We measured the energies, widths, and cross sections of the isovector monopole and dipole resonances in various nuclei between ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ with the reactions (${\pi }^{\pm }$,${\pi }^0$). Both resonances exhaust approximately the same substantial fraction of the cross section calculated in a random-phase-approximation–distorted-wave-impulse-approximation model. The excitation energies and widths of the monopole and dipole are in good agreement with random-phase-approximation calculations and for the dipole they are also in agreement with other data. No isovector quadrupole resonance was observed, and the upper limits for the cross sections for the light elements are well below the sum rule strength for the isovector monopole and giant dipole resonance.

It is shown that strongly-bound η-nucleus systems, which we term η-mesic nuclei, can be formed between an η meson and nuclei of mass number A>10. We show that a distinct experimental signature for the formation of the η-mesic nucleus can be observed in (${\pi }^{+}$,p) reactions. The formation cross sections are predicted. Effects of higher order dynamics on the predicted width of the η-mesic nucleus are also estimated.

We show that, when the potential is separable, the Dirac equation can be solved in a closed form. We consider an example which simulates the nucleon-nucleon scattering and bound state (deuteron), and examine relativistic effects.

A systematic construction of the general forms of relativistic scattering operators for spin-1/2 particles is presented. Lorentz-invariant two-body scattering operators for the spin-1/2-spin-1/2 and spin-1/2-spin-0 systems are explicitly represented in a manner which is the relativistic generalization of the Wolfenstein representation of Galilean-invariant scattering operators. The simpler spin-1/2-spin-0 case serves as a prototype for the much more complicated spin-1/2-spin-1/2 case. For each case a complete set of independent Lorentz invariants is obtained directly in terms of the available four-momenta and the Dirac γ matrices. The most general forms of the scattering operators are derived in terms of these.

The implications of parity and time-reversal symmetries are obtained and the resultant constraints are imposed upon the scattering operator. The resulting analysis is in terms of independent true scalar amplitudes that are invariant to all the symmetries imposed. In this way a separation of the purely off-mass-shell components of the scattering operators is obtained and the characteristic structure of such components is explicated. Partially and fully on-mass-shell limits are subsequently obtained. The full implications of the Pauli principle are developed for the spin-1/2-spin-1/2 identical particle case and a generalization of the Fierz transformation is developed.

Isospin symmetry is also incorporated into the analysis. The connection to the optical potential for the scattering of a spin-1/2 particle from a composite spin-0 object (such as a nucleus) is described, com- pleting a technical basis for the construction of such optical models from spin-1/2-spin-1/2 scattering operators. The systematic development also provides a natural basis for extensions to investigate symmetry violating contributions in a relativistic context for both the identical and nonidentical particle spin-1/2-spin-1/2 cases. A general framework for the reconstruction of invariant scattering operators from (known) matrix elements in the barycentric frame is developed.

This framework reveals the relationship between the relativistic invariants and the Pauli spin structure of their matrix elements in each of the ρ-spin sectors of the full space. Constraints upon, ambiguities of, and alternatives in the reconstruction procedure are made apparent. A specific reconstruction scheme is developed which directly maps Pauli-space rotational invariant operators to Dirac-space Lorentz invariant operators via a covariant extension technique. This scheme for direct reconstruction on the full Dirac space precludes the inadvertent introduction of kinematic singularities, as well as instabilities in fitting and approximations; it also provides a vehicle for the analysis of alternative schemes. The formalism developed here is compared to methods employed in recent work on the reconstruction of the invariant nucleon-nucleon scattering operator from matrix elements of the solution of a relativistic scattering equation. A prospectus for further work is given.

The sensitivity of pion double charge exchange to nuclear structure in the shell model is examined. We consider the nonanalog ground-state to ground-state (T=0 to T=2) transitions on a variety of nuclear targets. The reaction model, which assumes that double charge exchange is driven by a π+ρ-meson–mediated, ${\Delta }_{33}$-nucleon interaction, reproduces the energy dependence and shape of the empirical cross section for all the (${\pi }^{+}$,${\pi }^{\mathrm{-}}$) transitions examined. The magnitude of the cross section is particularly sensitive to collectivity in the nuclear wave functions. All parameters of the model, with the exception of the range of the meson-${\Delta }_{33}$ form factor, are fixed by theoretical arguments. The form factor is then determined by normalizing to the ${}_{}{}^{16}{}_{}{}^{}$O(${\pi }^{+}$,${\pi }^{\mathrm{-}}$)${}^{16}$ Ne cross section. Predictions are made for a variety of other low-lying $0^{+}$ transitions.

