An experimental search for a p-wave, strangeness -1 dibaryon (${\mathit{D}}_{\mathit{s}}$) was undertaken at the Brookhaven Alternating Gradient Synchrotron using, for the first time, the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ (${\mathit{K}}^{\mathrm{-}}$,${\mathrm{\pi }}^{+}$)${\mathit{D}}_{\mathit{s}}$n reaction at 870 MeV/c. This dibaryon is predicted to be a spin singlet resonance lying below the ΣN threshold. In the region between ΛN and ΣN thresholds there is significant Λ production through two-step reactions and through virtual Σ production with subsequent conversion to a Λ. At an experimental sensitivity (statistical, at the 2σ confidence level) of about 1.0 μb/sr, we find no evidence for a dibaryon in a region between the Λ-N and Σ-N masses.

The mean multiplicity of intermediate mass fragments (IMF) 〈${\mathit{M}}_{\mathrm{IMF}}$〉 produced by fragmentation of Au projectiles interacting with targets of C, Al, Cu, and Pb at an incident energy of E/A=600 MeV is compared to predictions of statistical multifragmentation and sequential evaporation models. The initial conditions for the calculations were provided by Boltzmann-Uehling-Uhlenbeck simulations. In the high excitation energy regime where the IMF multiplicity reaches its maximum the observed universal correlation between 〈${\mathit{M}}_{\mathrm{IMF}}$〉 and the total charge ${\mathit{Z}}_{\mathrm{bound}}$ of projectile fragments with charges Z≥2 cannot be reproduced by a sequential evaporation code. In this regime the data are better described by statistical decay calculations which assume the formation of an expanded nuclear system and a rather fast breakup.

We describe identical, or twinned bands, within the cranked Hartree-Fock model, with a Skyrme effective interaction. We show that the filling of specific orbitals can lead to bands with deexcitation γ-ray energies differing by at most 2 keV in nuclei differing by two mass units and over a range of angular momenta comparable to the experimental one. We show also that the continuous change of the mean field with angular momentum is a key ingredient for twinning.

The occurrence of low-spin identical bands in the rare-earth region is shown to be the manifestation of a more general property of nuclear excitation mechanism, i.e., a smooth dependence of the moment of inertia on a very simple function of the valence proton and neutron numbers.

The asymmetry for quasielastic inclusive scattering of polarized electrons by polarized ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ has been computed for the first time in terms of a spin dependent spectral function obtained from a realistic three-body wave function without using the closure approximation. It is shown that a proper choice of kinematics minimizes the proton contribution to the asymmetry, which therefore becomes very sensitive to different models of the electromagnetic form factors of the neutron. The calculated asymmetry qualitatively agrees with the available experimental data.

Factorial moments for fragment charges have been calculated using the expanding-emitting-source model. Signals suggestive of intermittency are found when events are summed over the wide range of excitation energy approximating reactions of Au on emulsion at 1 GeV/nucleon. Of particular importance are events at high excitation energy which lack final residues and are associated with the vaporization of the source. A link between the behavior of the factorial moments and vaporization is suggested.

The ${}_{}{}^3{}_{}{}^{}\to$(p→,2p) and ${}_{}{}^3{}_{}{}^{}\to$(p→,pn) knockout reactions were observed in quasielastic kinematics at 290 MeV. Spin observables ${\mathit{A}}_{\mathit{n}0}$, ${\mathit{A}}_{0\mathit{n}}$, and ${\mathit{A}}_{\mathit{n}\mathit{n}}$ were obtained for both reactions. Calculations using the plane wave impulse approximation (PWIA) and the free nucleon-nucleon scattering amplitudes were performed and compared with the data. The proton knockout data are in qualitative agreement with the calculations which predict ${\mathit{A}}_{\mathit{n}\mathit{n}}$ to be sensitive to the presence of mixed-symmetry S’ components in the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ wave function. Proton spins are expected to be exactly paired at momenta q≊80 MeV/c, in agreement with the ${\mathit{A}}_{\mathit{n}\mathit{n}}$ data. Spin observables ${\mathit{A}}_{0\mathit{n}}$ and ${\mathit{A}}_{\mathit{n}\mathit{n}}$ for the ${}_{}{}^3{}_{}{}^{}\to$(p→,pn) reaction deviate significantly from the PWIA predictions. The qualitative differences between proton and neutron knockout results may be caused by final-state interaction effects.

