We calculated the mass and width of the ${\mathit{d}}^{\prime }$ resonance inside nuclei within a nucleon-Δ model by including the self-energy of the Δ in the NΔ propagator. We found that in the nuclear medium the width of the ${\mathit{d}}^{\prime }$ is increased by 1 order of magnitude while its mass changes only by a few MeV. This broadening of the width of the ${\mathit{d}}^{\prime }$ resonance embedded in nuclei is consistent with the experimental observations so that the ${\mathit{d}}^{\prime }$ can be understood as a NΔ resonance. Thus, given the freedom between either isospin 0 or isospin 2 for the ${\mathit{d}}^{\prime }$, our results give weight to the isospin-2 assignment. © 1996 The American Physical Society.

High spin states in ${}_{}{}^{175}{}_{}{}^{}\mathrm{Ta}$ are populated by the ${}_{}{}^{160}{}_{}{}^{}\mathrm{Gd}$ ${(}^{19}$F,4n) ${}_{}{}^{175}{}_{}{}^{}\mathrm{Ta}$ reaction. This experiment, carried out at the HI-13 tandem accelerator at the China Institute of Atomic Energy which measured the γ-γ coincidences, gives rise to a new level scheme. Two important new features are embedded in this scheme. First, the seven decay sequences built on 1/2 [541], 7/2 [404], 5/2 [402], and 9/2 [514] proton Nilsson configurations are significantly extended to higher spins. For example, for the 1/2 [541] band, the levels have extended from 33/$2^{\mathrm{-}}$ to 61/$2^{\mathrm{-}}$ and, for the 7/2 [404] band, from 21/$2^{\mathrm{-}}$ to 41/$2^{\mathrm{-}}$. Second, compared to the neighboring even-even nuclides, the neutron AB crossing frequency built on the ${\mathit{h}}_{9/2}$ proton Nilsson state 1/2 [541] is significantly larger, which according to the conventional cranking shell model (CSM) is an anomaly. In this paper, this large crossing frequency is also discussed within the framework of the projected shell model. It is shown that this anomaly found in CSM can be satisfactorily explained, thus suggesting an alternative understanding. © 1996 The American Physical Society.

Nuclear magnetic resonance measurements were performed on the ground states of ${}_{}{}^{169}{}_{}{}^{}\mathrm{Lu}$, ${}_{}{}^{171}{}_{}{}^{}\mathrm{Lu}$, ${}_{}{}^{172}{}_{}{}^{}\mathrm{Lu}$, ${}_{}{}^{173}{}_{}{}^{}\mathrm{Lu}$, and ${}_{}{}^{177}{}_{}{}^{}\mathrm{Lu}$ and on the $\frac{23}{2^{-}}$ isomeric state ${}_{}{}^{177m}{}_{}{}^{}\mathrm{Lu}$. The radioactive isotopes were implanted into hcp Co single crystals using the mass separator ISOLDE at CERN. For ${}_{}{}^{169}{}_{}{}^{}\mathrm{Lu}$, ${}_{}{}^{171}{}_{}{}^{}\mathrm{Lu}$, ${}_{}{}^{172}{}_{}{}^{}\mathrm{Lu}$, ${}_{}{}^{173}{}_{}{}^{}\mathrm{Lu}$, and ${}_{}{}^{177}{}_{}{}^{}\mathrm{Lu}$ the quadrupole subresonance structure could be resolved well. With the magnetic hyperfine fields and the electric field gradient of $\mathrm{Lu}Co\left(\mathrm{hcp}\right)$ derived from the results on ${}_{}{}^{177}{}_{}{}^{}\mathrm{Lu}$, the magnetic moments and electric quadrupole moments of ${}_{}{}^{169}{}_{}{}^{}\mathrm{Lu}$, ${}_{}{}^{171}{}_{}{}^{}\mathrm{Lu}$, ${}_{}{}^{172}{}_{}{}^{}\mathrm{Lu}$, and ${}_{}{}^{173}{}_{}{}^{}\mathrm{Lu}$ were determined. The nuclear moments of the high-spin isomer ${}_{}{}^{177m}{}_{}{}^{}\mathrm{Lu}$ were determined with a resonance-offset technique.

