The pnn and dn final states after the absorption of stopped pions in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ have been measured in a kinematically complete experiment covering the whole phase space. Proton-neutron, deuteron-neutron, and neutron-neutron coincidences have been detected with a charged-particle hodoscope and large-area time-of-flight counters. For the first time, triple coincidences between the pionic K x rays and two particles have been measured thus selecting absorption from the atomic 1s state. It has been found that the absorption is dominated by the two-nucleon mechanism (2NA) on isoscalar nucleon pairs as indicted by the measured ratio of 6.3±1.1 for back-to-back correlated nn and pn pairs. A substantial amount of the three-body final state pnn is affected by the final-state interaction (FSI) or leads to the two-particle final state dn. Ratios of 3.1±0.4 for 2NA to FSI and of 4.2±0.6 for the pnn to the dn final state are measured. No evidence has been found for three-nucleon absorption with an upper limit of %/${\mathrm{\pi }}_{\mathrm{stop}}^{\mathrm{-}}$.

The dipole resonances in the light nucleus ${}_{}{}^{11}{}_{}{}^{}\mathrm{Be}$ were studied measuring the energy spectra and angular distributions of charged pions in the spin-flip charge-exchange reaction ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}$(e,${\mathrm{\pi }}^{+}$${)}^{11}$Be at ${\mathit{E}}_{\mathit{e}}$=200 MeV. The ground state and eight excited states below ${\mathit{E}}_{\mathit{x}}$=18 MeV in ${}_{}{}^{11}{}_{}{}^{}\mathrm{Be}$ were observed. The angular distributions were analyzed within the framework of the distorted-wave impulse approximation. A considerable amount of the deduced E1 strengths is distributed over excitation energies much lower than 18 MeV in ${}_{}{}^{11}{}_{}{}^{}\mathrm{Be}$. The energy distributions of the E1 strengths of transitions to the s- and d-shell states were compared with the results of theoretical calculations with the effect of loosely bound neutron states.

Spins and parities of the low-lying states in ${}_{}{}^{132}{}_{}{}^{}\mathrm{Sb}$ populated in the ${\mathrm{\beta }}^{\mathrm{-}}$ decay of ${}_{}{}^{132}{}_{}{}^{}\mathrm{Sn}$ have been determined from conversion electron and γγ(θ) studies. B(M1) and B(E2) transition rates were obtained for a number of transitions in ${}_{}{}^{132}{}_{}{}^{}\mathrm{Sb}$ using the δ(E2/M1) ratios deduced from the γγ(θ) data and the level lifetimes measured with the fast timing βγγ(t) method. A close agreement between the experimental transition rates and those calculated with a quasiboson approximation model provides a strong confirmation of the theoretical scheme and the effective forces used in the calculations.

The half-life of the $2_1^{+}$ state in ${}_{}{}^{154}{}_{}{}^{}\mathrm{Gd}$ has been measured as ${\mathit{T}}_{1/2}$=1.184(5) ns using the fast timing βγγ(t) method. The high precision of the measurement allows verification of the calculated as well as the previously measured total conversion coefficient for the $2_1^{+}$→$0_1^{+}$ transition.

The transient-field technique has been used to measure the g factors of yrast states in ${}_{}{}^{86}{}_{}{}^{}\mathrm{Zr}$ over the spin region I=8ħ–14ħ in order to ascertain the nature of the alignments at the first and second backbends. The states of interest were populated in the reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${(}^{77}$Se,3n) at 260 MeV. The results demonstrate that the first crossing at the $8_1^{+}$ state involves the alignment of neutron ${\mathit{g}}_{9/2}$ quasiparticles, and that proton ${\mathit{g}}_{9/2}$ quasiparticles align at higher spin.

Isomeric transitions in ${}_{}{}^{69}{}_{}{}^{}\mathrm{Se}$ are investigated using charged particle-γ and γ-γ delayed coincidence measurements. A precise three-point angular distribution shows that the decay of the 9/$2^{+}$ isomer is nearly isotropic, suggesting either significant dealignment during the lifetime of the isomer or a small E3 admixture in this transition. An improved measurement of the lifetime of the isomer yields a half-life of 960±23 ns. The single particle level structure of negative parity states in ${}_{}{}^{69}{}_{}{}^{}\mathrm{Se}$ below the 9/$2^{+}$ isomer is investigated using a recoil shadowing technique. A 39.4 keV gamma ray with a total-internal conversion coefficient of 28.0±2.5 is observed deexciting the 5/$2^{\mathrm{-}}$ first excited state, which is found to be isomeric with a half-life of 2.0±0.2 μs. The observed lifetime, along with the internal conversion coefficient, suggests E2 multipolarity for this transition and strongly favors a spin and parity assignment of 1/$2^{\mathrm{-}}$ for the ${}_{}{}^{69}{}_{}{}^{}\mathrm{Se}$ ground state.