Three-body channels constructed from two-body NΔ and ΔΔ states with non-nucleonic JTπ values (J,T, and π denote conserved angular momentum, isospin, and parity, respectively) appear in the three-body Faddeev equation. The effects of such ‘‘exotic’’ channels on the triton binding energy (${\mathit{E}}_{\mathit{T}}$) are studied here for the first time, using the Argonne V28 Δ model. Two types of exotic JTπ sectors are distinguished: ‘‘Pauli exotic’’ sectors from which NN channels are absent due to the Pauli principle and spin considerations, and ‘‘isospin exotic’’ sectors which have the non-nucleonic value (T=2) of the two-body isospin. Pauli exotic contributions to ${\mathit{E}}_{\mathit{T}}$ are found to yield about 90 keV of repulsion, while isospin exotics add another 55 keV to this figure, for a total effect of about 145 keV. Exotic effects thus only slightly modify our previous V28-model result for ${\mathit{E}}_{\mathit{T}}$ based on nonexotic NNN, NNΔ, NΔΔ, and ΔΔΔ configurations, moving it from about 7.29 MeV down to about 7.14 MeV. This worsens the triton binding energy defect to about 1.5 MeV. Exotic effects are further decomposed and overall implications are discussed as well.

We have studied the role of rho meson exchange in the transition potential for the charge-exchange reactions p(n,p)n and p(p,n)${\mathrm{\Delta }}^{++}$ at intermediate energies. The cross sections are calculated in the distorted-wave Born approximation. The calculated results are compared with the available experimental data. It is found that, for reproducing these data, while in the p(n,p)n reaction, in addition to one-pion exchange, we need the rho exchange in the transition potential; in the delta excitation the rho exchange is not needed.

The ground-state energy of a system consisting of four identical bosons or fermions is calculated using the Yakubovsky differential equations which are formulated in configuration space. The solution is restricted to include s waves only. Spline approximation and orthogonal collocation reduce the Yakubovsky equations to a matrix equation which is solved using the Lanczos algorithm. Storage requirements are reduced by more than three orders of a magnitude by exploiting the tensor structure present in the equation. Some of the results obtained with these methods are presented. All calculations are done on a workstation. The calculated binding energies have more than five significant digits, and it is therefore expected that the exploitation of the tensor structure makes it possible to use the Yakubovsky differential equations for realistic ground-state energy calculations with a higher accuracy than is possible with other methods.

${}_{}{}^{174}{}_{}{}^{}\mathrm{Ta}$ has been studied through the ${}_{}{}^{169}{}_{}{}^{}\mathrm{Tm}$${(}^9$Be,4n) fusion-evaporation reaction in the energy range E${(}^9$Be)=40–65 MeV. γ- and x-ray in-beam and activity singles spectra, γ-γ-t coincidences, and angular-distribution measurements were performed. Four rotational structures have been found and interpreted on the basis of coupling systematics. Mixing ratio signs have been calculated using a semiclassical method and compared with the signs of the angular-distribution coefficients, in order to consolidate configuration assignments. ‘‘Identical bands,’’ i.e., bands with similar transition energies, have been found in neighboring odd and doubly-odd ${}_{}{}^{171\mathrm{-}174}{}_{}{}^{}\mathrm{Ta}$. This similarity is interpreted here as due to fortuitous compensations between different transverse and collective angular momenta and moments of inertia.

The ${}_{}{}^{206}{}_{}{}^{}\to _{}^{202}{}_{}{}^{}$At${\to }^{198}$Bi, ${}_{}{}^{204}{}_{}{}^{}\to _{}^{200}{}_{}{}^{}$At${\to }^{196}$Bi, and ${}_{}{}^{202}{}_{}{}^{}\to _{}^{198}{}_{}{}^{}$At${\to }^{194}$Bi a-decay chains have been studied by standard spectroscopic techniques using an on-line isotope separator. All the studied doubly odd isotopes have at least two isomers, which decay by a combination of the following decay modes: a emission, ${\mathrm{\beta }}^{+}$/EC (electron capture) decay, and internal transition (IT). The internal transition, a highly retarded E3, is the j-forbidden transition between the [π${\mathit{h}}_{9/2}$⊗ν${\mathit{i}}_{13/2}$${]}_{10}^{\mathrm{-}}$ and the [π${\mathit{h}}_{9/2}$⊗ν${\mathit{f}}_{5/2}$${]}_7^{+}$ states. The B(E3) values of these IT’s together with their energy behavior as a function of the neutron and proton number, compared to the energy difference between the 13/$2^{+}$(ν${\mathit{i}}_{13/2}$) and 5/$2^{\mathrm{-}}$(ν${\mathit{f}}_{5/2}$) states in the odd-mass Pb isotones, indicate that these proton-neutron-coupled states have a rather pure shell-model character.