High-spin states in ${}_{}{}^{78}{}_{}{}^{}\mathrm{Rb}$ were studied using the ${}_{}{}^{54}{}_{}{}^{}\mathrm{Fe}$${(}^{28}$Si,3pn) reaction at 120 MeV and the ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$${(}^{23}$Na,2pn) reaction at 65 and 70 MeV. Prompt and delayed γ-γ coincidences were measured using the Pitt-FSU detector array. Results from these experiments have led to new levels partly grouped into new bands, new spin-parity assignments, and a rearrangement of the low-lying portion of the level scheme. States were observed up to (${19}^{+}$) and (${15}^{\mathrm{-}}$) in the lowest energy positive- and negative-parity bands. Spin assignments were based on both directional correlation of oriented nuclei ratios and angular distributions. For some low-lying levels parity assignments were supported by a measurement of the linear polarizations of γ rays. Lifetimes were determined using the Doppler-shift attenuation method and direct timing. A reversal of signature splitting was observed in the yrast band at the ${10}^{+}$ state. Large alternations were seen in the B(M1) strengths in the yrast band, while the B(E2) values in the two most strongly populated bands show a considerable collective enhancement. © 1996 The American Physical Society.

We have measured lifetimes and deduced deformation parameters for rotational bands in ${}_{}{}^{133}{}_{}{}^{}\mathrm{Pm}$ by the Doppler-shift attenuation method. A strongly coupled band based on the configuration with a hole in the ${\mathit{g}}_{9/2}$ orbital has deformation parameter ${\mathrm{\beta }}_2$=0.40 (5), which is comparable to or larger than typical superdeformed bands in the A∼130 region. We observe this band in ${}_{}{}^{133}{}_{}{}^{}\mathrm{Pm}$ down to its I=K=9/2 bandhead. Calculations with a configuration-dependent shell correction to the cranked Nilsson potential can explain the existence of such low-spin superdeformed structures in the A∼130 region. These shapes, which also occur in ${}_{}{}^{129,131}{}_{}{}^{}\mathrm{Pr}$, can be observed experimentally because of relatively low-lying shell gaps for ${\mathrm{\beta }}_2$=0.4 near Z=58, N=72. No high-spin intruder orbitals (υ${\mathit{i}}_{13/2}$) are occupied (over the spin range observed), however the strongly deformation-driving properties of a hole in the extruder π${\mathit{g}}_{9/2}$ orbital appear to be an essential ingredient in lowering the energy of the superdeformed shape. © 1996 The American Physical Society.

The ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$${(}^7$Li${,}^7$Be${)}^6$He charge-exchange reaction leading to the neutron-halo nucleus ${}_{}{}^6{}_{}{}^{}\mathrm{He}$ has been studied at E${(}^7$Li) = 350 MeV. Magnetic analysis was used to observe transitions to the known ${\mathit{J}}^{\mathrm{\pi }}$ = $0^{+}$ ground state and the ${\mathit{J}}^{\mathrm{\pi }}$ = $2^{+}$ state at ${\mathit{E}}_{\mathit{x}}$ = 1.8 MeV as well as pronounced resonances at ∼5.6 MeV, ∼14.6 MeV, and ∼23.3 MeV. Coincidences with 430-keV Doppler-shifted γ rays from the deexcitation in flight of the ${\mathit{J}}^{\mathrm{\pi }}$ = 1/$2^{\mathrm{-}}$ first-excited state in ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ were measured to permit the identification of spin-flip transitions. All observed transitions appear to have spin-flip characteristics. The shapes of the experimental angular distributions from ${\mathrm{\theta }}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$ = 0° to 18° are well described by microscopic one-step finite-range distorted-wave calculations with theoretical shell-model transition amplitudes. For the two low-lying shell-model states the absolute cross sections are also well described. The internal structures of the projectile and ejectile are taken into consideration. A large number of contributions is permitted by the angular momentum couplings. Only the ground state of ${}_{}{}^6{}_{}{}^{}\mathrm{He}$ carries significant Gamow-Teller strength B(GT). Contributions with higher L values from the central spin flip and the tensor interactions ${\mathit{V}}_{\mathrm{\sigma }\mathrm{\tau }}$ and ${\mathit{V}}_{\mathit{T}\mathrm{\tau }}$ are responsible for the mostly structureless distributions observed, and the 0° cross sections are not proportional to B(GT). The strong resonances at ∼5.6 MeV and ∼14.6 MeV are interpreted as $2^{+}$ and (1,2${)}^{\mathrm{-}}$ resonances, respectively, with cross sections stronger than predicted presumably due to mixing with continuum states leading to quadrupole and dipole enhancements. It appears that the resonance at ∼5.6 MeV does not represent a soft dipole mode originally predicted at ${\mathit{E}}_{\mathit{x}}$=4–7 MeV. © 1996 The American Physical Society.

