A new method to incorporate the Pauli principle into the double folding approach to the nucleus-nucleus potential is proposed. The description of the exchange terms at the level of the quasiclassical one-body density matrix is used. It is shown that in order to take into account the Pauli blocking properly, a redefinition of the density matrices of the free isolated nuclei must be done. A solution to the self-consistent incorporation of the Pauli blocking effects in the mean-field nucleus-nucleus potential is obtained in the Thomas-Fermi approximation.

Inclusive electron scattering data are presented for ${}^2\mathrm{H},$ C, Fe, and Au targets at an incident electron energy of 4.045 GeV for a range of momentum transfers from $Q^2=1\mathrm{}$ to $7\hspace{0.5em}(\mathrm{GeV}{/c)}^2.$ Data were taken at Jefferson Laboratory for low values of energy loss, corresponding to values of Bjorken $x\gtrsim 1.$ The structure functions do not show scaling in x in this range, where inelastic scattering is not expected to dominate the cross section. The data do show scaling, however, in the Nachtmann variable $\xi .$ This scaling appears to be the result of Bloom- Gilman duality in the nucleon structure function combined with the Fermi motion of the nucleons in the nucleus. The resulting extension of scaling to larger values of $\xi$ opens up the possibility of accessing nuclear structure functions in the high-$x$ region at lower values of $Q^2$ than previously believed.

An extended Lipkin-Meshkov-Glick model for testing the proton-neutron random-phase approximation $\left(pn\mathrm{RPA}\right)$ method is developed, taking into account explicitly proton and neutron degrees of freedom. Besides the proton and neutron single-particle terms two types of residual proton-neutron interactions, one simulating a particle-particle and the other a particle-hole interaction, are included in the model Hamiltonian so that the model is exactly solvable in an isospin $\mathrm{SU}\mathrm{}\left(2\right)\mathrm{}\otimes \mathrm{SU}\mathrm{}\left(2\right)\mathrm{}$ basis. The behavior of the first excited (collective) state obtained by (i) exact diagonalization of the Hamiltonian matrix and (ii) with the $\mathrm{pn}\mathrm{RPA}$ is studied as a function of the model parameters and the two results are compared with each other. Furthermore, charge-changing operators simulating nuclear beta decay and their action on eigenfunctions of the model Hamiltonian are defined and transition amplitudes of them are calculated using exact, the Tamm-Dancoff, and $\mathrm{pn}\mathrm{RPA}$ eigenfunctions.

Localized fluctuations in the multiplicity of charged particles and photons produced in central $158A\hspace{0.5em}\mathrm{GeV}/c$ Pb+Pb collisions are studied. The charged versus neutral correlations in common $\eta -\phi$ phase space regions of varying azimuthal size are analyzed by two different methods. The analysis provides a model-independent demonstration of nonstatistical fluctuations in both charged particle and photon multiplicities in limited azimuthal regions. However, no correlated charge-neutral fluctuations are observed, contrary to expectations for the production of a disoriented chiral condensate. The result is not explained by the widely used VENUS model.

In a study parallel to one recently carried out for the interacting boson model, the behavior of the geometric collective model (GCM) with (partially restricted) random interactions is studied. In particular, we study the frequency distribution of ${E(4\mathrm{}}_1^{+}{)/E(2\mathrm{}}_1^{+})$ ratios. In addition, we characterize those GCM potentials giving E(5) spectra and distinguish them from others giving $R_{4/2}\sim 2.3$ but non-E(5) spectra.

For pedagogical reasons we compute the caloric curve for 11 particles in a $3^3$ lattice. Monte Carlo simulation can be avoided and exact results are obtained. We compare canonical and microcanonical results for the caloric curve. Even down to this small system, agreement between the canonical model and the microcanonical model is surprisingly good. We point out that the introduction of kinetic energy in the nuclear lattice gas model modifies the results of the standard lattice gas model in a profound way. The model is also used to test the accuracy of the saddle-point approximation for density of states.

The moleculelike structure of the C isotopes $(A=12,14,16)$ is investigated using a microscopic $\alpha +\alpha +\alpha +n+n+\cdot \cdot \cdot$ model. The valence neutrons are classified based on the molecular-orbit model, and both $\pi$ orbit and $\sigma$ orbit are introduced around three $\alpha$ clusters. The valence neutrons which occupy the $\pi$ orbit increase the binding energy and stabilize the linear chain of $3\alpha$ against the breathinglike breakup. However, ${}^{14}\mathrm{C}$ with the $\pi$ orbit does not show a clear energy minimum against the bendinglike path. The combination of the valence neutrons in the $\pi$ and $\sigma$ orbits is promising to stabilize the linear-chain state against the breathing and bending modes, and it is found that the excited states of ${}^{16}\mathrm{C}$ with the ${(3/2\mathrm{}}_{\pi }^{-}{)}^2{(1/2\mathrm{}}_{\sigma }^{-}{)}^2$ configuration for the four valence neutrons is one of the most promising candidates for such a structure.

