The excited $4^{+}$ state at 7117 keV in ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ is studied via the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${(}^7$Li,pγ${)}^{18}$O reaction. We show that it is highly improbable that the state is energetically degenerate with a state of different decay properties and that its γ decay is consistent with previously reported values. We obtain a γ-branching fraction ${\mathrm{\Gamma }}_{\gamma }$/(${\mathrm{\Gamma }}_{\gamma }$+${\mathrm{\Gamma }}_{\mathrm{\alpha }}$)=0.561±0.013 which together with recent results for other decay properties gives a B(E2) value of 6.4±1.6 Wu for the 4p-2h intraband transition 7117 $4_2^{+}$→5260 $2_3^{+}$. Shell-model calculations in a full (0+2)ħω basis supplement a previous ${\mathrm{SU}}_3$-truncated (0+2)ħω calculation to the effect that the calculations result in a considerably more collective B(E2) value of >15 Wu for this transition leaving a rather puzzling discrepancy between experiment and theory.

Levels in ${}_{}{}^{57}{}_{}{}^{}\mathrm{Co}$ have been studied in the region of resolved levels (E<5.5 MeV) with measurements of the ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$(p,n${)}^{57}$Co neutron spectrum with resolution ΔE∼5 keV. Seventeen previously unknown levels are located. Level density parameters in the continuum region are deduced from thick target measurements of the same reaction and additional level density information is deduced from Ericson fluctuation studies of the reaction ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$(p,n${)}^{56}$Co. A set of level density parameters is found which describes the level density of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Co}$ at energies up to 14 MeV. Efforts to obtain level density information from the ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$(d,n${)}^{57}$Co reaction were unsuccessful, but estimates of the fraction of the deuteron absorption cross section corresponding to compound nucleus formation are obtained.

We have measured the lifetime for evaporation residues in the decay of ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ti}$ at initial excitation energies of 55.8 and 64.8 MeV from changes in the blocking dip. The lifetime information was obtained from both minimum yield and dip volume and they give consistent results. The lifetime for evaporation residues is found to be ∼(6-8)×${10}^{\mathrm{-}18}$ s and shows a very weak dependence on initial excitation energy.

A systematic study of even-even deformed nuclei in s-d shell is performed in the QHD framework by using relativistic Hartree-Fock calculations. The exchange of σ, ω, ρ, and π mesons and photons are included, the parameters of the model (meson masses and coupling constants) adopted are from an earlier least-squares fit to finite nuclear ground-state properties. We compare to the results of a similar calculation using parameters adjusted to fit the nuclear matter saturation data. We found great improvement in the total binding energy, however the deformation pattern is essentially not changed; for closed subshell nuclei we still find that the ground state favors a spherical solution. A well-defined constant Fermi surface in the s-d shell is obtained which is consistent with the experiment observation. The results are also compared to the corresponding relativistic Hartree calculations.

Theoretical approaches for investigating nuclear structure with (e,e’), (π,π’), and (γ,π) reactions are presented and applied to study the shell-model description of ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$. The distorted wave impulse approximation formulated in momentum space is used to calculate the cross sections of (π,π’) and (γ,π) reactions from the πN→πN and πN→γN off-shell amplitudes which are generated from the model of Nozawa, Blankleider, and Lee[1]. It is found that the nonlocal effects due to πN off-shell dynamics and nucleon Fermi motion are important in predicting (γ,π) cross sections. The one-pion-exchange two-body exchange currents are included in (e,e’) calculations. It is shown that the core polarization effects, calculated in a perturbation approach including excitations up to 6ħω, are essential in obtaining quantitative agreements with the data with no adjustable parameters. The predictions based on the shell model of Cohen and Kurath [2] and Hague and Maripuu [3] are compared in order to illustrate the use of (e,e’), (π,π’), and (γ,π) reactions in distinguishing nuclear structure theories which are almost equivalent in describing static properties in nuclei. Predictions for future (e,e’) and (γ,π) experiments are also presented.