Within a unitary πNN theory a set of coupled integral equations have been developed for the study of pion production from NN collisions, and have been applied to calculate the coincidence cross sections of pp→pn${\pi }^{+}$ at 800 MeV. The calculation is based on a meson-exchange Hamiltonian which was previously constructed to describe NN elastic scattering up to 1 GeV by extending the Paris potential to include Δ excitation. It involves solving a Faddeev-Alt-Grassberger-Sandhas scattering equation for the final πNN state and a NN⊕NΔ coupled-channel equation for the initial NN state. We present the procedure of using the newly developed spline function method to solve the considered Faddeev-Alt-Grassberger-Sandhas equation directly on the real momentum axis. The importance of using a unitary approach to treat the initial NN and final πNN scattering is analyzed in detail, in order to understand the results obtained in several previous approaches by Betz, Dubach et al., and Verwest. The calculated cross sections reproduce the main features of the data both in magnitude and shape. The main difficulty of the present theory is found to be in reproducing the polarization data $A_y$. Our results provide further evidence that the πNN dynamics cannot be described completely by the conventional meson-exchange model.

Angular distributions of deep spallation and fragmentation products of the interaction of 800 GeV protons with lanthanum, terbium, and lutetium have been measured. The angular distributions can be characterized by two parameters, $A_1$ and $A_2$, which determine the asymmetry and the anisotropy, respectively. For products with A≳30, values of $A_1$ and $A_2$ derived from high-energy proton data for targets ranging from silver to uranium are found to scale with the mass difference between target and product.

A Bose-Fermi dynamical symmetry scheme to describe odd-odd nuclei is proposed. A better agreement with the experimental spectra of ${}_{}{}^{196}{}_{}{}^{}\mathrm{Au}$ and ${}_{}{}^{198}{}_{}{}^{}\mathrm{Au}$ is obtained as compared to previous studies.

An exact three-dimensional reduction of the Bethe-Salpeter equation is presented for the case of two spin-(1/2) fermions exchanging scalar and pseudoscalar bosons. The resulting three-dimensional integral equation involves only a truncated basis, and once it is solved to get an auxiliary scattering amplitude T̃, the fully off-shell Bethe-Salpeter amplitude T is given essentially as an integral over T̃, thereby considerably simplifying its calculation. Similar remarks apply to bound-state equations as well. Partial-wave decomposition of the latter equations is carried out leading to Schrödinger-type equations for two-body relativistic wave functions. By means of a simple order-of-magnitude estimate we show that in the deuteron wave functions the admixture of virtual states with both nucleons in negative-energy states is more likely than that of the states with one nucleon in a positive-energy and the other in a negative-energy state, provided the coupling is pseudoscalar-pseudoscalar. This effect has not received sufficient attention in the literature. Another interesting result is that if the effective interaction in our equations is calculated to the lowest order in the coupling constant, only six out of the eight components of the deuteron wave functions are nonzero, the other two appear only in the higher order.

A method is proposed for applying the cranking model to the calculation of M1 transition rates between high spin states. The accuracy is checked by comparing numerical results with recent high-spin data for ${}_{}{}^{165}{}_{}{}^{}\mathrm{Lu}$, which provides a critical test, and with a physically equivalent three-quasiparticle plus rotor calculation. The nucleus ${}_{}{}^{81}{}_{}{}^{}\mathrm{Kr}$ is also considered. The behavior of the M1 rates at high spin is qualitatively and semiquantitatively reproduced.

The temperature dependence of deformations and pair gaps is calculated for ${}_{}{}^{148}{}_{}{}^{}\mathrm{Sm}$, ${}_{}{}^{170}{}_{}{}^{}\mathrm{Er}$, and ${}_{}{}^{186}{}_{}{}^{}$,188Os. Increasing the temperature induces a variety of shape phase transitions: prolate and oblate to spherical, triaxial to oblate, and spherical to prolate. Heating also produces the superfluid to normal phase transition.

A system of coupled rate equations which predict the time evolution of the droplet distribution in dilute nuclear matter as it approaches equilibrium is proposed. The coupled equations are solved numerically giving information on the time scale involved at different temperatures.

The Coulomb excitation of ${}_{}{}^{195}{}_{}{}^{}\mathrm{Pt}$ by 125 MeV ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ projectiles has been studied using γ ray spectroscopic techniques. On the basis of supersymmetry considerations, the observation of new levels, B(E2) ratios, and B(E2) values, a new assignment of negative-parity states within the U(6/12) multi-j supersymmetry scheme of the interacting-boson-fermion model is proposed for the 〈${\sigma }_1$,${\sigma }_2$,${\sigma }_3$〉-(τ ${}_1{}^{}{}_{}{}^{}$,${\tau }_2$)=〈7,0,0〉-(2 ,0) and 〈6,1,0〉-(2,0) quadruplets. With this classification the simultaneous description of the low lying ${}_{}{}^{195}{}_{}{}^{}\mathrm{Pt}$ and ${}_{}{}^{194}{}_{}{}^{}\mathrm{Pt}$ levels within the framework of the supersymmetry scheme is greatly improved. The predicted E2 branching ratios for the decay of the (${\tau }_1$,${\tau }_2$)-L=(2,0)-4 levels in ${}_{}{}^{195}{}_{}{}^{}\mathrm{Pt}$ are well reproduced, while for the decay of the (2,0)-2 levels discrepancies occur in both the new and the old classification.