Unknown β-delayed proton precursor ${}^{142}\mathrm{Ho}$ was synthesized in the reaction ${}^{106}\mathrm{Cd}$ ${(}^{40}\mathrm{Ca},p3n)$ and identified for the first time using proton-gamma coincidence measurements in combination with a helium-jet fast tape-transport system. Its β-delayed proton spectrum was observed. The half-life of ${}^{142}\mathrm{Ho}$ was determined to be $0.4\pm 0.1\hspace{0.5em}\mathrm{s}.$ According to the estimated relative branching ratios to the final states in the daughter nucleus, the ground-state spin of ${}^{142}\mathrm{Ho}$ could be assigned as 6, 7, or 8.

The emission of light charged particles and intermediate-mass fragments (IMF’s) from central collisions of 45 MeV/nucleon ${}^{84}\mathrm{Kr}$ with ${}^{93}\mathrm{Nb}$ has been studied. Violent collisions have been selected using the total collected charge condition. The analysis of the primary IMF excitation energies has been performed for four bins of the detected IMF charge $(2<Z_{\mathrm{IMF}}<20).\mathrm{}$ We find evidence that (a) the mean excitation energy per nucleon for these fragments is independent of fragment charge and approximately equal to 2.5 MeV, (b) the primary fragments at freeze-out preserve the entrance channel (combined system) $N/Z$ ratio, and (c) the freeze-out volume itself is far from spherical.

The higher-order terms of a novel boson-fermion expansion formalism previously introduced by one of the authors are discussed within the framework of the soluble SU(2) LMG model. A new formulation is provided to rectify certain undesirable features of the original expansion. In particular, the subsidiary condition that defines the physical subspace is obtained in a much simpler form. With the new formulation, the infinite expansion is summed in closed form. A comparison is made with earlier extended Holstein-Primakoff boson-fermion expansions.

High-spin states of ${}^{89}\mathrm{Sr}$ and ${}^{90}\mathrm{Sr}$ were studied via the reactions ${}^{82}\mathrm{Se}{(}^{11}\mathrm{B},$ $p3n)$ and ${}^{82}\mathrm{Se}{(}^{11}\mathrm{B},$ $p2n),$ respectively, at a beam energy of 37 MeV. Gamma rays were detected with the GASP spectrometer. The level schemes of ${}^{89}\mathrm{Sr}$ and ${}^{90}\mathrm{Sr}$ were extended up to $E\approx 8$ MeV and $E\approx 10$ MeV, respectively. Level structures in ${}^{89}\mathrm{Sr}$ and ${}^{90}\mathrm{Sr}$ were interpreted in terms of the spherical shell model. The calculations were performed in the configuration space ${(0f}_{5/2}{,1p}_{3/2}{,1p}_{1/2}{,0g}_{9/2})$ for the protons and ${(1p}_{1/2}{,0g}_{9/2}{,1d}_{5/2})$ for the neutrons. High-spin level sequences in ${}^{89}\mathrm{Sr}$ are characterized by coupling the unpaired $d_{5/2}$ neutron to proton excitations of the core nucleus ${}^{88}\mathrm{Sr}.$ An equidistant level sequence with $\Delta J=2\mathrm{}$ found in ${}^{90}\mathrm{Sr}$ is well described by the configuration $\pi \left[{(0f}_{5/2}^{-2}{\left)\right(0g}_{9/2}^2\right)\left]\nu {(1d}_{5/2}^2\right)$ favoring even spins.

The effects of setting all $T=0\mathrm{}$ two body interaction matrix elements equal to a constant (or zero) in shell model calculations (designated as $〈T=0\mathrm{}〉=0)$ are investigated. Despite the apparent severity of such a procedure, one gets fairly reasonable spectra. We find that using $〈T=0\mathrm{}〉=0\mathrm{}$ in single-j shell calculations degeneracies appear, e.g., the $I={\frac{1}{2}}^{-}$ and ${\frac{13}{2}}^{-}$ states in ${}^{43}\mathrm{Sc}$ are at the same excitation energies; likewise the ${I=3\mathrm{}}_2^{+},7_2^{+},9_1^{+},$ and ${10}_1^{+}$ states in ${}^{44}\mathrm{Ti}.$ The above degeneracies involve the vanishing of certain $6j$ and $9j$ symbols. The symmetry relations of Regge are used to explain why these vanishings are not accidental. Thus for these states the actual deviation from degeneracy are good indicators of the effects of the $T=0\mathrm{}$ matrix elements. A further indicator of the effects of the $T=0\mathrm{}$ interaction in an even-even nucleus is to compare the energies of states with odd angular momentum with those that are even.

We investigate QCD sum rules for vector currents in the rho meson channel in the nuclear medium. For increased sensitivity, we subtract out the vacuum contributions. With a saturation scheme often considered in the literature, we find these “subtracted” sum rules to be unstable. It indicates the importance of other contributions neglected in the saturation scheme. These include more Landau singularities at low energy, additional operators in the medium, and possibly the in-medium width of the rho meson.

