The recent ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}(e, e^{\prime }p){}_{}{}^{207}{}_{}{}^{}\mathrm{Tl}$ data from NIKHEF-K at high missing momentum ($p_m>300\mathrm{}$ MeV/c) are compared to theoretical results obtained with a fully relativistic formalism previously applied to analyze data on the low missing momentum ($p_m<300\mathrm{}$ MeV/c) region. The same relativistic optical potential and mean-field wave functions are used in the two $p_m$ regions. The spectroscopic factors of the various shells are extracted from the analysis of the low-$p_m$ data and then used in the high-$p_m$ region. In contrast to previous analyses using a nonrelativistic mean-field formalism, we do not find a substantial deviation from the mean-field predictions other than that of the spectroscopic factors, which appear to be consistent with both low- and high-$p_m$ data. We find that the difference between results of relativistic and nonrelativistic formalisms is enhanced in the $p_m<0\mathrm{}$ region that will be interesting to explore experimentally.

The very low-energy transition strength unique in neutron drip line neclei is studied, taking an example of ${}_8{}^{28}{}_{}{}^{}\mathrm{O}_{20}^{}{}_{}{}^{}$ and performing the Hartree-Fock plus RPA calculation with Skyrme interaction. The most dramatic example is monopole modes, however, an appreciable amount of isovector dipole strength may appear also in the very low excitation energy. Unperturbed response functions are carefully studied, which contain all basic information on the exotic behavior of the RPA strength function. The low-energy transition strength is induced by the excitations of neutrons, which have smaller binding energies and smaller angular momenta. The neutrons with a few MeV binding energies are sufficient for obtaining this strength, and the phenomena are differentiated from the so-called soft multipole excitations in halo nuclei.

The reactions ${}_{}{}^3{}_{}{}^{}\mathrm{He}$(${\mathrm{\pi }}^{+}$,pp)p and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$(${\mathrm{\pi }}^{\mathrm{-}}$,pn)n were studied at 37.0 MeV by coincidence detection of two nucleons. The differential cross sections were separated to two-nucleon (${\mathrm{\sigma }}_{2\mathit{N}}$), three-nucleon (${\mathrm{\sigma }}_{3\mathit{N}}$), and final-state interaction (${\mathrm{\sigma }}_{\mathrm{FSI}}$) components. For ${\mathrm{\pi }}^{+}$, the ${\mathrm{\sigma }}_{2\mathit{N}}$ angular distribution is symmetric about 90°, and the total cross section is 1.5 times the cross section measured for d(${\mathrm{\pi }}^{+}$,pp). For ${\mathrm{\pi }}^{\mathrm{-}}$, the angular distribution is asymmetric (backward peaked). The asymmetry increases with decreasing energy, indicating increasing pion s-wave contribution at lower energies. The fraction of the cross section induced by s-wave pions as calculated by a partial wave amplitude analysis is 13%. The measured total cross sections are ${\mathrm{\sigma }}_{2\mathit{N}}$(${\mathrm{\pi }}^{\mathrm{-}}$)=0.85±0.08 mb and ${\mathrm{\sigma }}_{2\mathit{N}}$(${\mathrm{\pi }}^{+}$)=7.9±0.5 mb; ${\mathrm{\sigma }}_{3\mathit{N}}$(${\mathrm{\pi }}^{\mathrm{-}}$)=1.6±0.7 mb and ${\mathrm{\sigma }}_{3\mathit{N}}$(${\mathrm{\pi }}^{+}$)=1.3±0.3 mb. A new evaluation of ${\mathrm{\sigma }}_{3\mathit{N}}$ at ${\mathit{T}}_{\mathrm{\pi }}$=62.5 and 82.8 MeV is given, using data from an earlier experiment. The cross sections leading to the two-nucleon final-state interaction at ${\mathit{T}}_{\mathrm{\pi }}$=37.0 MeV are also estimated. © 1996 The American Physical Society.

Measurements are reported for the np-elastic analyzing power from 30° to 128° c.m., at 485 and 788 MeV, with a typical precision of 0.005 and absolute accuracy of 2%. Results strengthen the isospin-0 phase-shift analysis, and clarify the absolute normalization of the polarized neutron beam and the isospin-0 inelasticity. © 1996 The American Physical Society.

By using the thermofield dynamics, we have calculated the effective coupling of nucleon-nucleon mesons by summing the three-lines vertices and the masses of nucleon and mesons by summing the corresponding self-energy diagrams of the Bonn potential model at finite temperature. Through the temperature dependence of effective couplings and the screening masses, we have extended the Bonn potential to finite temperature. © 1996 The American Physical Society.