The neutron rich nuclei ${}_{}{}^{61,63}{}_{}{}^{}\mathrm{Co}$ have been studied using the reactions ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${(}^{48}$Ca,p2n${)}^{61}$Co and ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$${(}^{48}$Ca,p2n${)}^{63}$Co at a bombarding energy of 110 MeV. Discrete γ rays from the channels of interest were investigated using prescaled γ singles, charged-particle–γ, neutron–charged-particle–γ, and charged-particle–γ–γ coincidence techniques. Decay schemes, with level spins deduced from two-point angular distribution data, are presented together with some approximate information on apparent state lifetimes. The experimental results are compared with previous light ion data for these systems and with theoretical shell model predictions. These data represent the first study of medium to high spin states in these nuclei. © 1996 The American Physical Society.

β-delayed proton decays of the nuclides ${}_{}{}^{27}{}_{}{}^{}\mathrm{P}$ and ${}_{}{}^{31}{}_{}{}^{}\mathrm{Cl}$ were measured using the helium-jet recoil collection technique and low-energy particle identification detector telescopes. In ${}_{}{}^{27}{}_{}{}^{}\mathrm{P}$, two new proton groups at 466±3 keV and 612±2 keV, with intensities of 9±2% and 97±3% relative to the main (100%) group at 731±2 keV, were discovered. Additionally, during the ${}_{}{}^{27}{}_{}{}^{}\mathrm{P}$ experiments, a new proton transition was identified following the β decay of ${}_{}{}^{28}{}_{}{}^{}\mathrm{P}$. This group, at a proton energy of 1452±4 keV, had a 2±1% intensity relative to the 100% group at 679±1 keV. A total ${}_{}{}^{27}{}_{}{}^{}\mathrm{P}$ β-delayed proton branch of 0.07% was estimated. The experimental Gamow-Teller β-decay strengths of the observed transitions from ${}_{}{}^{27}{}_{}{}^{}\mathrm{P}$ were compared to results from shell model calculations. A search for new proton transitions in ${}_{}{}^{31}{}_{}{}^{}\mathrm{Cl}$, the next member of this A=4n+3, ${\mathit{T}}_{\mathit{z}}$=-3/2 series, was unsuccessful. However, several proton peaks that had been previously assigned to ${}_{}{}^{31}{}_{}{}^{}\mathrm{Cl}$ decay were shown to be from the decay of ${}_{}{}^{25}{}_{}{}^{}\mathrm{Si}$. © 1996 The American Physical Society.

Four bands of enhanced dipole transitions, with weak crossovers, have been observed in ${}_{}{}^{193}{}_{}{}^{}\mathrm{Pb}$. Three of these bands are connected to the spherical levels. In addition, the spherical level scheme has been extended. The nuclear spectroscopy was done with the early implementation of GAMMASPHERE and HERA arrays of Ge detectors. The nucleus ${}_{}{}^{193}{}_{}{}^{}\mathrm{Pb}$ was populated in the ${}_{}{}^{174}{}_{}{}^{}\mathrm{Yb}$${(}^{24}$Mg,5n) reaction at beam energies of 129, 131, and 134 MeV. The experimental results are compared to tilted-axis cranking calculations. The systematical behavior of the dipole bands in the heavier odd-A Pb isotopes, ${}_{}{}^{195,197,199,201}{}_{}{}^{}\mathrm{Pb}$, is also discussed. © 1996 The American Physical Society.

