Angular distributions of the differential cross section for elastic and inelastic scattering of 50-MeV ${\pi }^{+}$ and ${\pi }^{\mathrm{-}}$ on ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ and ${}_{}{}^{30}{}_{}{}^{}\mathrm{Si}$ have been measured to a relative accuracy of 5–10? We fitted the cross section of elastic ${\pi }^{+}$ and ${\pi }^{\mathrm{-}}$ scattering from ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ simultaneously with an optical model using a second-order potential of the Michigan State University form. Our best-fit parameters differ from those given previously. The ratio of the neutron and proton transition-matrix elements for the first $J^{\pi }$${=2\mathrm{}}^{+}$ state in ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ is found from the inelastic cross section to be 1.13±0.09. For ${}_{}{}^{30}{}_{}{}^{}\mathrm{Si}$, the ratio is found to be 0.93±0.09, which differs significantly from the value derived from lifetime measurements on mirror nuclei.

A dynamically consistent, gauge invariant model for πN bremsstrahlung is developed. The πN dynamics are described through an isobar model fit to the experimental phase shifts. The charge and current operators are constructed in a gauge invariant fashion and include contributions from interaction currents at the πNΔ vertices and from the bare Δ electromagnetic moments. The meaning of such moments for an unstable particle is discussed in detail. From a fit to the ${\pi }^{+}$p bremsstrahlung data, we extract a dipole moment for the bare ${\Delta }^{++}$ in the range &/${\mathrm{\mu }}_{\mathrm{p}\mathrm{\approxeq }2.5}$ to 3.5; if the contributions from internal pion and nucleon currents are included, this ratio is somewhat smaller. The ${\pi }^{\mathrm{-}}$p bremsstrahlung data are consistent &, including &=0. The Δ quadrupole moment cannot be extracted meaningfully from the data. We discuss the sensitivity of the extracted values of ${\mu }_{\Delta }$ to the off-shell extension of the πN scattering amplitude. The polarization asymmetry is found to be sensitive to ${\mu }_{\Delta }$ while being less sensitive to off-shell scattering.

We consider the amplitude for π-N scattering within the framework of a Lagrangian of the form suggested by the cloudy bag model with volume coupling. By first exposing two-body, and then three-body unitarity, we derive a set of integral equations that couple the πN to the ππN channel. These equations satisfy two- and three-body unitarity, and can be used to describe π-N scattering both below and above the threshold for pion production. Below this threshold, the equations have the form of the Lippmann-Schwinger equation with the new feature that in the potential, the vertices in the pole diagram are undressed, while those in the crossed diagram are dressed. This feature allows for the proper description of the $P_{11}$ amplitude.

The total Coster-Kronig transition probability $f_{23}$ for the $L_2$-$L_3$ atomic transition was measured utilizing resolved L-K x-ray coincidence techniques for Z=54 with radioactive sources of 9.69 day ${}_{}{}^{131}{}_{}{}^{}\mathrm{Cs}$. The value of $f_{23}$ is 0.148±0.029.

The half-life of tritium implanted into a Si(Li) x-ray detector has been determined to be 12.32±0.03 yr by following the decay for about 5.5 years. Using a recently determined β-decay end-point energy for the same system, the product ($G_A$/$G_V$)〈στ〉 for tritium has been determined to be 2.094±0.004.

α${\mathrm{-}}^{18}$O and α-Ca cluster configurations of ${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}$ and the ${}_{}{}^{46}{}_{}{}^{}$,48,52Ti isotopes, respectively, have been studied in a microscopically founded model, treating antisymmetrization between the clusters correctly. Depending on the respective ground state structure, these systems show rotational bands with weak (Ti isotopes) and strong ${(}^{22}$Ne) parity splitting. Irrespective of the degree of parity splitting, both cases exhibit E1 transitions between these cluster states, which are strong on the appropriate molecular scale. Though the influence of inelastic channels is discussed in qualitative terms only, both ${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}$ and the Ti isotopes appear to be promising candidates for the molecular-dipole degree of freedom to be seen in light nuclei.