Fragmentation and splitting of the Gamow-Teller (GT) strength has been observed in a systematic study of the ${(}^3$He,t) charge-exchange reaction at E${(}^3$He)=200 MeV over the entire range of stable Sn isotopes. Triton energy spectra were observed with a high-resolution magnetic spectrometer at angles near θ=0° where ΔL=0 transitions are enhanced. Excitation energies, widths, 0° cross sections, and strengths B(GT) were determined. A theoretically predicted configuration splitting of the main Gamow-Teller component into two components, expected to be dominant near A=118 at the onset of the filling of the 1${\mathit{h}}_{11/2}$ neutron orbital, could not be observed. This may be due to the fact that the total widths of the resonances of 5–6 MeV exceed the predicted splitting. A comparison of the 0° cross sections for the transitions to the Gamow-Teller resonances and the isobaric analog states leads to strengths B(GT) for the main Gamow-Teller components of typically 65% of the sum-rule value of 3(N-Z). Three to four additional Gamow-Teller fragments (‘‘pygmy resonances’’) were observed in all final nuclei at lower excitation energies. The excellent energy resolution of the experiment made it possible to observe a pronounced fine structure in these low-lying resonances which is believed to be due to coupling to two-particle–two-hole doorway states. Also seen with all target nuclei was a systematic sequence of strong ${\mathit{J}}^{\mathrm{\pi }}$=$1^{+}$ states near the ground states in all Sb isotopes (${\mathit{E}}_{\mathit{x}}$=0 to 220 keV). In addition, strong ΔL=1 resonances were observed in all nuclei at excitation energies of typically 20 MeV. Furthermore, nonresonant background from quasifree charge exchange was observed. An average of ∼85% of all excess neutrons seems to contribute to this background in approximate agreement with results from (e,e’p) experiments.

We investigate the influence of hypernuclear magnetic moments of Λ-Σ mixing due to the strong ΛN⇆ΣN interaction. The case of a Λ coupled to an I=1 nuclear core (example ${}_{\mathrm{\Lambda }}{}^{15}{}_{}{}^{}\mathrm{C}$) is found to be a particularly sensitive probe of this mixing. Qualitative estimates indicate a significant deviation of the magnetic moment from the Schmidt values. The examples of ${}_{\mathrm{\Lambda }}{}^3{}_{}{}^{}\mathrm{H}$, ${}_{\mathrm{\Lambda }}{}^4{}_{}{}^{}\mathrm{H}$($1^{+}$) and ${}_{\mathrm{\Lambda }}{}^4{}_{}{}^{}\mathrm{He}$($1^{+}$) have also been studied, as well as the influence of Λ-Σ mixing on the lifetime associated with the $1^{+}$→$0^{+}$ electromagnetic transition in the A=4 system. We also mention the ${\mathrm{\pi }}^{+}$/${\mathrm{\pi }}^{\mathrm{-}}$ ratio in hypernuclear weak decay as another probe of the degree of Λ-Σ mixing.

A general class of many-body Hamiltonians containing one- and two-body interactions that obey at least one dichotomic symmetry are considered. A rich subset in that class with several important physical applications (such as, e.g., in nuclear superfluidity and/or particle number nonconserving Hamiltonians) are studied from a unitary-group structure point of view. Those Hamiltonians are shown to obey a symmetry called further on scrP symmetry. A corresponding Casimir operator is constructed together with its eigenvalues and the implied classification of the spectra is illustrated on a nuclear-physics example with a single-j shell Hamiltonian. The most general form of a scrP-symmetric Hamiltonian is discussed.

The energies and wave functions of nonrotational states below 2.3 MeV in ${}_{}{}^{166}{}_{}{}^{}\mathrm{Er}$ are calculated within the quasiparticle-phonon nuclear model. It is shown that the wave functions have a dominating one-phonon component. The contribution of the two-phonon configurations to the wave function of ${\mathit{K}}^{\mathrm{\pi }}$≠$0^{+}$ and $4^{+}$ states below 2.3 MeV is less than 6%. The existence of the double-γ vibrational state with ${\mathit{K}}^{\mathrm{\pi }}$=$4^{+}$ at 2.0-2.2 MeV in ${}_{}{}^{166}{}_{}{}^{}\mathrm{Er}$ is predicted. The calculated excitation energies and B(E2) and B(E3) values for transitions from the ground state are found to be in agreement with experimental data. Large spectroscopic factors of one-nucleon transfer reactions are explained by the large two-quasiparticle components of the one-phonon terms of the wave functions.

