Four new superdeformed (SD) bands have been observed in ${}_{}{}^{147}{}_{}{}^{}\mathrm{Gd}$ using the EUROGAM II spectrometer. By comparison with ${}_{}{}^{146,148,149}{}_{}{}^{}\mathrm{Gd}$ SD bands, we use the effective alignment to assign excited band configurations, with the support of the Nilsson-Strutinsky cranking formalism. The effect of the crossing of the [642]5/2 and [651]1/2 neutron orbitals lying just below the magic N=86 SD shell gap has been investigated for the ${}_{}{}^{146,147,148}{}_{}{}^{}\mathrm{Gd}$ bands. Evidence for the [411]1/2 orbital is also given. © 1996 The American Physical Society.

The ${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}$(p,γ) reaction has been studied for 30 resonances in the range ${\mathit{E}}_{\mathit{p}}$=1.75–2.51 MeV. Branching ratios have been measured for 28 of these resonances. The separation energy ${\mathit{S}}_{\mathit{p}}$ for ${}_{}{}^{30}{}_{}{}^{}\mathrm{P}$ has been determined to be 5594.5±0.5 keV. Improved spin, parity, and isospin assignments have been made to a number of the resonant states. A new level has been identified in ${}_{}{}^{30}{}_{}{}^{}\mathrm{P}$ at ${\mathit{E}}_{\mathit{x}}$=6006 keV, and its γ-ray branching ratios have been measured. © 1996 The American Physical Society.

The low-lying level structure of the neutron-deficient isotope ${}_{}{}^{200}{}_{}{}^{}\mathrm{Rn}$ has been studied using the ${}_{}{}^{176}{}_{}{}^{}\mathrm{Hf}$${(}^{28}$Si,4n) reaction at a beam energy of 142 MeV. Evaporation residues were selected using an in-flight recoil mass separator, the Argonne Fragment Mass Analyzer, and implanted in a double-sided silicon strip detector. Prompt γ rays in ${}_{}{}^{200}{}_{}{}^{}\mathrm{Rn}$ were observed at the target position using the AYEBALL array of 19 Compton-suppressed germanium detectors, and were identified by the subsequent radioactive decay of associated recoiling ions in the strip detector. Isotopic assignments of the nuclei produced were made on the basis of the mass-to-charge ratio of the recoiling ion and the energy and half-life of its α decay. Previous results concerning transitions in ${}_{}{}^{202}{}_{}{}^{}\mathrm{Rn}$ were confirmed. The level scheme deduced for ${}_{}{}^{200}{}_{}{}^{}\mathrm{Rn}$, compared with those of heavier radon isotopes, is not consistent with the onset of deformation predicted by theoretical calculations. The estimated production cross section for ${}_{}{}^{200}{}_{}{}^{}\mathrm{Rn}$ in this reaction was 5 μb. © 1996 The American Physical Society.

Deexcitation properties of low-spin levels in ${}_{}{}^{105}{}_{}{}^{}\mathrm{Pd}$ populated in the decay of ${}_{}{}^{105}{}_{}{}^{}\mathrm{Ag}_{}^{\mathit{m}}{}_{}{}^{}$ and ${}_{}{}^{105}{}_{}{}^{}\mathrm{Ag}_{}^{\mathit{g}}{}_{}{}^{}$ are investigated. The calculation for ${}_{}{}^{105}{}_{}{}^{}\mathrm{Pd}$ is performed in the interacting boson-fermion model (IBFM), using a nearly spherical boson core corresponding to ${}_{}{}^{104}{}_{}{}^{}\mathrm{Pd}$. As a result, we obtain an approximate quasiweak-coupling pattern, which is in contrast to previously assumed symmetric rotor model calculations. Rather good agreement between theory and experiment was obtained. The extension of the IBFM calculations to lighter N=59 isotones is consistent with the recent discovery of coexisting structures and dual double-subshell closure in respective even-even core nuclei. © 1996 The American Physical Society.

The high-spin states of ${}_{}{}^{198}{}_{}{}^{}\mathrm{Bi}$ have been studied via the reaction ${}_{}{}^{187}{}_{}{}^{}\mathrm{Re}$${(}^{16}$O,5n${)}^{198}$Bi at ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ energies from 85 to 105 MeV. In-beam measurements of γ-ray excitation functions, γ-γ-t coincidences, and γ-ray angular distributions were carried out with 6 BGO(AC)HPGe detectors and one intrinsic Ge planar detector. A level scheme for ${}_{}{}^{198}{}_{}{}^{}\mathrm{Bi}$ with 26 γ rays was established for the first time, including a ${15}^{+}$ isomer with a measured half-life of 8.0±3.6 ns. The level structure of ${}_{}{}^{198}{}_{}{}^{}\mathrm{Bi}$ was qualitatively interpreted by using semiempirical methods. © 1996 The American Physical Society.