A parameter-free and relativistic extension of the RuhrPot meson-baryon model is used to define the dominant isoscalar meson-exchange currents. We compute pp-bremsstrahlung observables below the π-production threshold using a relativistic hadronic current density that includes impulse, wave function reorthonormalization, meson-recoil, N¯N creation and annihilation, ρπγ + ωπγ + ρηγ + ωηγ vector-meson decay, and NΔγ(π,ρ) exchange currents. We obtain a good description of the available data. The NΔγ(π) current is shown to dominate the large two-body contributions and closed-form expressions for various nonrelativistic approximations are analyzed. An experimental sensitivity to the admixture of pseudoscalar and pseudovector admixture of the NNπ interaction is demonstrated. We examine the Lorentz invariance of the NN⇄NN t matrices and show a dominantly pseudovector NNπ coupling renders impulse approximation calculations without boost operators to be essentially exact. Conversely, a similar analysis of the ΔN⇄NN transitions shows that boost operators and the two-body NΔγ wave function reorthonormalization meson-recoil currents are required in NN, ΔN, and ΔΔ coupled channel t-matrix applications. The need for additional data is stressed. © 1996 The American Physical Society.

A multipole analysis of vector meson photoproduction is formulated as a generalization of the pseudoscalar meson case. Expansion of spin observables in the multipole basis and behavior of these observables near threshold and resonances are examined. © 1996 The American Physical Society.

We compute isospin-violating meson-nucleon coupling constants and their consequent charge-symmetry-breaking (CSB) nucleon-nucleon potentials. The couplings result from evaluating matrix elements of quark currents between nucleon states in a nonrelativistic constituent quark model; the isospin violations arise from the difference in the up and down constituent quark masses. We find, in particular, that isospin violation in the omega-meson–nucleon vertex dominates the class IV CSB potential obtained from these considerations. We evaluate the resulting spin-singlet–triplet mixing angles, the quantities germane to the difference of neutron and proton analyzing powers measured in elastic n→-p→ scattering, and find them commensurate to those computed originally using the on-shell value of the ρ-ω mixing amplitude. The use of the on-shell ρ-ω mixing amplitude at ${\mathit{q}}^2$=0 has been called into question; rather, the amplitude is zero in a wide class of models. Our model possesses no contribution from ρ-ω mixing at ${\mathit{q}}^2$=0, and we find that omega-meson exchange suffices to explain the measured n-p analyzing power difference at 183 MeV. © 1996 The American Physical Society.

In a nonrelativistic formalism we derive a charge-symmetry-breaking (CSB) two-pion exchange interaction ${\mathit{V}}_{\mathit{nn}}$(2π)-${\mathit{V}}_{\mathit{pp}}$(2π), which includes both CSB vertex corrections and the CSB effect of propagators arising from the mass differences of the intermediate baryons in different charge states. While the former are small, the latter gives a contribution of the sign and scale comparable to the experimental difference in the effective range parameters and the binding energy difference between ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$. © 1996 The American Physical Society.

The quark delocalization and color screening model is used to study the N-N interaction of spin-isospin (00) and (11) channels. The predicted ${}_{}{}^1{}_{}{}^{}$${\mathit{p}}_1$ phase shifts qualitatively fit the phase shift analysis of scattering data. The ${}_{}{}^3{}_{}{}^{}$${\mathit{p}}_{\mathit{ls}}$ phase shifts are enhanced by the quark delocalization effect, but the ${}_{}{}^3{}_{}{}^{}$${\mathit{p}}_{\mathit{c}}$ is too strongly repulsive. © 1996 The American Physical Society.

Angular distributions for ${\mathrm{\pi }}^{+}$ and ${\mathrm{\pi }}^{\mathrm{-}}$ elastic and inelastic scattering from the Z=28 closed-proton-shell nuclei ${}_{}{}^{58,60,62,64}{}_{}{}^{}\mathrm{Ni}$ have been measured at an incident pion kinetic energy of 180 MeV. Values for the neutron and proton matrix elements for the transition to the ${\mathit{J}}^{\mathrm{\pi }}$=$2_1^{+}$ state have been extracted using the distorted wave impulse approximation in which the ${\mathrm{\pi }}^{+}$ and ${\mathrm{\pi }}^{\mathrm{-}}$ data were fitted simultaneously and the neutron and proton vibrational transition strengths were treated as free parameters. While all transitions are predominantly collective, extracted values of ${\mathit{M}}_{\mathit{n}}$/${\mathit{M}}_{\mathit{p}}$ indicate increasing collectivity as a function of neutron number and are consistent with the collective limit of N/Z for ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$. © 1996 The American Physical Society.