The sum and energy-weighted sum of isovector spin-longitudinal and -transverse response of ${}_{}{}^2{}_{}{}^{}\mathrm{H}$, ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, and nuclear matter are studied with realistic models of nuclear forces. The results for ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ are compared with those obtained using effective interactions and the random-phase approximation. The responses of ${}_{}{}^2{}_{}{}^{}\mathrm{H}$ are also calculated. We confirm the earlier predictions that nuclear forces enhance the isovector spin-longitudinal response over the spin-transverse. However, we find that they also push the strength of both these responses to higher energies. Indications of the predicted enhancement have not been observed in p→,n→ experiments on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ recently carried out at Los Alamos. We find that conventional nuclear theory predicts a measurable enhancement in ${}_{}{}^2{}_{}{}^{}\mathrm{H}$ and a significant enhancement in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. Since many properties of these few-body nuclei are well explained with realistic nuclear forces an experimental verification of the enhancement, or its absence, in ${}_{}{}^2{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ will be very interesting.

Following recent discussions of critical phase transitional behavior of nuclei, additional data are collected and used to test if there is further evidence supporting such phenomena. Data from nuclear masses, radii, and E2 transition rates are used to construct differential observables. Inspection of these for the rare earth region shows that they exhibit the characteristic phase transitional behavior found in condensed matter and thermodynamic systems, namely, nearly constant values before the critical point, and a sharp change in the critical region, followed by a different set of values after the critical point.

We suggest that it is imprudent to do away entirely with effective charges for nucleons in normal-parity states when calculating the B(E2) values of deformed nuclei within the sympletic pseudo-SU(3) model. Such effective charges are needed to take into account the contributions to the B(E2) values resulting from the quadrupole polarization of the spherical shape attributed in this model to nucleons in abnormal-parity states.

The beta delayed deuteron emission from ${}_{}{}^6{}_{}{}^{}\mathrm{He}$ is studied in a dynamical microscopic cluster model. This model gives a reasonably good description for all the subsystems of ${}_{}{}^6{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ in a coherent way, without any free parameter. The beta decay transition probability to the ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ ground state is underestimated by a few percent. The theoretical beta delayed deuteron spectrum is close to experiment but it is also underestimated, by about a factor of 1.7. We argue that, in spite of their different magnitudes, both underestimations might have a common origin. The model confirms that the neutron halo part of the ${}_{}{}^6{}_{}{}^{}\mathrm{He}$ wave function plays a crucial role in quenching the beta decay toward the α+d channel.

Calculations are presented for four relatively strong first-forbidden β decays in the region A=11–16 in order to study the very large mesonic-exchange-current enhancement of the rank-zero components. The ${\mathrm{\mu }}^{\mathrm{-}}$ capture on ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ is considered on the same footing. The wave functions utilized include up to 4ħω excitations. Two-body exchange-current matrix elements are calculated as well as one-body impulse-approximation matrix elements. The resultant enhancement factor that multiplies the impulse-approximation axial-charge matrix element is thereby determined by comparison to experiment to be ${\mathrm{\epsilon }}_{\exp }$=1.61±0.03 from three ${\mathrm{\beta }}^{\mathrm{-}}$ decays and ${\mathrm{\mu }}^{\mathrm{-}}$ capture on ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, which is in excellent agreement with meson-exchange calculations in the soft-pion approximation.

We study the algebra Sp(n,R) of the symplectic model, in particular for the cases n=1,2,3, in a new way. Starting from the Poisson-bracket realization we derive a set of partial differential equations for the generators as functions of classical canonical variables. We obtain a solution to these equations that represents the classical limit of a boson mapping of the algebra. We show further that this mapping plays a fundamental role in the collective description of many-fermion systems whose Hamiltonian may be approximated by polynomials in the associated algebra, as is done in the simplest versions of the symplectic model. The relationship to the collective dynamics is formulated as a theorem that associates the mapping with an exact solution of the time-dependent Hartree approximation. This solution determines a decoupled classical symplectic manifold, thus satisfying the criteria that define an exactly solvable model in the theory of large amplitude collective motion. The models thus obtained also provide a test of methods for constructing an approximately decoupled manifold in fully realistic cases. We show that an algorithm developed in one of our earlier works reproduces the main results of the theorem.

