We reply to the Comment (preceding paper) by J.-M. Richard on our partial-wave analysis of low-energy p¯p scattering data [Phys. Rev. C 50, 48 (1994)], in which we determined for the first time the p¯p phase parameters.

We have measured the relative differential cross section and spin observables for the reaction np→pp${\mathrm{\pi }}^{\mathrm{-}}$ at 443 MeV. Our measurements have been compared with predictions of the model of Kloet and Lomon. Some of the variables show marked disagreement with predictions; for other variables there is surprisingly good agreement.

The Faddeev-Yakubovsky equations for four identical spinless particles in one-dimensional space interacting via δ-function potentials are solved analytically for a bound state.

A two step method is developed for determining the NN→ΔN transition amplitudes. The purpose of the study is to select a set of 31 observables, which determines, firstly, the 16 magnitudes of the amplitudes, and secondly, 15 independent relative phases. For determining NN→(Nπ)N experiments needed to such an amplitude analysis, the decay distribution is expressed in the density matrix formalism. Helicity and transversity frames are studied. The knowledge of helicity amplitudes requires experiments involving four polarized nucleons at a time. For transversity amplitudes, the use of Bohr’s rules simplifies the problem. A complete transversity amplitude analysis avoids the detection of the polarization of the outgoing decay nucleon.

We argue that the minimal chiral background for the two-pion exchange nucleon-nucleon interaction has nowadays a rather firm conceptual basis, which entitles it to become a standard ingredient of any modern potential. In order to facilitate applications, we present a parametrized version of a configuration space potential derived previously. We then use it to assess the phenomenological contents of some existing NN potentials.

Based on a quark cluster model for the nonstrange sector that reproduces reasonably well the nucleon-nucleon system and the excitation of the Δ isobar, we generate a nucleon-Δ interaction and present the predictions for the several isospin-2 channels. The only attractive channels are $0^{+}$ and $0^{\mathrm{-}}$, but not attractive enough to generate a resonance. If a resonance is artificially generated and is required to have the observed experimental mass, then our model predicts a width that agrees with the experimental result.

Using multiple scattering theory the scattering lengths of η mesons on helium nuclei are calculated and checked against final state η interactions from the pd→${\mathrm{\eta }}^3$He and dd→${\mathrm{\eta }}^4$He reactions. The existence of an ${\mathrm{\eta }}^4$He quasibound state is indicated.

The Ward-Takahashi identities are central to the gauge invariance of the photoproduction amplitude. Here we demonstrate that unitarity and in particular the inclusion of both the πN and γπN thresholds on equal footing yields a photoproduction amplitude that satisfies both two-body unitarity and the generalized Ward-Takahashi identities. The final amplitude is a solution of a set of coupled channel integral equations for the reactions πN→πN and γN→πN.

Relativistic Hamiltonians are defined as the sum of relativistic one-body kinetic energies, two- and many-body interactions and their boost corrections. We review the calculation of the boost correction of the two-body interaction from commutation relations of the Poincaré group and show that its important terms can be easily understood from classical relativistic mechanics. The boost corrections for scalar- and vector-meson-exchange interactions, obtained from relativistic field theory, are shown to be in agreement with the results of the classical calculation. These boost corrections are also shown to be necessary to reproduce the known results of relativistic mean-field theories. We conclude with comments on the relativistic boost operator for the wave function of a nucleus. Some of the results presented in this article are known. We hope that a better understanding of relativistic Hamiltonians and their relation to relativistic field theory is obtained by putting them together with the new relations.