We study a relation between the spreading width of the isobaric analog state and the isospin mixing probability of the corresponding parent state by using the Feshbach projection method. The formula is applied for calculations of the spreading width of several heavy isotopes and compared with available experimental data. Contributions from isovector monopole states are found to be important to explain quantitatively the experimental spreading width. The isospin dependence of the calculated width of several isotopes is also found to be consistent with the experimental observations. © 1996 The American Physical Society.

A continuum random phase approximation (RPA) method for evaluating the structure function of nuclear matter is developed, where exchange terms for any particle-hole interaction are explicitly included. The method is applied to the inclusive transverse quasielastic electron scattering response at momentum transfer ranging from q=300 to 550 MeV/c. The interaction employed is a ${\mathit{g}}^{\prime }$ Landau-Migdal constant plus a (π+ρ)-meson exchange interaction. A comparison with the standard ring series is made showing that the inclusion of finite range effects in the exchange terms is necessary. © 1996 The American Physical Society.

A recent understanding of ΔI=4 bifurcation (or, ΔI=2 staggering) based on the projected shell model is used to investigate optimal situations for observing this effect. A set of nuclei is proposed that may represent favorable cases for observation of this effect in normally deformed nuclei. It is found that the occurrence of ΔI=4 bifurcation is extremely sensitive to the quasiparticle distribution near the Fermi surface; therefore such effects probe the microscopic quasiparticle structure of rotational bands in a very sensitive manner. © 1996 The American Physical Society.

β-decay properties of nuclei are studied in the framework of proton-neutron quasiparticle random-phase approximation with a schematic Gamow-Teller residual interaction. Particle-hole and particle-particle terms of the separable Gamow-Teller force are consistently included for both ${\mathrm{\beta }}^{+}$ and ${\mathrm{\beta }}^{\mathrm{-}}$ directions, and their strengths are fixed as smooth functions of mass number A of nuclei in such a way that the calculation reproduces observed β-decay properties of nuclei. Using the fixed interaction strengths, β-decay half-lives of nuclei up to A=150 are calculated, and generally good agreement with experiment is obtained. A schematic force which is relevant to the unique first-forbidden decay is also included in a similar way to the Gamow-Teller force, and its effects are studied. © 1996 The American Physical Society.

Large-space no-core shell-model calculations have been performed for ${}_{}{}^3{}_{}{}^{}\mathrm{H}$, ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^5{}_{}{}^{}\mathrm{He}$, ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$, and ${}_{}{}^6{}_{}{}^{}\mathrm{He}$, using a starting-energy-independent two-body effective interaction derived by application of the Lee-Suzuki similarity transformation. This transformation can be performed by direct calculation or by different iteration procedures, which are described. A possible way of reducing the auxiliary potential influence on the two-body effective interaction has also been introduced. The many-body effects have been partially taken into account by employing the recently introduced multivalued effective interaction approach. Dependence of the ${}_{}{}^5{}_{}{}^{}\mathrm{He}$ energy levels on the harmonic-oscillator frequency as well as on the size of the model space has been studied. The Reid 93 nucleon-nucleon potential has been used in the study, but results have also been obtained using the Nijmegen II potential for comparison. © 1996 The American Physical Society.

Nine low-lying ${\mathrm{O}}_{\mathit{n}}^{+}$ states of ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ and their possible rotational bands have been studied by employing the isomorphic shell model which is a hybrid between conventional shell model and the liquid drop model in conjunction with the nucleon finite size and which in addition uses no adjustable parameters. The configurations of six out of these nine ${\mathrm{O}}_{\mathit{n}}^{+}$ states have an α-planar structure when, for each set of four closeby nucleon average positions (two protons and two neutrons), possessing the same principal quantum number n and forming an instant α-like particle, the center of gravity is considered. The novelty of the present study is focused on the fact that the axis of rotation and the number of rotating nucleons inside the same rotational band may change in such a way that the relevant moment of inertia increases monotonically in steps forming for each step a new branch of the band. Up to five such branches have been found and each time the moment of inertia of the last of them approaches the rigid body limit, creating superdeformed bands. The coexistence of a superdeformed band and of lower deformation bands include several states with the same ${\mathit{I}}^{\mathrm{\pi }}$ value. Two rotational bands are introduced for the first time and the model predictions of states in all cases are very close to the experimental data. Another important feature of the present study is that two different configurations possess identical binding energy (the maximum among all possible configurations) and are assigned, by 50% each, to the g.s. of ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$. This has been verified by successfully employing many observables and results of other models. © 1996 The American Physical Society.