We present a new combinatorial method for the calculation of the nuclear level density. It is based on a Monte Carlo technique, in order to avoid a direct counting procedure which is generally impracticable for high-A nuclei. The Monte Carlo simulation, making use of the Metropolis sampling scheme, allows a computationally fast estimate of the level density for many fermion systems in large shell model spaces. We emphasize the advantages of this Monte Carlo approach, particularly concerning the prediction of the spin and parity distributions of the excited states,and compare our results with those derived from a traditional combinatorial or a statistical method. Such a Monte Carlo technique seems very promising to determine accurate level densities in a large energy range for nuclear reaction calculations.

A statistical analysis of the spectrum of two-particle–two-hole doorway states in a finite nucleus is performed. On the unperturbed mean-field level sizable attractive correlations are present in such a spectrum. Including particle-hole rescattering effects via the residual interaction introduces repulsive dynamical correlations which generate the fluctuation properties characteristic of the Gaussian orthogonal ensemble. This signals that the underlying dynamics becomes chaotic. This feature turns out to be independent of the detailed form of the residual interaction and hence reflects the generic nature of the fluctuations studied.

The calculated single particle spectrum for odd mass systems using relativistic mean field (RMF) theory are analyzed. Assuming these states for nuclei having one particle (hole) in addition to the conventional doubly magic core, of pure single particle (hole) character, the spin-orbit splittings are calculated. The effect of time reversal breaking which exists for these odd A systems seems to cancel while taking the difference between the single particle energies. Therefore one can solve the RMF equations with time reversal invariance and obtain a reasonable estimate of the spin-orbit splittings. The RMF reproduces the spin-orbit splittings quite well. The agreement between the theory and the experiment is impressive in view of the fact that the RMF incorporates leftover correlations only phenomenologically through the choice of effective Lagrangian parameters rather than incorporating them explicitly.

Pion-nucleus bound states are investigated in momentum space using a microscopic optical potential with energy dependences and nonlocalities arising from elementary potential models. We confirm the existence of deep, hybrid Coulomb-nuclear 1s, 2s, and 2p bound states, but find them to be considerably broader (∼20–300 %) than reported previously for other potentials and slightly (∼7%) more bound. Although the states still remain nonoverlapping, their larger widths may affect experimental searches.

E2 properties of A=6–10 nuclei, including those of nuclei far from stability, are studied by a (0+2)ħω shell-model calculation which includes E2 core-polarization effects explicitly. The quadrupole moments and the E2 transition strengths in A=6–10 nuclei are described quite well by the present cal- culation. This result indicates that the relatively large value of the quadrupole moment of ${}_{}{}^8{}_{}{}^{}\mathrm{B}$ can be understood without introducing the proton halo in ${}_{}{}^8{}_{}{}^{}\mathrm{B}$. An interesting effect of the 2ħω core-polarization is found for effective charges used in the 0ħω shell model; although isoscalar effective charges are almost constant as a function of nucelus, appreciable variations are needed for isovector effective charges which play important roles in nuclei with high isospin values.

The expansion of the square of the ratio of the deuteron radius to the triplet neutron-proton scattering length is generalized to include the D-state component of the deuteron wave function. Although more than 98% of this ratio is independent of the potential model, the remainder is discussed in terms of the dependence on the deuteron D state and the nonlocality of the potential. The convergence for different expansion parameters, all of which can be directly obtained from experimental data, is investigated and an optimal choice is proposed.

