Hypernuclear lifetime and partial decay-rate measurements made at the Brookhaven National Laboratory Alternating Gradient Synchrotron are reported for ${}_{\mathrm{\Lambda }}{}^5{}_{}{}^{}\mathrm{He}$ and ${}_{\mathrm{\Lambda }}{}^{12}{}_{}{}^{}\mathrm{C}$. The mesonic and nonmesonic decays are compared to existing weak-interaction calculations. In particular, the nonmesonic reaction ΛN→NN is discussed as an example of a nonleptonic weak process for which calculations have been reported using various effective weak Hamiltonians.

A quark-model picture which incorporates SU(6${)}_{\mathit{w}}$ symmetry is utilized to calculate the weak Δ-nucleon-meson and Δ-Δ-meson parity-violating vertices for π, ρ, and ω mesons, thus extending previous work in the nucleon sector. The effective quark Hamiltonian is based upon the renormalization-group-corrected Weinberg-Salam model. The calculated parity-violating vertices are used to determine the coupling constants in an effective baryon Hamiltonian. We give ‘‘best’’ values as well as estimates of the ranges of uncertainty.

The ${}_{}{}^3{}_{}{}^{}\mathrm{H}$${(}^7$Li,${\mathit{n}}_0$${)}^9$Be cross section was measured for 0.15<${\mathit{E}}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$<1.24 MeV at ${\mathrm{\theta }}_{\mathrm{lab}}$=0°, 45°, 90°, and 135° using Si(Li) diodes as neutron spectrometers. The ${}_{}{}^3{}_{}{}^{}\mathrm{H}$${(}^7$Li,${\mathit{n}}_{\mathrm{tot}}$) cross section was measured for 0.05<${\mathit{E}}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$<1.5 MeV using a 4π neutron detector. The cross section for ${}_{}{}^3{}_{}{}^{}\mathrm{H}$${(}^7$Li,${\mathit{n}}_0$${)}^9$Be was used to calculate the thermonuclear reaction rate for the temperature range 0.3–10 GK. The results support predictions that ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ may be produced in quantities near spectroscopic limits of observation according to some models of inhomogeneous primordial nucleosynthesis.

Total cross sections and resonance yields have been measured for the ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}$(α,n${)}^{14}$N reaction for ${\mathit{E}}_{\mathrm{\alpha }}$=350–2400 keV, and for the ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$(p,n${)}^{14}$N reaction for ${\mathit{E}}_{\mathit{p}}$=1000–1550 keV, using 4π neutron detectors. Differential cross sections for the ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}$(α,p${)}^{14}$C reaction were measured for ${\mathit{E}}_{\mathrm{\alpha }}$=600–1820 keV. A strong and narrow (Γ=2.2 eV) new resonance was found at ${\mathit{E}}_{\mathrm{\alpha }}$=606 keV, with ${\mathit{J}}^{\mathrm{\pi }}$=7/$2^{\mathrm{-}}$ established by (α,γ) and (α,p) angular distributions. This resonance dominates the thermonuclear (α,n) and (α,p) reaction rates for T∼0.5×${10}^9$ K. The ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}$(α,n), (α,p), and (α,γ) reaction rates versus temperature are presented and compared with ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}$(n,γ) rates.

Photoexcitation of the long-lived isomers ${}_{}{}^{123}{}_{}{}^{}\mathrm{Te}_{}^{\mathit{m}}{}_{}{}^{}$, ${\mathit{T}}_{1/2}$=119.7 d, and ${}_{}{}^{125}{}_{}{}^{}\mathrm{Te}_{}^{\mathit{m}}{}_{}{}^{}$, ${\mathit{T}}_{1/2}$=58 d, was produced with bremsstrahlung from the superconducting Darmstadt linear accelerator. The excitation function for the reaction ${}_{}{}^{123}{}_{}{}^{}\mathrm{Te}$(γ,γ’${)}^{123}$${\mathrm{Te}}^{\mathit{m}}$ was measured between 2 and 6 MeV. It indicated that the isomer was populated by resonant absorption through isolated intermediate states having integrated cross sections in excess of ${10}^{\mathrm{-}26}$ ${\mathrm{cm}}^2$ keV, i.e., values about 100 times larger than most (γ,γ’) activation reactions reported previously. An excitation function was also obtained for the reaction ${}_{}{}^{125}{}_{}{}^{}\mathrm{Te}$(γ,γ’${)}^{125}$${\mathrm{Te}}^{\mathit{m}}$ in this energy range.

Employing a simple pairing-plus-quadrupole-plus-hexadecapole model interaction in the cranked Hartree-Fock-Bogoliubov theory the ground as well as low spin (I≤6) properties of ${}_{}{}^{192}{}_{}{}^{}\mathrm{Os}$ are studied. It is found that only in the presence of a hexadecapole term when the ground intrinsic shape comes out to be prolate the rotational g factors agree well with the experimental data known for I=2 and 4.