An isomer, with ${\mathit{t}}_{1/2}$=35±10 ns and J,${\mathit{K}}^{\mathrm{\pi }}$=14,${14}^{+}$, has been observed in the nucleus ${}_{}{}^{176}{}_{}{}^{}\mathrm{W}$ using the reaction ${}_{}{}^{150}{}_{}{}^{}\mathrm{Nd}$${(}^{30}$Si,4n) at a beam energy of 133 MeV. The isomer exhibits an unusual pattern of decay in which the majority of the flux proceeds directly to states with 〈K〉=0, bypassing available levels of intermediate K. This severe breakdown of normal K-selection rules in ${}_{}{}^{176}{}_{}{}^{}\mathrm{W}$ is compared with recent observations of K violation in neighboring nuclei, within the framework of proposed theoretical approaches. The available data on these K-violating decays seem to have a consistent explanation in models of K mixing which include large-amplitude fluctuations of the nuclear shape. © 1996 The American Physical Society.

The level structures of the neutron-rich ${}_{}{}^{104}{}_{}{}^{}\mathrm{Mo}$ and ${}_{}{}^{108}{}_{}{}^{}\mathrm{Mo}$ nuclei have been investigated by observing prompt γ rays emitted in the spontaneous fission of ${}_{}{}^{248}{}_{}{}^{}\mathrm{Cm}$ with the EUROGAM spectrometer. Levels with spins up to 12ħ have been observed and γ branching obtained. The data can be satisfactorily described when ${}_{}{}^{104,108}{}_{}{}^{}\mathrm{Mo}$ are considered as axially symmetric nuclei: in ${}_{}{}^{104}{}_{}{}^{}\mathrm{Mo}$, rotational bands based on the ground state, the one-phonon and the two-phonon γ-vibrational states and a quasiparticle state have been observed, whereas in ${}_{}{}^{108}{}_{}{}^{}\mathrm{Mo}$ the information is limited to the yrast band and the one phonon γ band. © 1996 The American Physical Society.

We have measured angular distributions for the ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$${(}^6$Li,d${)}^{19}$F and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${(}^6$Li,d${)}^{20}$Ne reactions at a bombarding energy of 22 MeV. Distorted-wave Born approximation and Hauser-Feshbach calculations were used to analyze the data. Alpha spectroscopic factors were obtained for all the states up to 4.1 MeV in ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ and 6 MeV in ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$. © 1996 The American Physical Society.

A four quasiparticle high-K isomer with a meanlife of 45(2) μs has been identified at 1451 keV in ${}_{}{}^{180}{}_{}{}^{}\mathrm{Ta}$, populated in the ${}_{}{}^{176}{}_{}{}^{}\mathrm{Yb}$${(}^{11}$B,α3n${)}^{180}$Ta reaction. The isomer decays into a rotational band which is associated with the two-quasiparticle $9^{\mathrm{-}}$ isomer at 75.3 keV. Analysis of the branching ratios within that band and the magnetic moment for the $9^{\mathrm{-}}$ isomer, supports the configuration assignment to the $9^{\mathrm{-}}$ isomer. The K hindrance for the E2 decay of the ${15}^{\mathrm{-}}$ isomer to the $9^{\mathrm{-}}$ band is substantially lower than that for an apparently similar ${15}^{\mathrm{-}}$ isomer in ${}_{}{}^{178}{}_{}{}^{}\mathrm{Ta}$, a difference which can be attributed partly to a change from the π9/$2^{\mathrm{-}}$[514]${\nu }^3$9/$2^{+}$ [624]7/$2^{\mathrm{-}}$[514]5/$2^{\mathrm{-}}$[512] configuration in ${}_{}{}^{178}{}_{}{}^{}\mathrm{Ta}$ to the ${\mathrm{\pi }}^3$9/$2^{\mathrm{-}}$[514]7/$2^{+}$[404]5/$2^{+}$[402]ν9/$2^{+}$[624] configuration in ${}_{}{}^{180}{}_{}{}^{}\mathrm{Ta}$. The reduced hindrance factors for E2 decays from related four-quasiparticle isomers in the isotopes ${}_{}{}^{176,178,180}{}_{}{}^{}\mathrm{Ta}$ match the hindrances of the corresponding E2 decays from component $6^{+}$ core states in the hafnium isotopes, ${}_{}{}^{174,176,178}{}_{}{}^{}\mathrm{Hf}$. © 1996 The American Physical Society.