We have investigated the fragmentation of ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ projectiles at 0.85 to 1 GeV/nucleon in collisions with targets (${\mathrm{CH}}_2$${)}_{\mathit{n}}$, C, and Pb. Using plastic nuclear track detectors all projectile fragments with charge 6≤${\mathit{Z}}_{\mathit{F}}$≤77 produced in a collision were observed in coincidence. The combination of C and (${\mathrm{CH}}_2$${)}_{\mathit{n}}$ data allows us to extract the hydrogen component in measured distributions by the use of the statistical subtraction method. Our data show a target dependence of the multifragmentation process which indicates a nonequilibrated source of the fragments and/or the influence of the target nucleus on the relation between size and excitation energy of the spectator. In comparison to the prediction of the statistical model, the transverse momentum dispersions are enhanced with a dominant contribution by Coulomb repulsion between the fragments. Based on the sum of transverse momentum vectors of all fragments we conclude that multifragmentation is observed in collisions with a large momentum and energy transfer to the prefragment. Correlations in the azimuthal emission angles of the fragments are caused by mutual repulsion and momentum conservation. The idea that a liquid-gas phase transition of nuclear matter is the origin of multifragmentation is supported by our observations.

The absolute differential cross sections and vector and tensor analyzing powers for the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$(d→,γ${)}^5$Li and ${}_{}{}^3{}_{}{}^{}\mathrm{H}$(d→,γ${)}^5$He reactions have been measured both in the ${\mathit{j}}^{\mathrm{\pi }}$=3/$2^{+}$ fusion resonance region [${\mathit{E}}_{\mathit{d}}$(lab)=0.45 MeV and ${\mathit{E}}_{\mathit{d}}$(lab) = 0.1 MeV, respectively] and at ${\mathit{E}}_{\mathit{d}}$(lab)=8.6 MeV for several angles. In the fusion resonance region, a transition matrix element (TME) analysis of the observables leads to multiple solutions for both reactions, all of which indicate that the reactions proceed predominantly through s-wave (E1) capture, with small admixtures of M1 or E2 radiation. One solution for each reaction is dominated by a large (∼90%) ${}_{}{}^4{}_{}{}^{}$${\mathit{s}}_{3/2}$(E1) capture strength. Coupled-channels resonating group model (CCRGM) calculations have been performed which favor these solutions. In the CCRGM picture, the ${\mathit{j}}^{\mathrm{\pi }}$=3/$2^{+}$ fusion resonance in the capture cross section is a consequence of the tensor force, which couples the s=3/2, d${+}^3$He (or d${+}^3$H) channel to the s=1/2, p${+}^4$He (or n${+}^4$He) channel, enabling the reactions to proceed via the spin-independent (E1) transition to the ground state. At ${\mathit{E}}_{\mathit{d}}$(lab)=8.6 MeV, a TME analysis of the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$(d→,γ${)}^5$Li reaction yields a single solution which has >80% s-wave (E1) capture strength, whereas two TME solutions exist for the ${}_{}{}^3{}_{}{}^{}\mathrm{H}$(d→,γ${)}^5$He reaction with 45% and 65% s-wave (E1) capture strength. These data are also compared to the results of the CCRGM calculations.

Using the fragment folding angle technique, the complete fusion-fission is separated from the transfer-induced fission. The cross sections of the complete fusion-fission and fragment angular distributions for the systems of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${+}^{232}$Th, ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$${+}^{232}$Th, and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${+}^{238}$U at near- and sub-barrier energies have been measured. The observed fission excitation functions can be fitted very well by coupled-channels theory calculations. It is found that fragments from complete fusion fission show a smaller angular anisotropy as compared with our previous measurements in which the transfer-induced fission component was not excluded. However, the measured angular anisotropies of complete fusion-fission are obviously greater than expected on the basis of theoretical models in which the effect of prefission neutron emission was taken into account. Also the peak in the variation of the anisotropy with incident energy still persists in the ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$${+}^{232}$Th case.