Elastic photon scattering cross sections have been measured on ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ in the region of the giant dipole resonance (GDR) using the tagged-photon technique. These data place stringent constraints on the total photoabsorption ${\mathrm{\sigma }}_{\gamma }$ at the peak of the GDR, which to very good approximation is the sum of the (γ,p) and (γ,n) cross sections. We find the peak cross section to be ${\mathrm{\sigma }}_0$=2.86±0.12 mb. This result is inconsistent with the sum of the most recent measurements of the (γ,p) and (γ,n) cross sections. Thus any conclusion about charge symmetry based on the ratios of these cross sections is suspect.

Exclusive electrodisintegration of the deuteron using a polarized beam and an oriented target is systematically investigated in a nonrelativistic framework. The structure functions are expanded in terms of Legendre functions whose coefficients are quadratic forms in the electric and magnetic multipole moments. Their experimental separation by specific experimental settings is outlined. The structure functions are studied with respect to their sensitivity to the potential model, to subnuclear degrees of freedom, and to electromagnetic form factors in different kinematical regions.

A system constituted of three bosons interacting via two-body separable potentials with fixed two-boson binding is known to lead to bound-state collapse in the case where the potential parameters allow two-boson S-matrix poles close to (resonance) and on (continuum bound state) the real momentum axis. The collapse is shown to be accompanied by an increase in the average kinetic energy of the two-body bound state, which signals a decrease in the range of the two-body interaction for fixed two-body binding. The collapse is claimed to be a manifestation of the well-known Thomas effect which leads to a collapse of the three-body system when the range of the two-body interaction goes to zero for a fixed two-body binding.

Measurements were made of pion double charge exchange on ${}_{}{}^{128,130}{}_{}{}^{}\mathrm{Te}$ at ${\mathrm{\theta }}_{\mathrm{lab}}$=5° and ${\mathit{T}}_{\mathrm{\pi }}$=292 MeV. Observations were made of the double isobaric analog, the giant dipole resonance built upon the isobaric analog, and the giant dipole resonance built upon itself. Cross sections for these states were found and compared with all previously known cross sections at ${\mathit{T}}_{\mathrm{\pi }}$=292 MeV, and new mass dependences were fitted to these data. A new state below the double isobaric analog state in ${}_{}{}^{128}{}_{}{}^{}\mathrm{Te}$ was observed and its cross section and width were determined.

High-spin states in ${}_{}{}^{152}{}_{}{}^{}\mathrm{Er}$ have been populated through the ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}$${(}^{40}$Ar,4n${)}^{152}$Er reaction. Prompt and delayed γ-γ-γ-t and γ-e-t coincidences have been measured. Levels and transitions are assigned up to an excitation energy of 15 MeV and spin and parities up to ${28}^{+}$ at 9.7 MeV. A new isomer [${\mathit{t}}_{1/2}$=11(1) ns] has been observed at 13.4 MeV. The results are discussed in comparison with neighboring nuclei and with shell-model calculations.

Elastic and inelastic ${\mathrm{\pi }}^{\pm }$ scattering by ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$ has been studied to measure the isospin character of transitions to bound states. The data have been interpreted using both distorted wave impulse approximation and optical model potentials. The data for the collective states at 2.647 MeV ($3^{\mathrm{-}}$) and 4.111 MeV ($2^{+}$) are well reproduced with ${\mathrm{\delta }}_{\mathit{l}}^{+}$=${\mathrm{\delta }}_{\mathit{l}}^{\mathrm{-}}$=${\mathrm{\delta }}_{\mathit{l}}^{\mathit{p}}$, i.e., assuming that these transitions are isoscalar. For the 0.803-MeV, $2^{+}$ level we deduce ${\mathit{M}}_{\mathit{n}}$/${\mathit{M}}_{\mathit{p}}$=2.6±0.3 which is in excellent agreement with a value obtained from inelastic heavy-ion scattering.

High-spin, stretched-state excitations were studied in the ${}_{}{}^{38}{}_{}{}^{}\mathrm{Ar}$(p,n${)}^{38}$K reaction at 135 MeV with the beam-swinger system at the Indiana University Cyclotron Facility. Neutron kinetic energies were measured by the time-of-flight technique with large-volume plastic-scintillator neutron detectors at flight paths ranging from 81 to 131 m. Overall time resolutions of about 825 ps provided energy resolutions from 320 to 450 keV. The target was a 4-cm-long gas cell filled to ∼3 atm absolute. Angular distributions were extracted for the low-lying excitations observed at wide angles. A known $7^{+}$ state at ${\mathit{E}}_{\mathit{x}}$=3.5 MeV was observed, plus two states at 5.3 and 5.9 MeV, which are tentatively identified as $6^{\mathrm{-}}$ excitations, based on comparisons with distorted wave Born approximation and sdpf shell-model calculations. The ${}_{}{}^{38}{}_{}{}^{}\mathrm{K}$ spectrum is in reasonable agreement with the shell-model calculations. In contrast to the analysis of 80 MeV ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$(d,α${)}^{38}$Ar measurements, these results do not indicate a significant problem for the nuclear shell model near A=40.

