The independent yields of ${}_{}{}^{101}{}_{}{}^{}\mathrm{Tc}$, ${}_{}{}^{103}{}_{}{}^{}\mathrm{Tc}$, ${}_{}{}^{104}{}_{}{}^{}\mathrm{Tc}$, and ${}_{}{}^{105}{}_{}{}^{}\mathrm{Tc}$ have been determined in the thermal-neutron-induced fission of ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$ using fast radiochemical separation techniques followed by gamma-ray spectrometry. The most probable fragment mass $A_p^{\mathcal{’}}$ and mass dispersion ${\sigma }_A^{\mathcal{’}}$ are obtained from the measured independent yields as 108.35±0.45 and 1.80±0.25 mass units, respectively. A comparison of the elemental yield ($Y_z$) of technetium obtained from the present work and the literature for the thermal-neutron-induced fission of ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$ and ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$ and the spontaneous fission of ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$ shows that the $Y_z$ of technetium in the case of fission of ${}_{}{}^{240}{}_{}{}^{}\mathrm{Pu}$ and ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$ is very high compared to that of ${}_{}{}^{236}{}_{}{}^{}\mathrm{U}$. The enhancement of the yields in the case of ${}_{}{}^{240}{}_{}{}^{}\mathrm{Pu}$ and ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$ is attributed to the proximity of spherical-deformed neutron shells 82–88 in the complementary fragments antimony and cesium, respectively.

A pion optical potential is constructed which incorporates the Δ dynamics found to be important in Δ-hole analyses of pion scattering from light nuclei. These dynamics include Δ propagation, binding and Pauli blocking, and a Δ spreading potential. We employ a local density approximation for the medium-modified Δ propagator, resulting in a computationally flexible tool for the analysis of pion-nucleus data. We reproduce the Δ-hole results for π${\mathrm{-}}^{16}$O scattering satisfactorily. Elastic ${\pi }^{\pm }$${\mathrm{-}}^{208}$Pb scattering is described very well with the same strongly damping spreading potential found for light nuclei. The pion wave functions in the medium are substantially modified by the Δ dynamics.

Inclusive differential cross sections and analyzing powers of the (p,${\pi }^{+}$) reaction on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ have been obtained at 400 and 450 MeV incident proton energies. The energy domain investigated spans the region of pion energies that arise in the pp→d${\pi }^{+}$ reaction, a reaction which was measured at the same time. A 65 cm Browne-Buechner spectrometer, in a single-arm configuration, was used for detecting the pions. Measurements were made in the angular range of 46°–88° (lab). At forward angles the measured analyzing powers in the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(p,${\pi }^{+}$)X reaction are quantitively similar to those of the pp→d${\pi }^{+}$ and pp→pn${\pi }^{+}$ reactions, but at backward angles they are considerably more negative. The analyzing power data for angles ≲70° (lab) are consistent with the predictions of a simple quasifree model that incorporates the free pN→NN${\pi }^{+}$ data. Moreover, this model makes a reasonable prediction of the overall strength of the differential cross sections and also reproduces the qualitative shape of the pion energy distributions.

By reformulating Kadyshevsky’s perturbation theory for the S matrix in quantum field theory, a covariant version of time-ordered perturbation theory is obtained. The new graphical rules are just like those of time-ordered perturbation theory except for the replacement of three-momentum-conserving δ functions with covariant three-dimensional δ functions and the use of invariant denominators instead of energy denominators. The new rules are illustrated by deriving an approximate three-dimensional integral equation which describes the scattering of two identical scalar particles which interact by exchanging a different scalar particle.

The n-d and p-d s-wave scattering lengths are calculated for the spin-doublet configuration, including a three-nucleon potential in the Hamiltonian. Numerical results for the Reid-soft-core two-body potential plus the Tucson-Melbourne or Brazil three-body forces are presented. Comparison is made with Kohn variational estimates computed using the wave functions obtained by solving the Faddeev equations. Inclusion of the three-nucleon potentials does not alter our previous conclusions about the scattering lengths; all calculated ${}_{}{}^2{}_{}{}^{}\mathrm{a}_{\mathrm{nd}}^{}{}_{}{}^{}$ and ${}_{}{}^2{}_{}{}^{}\mathrm{a}_{\mathrm{pd}}^{}{}_{}{}^{}$ values lie on separate Phillips curves. The experimental value of ${}_{}{}^2{}_{}{}^{}\mathrm{a}_{\mathrm{nd}}^{}{}_{}{}^{}$ lies on the n-d Phillips curve, while a considerable discrepancy remains for the p-d case.