Hypernuclear mass spectra of ${\mathrm{}}_{\mathrm{\Lambda }}^{10}$B, ${\mathrm{}}_{\mathrm{\Lambda }}^{12}$C, ${\mathrm{}}_{\mathrm{\Lambda }}^{28}$Si, ${\mathrm{}}_{\mathrm{\Lambda }}^{89}$Y, ${\mathrm{}}_{\mathrm{\Lambda }}^{139}$La, and ${\mathrm{}}_{\mathrm{\Lambda }}^{208}$Pb were measured by the (${\mathrm{\pi }}^{+}$,${\mathit{K}}^{+}$) reaction with an energy resolution of 2 MeV (FWHM). The experiment was carried out with a 1.06 GeV/c ${\mathrm{\pi }}^{+}$ beam from the KEK 12-GeV PS and with the superconducting kaon spectrometer (SKS). For light hypernuclei, core-excited states were resolved for the first time. For heavy hypernuclei, peak structure reflecting Λ shell structure was observed. © 1996 The American Physical Society.

High spin states in the odd-odd ${}_{}{}^{164}{}_{}{}^{}\mathrm{Lu}$ nucleus have been investigated for the first time, through in-beam gamma-ray spectroscopy, following the ${}_{}{}^{150}{}_{}{}^{}\mathrm{Sm}$${(}^{19}$F,5n) reaction at beam energy ${\mathit{E}}_{\mathrm{lab}}$=105 MeV. Four bands, including two signature split bands are identified. The interpretation of the experimental results is discussed in comparison with the existing data in the neighboring nuclei and in the framework of the cranked shell model. The π${\mathit{h}}_{11/2}$⊗ν${\mathit{i}}_{13/2}$ yrast band exhibits anomalous signature splitting and signature inversion is observed at a spin of 18ħ. This provides the missing datum for the systematics of staggering and signature inversion for the neighboring odd-odd N=93 isotones and supports the predictions of angular-momentum projection calculations by Hara and Sun. In the second signature split πh ${}_{11/2}{}^{}{}_{}{}^{}\mathit{h}_{9/2}^{}{}_{}{}^{}$ band, the AB neutron crossing occurs at a rotational frequency of ∼0.29 MeV. This is indicative of the disappearance of the blocking effect of the odd neutron.

Evolution of the large-amplitude dissipative collective motion in a simple soluble model is studied within the time-dependent Hartree-Fock theory, by using a general microscopic transport theory, which optimally divides the total system into the collective and intrinsic subsystems. Even though the total system reaches some statistical stationary state, it is shown that the subsystem cannot alone remain stationary by being separated from the other subsystem, when they are strongly correlated with each other. Dynamic response functions are used in exploring an instantaneous structure of each subsystem. When the total system reaches a statistical stationary state, it is shown by using the dynamical response function that the influence of the intrinsic subsystem on the collective one can be effectively taken into account by replacing the intrinsic system by the heat bath. © 1996 The American Physical Society.

The distribution of valence neutrons of odd-odd ${}_{}{}^{120,122,124}{}_{}{}^{}\mathrm{Sb}$ nuclei was investigated in the framework of the interacting boson-fermion-fermion model. It was found that the occupation probability of the ν${\mathit{h}}_{11/2}$ orbit increased by 0.084±0.037 when exciting the odd proton from the ${\mathit{d}}_{5/2}$ to the ${\mathit{g}}_{7/2}$ state. The change was interpreted as a result of the proton-neutron interaction. © 1996 The American Physical Society.

In conventional Green’s function methods the vertex function Γ is generally energy dependent. However, a model-space Green’s function method where the vertex function is manifestly energy independent can be formulated using energy-independent effective interaction theories based on folded diagrams and/or similarity transformations. This is discussed in general and then illustrated for a 1p1h model-space Green’s function applied to a solvable Lipkin many-fermion model. The poles of the conventional Green’s function are obtained by solving a self-consistent Dyson equation and model space calculations may lead to unphysical poles. For the energy-independent model-space Green’s function only the physical poles of the model problem are reproduced and are in satisfactory agreement with the exact excitation energies. © 1996 The American Physical Society.