The decay of ${}_{}{}^{120}{}_{}{}^{}\mathrm{Ba}$ has been studied with an on-line isotope separator. Its half-life was determined to be ${\mathit{t}}_{1/2}$=24±2 s. A decay scheme is proposed, based on γ-γ, γ-X, and γ-${\mathrm{\beta }}^{+}$ coincidence measurements, which takes account of all 16 observed γ rays. The total decay energy was measured to be ${\mathit{Q}}_{\mathrm{EC}}$=50±0.3 MeV.

The high-spin states of ${}_{}{}^{75}{}_{}{}^{}\mathrm{Se}$ have been investigated using the ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$ ${(}^{19}$F, 2pn) reaction at 55 MeV. The positive-parity band has been extended to ${\mathit{I}}^{\mathrm{\pi }}$=29/$2^{+}$ and the unfavored signature has been identified. The negative-parity band has been extended to ${\mathit{I}}^{\mathrm{\pi }}$=19/$2^{\mathrm{-}}$ and band crossings were observed for the first time in both bands. Eleven new lifetimes were measured using the Doppler-shift attenuation method which allowed for extraction of transition strengths and transition quadrupole moments. The B(M1) strengths exhibit a staggering dependent on the signature splitting. Calculations based on the Woods-Saxon-Bogolyubov cranking model explain the signature-dependent alignment process in the ${\mathit{g}}_{9/2}$ bands and predict signature inversion in all bands at high rotational frequencies. It is argued that the data are consistent with the transition from triaxial shapes with γ∼-30°, characteristic of one-quasiparticle configurations, to triaxial shapes with γ∼30°, characteristic of a three-quasiparticle configuration containing one aligned pair of ${\mathit{g}}_{9/2}$ protons.

Analyses of data of the ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$${(}^6$Li,d${)}^{44}$Ti reactions at incident energies of 28 and 50 MeV have been carried out within the framework of the breakup-fusion approach, which allows us to treat reactions to both bound and unbound final states on a single footing. The resultant spectroscopic information, particularly concerning the α-cluster structure of ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ti}$, is presented and discussed.

Shell-model particle-hole intruder excitations and the collective bands built on them near closed shells are studied and classified, together with low-lying collective bands in adjacent nuclei with the same number of ‘‘valence’’ protons and neutrons, into multiplets. A detailed numerical study within the interacting boson model gives support to such a classification scheme. We introduce the concepts of intruder spin and intruder analog states and show how such a symmetry can be useful to understand nuclear collective structures at and near to closed shells.

The ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$+α system is described in terms of the new semimicroscopic algebraic cluster model, which is based on the coupling of the SU(3) shell model to the vibron model. Molecular states of the ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ nucleus built on the ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ levels with (0,2) SU(3) quantum numbers are constructed, and the corresponding energy eigenvalues are obtained from a model Hamiltonian with SU(3) dynamical symmetry. The model is able to account for 34 experimental ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ states assigned to even- or odd-parity bands, some of which are new. Enhanced E1 and E2 transitions are also obtained.

The influence of thermal fluctuations upon escape widths of giant resonances is analyzed within a thermal random phase approximation that includes the effect of the continuum through the use of resonant single-particle states in the basis set of states. It is found that those escape widths are only weakly dependent on the temperature.

The validity of the standard quasiparticle approximation is tested by treating the complex self-energy in nuclear matter self-consistently. Hole-hole propagation is ignored. The real part of the mass operator is modified only slightly for both hole and particle states. Therefore the binding energy/saturation density problem remains unaltered. The imaginary part of the mass operator changes noticeably for particles propagating substantially above the Fermi surface. This effect may be relevant in determining the absorptive part of the optical potential for intermediate energy scattering.

We discuss matrix elements of the axial current and the Gell-Mann-Oakes-Renner relation in the presence of nuclear matter. The density dependence of hadron masses and of the pion decay constant is also considered. We define a scalar order parameter that describes the modification of the quark scalar density in the presence of nuclear matter and go on to relate that parameter to the scalar field that appears in the relativistic Brueckner-Hartree-Fock (RBHF) theory. We suggest that the field-theoretic formulation provides a value for only the Hartree term in the calculation of the nucleon self-energy and present some estimates of how exchange (Fock) terms and short-range correlations modify the value obtained for the nucleon self-energy when calculations are made in the RBHF formalism. [Because of various cancellations, it is seen that the magnitude of the scalar part of the nucleon self-energy is largely unchanged when exchange (Fock) terms and short-range correlations are taken into account.]