We present a schematic solution of the color dielectric model for the nucleon and demonstrate how the nucleon can be bound in nuclear matter. The gluon field surrounding the bound nucleon is obtained from the linearized field equations of motion in the color dielectric. This schematic model of the baryon allows a comparison of the neutron and proton mass in the nucleus. We calculate the Nolen-Schiffer anomaly for several light nuclei.

The SU(3) representations occurring in the seniority-zero subspace of an isospin-invariant version of the fermion dynamical symmetry model (monopole and quadrupole pairing model) for the sd shell are presented. Comparisons are made, on a phenomenological level, of the resulting band structure, that arising from the most symmetric orbital states in the standard SU(3) classification, and the data. Both schemes are able to reflect most trends in the data, each failing, however, in different nuclei, to explain naturally certain specific features.

The dynamical symmetries of the extended interacting boson model of light nuclei are discussed. Seven possible group chains and the corresponding dynamical symmetries are obtained. An example of O(6) symmetry is given, including the even-even nucleus ${}_{}{}^{30}{}_{}{}^{}\mathrm{Si}$ and odd-odd nucleus ${}_{}{}^{30}{}_{}{}^{}\mathrm{P}$ in a multiplet.

The eigenvalue problem is solved exactly for a one-dimensional system composed of many protons and neutrons interacting via delta-function potentials which conserve the total spin and isospin of protons and neutrons. It is shown that simultaneous eigenstates of spin, isospin, and energy, and energy eigenvalues are determined by the solutions of some transcendental coupled equations for given quantum numbers.

The distortion of composite particles (clusters) during their mutual interaction leads to effective three-body forces. In a nonrelativistic theory, they originate from two sources. One is the coupling potential which couples a channel to a distortion channel. The second one is the energy denominator (propagator) which arises whenever a distortion channel is formally eliminated and represented by an elimination potential. In the present paper this second source is studied. A three-cluster system with only one distortion state in a two-cluster subsystem is considered. Two possibilities of defining a three-body potential from the three-cluster elimination potential are tested, namely (i) extraction of a two-body potential with ‘‘frozen’’ energy dependence and (ii) off-shell transformation and subsequent extraction of a two-body potential. The mathematical formalism is illustrated by a numerical example. In a simplified model of the triton, two Δ particles and a nucleon form the distortion channel. It is seen that the interaction of the third nucleon with the two Δ particles has a remarkable influence on the effective three-body potential. Considering the fact that excited nucleons like Δ particles tend to interact more strongly with nucleons than nucleons interact among themselves, we find the overbinding problem of the triton becoming more serious. From the present microscopic study it also becomes clear that an N-body Schrödinger equation with purely phenomenological energy-dependent two-body potentials is in general undefined because of insufficient information.

Dyson boson mapping of a system of 2n fermions distributed among k single-particle states uses a space generated by two-index ideal bosons. We define a unitary group U(k) to classify this ideal-boson space. The physical subspace is shown to correspond to the antisymmetric irreducible representation [$1^{2n}$]. This classification enables one to introduce a ‘‘Majorana’’ operator S which is a linear combination of one- and two-body Casimir operators of U(k). A zero eigenvalue of S characterizes the physical subspace while positive eigenvalues identify all other irreducible representations that occur. The Hermitian boson image of the Hamiltonian does not connect physical and spurious states because it is a function of the generators of U(k). All the nonphysical eigenvalues and eigenstates of a physical boson Hamiltonian (Dyson boson image of a physical fermion Hamiltonian) which could be Hermitian or non-Hermitian, can be removed without affecting the physical eigenvalues and eigenvectors, by adding a suitable multiple of S to the Hamiltonian.

The behavior of the specific heat, for a system with a finite number of nucleons interacting through a pairing force, is studied. The formalism is based on the finite temperature Bardeen-Cooper-Schrieffer plus random phase approximation treatment of the interaction. The fermionic and bosonic excitations are described, as a function of the temperature, both in the superfluid and normal phases.