Damping of giant collective vibrations in nuclei is studied within the framework of the Landau-Vlasov kinetic equation. A phenomenological method of independent sources of dissipation is proposed for taking into account the contributions of one-body dissipation, the relaxation due to the two-body collisions and the particle emission. An expression for the intrinsic width of slow damped collective vibrations is obtained. In the general case, this expression cannot be represented as a sum of the widths associated with the different independent sources of the damping. This is a peculiarity of the collisional Landau-Vlasov equation where the Fermi-surface distortion effect influences both the self-consistent mean field and the memory effect at the relaxation processes. The interplay between the one-body, the two-body, and the particle emission channels which contribute to the formation of the total intrinsic width of the isoscalar $2^{+}$ and $3^{\mathrm{-}}$ and isovector $1^{\mathrm{-}}$ giant multipole resonances in cold and hot nuclei is discussed. We have shown that the criterion for the transition temperature ${\mathit{T}}_{\mathrm{tr}}$ between the zero-sound and first-sound regimes in hot nuclei is different from the case of infinite nuclear matter due to the contribution from the one-body relaxation and the particle emission. In the case of the isovector GDR the corresponding transition can be reached at temperature ${\mathit{T}}_{\mathrm{tr}}$=4–5 MeV. © 1996 The American Physical Society.

In this work we perform an analysis of the onset of chaos in mean-field dynamics in the presence of volume instabilities. As a main finding, we show that the mean-field evolution presents two different regimes: a first one dominated by the almost decoupled amplification of several collective unstable modes, leading to the early condensation of the system into clusters, which is followed by a second stage dominated by a coalescence mechanism among the large-density domains. Finally we show that, even at the latest stage considered, chaos does not appear as fully developed since a hierarchy of the different unstable modes, inherited from the initial regular amplification of instabilities, remains. © 1996 The American Physical Society.

Spherical Hartree-Fock calculations at equilibrium and under radial compression are presented for ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ and ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$ in a model space of seven major oscillator shells. We employ an effective baryon-baryon interaction which includes the Δ(1236) resonance explicitly. The nucleon-nucleon (N-N) interactions are based on the Nijmegen and Reid soft core potentials. The results indicate a significant dependence on the choice of the N-N interaction at large nuclear compression. We found mixing between nucleons and Δ’s even at equilibrium in ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$ with either choice of potentials, but not in ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$. Substantial amounts of the excitation energy induced by compression goes to the creation of Δ excitations. © 1996 The American Physical Society.

We calculate the nuclear induced breakup of ${}_{}{}^{11}{}_{}{}^{}\mathrm{Be}$ and ${}_{}{}^8{}_{}{}^{}\mathrm{B}$ using a more realistic treatment of the diffraction and stripping processes than in previous work. The breakup is treated in the eikonal approximation with a profile function calculated from a realistic optical potential at low energies and from free nucleon-nucleon cross sections at high energies. This treatment gives a good description of measured breakup cross sections, as well as the longitudinal momentum distribution of the corelike fragments, which is narrower than predicted in the transparent limit. The real part of the potential is found to be significant and enhances the diffractive breakup at low energies. © 1996 The American Physical Society.

We have measured the excitation functions of several reactions occurring in the fusion of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ with ${}_{}{}^{103}{}_{}{}^{}\mathrm{Rh}$ at incident energies up to about 230 MeV. The data can be satisfactorily reproduced by considering the preequilibrium emission of particles during the thermalization of the composite nucleus. The energy evolution of the mean-field interaction is also discussed. © 1996 The American Physical Society.

Measurements of the partial linear momentum transfer and production cross sections for light charged particles are reported for the reaction 680 MeV ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$${+}^{\mathrm{nat}}$Ag. From examination of light charged particle invariant cross section maps and comparison of experimental angular distributions and energy spectra to a reaction kinematics simulation, an average value of 85% linear momentum transfer is deduced, with a spin range of (0–75)ħ. Integration over energy and angle yields single and coincident light charged particle production cross sections. © 1996 The American Physical Society.

Fission excitation functions of compound nuclei in a mass region where shell effects are expected to be very strong are shown to scale exactly according to the transition state prediction once these shell effects are accounted for. Furthermore, the method applied in this paper allows for the model-independent determination of the nuclear shell effects. © 1996 The American Physical Society.

Fusion excitation functions spanning the entire barrier region in 1 MeV energy steps for the two systems ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ + ${}_{}{}^{192}{}_{}{}^{}\mathrm{Os}$, ${}_{}{}^{194}{}_{}{}^{}\mathrm{Pt}$ are presented. The results of fission fragment angular distribution measurements for fusion-fission of ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ + ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ at several projectile energies within the barrier region are also presented. The fusion data are of high enough precision to allow for extraction of the distribution of fusion barriers from the second differential of the product of E and σ. Basic coupled channels calculations which are in quite good agreement with the data are shown and discussed. © 1996 The American Physical Society.

Absolute differential cross sections for the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(γ,p${)}^{11}$B reaction have been measured for low-lying regions of residual excitation energy in ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}$. Cross sections with low systematic uncertainties are presented for proton detection angles ranging from 30° to 150°, measured with tagged photons of 25–75 MeV energy. The experimental results resolve the discrepancies between the older data sets. In addition, a reinterpretation of the low-lying states excited in ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}$ is presented. It is concluded that HF-RPA calculations with essential contributions of meson exchange currents (MEC) provide a qualitative description of the angular distributions obtained for the negative parity states in the (γ,p) reaction. © 1996 The American Physical Society.