In relativistic Hamiltonians the two-nucleon interaction is expressed as a sum of v${\mathrm{̃}}_{\mathit{i}\mathit{j}}$, the interaction in the ${\mathbf{P}}_{\mathit{i}\mathit{j}}$=0 rest frame, and the ‘‘boost interaction’’ δv(${\mathbf{P}}_{\mathit{i}\mathit{j}}$) which depends upon the total momentum ${\mathbf{P}}_{\mathit{i}\mathit{j}}$ and vanishes in the rest frame. The δv can be regarded as a sum of four terms: δ${\mathit{v}}_{\mathrm{RE}}$, δ${\mathit{v}}_{\mathrm{LC}}$, δ${\mathit{v}}_{\mathrm{TP}}$, and δ${\mathit{v}}_{\mathrm{QM}}$; the first three originate from the relativistic energy-momentum relation, Lorentz contraction, and Thomas precession, while the last is purely quantum. The contributions of δ${\mathit{v}}_{\mathrm{RE}}$ and δ${\mathit{v}}_{\mathrm{LC}}$ have been previously calculated with the variational Monte Carlo method for ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. In this paper we report the results of similar calculations for the contributions of δ${\mathit{v}}_{\mathrm{TP}}$ and δ${\mathit{v}}_{\mathrm{QM}}$. These are found to be rather small.

At very high spins an oblate-to-triaxial transition in the equilibrium shape of hot medium mass nuclei is expected, with superdeformed major to minor axis ratios of 2:1 and larger. To search for this shape transition, we measured γ ray production cross sections and angular distributions for the decay of ${}_{}{}^{59,63}{}_{}{}^{}\mathrm{Cu}$ compound nuclei populated in the fusion of ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$${+}^{27}$Al and ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$${+}^{45}$Sc over a wide range of spin (J=0-47ħ) and excitation energy (${\mathit{E}}^{\mathrm{*}}$=55–130 MeV). Very broad giant dipole resonance (GDR) strength functions are deduced at high bombarding energy (spin), implying the existence of large deformation in the ensemble of decaying states. Thermal shape and orientation fluctuation calculations based on the rotating liquid drop model provide a good description of the GDR strength functions for all cases. The calculations fail to reproduce the GDR strength functions at high bombarding energy (spin) cases when the oblate-to-triaxial shape transition and the associated softness in the PES are removed, indicating the observed broadening of the GDR strength function is due mostly to spin-driven deformation. Threshold bremsstrahlung production is inferred from measured angular distribution anisotropies in ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$${+}^{45}$Sc collisions at 125 and 149 MeV.

The high-spin states in ${}_{}{}^{184}{}_{}{}^{}\mathrm{Hg}$ have been investigated via the ${}_{}{}^{154}{}_{}{}^{}\mathrm{Gd}$ ${(}^{32}$S,4n) reaction at a beam energy of 160 MeV, with an array of Compton suppressed Ge detectors in the Spin Spectrometer at HHIRF. The ground state oblate band and excited prolate band were extended to ${10}^{+}$ and ${26}^{+}$, respectively, and seven new bands are observed. A new band with odd spins, 13 to 25, has a much larger moment of inertia than the other bands in ${}_{}{}^{184}{}_{}{}^{}\mathrm{Hg}$. Two of the new bands feed the prolate excited band and are interpreted as quadrupole vibrational bands. Also, two new signature partner bands are observed for which the configuration of ν${\mathit{i}}_{13/2}$${\mathit{f}}_{7/2}$ is proposed. The similarity of the band with odd spins to the band with intermediate deformation (${\mathrm{\beta }}_2$∼0.34) in ${}_{}{}^{186}{}_{}{}^{}\mathrm{Hg}$, and signature partner bands to the bands observed in 104 isotones ${}_{}{}^{180}{}_{}{}^{}\mathrm{Os}$ and ${}_{}{}^{182}{}_{}{}^{}\mathrm{Pt}$, is discussed.