Alpha particle cluster models have been very successful in reproducing energy spectra, static and dynamic electromagnetic properties, α-emission widths and α-nucleus elastic scattering data in light nuclei around the double shell closures at ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$. We extend the application of one such model to the heavier mass regions above ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$ and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$. In all cases we employ a potential of given geometric form with all parameters fixed except for the radius that is tailored to each nucleus in turn. We find that the potentials needed for ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ and ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ti}$ are very similar to the real parts of the optical potentials used in an accurate description of α${\mathrm{-}}^{16}$O and α${\mathrm{-}}^{40}$Ca elastic scattering up to high energies. By suitable choice of the quantum numbers that describe the relative motion of the α particle and the core nucleus we are able to give a good account of the spectra, the reduced E2 transition strengths, and the α-particle emission widths (or lifetimes) of the members of the ground state bands in the four nuclei ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$, ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ti}$, ${}_{}{}^{94}{}_{}{}^{}\mathrm{Mo}$, and ${}_{}{}^{212}{}_{}{}^{}\mathrm{Po}$. The potential chosen also allows a consistent description of the half-lives for favored α decay throughout the Periodic Table.

Motivated by new, precise magnetic proton form factor data in the timelike reigon, a hybrid vector meson dominance (hVMD) formalism is employed to investigate the significance of excited vector meson rsonances on electromagnetic nucleon structure. We find that the ρ(1700), ω(1600), and two previously unobserved states are required to reproduce the local structure seen in the new LEAR data just above the pp¯ threshold. We also investigate sensitivity to the φ meson. The model dependence of our result is tested by introducing an alternative model which couples the isoscalar vector meson states to a hypothetical vector glueball resonance. We obtain nearly identical results from both models, except for ${\mathit{G}}_{\mathit{E}}^{\mathit{n}}$(${\mathit{q}}^2$) in the spacelike region which is very sensitive to the glueball mass and the effective φNN coupling.

The Kr isotopes with A=72 to 84 are investigated within the interacting boson model (IBM-2) using two different approaches. In the first investigation the single-particle energies of the neutron and proton bosons are assumed equal, ε=${\mathrm{\epsilon }}_{\nu }$=${\mathrm{\epsilon }}_{\mathrm{\pi }}$, whereas the second investigation is based on their being different (${\mathrm{\epsilon }}_{\nu }$≠${\mathrm{\epsilon }}_{\mathrm{\pi }}$). The results of these calculations are compared with the experimental data and previous theoretical investigations. We also attempt to determine the shape transition in these nuclei.

A fast method for obtaining finite range corrected potential energy surfaces is described. The potential energy of heavy nuclei (A≳160) as a function of distance between mass centers and thus fission barrier heights, equilibrium, and saddle point moments of inertia and curvatures can all be obtained as a function of mass, atomic number, and angular momentum in a straightforward way using the expressions and tabulated functions presented in this paper.

The structure of ${}_{}{}^{42}{}_{}{}^{}\mathrm{Ca}$ is investigated by the α${+}^{38}$Ar orthogonality condition model. The energy spectra, α-spectroscopic factors, E2 transitions, and charge form factors are analyzed. On the whole, the calculated properties are in very good agreement with the experimental data. The levels are classified into the cluster and shell-model states through the analysis of the wave functions. It is emphasized that the coexistence and interplay of cluster and shell-model states are essential to understand the properties of ${}_{}{}^{42}{}_{}{}^{}\mathrm{Ca}$.

We investigate the influence of nuclear masses, radii, and interaction potentials on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ radioactivity of ${}_{}{}^{114}{}_{}{}^{}\mathrm{the}$ best representative of a new island of cluster emitters leading to daughter nuclei around the doubly magic ${}_{}{}^{100}{}_{}{}^{}\mathrm{Sn}$. Three different models are considered: one derived by Blendowske, Fliessbach, and Walliser (BFW) from the many-body theory of α decay, as well as our analytical (ASAF) and numerical (NuSAF) superasymmetric fission models. A Q value larger by 1 MeV or an ASAF potential barrier reduced by 3% are producing a half-life shorter by 2 orders of magnitude. A similar effect can be obtained within BFW and NuSAF by a decrease of the action integral with less than 10% and 5%, respectively. By increasing the radius constant within ASAF or BFW models by 10%, the half-life becomes shorter by 3 orders of magnitude.

The realistic single-particle Woods-Saxon potential was used to evaluate the mean-square charge radii of even-even nuclei. The results are compared with experimental data and theoretical values obtained with the single-particle Nilsson potential. An evidence for a need of improving of the ‘‘universal’’ parametrization of the deformed Woods-Saxon Hamiltonian, suggested earlier, is investigated in more detail and a possible solution of the optimization problem is formulated.

Calculations of nuclear level densities with moment methods now include moments of order larger than two. The level density can be expanded in an orthogonal polynomial series, but this procedure has the disadvantage that the resulting level density is not positive definite. A recent publication advocates the use of an alternative technique which reduces the likelihood of negative excursions of the level density. We propose a modification of the previously proposed method which produces expansions which are of equivalent quality and are always positive definite. The new method produces better representations of an exact result than an Hermite polynomial expansion. The resulting representation is continuous and analytic and does well in representing the spin cutoff parameter and parity ratio as well.

The collisional relaxation rates of the giant monopole vibrations in nuclei are calculated using a semiclassical transport equation with a memory dependent collision term. Calculations show that depending on the mass the collisional damping accounts for about ten to twenty percent of the experimental damping widths.