We have measured cross sections and analyzing powers for the ${}_{}{}^4{}_{}{}^{}(\mathrm{p}\to$,d${)}^3$He(g.s.) reaction at 200 and 400 MeV. In contrast with the cross sections, angular distributions of the analyzing powers are highly structured. Exact finite range distorted-wave Born approximation calculations are compared with the data. Agreement with the present data is reasonable, but earlier 770 MeV cross section data are poorly described by this method.

It is shown that usual derivations of the inhomogeneous and homogeneous multiparticle Lippmann-Schwinger equations are lacking from a rigorous mathematical basis. Then, contrary to a more often than not proclaimed assertion, the validity of these equations is still to be settled.

An isospin-mixing parameter due to charge-symmetry breaking in the neutron-proton system is calculated in a new way, using the distorted-wave Born approximation. Three mechanisms of charge-symmetry breaking are investigated: one-photon exchange, rho-omega mixing, and the nucleon mass-difference effect in one-pion exchange. Numerical calculation of this parameter for a number of energies and angular momenta yields some interesting systematic behavior. In particular, for center-of-mass energies 100 MeV and greater, the largest values are obtained for total angular momentum J=2 (or 4). The mass-difference effect is the most dominant one for all energies greater than 100 MeV. The analyzing-power difference, which is measurable experimentally, is also calculated.

An approximation to scattering on a bound system which minimizes the correction term is derived. This ‘‘optimal’’ approximation is found to be more precise and more simple for application than the weak binding impulse approximation. The derivations are presented in the framework of a local many-body nuclear interaction for the elastic and inelastic single scattering amplitude for the first-order optical potential and for distorted wave approximations. A simple formula for the correction terms to the optimal approximation is obtained. Pauli antisymmetrization effects and spin-orbit forces are not considered.

A separable representation of a boson-exchange nucleon-nucleon potential is constructed via the Ernst-Shakin-Thaler method. The resulting separable interactions provide for a satisfactory approximation of the on-shell as well as off-shell properties of the Bonn potential. Their form factors are composed of rational functions suitable for today’s computer codes for few-body systems. First results obtained with these separable potentials for elastic nucleon-deuteron scattering are presented.

Elastic and charge exchange scattering of intermediate energy protons from ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and tritium is calculated with a microscopic, momentum space optical potential. Full spin dependences, form factors derived from realistic three-body calculations, and off-shell kinematics are included. High sensitivity is found to the removal of meson exchange currents from nuclear densities and to the choice of input NN phase shifts.

The Bethe-Salpeter equation is solved with a separable kernel for the most important nucleon-nucleon partial wave states. We employ the Ernst-Shakin-Thaler method in the framework of minimal relativity (Blankenbecler-Sugar equation) to generate a separable representation of the meson-theoretical Paris potential. These separable interactions, which closely approximate the on-shell and half-off-shell behavior of the Paris potential, are then cast into a covariant form for application in the Bethe-Salpeter equation. The role of relativistic effects is discussed with respect to on-shell and off-shell properties of the NN system.

A simple connection is established between a recently proposed method of continued fractions for on- and off-shell t matrix elements of local and nonlocal potentials and a more conventional iteration-subtraction method for the same problem. We compare the numerical convergence rates of these methods and the method of Padé approximants for the case of two nucleons interacting via the ${}_{}{}^1{}_{}{}^{}\mathrm{S}_0^{}{}_{}{}^{}$ Reid soft core potential.

When the energy resolution of a reaction is considerably large compared to the width and spacing of compound nuclear states, but small compared to optical model shape resonances, one observes the well-known intermediate structure resonances. In the case of compound nuclear processes, a dynamical account of intermediate structure resonances exists, where one assumes the existence of a doorway state through which the incident (or the final) state couples to the compound nuclear states. In the case of compound nuclear reactions the incident and the final states are, in general, different and so are the doorway states which lead the incident and the final states to compound nuclear states, the former doorway states being the usual entrance doorway states and the latter the exit doorway states. A new dynamical formalism is developed using a recently proposed nested doorway model, which explains how intermediate structure resonances arise because of these two types of doorway states. In this model the system develops through a series of doorway hallway states before entering the true compound nuclear state. The first stage of the doorway hallway states is the usual entrance doorway and the last stage is the exit doorway. Finally, we present experimental evidence of the occurrence of intermediate structure resonances due to isolated exit doorway states.