The oscillations observed in the excitation functions for the fusion of four light heavy ion systems have been analyzed with the spectral density method to extract the values of the coherence width. The hypothesis is made that these structures are due to the excitation of overlapping states of a dinuclear intermediate system. The deduced values of the widths are found to be in agreement with the predictions of the orbiting-cluster model.

The preequilibrium emission of α particles was studied by observing the precompound decay of the ${}_{}{}^{65}{}_{}{}^{}\mathrm{Zn}_{}^{\mathrm{*}}{}_{}{}^{}$ composite system. Several entrance channels were used, covering a range of angular momenta up to about 40ħ. A model interpretation is presented which does not employ cluster preformation assumptions or parameters. The results suggest that angular momentum conservation governs preequilibrium cluster emission to a large extent.

Angular distributions of the cross sections and analyzing powers for the ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$(p,${\pi }^{\pm }$) reactions leading to the ground and first two excited states of the isobaric analog final nuclei ${}_{}{}^8{}_{}{}^{}\mathrm{Li}$ and ${}_{}{}^8{}_{}{}^{}\mathrm{B}$ have been measured at $T_{\mathrm{p}=200.4\mathrm{}}$ MeV and 199.2 MeV, respectively. The (p,${\pi }^{+}$) cross sections are an order of magnitude larger than those of the (p,${\pi }^{\mathrm{-}}$) reaction and exhibit a much stronger angular dependence. The (p,${\pi }^{+}$) analyzing power patterns are essentially state independent and similar to that of the elementary pp→d${\pi }^{+}$ reaction near threshold. The analyzing power angular distribution for the ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$(p,${\pi }^{\mathrm{-}}$${)\mathrm{}}^8$B(2.32 MeV, $3^{+}$) transition exhibits a ‘‘signature’’ characteristic of (p,${\pi }^{\mathrm{-}}$) transitions to stretched high-spin two-particle one-hole final states, which is distinctly different from the pattern observed for transitions to low-spin final states. The differences between the two reactions are interpreted in terms of the dynamics of the elementary pp→d${\pi }^{+}$ and pn→pp${\pi }^{\mathrm{-}}$ processes.

Fission cross sections have been measured for the ${}_{}{}^{58}{}_{}{}^{}$Ni${+\mathrm{}}^{124}$Sn system at energies near and below the Coulomb barrier. Using the sensitivity of the fission yield to the high angular momentum partial fusion cross sections, various compound nucleus angular momentum distributions have been tested for the ${}_{}{}^{58}{}_{}{}^{}$Ni${+\mathrm{}}^{124}$Sn and ${}_{}{}^{64}{}_{}{}^{}$Ni${+\mathrm{}}^{118}$Sn systems. For these systems, the calculated fission cross sections using the very wide angular momentum distributions predicted by the elastic fusion model of Udagawa, Kim, and Tamura are in good agreement with the experimental data.

I investigate the role of correlations, final state interactions, and meson exchange mechanisms in the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$(e,e’2p)n reaction.

Using the equivalent photon method, the cross sections for muon- and tau-pair production in relativistic heavy ion collisions are calculated. A simple analytical formula is obtained, valid for the relativistic Lorentz factor γ≲16 for muon-pair and γ≲270 for tau-pair production. The absolute values of the pair production cross sections are found to be very small, quite in contrast to the case of electron-positron pair production.

A recent measurement of the level shift in the ${\pi }^{\mathrm{-}}$p atom obtains a value in apparent contradiction with the currently accepted ${\pi }^{\mathrm{-}}$p scattering length. The inferred equivalence of level shift and scattering length involved the use of the Deser-Goldberger-Baumann-Thirring formula. We have checked this formula for the case of ${\pi }^{\mathrm{-}}$p atoms and find that it is accurate well beyond the degree of the present discrepancy. Thus the disagreement between the recent experiment and previous analyses persists.