We have implemented a dynamical microscopic α+p+n model for the description of the ground state (g.s.) of ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ in an attempt to achieve the perfection of macroscopic α+p+n three-body models. We use a generator-coordinate approach, which includes (pn)α,(αn)p, and (αp)n partitions with all angular-momentum components of any significance. The trial function is constructed out of 0s and a set of 0s,0p,0d harmonic-oscillator (h.o). eigenfunctions of the α intrinsic and of intercluster Jacobi coordinates, respectively, with the generator coordinates being the h.o. size parameters. The effective nucleon-nucleon force used contains tensor and spin-orbit terms. We have determined its parameters by fitting to the properties of the subsystems. We found that the description of the subsystems is less perfect than with central forces, and explained this by the inconsistency of the use of a tensor force with describing the α g.s. by 0s oscillator states. The binding of ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ with this force was found to be about 1 MeV too weak. After readjusting the force to yield the correct energy, we calculated some properties of ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$. The radius obtained is somewhat too large, and the tiny quadrupole moment has the wrong sign. The results for the weights of the components of summed nucleon spin and orbital momentum (S,L)=(1,0), (1,1), (1,2), and (0,1) are 94.6%, 0.2%, 3.9%, and 1.3%, respectively.

The (1,2) component comes predominantly from clusterization (pn)α; the others can be attributed to any of the highly overlapping partitions. The α+d and ${}_{}{}^5{}_{}{}^{}\mathrm{He}$+p spectroscopic factors were calculated with a new formula, which expresses them in the generator-coordinate basis directly, without resort to integral transformations. The estimates for the α+d spectroscopic factor, ∼0.9, are realistic, but those for ${}_{}{}^5{}_{}{}^{}\mathrm{He}$+p are a factor of 2 too high. This is understood to be a consequence of the model’s tendency to compress the low-energy continuum, which appears to be a general defect of forces that are constrained to reproduce the bulk properties of the α particle in terms of 0s states. Thus a radical remedy would require an improvement of the description of the cluster internal motion.

The ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$${+}^{12}$C reaction has been studied by a kinematic coincidence technique at 13 incident energies ranging from ${\mathit{E}}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$=19.35 to 24.9 MeV. The resonances previously reported from γ-ray yield measurements were observed in the equivalent excitation functions, as well as in the large angle elastic scattering data, of the present measurements. Spin assignments were made to the two resonances in this energy range. These resonances are members of a band with angular momenta several units larger than the grazing values corresponding to ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ orbiting about each other at a distance significantly outside the strong absorption radius. Other structures which were observed were unrelated to the resonant behavior.

We have studied the two-dimensional energy correlation of the continuum γ rays in ${}_{}{}^{170}{}_{}{}^{}\mathrm{Hf}$ produced in a heavy-ion fusion reaction. The γ rays were measured with an array of Compton-suppressed Ge detectors and the Spin Spectrometer. A quantitative analysis has been carried out on the properties of the peaks and dips in the correlation spectra. The results indicate the existence of at least two widths in the γ-ray energy distribution: a narrow width of about 20 keV, most likely originating from decay along different discrete bands near the yrast line, and a wide width of about 200 keV from mixed states at higher excitation energy. Theoretical calculations including the effect of level mixing and fluctuations in rotational frequency and moment of inertia give results in general agreement with the experiment.

The production of positive and negative pions induced by 201 MeV protons on ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ and ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$ isotopes has been studied. The double differential cross sections have been measured at the laboratory angles 22°, 35°, 55°, 72°, 90°, 105°, 120°, 138°, 155° and from 20 MeV kinetic energy up to the kinematical limit. Features of the double differential cross sections relative to the two targets are discussed and compared to results obtained at higher incident energies.

Four-body ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$(α,2α)pn breakup cross sections were measured from 77 to 119 MeV. Spectral functions S for k=0.1 ${\mathrm{fm}}^{\mathrm{-}1}$ (where ħk is the p-n relative momentum) were deduced. Those obtained from the 89 to 119 MeV data are internally consistent, and agree with the k dependence of S found in earlier studies of the (α,2α)pn and (p,pα)pn reactions on ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$. However, the S found at 77 MeV was low, which may indicate distortion effects. Throughout this energy region, the four-body breakup cross section at low p-n excitation follows the α-α elastic scattering cross section as the latter changes by a factor of 50, showing that quasifree scattering is the dominant process.