The effective potential of the Δ isobar is calculated at the one-loop level. Although there are concerns about nonrenormalizability and the nonuniqueness of the Δ Lagrangian, the result is found to be both renormalizable and unique. In addition, the result is identical in form to the one-nucleon-loop effective potential, indicating that the noninteracting Dirac sea interpretation of the one-loop vacuum holds for the case of spin-3/2 particles.

A simple and exactly solvable unified model for fragmentation was recently proposed. It involved a single parameter which served to tune relative contributions of evaporation and multifragmentation to the mass-yield distribution for nuclear reactions. We have measured mass-yield curves for intermediate-mass products from medium-mass nuclei by radioactivation techniques. They are compared to the model’s predictions. No choice of the single parameter is able to reproduce the observed trend. It is argued that by disregarding initial intranuclear cascading, the model is incomplete. Its advantage might lie in combining it with intranuclear cascade/evaporation calculations.

Recent experiments with radioactive ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ beams suggest a neutron halo for this nucleus. The Nilsson model is used to exhibit the underlying reason for this occurrence.

A method of achieving the consistent solution of the adiabatic time-dependent Hartree-Fock theory as the optimal path is discussed. The method is applied to evaluate the valley path in the soluble three-level model.

The low-energy theorem (LET) prediction for neutral pion photoproduction on the proton remains valid even if isospin symmetry is broken. All rescattering effects are implicitly taken into account. Therefore, the data should not be corrected for final-state interactions in order to compare with the LET. As a consequence of such a correction, the previously quoted discrepancy between the LET and the experiment is overestimated.

Nuclear fission reactions induced by the electromagnetic field of relativistic nuclei are studied for energies relevant to present and future relativistic heavy-ion accelerators. Cross sections are calculated for ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ and ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$ fission induced by ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$, and ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ projectiles. It is found that some of the cross sections can exceed 10 b.

A unified treatment of relativistic many-body systems at finite temperature and density, incorporating both real- and imaginary-time formalisms, is applied to hadronic field theories of nuclear matter (quantum hadrodynamics). Covariant Feynman rules are given, which permit direct calculations in any convenient reference frame or in manifestly covariant form. The real-time rules are illustrated by the derivation of covariant expressions for the one-loop energy-momentum tensor. Next, the partition function is evaluated at one-loop order, which yields the thermodynamic potential and pressure in covariant form and verifies the virial theorem. Finally, covariant imaginary-time rules are shown to reproduce the real-time one-loop calculations.

This paper intends to introduce the reader to a recent method of determining the static quadrupole interaction of isomers in solids: LEMS (level mixing spectroscopy). First of all, the basic principle of level mixing is explained, and it is shown how this phenomenon can be observed in the angular distribution of radiation emitted by the decaying isomer. Furthermore, LEMS is compared to level mixing resonances and time differential perturbed angular distribution. It is shown that LEMS is a very attractive method in cases where high spin states are involved, and for isomers with lifetimes up to several milliseconds.

We have extended the nuclear structure calculations to deformations that break both axial and reflection symmetry. The deformation energy has been calculated within the Strutinsky method with the Woods-Saxon mean field for systems that show signatures of octupole-deformed ground states. In well octupole-deformed light actinides, and in the neutron-rich heavy-barium region, the octupole minima turn out to be rather well localized around axial symmetry. On the other hand, rather flat energy landscapes in nonaxiality degree of freedom are found in some Z≊N≊56 nuclei. The effect is especially well pronounced in ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ge}$.

The binding energy of the ΛΛ hypernucleus ${}_{\mathrm{\Lambda }\mathrm{\Lambda }}{}^{31}{}_{}{}^{}\mathrm{Si}$ has been calculated variationally with a ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$+n+Λ+Λ four-body model. The integrations have been carried out with the help of a Monte Carlo technique. Three different types of Λ-Λ and Λ-N potentials have been used. n${\mathrm{-}}^{28}$Si and Λ${\mathrm{-}}^{28}$Si potentials have been generated by folding the N-N and Λ-N potentials into the harmonic-oscillator shell-model density distribution of ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$. The calculated values of the binding energy for the three different potentials are 40.19, 46.30, and 39.90 MeV. These values are compared with the reported experimental value of 38.2±6.3 MeV. The dependence of the binding energy on the depth of the Λ-Λ interaction has also been investigated.

A generalized quantization formalism (QF) is proposed which works for the partial space (e.g., the orbital, or spin, or color) space as well as for the total space. The creation and annihilation operators in the generalized QF are in general neither boson nor fermion operators. However, if we restrict ourselves to the totally antisymmetric (symmetric) states (including any intermediate states), then they are reduced to the fermion (boson) operators. Therefore, the generalized QF is an extension of the second QF. The generalized QF is superior to both the first and second QF for computing the matrix elements in a basis which has definite symmetry in each subspace. Using the generalized QF, the shell-model calculation for the multishell, multispin case is reduced to that for the single-shell, single-spin case, and the Brussaard and Glaudemans results become the trivial case of two shell and zero spin, i.e., the case (${\gamma }_{11}^{\mathit{n}}$${\gamma }_{22}^{\mathit{n}}$), where γ=j or jt.