W.J. Gerace

Longitudinal electroexcitation of the low-lying states in 42Ca and 44Ca

Abstract The form factors in electron scattering have been measured for 2 + , 3 − and 5 − states up to 7 MeV excitation in 42 Ca and 44 Ca. The range of the incident electron energy and scattering angles were 62.5–250 MeV at relatively forward angles, over the momentum transfer from 0.4–1.8 fm − . The reduced transition probabilities B (E l ) for these states were determined using Tassie-type and shell-model-type transition densities. It is shown that the characteristics and the differences of the observed 2 + 1 and 2 + 2 form factors in 42 Ca and 44 Ca are explained by deformation effect and the coexistence model was well verified in 42 Ca. The form factor of the 6.1 MeV transition in 42 Ca may be interpreted as an isoscalar dipole transition by its E3-like q -dependence similar to those in the self-conjugate nucleus 40 Ca, and the isoscalar E1 transition density is deduced.

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.

Off-shell effects in scattering from the deuteron

Abstract A simple model for scattering from a deuteron is studied. Within this model exact coupled channel solutions, including all multiple scattering series terms, are obtained for a fixed separation of the two scattering potentials. These solutions are compared with approximations which involve a spherically averaged or non-overlapping potential. Our results indicate that the non-negligible contributions arising from the overlapping potential region can be adequately reproduced by a combination of simple approximations thereby facilitating calculations of scattering from a more physical deuteron model.

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.

The influence of overlapping potentials and short range correlations on high-energy scattering

Abstract High-energy nucleon scattering from light nuclei is investigated using several different scattering formalisms. Off-energy-shell effects due to overlapping target particle potentials and short range correlations are included in some of the calculations. The results indicate that the uncertainties in the computed cross section due to choice of scattering formalism, and due to neglect or inclusion of off-energy-shell effects, or two-body correlations are all of comparable size.

Isoscalar character of the Jπ = 6+, Ex = 5.125 MeV state in 58Ni

A measurement of the transverse (E6) and coulomb (C6) strengths from the 58Ni ground state to the J~ = 6+~ 5.125 MeV state has been made via medium-energy inelastic electron scattering. Comparison between previous measurements I of the C6 strength and simple particle-hole calculations without effective charges suggest that the 5.125 MeV 6 + state is essentially a pure spin-flip (f5/2 f7/2 ) excitation. We have made measurements of the transverse form factor to determine how well this simple interpretation holds up for the transverse or magnetic character of this state and to repeat the coulomb measurements with significantly better energy resolution. Measurements of the differential cross section for the 5.125 MeV state were made at the Bates Linear Accelerator Center at 13 incident electron energies, ranging from 120.4 to 263.9 MeV at ~ = 120 ° and e = 160 °. A direct measurement of the transverse strength was also made at E o = 195.1 MeV using the new 180 = scattering system. The transverse and coulomb strengths extracted via a Rosenbluth separation in PWBA at three distinct momentum transfers span the peak of the first maximum of the form factor.

Comparison of an optical potential with its separable representations: Fully off-shell behavior☆

Abstract The fully off-shell t -matrix elements of a local neutron optical potential are compared with those of separable representations for this potential. Two separable forms, each of which include the effects of three t -matrix poles per channel, are used; a single-term energy-dependent form and a rank-3 energy-independent form. Although these two representations give fairly equivalent fits to the on-shell and half-off-shell t -matrix elements, they have very different fully off-shell extrapolations. This difference is shown to result from the single term nature of the first representation. No conclusion can be made, however, as to which extrapolation is physically more realistic.