γ, γγ-coincidence, internal conversion electron, and γ-ray angular distribution spectra of the ${}_{}{}^{118}{}_{}{}^{}\mathrm{Sn}$(p,nγ${)}^{118}$Sb reaction were measured at different bombarding proton energies between 5.5 and 7.5 MeV. γ, γγ-coincidence, and internal conversion electron spectra of the ${}_{}{}^{115}{}_{}{}^{}\mathrm{In}$ (α,nγ${)}^{118}$Sb reaction were also measured at ${\mathit{E}}_{\mathrm{\alpha }}$=14.5 MeV. Ge(HP), Ge(Li), Ge(LEPS) γ-ray detectors, as well as a superconducting magnetic lens electron spectrometer [with Si(Li) detectors], were used in the experiments. About 210 (including ∼130 new) γ rays have been assigned to ${}_{}{}^{118}{}_{}{}^{}\mathrm{Sb}$. The deduced ${}_{}{}^{118}{}_{}{}^{}\mathrm{Sb}$ level scheme contains more than 70 new levels. On the basis of the internal conversion coefficients, Hauser-Feshbach analysis of (p,n) reaction cross sections, γ-ray angular distributions, and other arguments spin and parity values have been determined. The ‘‘parabolic rule’’ prediction of the energy splitting of different proton-neutron multiplets enabled the identification of many proton-neutron multiplet states. The energy spectrum and electromagnetic properties have been calculated in the framework of the interacting boson-fermion-fermion–odd-odd truncated quadrupole phonon model, and reasonably good agreement has been obtained between experimental and theoretical results.

The (α${,}^3$He) and (α,t) reactions on ${}_{}{}^{16,17,18}{}_{}{}^{}\mathrm{O}$ were studied at ${\mathit{E}}_{\mathrm{\alpha }}$=65 MeV. Measured cross sections for the states up to 15 MeV in the residual nuclei were analyzed with the distorted wave Born approximation theory. Many spin-parity and isospin assignments were proposed based on the strengths, angular distributions, and excitation energies. Nearly equal spectroscopic factors were obtained for bound and unbound analog pairs except for the $2_1^{+}$, T=1 states in ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{18}{}_{}{}^{}\mathrm{F}$. Almost full strengths were observed for the 0${\mathit{d}}_{5/2}$, 1${\mathit{s}}_{1/2}$, and 0${\mathit{d}}_{3/2}$ transfers. The obtained spectroscopic factors for the 0${\mathit{d}}_{5/2}$ and 1${\mathit{s}}_{1/2}$ transfers were in good agreement with shell-model calculations, while the agreement was unsatisfactory for the 0${\mathit{d}}_{3/2}$ transfer in many respects. The ${\mathit{d}}_{3/2}$ strengths in ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{17}{}_{}{}^{}\mathrm{F}$ were more fragmented than the shell-model prediction, while only half of the expected 0${\mathit{d}}_{3/2}$ strength was found in ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{19}{}_{}{}^{}\mathrm{O}$. The strength to the first excited 3/$2^{+}$, T=1/2 state in ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ was twice that predicted. Spectroscopic factors for many 0${\mathit{f}}_{7/2}$ transitions were also deduced. The 14.1 and 14.3 MeV states in ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$, in particular, proposed to be the stretched $6^{\mathrm{-}}$ states in a recent (e,e’) experiment, were found to be excited by pure l=3 transfer with spectroscopic factors 0.16 and 0.05, respectively.

The ground-state rotational bands of ${}_{}{}^{155}{}_{}{}^{}\mathrm{Gd}$ and ${}_{}{}^{157}{}_{}{}^{}\mathrm{Gd}$ have been investigated through multiple Coulomb excitation with beams of 240-MeV ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ and 305-MeV ${}_{}{}^{81}{}_{}{}^{}\mathrm{Br}$. Gamma-ray branchings and E2/M1 mixing ratios were determined by γ-ray angular-distribution measurement. Nuclear lifetimes of levels up to I=21/2 and 23/2 for ${}_{}{}^{155,157}{}_{}{}^{}\mathrm{Gd}$, respectively, have been measured using the Doppler-shift recoil-distance method. The observed signature dependence of M1 transition rates was found to be inverted in relation to the quasiparticle energy splitting. The data are analyzed in terms of the cranking model.

