^{13}\mathrm{Be}$ would make it unbound with respect to ${}^{12}\mathrm{Be}$ and a neutron by $<200\mathrm{}\hspace{0.5em}\mathrm{keV}.$

The kaon energy in neutron matter is calculated analytically with the Klein-Gordon equation, by making a Wigner-Seitz cell approximation and employing a $K^{-}N$ square well potential. The transition from the low density Lenz potential, proportional to scattering length, to the high density Hartree potential is found to begin at fairly low densities. Exact nonrelativistic calculations of the kaon energy in a simple cubic crystal of neutrons are used to test the Wigner-Seitz and the Ericson-Ericson approximation methods. In this case the frequently used Erickson-Erickson approximation is found to be fairly accurate up to twice nuclear matter density. All the calculations indicate that by $\sim 4$ times nuclear matter density the Hartree limit is reached. We also show that in the Hartree limit the energy of zero momentum kaons does not have relativistic energy dependent factors present in the low density expansions. The results indicate that the density for kaon condensation is higher than previously estimated.

We calculate the $\pi \Delta \Delta$ coupling $g_{{\pi }^0{\Delta }^{++}{\Delta }^{++}}$ using the light cone QCD sum rule. Our result is $g_{{\pi }^0{\Delta }^{++}{\Delta }^{++}}=(11.8\mathrm{}\pm 2.0).$

High-spin states have been studied in the ${}^{97}\mathrm{Mo}$ nucleus with the reaction ${}^{82}\mathrm{Se}{(}^{19}\mathrm{F},p3n\gamma )$ at 68 MeV. The main experimental result is the observation of the $\nu h_{11/2}$ quasiband structure up to the ${31/2}^{-}$ state at $E_x=5.5\mathrm{}\mathrm{MeV}.$ The systematic behavior of this structure along the isotopic and isotonic sequences is presented. The structure of the ${}^{97}\mathrm{Mo}\mathrm{}$ is discussed in terms of the interacting boson-fermion model 1.

A set of measurements consisting of γ-ray excitation functions and angular distributions has been performed using the ${(n,n}^{\prime }\gamma )$ reaction on ${}^{110}\mathrm{Cd}.$ Gamma-ray excitation functions allowed us to clarify the level scheme by placing ten new transitions and to establish one new level. From $\gamma$-ray angular distributions, the lifetimes for 16 excited states were extracted using the Doppler-shift attenuation method. The experimental $B\left(E2\mathrm{}\right),$ $B\left(M1\mathrm{}\right),$ and $B\left(E1\mathrm{}\right)\mathrm{}$ values of transitions from intruder, octupole, and three-phonon states are compared to different theoretical models.

New data on $\Lambda$ production in Au+Au collisions at $11.5A$ $\mathrm{GeV}/c$ are presented. The measurements cover the rapidity range from $y=2.0\mathrm{}$ to 3.5 and transverse momenta from $p_t=0.15\mathrm{}$ $\mathrm{GeV}/c$ to 1.5 $\mathrm{GeV}/c.\mathrm{}$ The rapidity distributions, transverse momentum spectra, and azimuthal distributions are presented for different centralities of the collision. A strong positive directed flow at forward rapidity is observed for semicentral collisions. The measured spectra, yields, and directed flow are compared with the predictions of relativistic quantum molecular dynamics (RQMD) v2.3 model.