The decays of the 9/$2^{+}$ and of the three-quasiparticle high spin isomer in ${}_{}{}^{97}{}_{}{}^{}\mathrm{Y}$ have been investigated following on-line mass separation with the ion-guide technique. Spins and parities for several of the lowest-lying levels in the daughter nucleus ${}_{}{}^{97}{}_{}{}^{}\mathrm{Zr}$ are revised and configurations are proposed. In particular, the 2264 keV level is identified as the ${\mathit{h}}_{11/2}$ single-neutron level. The population of a cascade on top of the ${\mathit{h}}_{11/2}$ level provides evidence for Gamow-Teller β decay of the high-spin ${}_{}{}^{97}{}_{}{}^{}\mathrm{Y}$ isomer. Levels and transition rates are qualitatively well reproduced by regarding ${}_{}{}^{97}{}_{}{}^{}\mathrm{Zr}$ as a single-neutron nucleus with respect to the doubly closed ${}_{}{}^{96}{}_{}{}^{}\mathrm{Zr}$ core. © 1996 The American Physical Society.

Nuclear magnetic resonance on oriented nuclei (NMR-ON) measurements were performed on the successive decays of ${}_{}{}^{89}{}_{}{}^{}\mathrm{-}_{}^{89}{}_{}{}^{}$${\mathrm{Y}}^{\mathit{m}}$ and ${}_{}{}^{191}{}_{}{}^{}\mathrm{-}_{}^{191}{}_{}{}^{}$${\mathrm{Ir}}^{\mathit{m}}$ in Fe. The NMR-ON spectra of ${}_{}{}^{89}{}_{}{}^{}\mathit{Fe}$ and ${}_{}{}^{191}{}_{}{}^{}\mathit{Fe}$ were obtained by detecting γ rays from the decay of the isomers, ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}_{}^{\mathrm{m}}{}_{}{}^{}$ and ${}_{}{}^{191}{}_{}{}^{}\mathrm{Ir}_{}^{\mathrm{m}}{}_{}{}^{}$, respectively. For ${}_{}{}^{89}{}_{}{}^{}\mathit{Fe}$, the anisotropy of the γ ray increased at the resonance. On the other hand, for ${}_{}{}^{191}{}_{}{}^{}\mathit{Fe}$ the anisotropy of the γ ray decreased at the resonance. These phenomena were explained using the spin inversion and spin noninversion processes including the lifetimes of the isomers and spin lattice relaxation times. NMR-ON measurements for such spin inversion and noninversion processes were reported. The resonance spectra were also observed by detecting β rays from ${}_{}{}^{89}{}_{}{}^{}\mathrm{Zr}$ and ${}_{}{}^{191}{}_{}{}^{}\mathrm{Os}$. In these experiments the magnetic moments of ${}_{}{}^{89}{}_{}{}^{}\mathrm{Zr}$ and ${}_{}{}^{191}{}_{}{}^{}\mathrm{Os}$ were determined to be -1.08 (2) ${\mathrm{\mu }}_{\mathrm{N}}$ and 0.962 (28) ${\mathrm{\mu }}_{\mathrm{N}}$, respectively. The signs of the magnetic moments of ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}_{}^{\mathrm{m}}{}_{}{}^{}$ and ${}_{}{}^{191}{}_{}{}^{}\mathrm{Ir}_{}^{\mathrm{m}}{}_{}{}^{}$ were also determined to be positive. © 1996 The American Physical Society.

The critical temperature for the dissipation of the collective degrees of freedom has been determined in a quantum field theoretical description of the Elliott model in which the U(3) symmetry is spontaneously broken in such a manner that rotational invariance is preserved. Results for ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$, with a reasonable choice of parameters, seem to indicate that this critical temperature lies below the liquid-to-gas critical temperature but above the temperature of deformed-to-spherical shape transitions which have been observed in finite temperature mean field calculations. © 1996 The American Physical Society.

The thermodynamical properties and Coulomb instability in hot nuclear system with Gogny interactions are studied by using the finite-temperature real-time Green’s function method. The isotherms, critical temperature, limiting temperature, saturation density, and isothermal incompressibility for various temperatures and different asymmetric parameters are calculated. To illustrate the importance of the finite-range part and density-dependence part of the interaction, we have compared our results with that given by the Skyrme interaction and Brink-Boeker interaction. © 1996 The American Physical Society.

A procedure for the calculation of the two-body spectral function of a finite nucleus is presented. This spectral function is used to calculate the longitudinal part of the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(e,${\mathit{e}}^{\prime }$pp) cross section assuming plane waves for the outgoing nucleons. Short-range correlation effects are included in the pair-removal amplitudes by adding corresponding defect wave functions that are obtained from the solution of the Bethe-Goldstone equation in the finite nucleus. The associated G matrix is used as the effective interaction in a large but finite model space to calculate the pair-removal amplitudes in a random-phase approach. The resulting spectral functions exhibit clear differences between different realistic interactions in the momentum range 2–5 ${\mathrm{fm}}^{\mathrm{-}1}$ for the initial proton momenta. © 1996 The American Physical Society.

