We consider loop expansions for the chirally symmetric linear σ model. The conventional loop expansion is reviewed, and the tachyon problems due to the large attractive σπ and σσ couplings are investigated. We then study a modified loop expansion that sums the repulsive baryon loops to all orders at each order in meson loops. Renormalizability is explicitly demonstrated to modified one-loop order, which corresponds to the relativistic random-phase approximation. We show that tachyons present in the conventional loop expansion are avoided to a large extent, but ghosts arise due to the unphysical behavior of the vacuum loops in this field theory that is not asymptotically free. Implications and possible solutions to this problem are discussed.

We use the semirelativistic constituent quark model in conjunction with the resonating group method to obtain a nonlocal Schrödinger equation for the two-nucleon system. As the quark-quark color exchange potential we use the lattice gauge theory result; the sum of the Breit potential and a linearly rising confining potential. Both the Breit potential and the quark kinetic energies are treated consistently to order (v/c${)}^2$ in the quark speeds; however, we ignore relativistic corrections to the confining potential and to the kinetic energy of relative motion of the nucleons. We distinguish carefully between the exact formulation and the approximations we use to make the calculations tractable. We present the resulting nonlocal nucleon-nucleon Schrödinger equation explicitly and analytically.

The nonlocal Schrödinger equation for the two-nucleon potential derived from the interaction between constituent quarks is applied to calculating the ground state properties of the deuteron, using quark parameters consistent with single baryon data. We conclude that the two-nucleon nonlocal equation affords a very decent description of the deuteron.

We study the implications of new data (from Brookhaven) on features of the weak nonmesonic decays of Λ hypernuclei and on our understanding of the ΛN→NN process. We follow the phenomenological analysis of Block and Dalitz; there is no need, however, to assume the validity of the ΔI=1/2 rule. The importance of and need for higher-quality and newer data are demonstrated.

Gamma rays from a mixed source of ${}_{}{}^{56}{}_{}{}^{}\mathrm{Co}$${+}^{46}$Sc were measured in a Ge(Li) detector. The ${}_{}{}^{56}{}_{}{}^{}\mathrm{Co}$${/}^{46}$Sc peak intensity ratios ${\mathit{I}}_{847}$/${\mathit{I}}_{889}$ were determined by careful analysis of line shapes and underlying backgrounds. Based on the known ${}_{}{}^{46}{}_{}{}^{}\mathrm{Sc}$ adopted half-life value of 83.810(10) d, the fit to the intensity ratios corrected for ${}_{}{}^{46}{}_{}{}^{}\mathrm{Sc}$ decay from 107 runs over an elapsed time of 172 days gave a half-life value of 77.29(3) d for ${}_{}{}^{56}{}_{}{}^{}\mathrm{Co}$.

One possible source of neutrons for the astrophysical s process is the ${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}$(α,n${)}^{25}$Mg reaction. However, the number of neutrons available to synthesize heavy elements may be limited by the rate of the ${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}$(n,γ${)}^{23}$Ne reaction. To aid in the interpretation of recent (n,γ) measurements, we have used the ${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}$(d,p${)}^{23}$Ne reaction to investigate the single-particle structure of states located near the ${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}$+n threshold. No states that correspond to astrophysically significant resonances were found, and so the (n,γ) rate is effectively determined by direct capture.

The information on the coexistence of deformed intruder states and normal spherical hole-core coupled states in odd-mass Ag nuclei has been extended to the neutron-rich isotopes ${}_{}{}^{113}{}_{}{}^{}\mathrm{Ag}_{66}^{}{}_{}{}^{}$ and ${}_{}{}^{115}{}_{}{}^{}\mathrm{Ag}_{68}^{}{}_{}{}^{}$. Data have been obtained from an investigation of the γ rays following the ${\mathrm{\beta }}^{\mathrm{-}}$ decay of the ${}_{}{}^{113,115}{}_{}{}^{}\mathrm{Pd}$ precursors. A minimum for the excitation energy of the intruder states occurs in ${}_{}{}^{113}{}_{}{}^{}\mathrm{Ag}_{66}^{}{}_{}{}^{}$, exactly at neutron midshell. The properties of the intruder states in ${}_{}{}^{109,111,113,115}{}_{}{}^{}\mathrm{Ag}$ are discussed and a description in the framework of the interacting-boson-fermion model is presented.

The ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}$ nucleus was studied with the (α,4n) reaction on ${}_{}{}^{116}{}_{}{}^{}\mathrm{Cd}$. Investigation of the interband and intraband transitions from the excited states of the ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}$ nucleus was carried out by measuring gamma-ray singles, gamma-gamma coincidence, and gamma-ray angular distribution. The excitation functions of several transitions have also been studied and the absolute cross sections of (α,xn) reactions have been measured.