The mass dependence of the E2-boson effective charges in the interacting-boson model is tested by comparison with measurements of B(E${2;0}_1^{+}$→$2_1^{+}$) for ${}_{}{}^{142}{}_{}{}^{}$,144,146,148,15 ${}_{}{}^0{}_{}{}^{}\mathrm{Nd}$. This mass dependence originates from g-boson renormalization effects. The magnitude of this renormalization, as required to reproduce experiment, is consistent with an earlier estimate based on the renormalizations of the single boson energies. The proton effective charge is found to be larger than the neutron effective charge, in agreement with the shell model, but in contrast to an earlier report.

We outline several sets of physical conditions which lead to periodic or multiply periodic solutions of the time-dependent Hartree-Fock equations. In every instance the Fourier components can be identified with transition matrix elements of the density fluctuation operator between collective eigenstates of the system. A simple variational derivation of the Bohr-Sommerfeld quantization condition for such solutions is described.

The origin of four-body correlations in heavy nuclei is studied. It is found that the physical picture for this phenomenon can be different in heavy and light nuclei. An application to the ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ region is made.

The magnetic moments of xenon atoms ${(}^{129}$${\mathrm{Xe}}^{\mathrm{m}}$ and ${}_{}{}^{131}{}_{}{}^{}\mathrm{Xe}_{}^{\mathrm{m}}{}_{}{}^{}$) have been measured with a high precision nuclear-magnetic-resonance method. The nuclei of gaseous xenon were polarized by spin exchange with optically pumped rubidium and the polarization was measured by gamma-ray anisotropy. The static magnetic field for the nuclear magnetic resonance experiment was stabilized and calibrated by optical pumping magnetometers. The measured magnetic moments are ‖μ(129m)‖=0.891 223(4) ${\mu }_{\mathrm{N}}$ and ‖μ(131>)‖=0.994 048(6) ${\mu }_{\mathrm{N}}$.

An experiment has been performed to measure the spontaneous fission branch of ${}_{}{}^{241}{}_{}{}^{}\mathrm{Am}$ and to search for decay events by emission of ${}_{}{}^{34}{}_{}{}^{}\mathrm{Si}$ nuclei. Lexan polycarbonate foils were used for the detection of decay fragments. Tracks produced in the foils by 81 MeV ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ ions from an accelerator and fission fragments from a ${}_{}{}^{248}{}_{}{}^{}\mathrm{Cm}$ source were compared with those produced by particles emitted from a 0.5 mCi ${}_{}{}^{241}{}_{}{}^{}\mathrm{Am}$ source. We identified 33 fission fragments corresponding to a fission/alpha branching ratio of (2.4±0.5)×${10}^{\mathrm{-}12}$, in fair agreement with previous measurements. No ${}_{}{}^{34}{}_{}{}^{}\mathrm{Si}$ tracks were observed which results in an upper limit of 4.2×${10}^{\mathrm{-}13}$ for the ${}_{}{}^{34}{}_{}{}^{}\mathrm{Si}$/alpha ratio at the 90% confidence level. Two theoretical calculations predict values of 4.0×${10}^{\mathrm{-}13}$ and 1.1×${10}^{\mathrm{-}15}$ for this branching.

The g factor of the $2_1^{+}$ state in ${}_{}{}^{142}{}_{}{}^{}\mathrm{Ba}$ was measured using the time integral perturbed angular correlation technique. The state was populated following the β decay of mass-separated ${}_{}{}^{142}{}_{}{}^{}\mathrm{Cs}$ produced by thermal neutron fission of ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$. A g factor of 0.48±0.14 was measured. This result is analyzed together with previous results for ${}_{}{}^{144}{}_{}{}^{}$,146Ba, using two different models: the hydrodynamic model including Greiner’s correction for different proton and neutron pairing forces, and the interacting boson approximation IBA-2.

The spectrum of neutrons following the ${}_{}{}^{169}{}_{}{}^{}\mathrm{Tm}$(γ,n${)}^{168}$Tm reaction induced by 8999 keV neutron capture gamma rays has been investigated with a ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ spectrometer. The data obtained, when combined with a Q value of 8032.5±2.3 keV quoted in the most recent atomic mass table, provide unambiguous evidence for the existence of a level at 17 keV. This level had not been clearly established in charged-particle reaction studies.