James F. Walker

Field-theory treatment of the pp→dπ+ reaction

Abstract A field-theoretic treatment of the pp→d π + reaction is presented. Qualitative agreement with the experimental total cross sections and angular distributions is obtained in a model which uses neither a fundamental cutoff in the π-nucleon interaction, nor a ρ-exchange between nucleons.

Separable energy-dependent approximation to local potentials

Abstract An extension of the single-pole separable approximation of a two-body t -matrix in which the effects of several poles are included is made. The simple form for the t -matrix derived from a single separable potential is retained. However, the separable potential is constructed using an energy-dependent superposition of the states corresponding to the various poles. The energy dependence is chosen so as to obtain the correct residue of both the on-shell and off-shell t -matrices at each of these poles, while preserving unitarity. The formalism is specialized to the case of s-wave scattering from an attractive square well. Comparison to the exact s-wave cross section gives good results.

Quadrupole core vibrations in the A = 211 isobars

Abstract States of the A = 211 isobars are described as three particles coupled to each other and to a vibrating 208 Pb core. Model parameters are extracted from available data on A = 209, 210 isobars, but it is necessary to postulate a form for the two-body interaction to obtain all necessary matrix elements. Energy spectra and reduced transition probabilities are calculated and compared with experiment.

Effects of 208Pb core vibrations on shell-model calculations for 211At and 211Pb

Abstract The low-lying states of 211 Pb and 211 At are described as three j = 9 2 particles coupled to each other and to a 208 Pb core. The core states are restricted to zero or one quadrupole-phonon excitations. All model parameters are determined uniquely from the available experimental data on nuclei having A = 208, 209, 210. The resulting wave functions and energy levels are given. Reduced transition probabilities for E2 transitions between the states of 211 At are calculated and compared with experiment. Good agreement is achieved.

Off-energy shell behavior of a single-term separable energy-dependent potential

Abstract Excellent fits to on-shell t -matrix elements of a realistic local potential are obtained using a single-term energy-dependent separable potential in each of five channels. The comparison of half-off-shell t -matrix elements is also very favorable. The optical potential used contains absorption as well as spin-orbit contributions and is appropriate for the low energy n- 27 Al system. The separable potential is constructed so as to have the correct t -matrix pole locations and residues in each of the five channels.

Equivalent neutron optical potentials in the separable energy-dependent approximation

Abstract The single-term separable energy-dependent approximation for the two-body t -matrix is extended to the case of non-hermitian potentials. The formalism is applied to construct a separable potential for neutron scattering at low energies. Comparison with the exact scattering data gives good agreement.

Hole and continuum contributions to the 42Ca(p, t)40Ca form factor

Abstract Contributions to the form factor for the reaction 42 Ca(p, t) 40 Ca deriving from hole and continuum state admixtures in the two-nucleon distribution function are studied by expanding the solution of the microscopic two-body hamiltonian equation in a sturmian basis. It is found that hole and continuum contributions are equally important for the stripping process but that the hole terms counteract the effect of the continuum admixtures. The sturmian form factors containing hole terms are found to closely resemble a standard form factor obtained using coexistence-model wave functions.

The effective Hamiltonian approach for the two-nucleon distribution function

Abstract The microscopic two-body effective Hamiltonian equation satisfied by the two-nucleon distribution function needed for two-particle transfer processes is derived. The usual approximations made in order to obtain a partial solution to this equation are discussed and compared. It is concluded that contributions to the distribution function from both core state and channel coupling terms are likely to be comparable to continuum configurations in importance. Such contributions must certainly be included if an unambiguous normalization for the distribution function is desired.