Both external and internal bremsstrahlung produced in the β decay of tritium and of tritium-rare gas mixtures have been investigated. The ratio of external to internal bremsstrahlung varied for the different sources by more than two orders of magnitude. From an analysis of the shape of the x-ray spectrum, the maximum kinetic energy of electrons emitted in the β decay of tritium molecules has been determined to be 18 556(6) eV.

The applicability of sum-coincidence measurements of two-step cascade γ-ray spectra for the determination of photon strength functions is discussed. The method is sensitive, not only to primary transitions, but also to secondary transitions proceeding from states of intermediate excitation. An experiment based on thermal neutron capture in a Nd target was undertaken at the Brookhaven National Laboratory High Flux Beam Reactor to test various hypotheses of E1 and M1 photon strength function in the ${}_{}{}^{144}{}_{}{}^{}\mathrm{Nd}$ nucleus. The results were compared to a series of model calculations, in which the back-shifted Fermi gas model is used to represent the level density. Models derived from the Fermi theory of liquids are strongly preferred.

Relativistic thermal Thomas-Fermi calculations for equilibrated hot nuclei have been performed for a nonlinear σ-ω model. To isolate the properties of the hot nucleus from the contributions of the surrounding nucleon vapor, a subtraction procedure based on the ‘‘equivalent sharp radius’’ is applied. Various quantities describing hot nuclei and their temperature dependence are investigated. Special attention is devoted to the study of the level density parameter; we compare our results with those of a recently published nonrelativistic investigation.

A collective model study using the interacting boson model-2 (IBM-2), as well as an approach explicitly treating both the shell-model and collective-model degrees of freedom, i.e., the particle-core coupling model (PCM), are applied to the N=84 isotones ${}_{}{}^{138}{}_{}{}^{}\mathrm{Xe}$ to ${}_{}{}^{146}{}_{}{}^{}\mathrm{Sm}$. A new mapping procedure from the PCM onto the IBM-2 model space is developed in order to more fully understand and discriminate between the shell-model and collective-model parts of the nuclear wave functions, and to study the criteria for which the IBM-2 is a valid approximation to the PCM in the N=84 nuclei. It is shown that the PCM gives the better description of all nuclear properties and that, although an apparently good fit is obtained within the IBM-2, its model space using only s and d bosons is too restricted to provide a comprehensive description of these N=84 nuclei.

The possible existence of a bound ${}_{\mathrm{\Sigma }}{}^7{}_{}{}^{}\mathrm{Li}$ state is investigated within the frame of the microscopic α+‘‘2N’’+Σ cluster model by employing an effective Σ-N interaction which reproduces the experimental binding energy and width of ${}_{\mathrm{\Sigma }}{}^4{}_{}{}^{}\mathrm{He}$. We found one bound state of ${}_{\mathrm{\Sigma }}{}^7{}_{}{}^{}\mathrm{Li}$ with about a 1.2 MeV binding energy and about a 5.4 MeV width, which is composed mainly of ${[}^6$Li(g.s.)⊗${\mathrm{\Sigma }}^0$] and ${[}^6$He(g.s.)⊗${\mathrm{\Sigma }}^{+}$] configurations. It is emphasized that the (${\mathbf{t}}_{\mathit{N}}$⋅${\mathbf{t}}_{\mathrm{\Sigma }}$)(${\mathbf{s}}_{\mathit{N}}$⋅${\mathbf{s}}_{\mathrm{\Sigma }}$) term of Σ-N interaction plays an important role to produce the bound state. If the bound state is observed in a strangeness exchange reaction such as a ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$(${\mathit{K}}^{\mathrm{-}}$,${\mathrm{\pi }}^{\mathrm{-}}$${)}_{\mathrm{\Sigma }}^7$Li experiment, we can get direct information on the (${\mathbf{t}}_{\mathit{N}}$⋅${\mathbf{t}}_{\mathrm{\Sigma }}$) (${\mathbf{s}}_{\mathit{N}}$⋅${\mathbf{s}}_{\mathrm{\Sigma }}$) term of Σ-N interaction.