Spin-isospin excitations in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Bi}$ have been investigated using the ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ ${(}^3$He,t${)}^{208}$Bi reaction at near θ≊0° at E${(}^3$He)=450 MeV. The microscopic structure of the Gamow-Teller resonance (GTR), the isobaric analog state (IAS), and the spin-flip dipole (ΔL=1) resonance (SDR) in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Bi}$ has been studied by observing their direct proton decays to the low-lying neutron-hole states in ${}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}$. Decay protons were measured at backward angles in coincidence with tritons detected at and near 0°. The total branching ratio for proton decay from the GTR is determined to be only 4.9±1.3%. The total branching ratio for proton decay from the SDR amounts to 14.1±4.2%. The deduced total widths as well as the total and partial proton escape widths of the GRR and IAS are found to be in reasonable agreement with recent theoretical estimates obtained in the framework of the continuum Tamm-Dancoff approximation.

The lifetimes of several low-lying excited levels in ${}_{}{}^{115}{}_{}{}^{}\mathrm{Sb}$ and ${}_{}{}^{117}{}_{}{}^{}\mathrm{Sb}$ have been measured by using the DSA method in the ${}_{}{}^{115,117}{}_{}{}^{}\mathrm{Sn}$(p,nγ${)}^{115,117}$Sb reactions, respectively. The structure of these nuclei is discussed in the frame of the interacting boson-fermion model.

We have studied via in-beam γ-ray spectroscopy ${}_{}{}^{196}{}_{}{}^{}\mathrm{Po}$ and ${}_{}{}^{198}{}_{}{}^{}\mathrm{Po}$, which are the first neutron-deficient Po isotopes to exhibit a collective low-lying structure. The ratios of yrast state energies and the E2 branching ratios of transitions from non-yrast to yrast states are indicative of a low-lying vibrational structure. The onset of collective motion in these isotopes can be attributed to the opening of the neutron ${\mathit{i}}_{13/2}$ orbital at N≊112 and the resulting large overlap between the two valence protons in the ${\mathit{h}}_{9/2}$ orbital and the valence neutrons in the ${\mathit{i}}_{13/2}$ orbital.

Structure of odd-even and even-even isotopes of Li and Be is studied systematically with antisymmetrized molecular dynamics which is a theoretical method free from any model assumptions such as the existence of clustering. The construction of energy-minimum intrinsic states with definite parity is made by the use of the frictional cooling method. Angular momentum projection is applied to these intrinsic states in order to obtain the eigenstates of angular momentum. It is shown that the clustering structure appears in the nuclei in the N≊Z region with N and Z standing for the neutron and proton numbers, respectively. The clustering structure changes toward the shell-model-like structure as N increases to around N≊8. Furthermore appearance of new-type clustering features is suggested in the neutron-richer region with N>8. Energy spectra and other quantities are shown to be reproduced well. Especially the calculated magnetic moments describe the observed data quite well, and the neutron number dependence of the observed magnetic moments is explained as the reflection of the structure change of the isotopes from the clustering structure to the shell-model-like structure. It is indicated that the density dependence of the effective interaction is important.

Structure of odd-even B isotopes up to the neutron dripline is studied systematically with the antisymmetrized molecular dynamics (AMD). The AMD method has already proved to be a powerful theoretical approach for the systematic study of nuclear structure in extensive region including exotic neutron-rich nuclei as well as ordinary nuclei. It is owing to its flexible nature free from any model assumptions such as the existence of clusters. The energies and other observed data of B isotopes are reproduced well. Especially very good reproduction of electromagnetic properties is obtained. The systematic behavior of the electromagnetic properties is explained in relation to the drastic change between clustering structure and shell-model-like structure. This explanation gives us an important indication that clustering structure in neutron-rich B nuclei is strongly suggested by the experimental data. It is shown that the structure change with increase of the neutron number is largely governed by the shell effect of neutron orbits. Exotic structure with new type of clustering is suggested to evolve in neutron-rich nuclei near the dripline.

The charge densities of several nuclei are calculated on the basis of a modified shell model with fractional number of states 2s,2p (eroding shells) and 1g,1h (gaining shells). The occupation probabilities of these states differ appreciably from the predictions of the simple shell model. Good agreement with model-independent (experimental) charge densities was obtained. The A dependence of oscillator parameters and root-mean-square radii are investigated.