The ground-state properties of He, Li, and Be nuclei are investigated by the Skyrme-Hartree-Fock approach with new force parameters SKI4 of Reinhard and Flocard [Nucl. Phys. A 584, 467 (1995)] plus a density-dependent pairing correlation. Calculations show that the Skyrme-Hartree-Fock model with above force parameters provides a good description on the binding energy and radii of He, Li, and Be isotopes. It also succeeds in reproducing neutron halos in nuclei ${}_{}{}^6{}_{}{}^{}\mathrm{He}$, ${}_{}{}^8{}_{}{}^{}\mathrm{He}$, ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$, and ${}_{}{}^{14}{}_{}{}^{}\mathrm{Be}$. A detailed discussion on numerical results is provided and an explanation for the above success is given. © 1996 The American Physical Society.

Thirty-one even-even isotopes (Z=72–80 and N=110–126) have two shape transition temperatures, where ${\mathit{T}}_{\mathit{c}2}$≳${\mathit{T}}_{\mathit{c}1}$. For temperatures above ${\mathit{T}}_{\mathit{c}1}$, the equilibrium shape is spherical if the rotational frequency is zero. For these 31 nuclei, a slow rotation of the spherical shape creates a prolate shape rotating about its symmetry axis if the temperature is between ${\mathit{T}}_{\mathit{c}1}$ and ${\mathit{T}}_{\mathit{c}2}$, and an oblate shape rotating about its symmetry axis if the temperature is above ${\mathit{T}}_{\mathit{c}2}$. © 1996 The American Physical Society.

A microscopic description of alpha decay to intruder $0_2^{+}$ states in the lead region is presented. The role played by proton-neutron correlations is emphasized. The calculated hindrance factors of transitions to the states $0_2^{+}$ with respect to the corresponding ground state transitions are in good agreement with available experimental data. The abrupt variations in the measured hindrance factors in some cases are related to shape transitions. Predictions for further measurements are given. © 1996 The American Physical Society.

Analysis of experiments with radioactive beams from ${}_{}{}^6{}_{}{}^{}\mathrm{He}$ to ${}_{}{}^{20}{}_{}{}^{}\mathrm{C}$ have yielded rms matter radii of neutron-rich nuclides. These radii increase more rapidly than ${\mathit{A}}^{1/3}$, suggesting the existence of neutron halos. We have used a single-particle potential model to compute these radii by adding the radius of a valence neutron in quadrature with that of the core. This radius is then taken to be the core radius of the next isotope, etc. The resulting radii are in reasonable agreement with reported values obtained with various models of reaction mechanism and nuclear structure. © 1996 The American Physical Society.

The decay out of the superdeformed (SD) bands in the 190-mass region is studied on the basis of the measured lifetimes and branching ratios of the low lying states in the SD bands of ${}_{}{}^{192}{}_{}{}^{}\mathrm{Hg}$ and ${}_{}{}^{194}{}_{}{}^{}\mathrm{Pb}$. The decay of these bands is governed by very small admixtures of normal deformed (ND) states to the decaying SD states and by very large transition probabilities for statistical γ decay in the first potential minimum. The interaction between SD and ND states, which is responsible for the depopulation of the SD bands, can be described consistently by a simple mixing of the SD states with only the nearest neighboring ND states. Estimated values for the maximum interaction strength between ND and SD states and lower limits for the height of the barrier between first and second potential minimum are presented. © 1996 The American Physical Society.

Based on Mackey’s theory of induced representations [G. W. Mackey, Induced Representation of Groups and Quantum Mechanics (Benjamin, New York, 1968)] a Bakamjian-Thomas [B. Bakamjian and L. H. Thomas, Phys. Rev. 92, 1300 (1953)] procedure for introducing interactions into n-body relativistic systems is formulated. The resulting models have manifest symmetries under exchange of identical particles and space reflection. The two-body interactions in the n-body equations are separately scattering equivalent to the input two-body interactions, but n-body dynamics does not satisfy the necessary cluster separability properties. The nature of the corrections needed to restore cluster properties is discussed. © 1996 The American Physical Society.