It is shown that two light-front potential models for the two-nucleon system whose interactions have the same momentum space matrix elements in the nonrelativistic regime lead to dramatically different ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}_0$ phase shifts at low energies. The ${}_{}{}^1{}_{}{}^{}$${\mathit{D}}_2$ phase shifts are in good agreement at low energies.

Level densities are calculated for the nucleus ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ using an exact iterative method for noninteracting fermions. Various single-particle energies are tested. It is found that the conventional Fermi-gas energy dependence provides a good representation of the actual level density only up to energies about 100 MeV. Above this point, the deviations rapidly grow, reaching many orders of magnitude at energies above 200 MeV. One calculation has also been made for ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$. These results are similar, with the point of breakdown of the Fermi-gas form raised to about 200 MeV. The present results should have significant consequences for heavy-ion reaction studies of equilibration and for astrophysics.

We use a microscopic semiclassical phase-space approach to study the possibility of a softening of the dipole mode in neutron-rich nuclei. In order to reproduce the expected low-energy strength in ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ we have to introduce two different mean fields for core and valence neutrons. The results are quite dependent on the extension of the neutron halo. The best agreement is obtained using the experimental value of the halo radius. Some fragmentation for the low-energy strength is also predicted.

The mean-square angular momenta of the compound nucleus ${}_{}{}^{227}{}_{}{}^{}\mathrm{Pa}$ becomes constant at and below the energy which shifted F MeV from barrier ${\mathit{V}}_{\mathit{b}}$ with respect to one-dimensional barrier penetration. This energy shift is borne out to be self-consistent with the total coupling strength extracted from the 〈${\mathit{l}}^2$〉 value at the barrier.

In a first application of the gamma-ray-induced Doppler broadening technique to a heavy mass nucleus the first absolute transition rates from a σ<N state in an O(6) nucleus ${(}^{196}$Pt) are obtained. The principal results concerns the 1402 keV $0^{+}$ base state of the σ=N-2 family, namely, that B(E2:[$0_3^{+}$(σ=4)-$2_1^{+}$(σ=6)])<0.034 ${\mathit{e}}^2$ ${\mathrm{b}}^2$. In agreement with the selection rule which forbids Δσ=2 transitions, this corresponds to at least an order-of-magnitude hindrance compared to allowed O(6) transitions and provides a critical test of the σ quantum number.

The observation of narrow, correlated structures in electron and positron spectra from heavy-ion collisions near the Coulomb barrier have prompted speculations that they may be due to the decay of an exotic bound state of the ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ system with an invariant mass of between 1.5 and 2.0 MeV. Many experiments have been carried out to detect the effects of such a bound state on the decay of nuclear states and in ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ elastic (Bhabha) scattering. We have made a measurement of the annihilation-in-flight cross section of positrons in germanium with energies between 1 and 4 MeV using a ‘‘tagged-positron’’ technique. Our limits on the strength of possible resonances decaying to two γ’s are between 15 and 50 meV. Special attention has been paid in the analysis to the effect of the response function of the detector system on the derived strength limit.

The y scaling exhibited in quasielastic electron scattering on nuclei is shown to occur in the same kinematic limit as x scaling in deep-inelastic lepton-nucleon scattering. Using the impulse approximation in a relativistic model, we demonstrate that the scaling function F(y) can be interpreted as the nucleon light-cone momentum distribution and the scaling variable y is related to the light-cone momentum ${\mathit{t}}^{+}$ of the nucleon. We also derive the convolution formula for deep-inelastic lepton-nucleus scattering and show that the same F(y) can be extracted from the experimental structure functions of the nucleon and nuclei.

The effect of driving force on the division of excitation energy between the asymmetric colliding partners in deep inelastic heavy-ion collisions is studied in the nucleon-exchange model. For this purpose an event-by-event analysis using Monte Carlo simulation technique is performed. It is seen that the fraction of the total excitation energy carried by the projectile-like fragment is sensitive to the mass drift. The model is also applied to analyze the correlation between fragment mass and excitation energy for a given total energy loss and significant correlation is found. The reactions induced by ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$ at 9 MeV/nucleon and ${}_{}{}^{74}{}_{}{}^{}\mathrm{Ge}$ at 8.5 MeV/nucleon on ${}_{}{}^{165}{}_{}{}^{}\mathrm{Ho}$ are considered in our analysis and the calculated correlations are in good agreement with the results obtained from the kinematic coincidence experiments.

It is demonstrated numerically that a separable expansion of the two-body t matrix gives us an exact method of solving the Faddeev equation with a local potential. The method of a separable expansion adopted is simple and systematic. The result of the three-body calculation on the n-d scattering is stable at least in four significant figures with a lower truncation of the separable series.

Benchmark solutions for n-d scattering using a single model interaction have been produced by five different groups using different methods. These s-wave results have been obtained at three energies for both quartet and doublet scattering.