We studied the exclusive reaction $e\overrightarrow{p}{e}^{\prime }{p}^{\prime }\phi$ using the $\overrightarrow{\phi }{K}^{+}{K}^{-}$ decay mode. The data were collected using a 4.2 GeV incident electron beam and the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. Our experiment covers the range in $Q^2$ from 0.7 to 2.2 ${\mathrm{GeV}}^2,$ and W from 2.0 to 2.6 GeV. Taken together with all previous data, we find a consistent picture of $\phi$ production on the proton. Our measurement shows the expected decrease of the t slope with the vector-meson formation time $c\Delta \tau$ below 2 fm. At $〈c\Delta \tau 〉=0.6\mathrm{}$ fm, we measure $b_{\phi }=2.27\mathrm{}\pm 0.42$ ${\mathrm{GeV}}^{-2}.$ The cross section dependence on W as $W^{0.2\pm 0.1}$ at $Q^2=1.3\mathrm{}$ ${\mathrm{GeV}}^2$ was determined by comparison with $\phi$ production at HERA after correcting for threshold effects. This is the same dependence as observed in photoproduction.

The total and $2p$ internal bremsstrahlung spectra accompanying the electron capture decay of ${}^{179}\mathrm{Ta}$ have been measured in singles and in coincidence with L x rays, respectively. The intensity of the total spectrum was found to be $(1.131\mathrm{}\pm 0.027)$ times that predicted by the calculations of Surić et al.; the intensity of the $2p$ spectrum was found to be $(1.097\mathrm{}\pm 0.028)$ times those calculations. The disagreement with theory is thus much smaller than the factor of 1.5–2 previously reported for ${}^{193}\mathrm{Pt}.$ The $Q_{\mathrm{EC}}$ value determined from the internal bremsstrahlung end point energy was found to be $105.61\pm 0.41$ keV. An independent value for $Q_{\mathrm{EC}}$ of $109.3\pm 3.1$ keV was determined by measuring the L to K capture ratio.

The locations of ${}^{18}\mathrm{Ne}+\alpha$ resonances have been measured as excited states in ${}^{22}\mathrm{Mg}$ using the ${}^{12}\mathrm{C}{(}^{16}\mathrm{O}{,}^6\mathrm{He}{)}^{22}\mathrm{Mg}$ reaction. Eighteen new levels were discovered in the range $0<~E_{\mathrm{c}.\mathrm{m}.\mathrm{}}<~3\mathrm{MeV}$ above the ${}^{18}\mathrm{Ne}+\alpha$ threshold. The ${}^{18}\mathrm{Ne}(\alpha {,p)}^{21}\mathrm{Na}$ reaction rate in the temperature range $0.2<~T<~1.0\mathrm{GK}$ has been calculated using the results from the present measurements, and the implications for nuclear burning in explosive stellar scenarios are discussed. This study also yielded energy-level information on low-lying ${}^{21}\mathrm{Na}+p$ resonances of importance to the ${}^{21}\mathrm{Na}(p,\gamma {)}^{22}\mathrm{Mg}$ reaction, one of the key links in the NeNa cycles in novae.

A simple analytical expression, which closely approximates the Coulomb potential between two uniformly charged spheres, is presented. This expression can be used in the optical potential semiclassical analyses which require that the interaction be analytic on and near the real r axis.

A multistep microscopic approach describing the dynamics of quasimolecular resonances is applied to the $\alpha {+}^{40}\mathrm{Ca}$ system. The lowest collective two-particle eigenmodes are used as building blocks of the four-particle states. The pair states are built on mean-field single-particle orbitals including also sharp resonances in continuum. The structure of ${}^{44}\mathrm{Ti}$ is analyzed and strong high-lying $\alpha$-like resonances are found in good agreement with the experimentally observed quasimolecular spectrum. The resonances turn out to be very collective and contain mostly proton-neutron pairs where the lowest proton single-particle resonance, $\pi p_{3/2},$ couples with the lowest neutron bound state $\nu f_{7/2}.$

The interaction of ${}^6\mathrm{He}$ with ${}^{209}\mathrm{Bi}$ has been studied over a range of energies well below the nominal Coulomb barrier. A ${}^4\mathrm{He}$ group of remarkable intensity, first observed in a previous experiment at near-barrier energies, continues to dominate the reaction in the sub-barrier regime. A total cross section of nearly 200 mb was measured for this group at 6 MeV below the barrier. This very large value is shown to be consistent with the total reaction cross section deduced from a simultaneously-measured elastic scattering angular distribution.

Very strong transfer/breakup yields have been reported for the interaction of a number of light, weakly bound nuclei with Pb and Bi targets in the vicinity of the Coulomb barrier. The systematic behavior of the excitation functions and absolute cross sections observed in these experiments is discussed.