Differential cross sections for inelastic scattering of neutrons to numerous levels in ${}_{}{}^{54}{}_{}{}^{}$,56Fe have been measured at incident neutron energies of 11 and 26 MeV. The data have been analyzed in terms of a collective model using a distorted-wave Born approximation as well as a full coupled-channels treatment. Analysis has also been performed with a microscopic folding model using an energy- and density-dependent effective interaction. Both collective and microscopic analyses have also been applied to inelastic proton scattering in the same energy region in order to extract information on the isospin nature of the measured excitations.

The calculations, presented earlier for the elastic breakup-fusion reactions, is extended here to include inelastic breakup-fusion reactions. As we did before, we take the necessary precautions to eliminate unphysical contributions, which are otherwise mixed into the breakup amplitudes, due to the nonorthogonality between wave functions in the entrance and breakup channels. Related theories by Ichimura et al., and by Hussein and McVoy, are also discussed and it is shown that they retain such unphysical contributions.

Negative results for the production of superheavy elements in damped collisions between ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ projectiles and ${}_{}{}^{248}{}_{}{}^{}\mathrm{Cm}$ targets are reported. This reaction was believed to permit a closer and more widespread approach to the predicted island of stability near Z=114 and N=184 than any practical fusion reaction. Aqueous and gas phase chemistry techniques were used to isolate superheavy element fractions. The fractions were counted for spontaneous fission activity, fragment kinetic energies, and neutron multiplicities. Cross-section limits for half-lives from hours to several years are >4×${10}^{\mathrm{-}35}$ ${\mathrm{cm}}^2$.

In a comparison of angle-integrated cross sections for ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$${(}^6$Li,p) and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${(}^7$Li,p), a striking correlation in selectivity of the two reactions is observed.

High-spin states of ${}_{}{}^{97}{}_{}{}^{}\mathrm{Rh}$ up to J=((31/2)) and an excitation energy of 7.1 MeV were established by means of the ${}_{}{}^{60}{}_{}{}^{}\mathrm{Ni}$${(}^{40}$Ca,3pγ${)}^{97}$Rh reaction. The states are found to decay through two separate γ-ray cascades with the assignments for the lower-spin states being in agreement with previous work. No strong evidence has been found for the existence of collectivity induced by intruder states. The empirical excitation energies are compared to those found recently for the nearby even-A isotones ${}_{}{}^{96}{}_{}{}^{}\mathrm{Ru}$ and ${}_{}{}^{98}{}_{}{}^{}\mathrm{Pd}$, and the systematics of the N=52 nuclides are discussed.

Neutron emission in coincidence with fusion-fission events and evaporation residues was measured in the heavy-ion reactions ${}_{}{}^{141}{}_{}{}^{}+(316\mathrm{}$ MeV) ${}_{}{}^{40}{}_{}{}^{}$Ar and ${}_{}{}^{175}{}_{}{}^{}$Lu+(192 MeV) ${\mathrm{}}^{12}$C. Both reactions are leading to similar composite systems and excitation energies as the previously investigated reaction ${}_{}{}^{165}{}_{}{}^{}$Ho${+\mathrm{}}^{20}$Ne. In order to determine the lifetimes of the composite systems prior to scission and to study entrance channel and angular-momentum effects, the results for all three systems are compared.

From measured cross sections of fission and evaporation residues, the angular momentum intervals leading to fission are deduced to be 50–109 ħ and 49–62 ħ for Pr+Ar and Lu+C, respectively. The corresponding prescission neutron multiplicities are deduced to be $M_{\mathrm{n}{}^{\mathrm{presc}=3.6\mathrm{}\pm 0.6}}$ and 6.3±0.8, whereas the respective postscission multiplicities are $M_{\mathrm{n}{}^{\mathrm{post}=4.4\mathrm{}\pm 0.4}}$ and 3.6±0.6. For the system ${}_{}{}^{175}{}_{}{}^{}$Lu${+\mathrm{}}^{12}$C it is found that 0.5±0.2 preequilibrium neutrons are emitted. In contrast to the evaporative neutrons, a strong anisotropy $a_{\mathrm{n}{}^{\mathrm{PE}=2.2\mathrm{}\pm 0.6}}$ relative to the reaction plane defined by one fission fragment and the beam direction is observed.

From the prescission neutron multiplicities, the evaporation time of the system prior to scission is deduced using the statistical model to ≊(3–12)×${10}^{\mathrm{-}20}$ s. Nucleus deformation effects and neutron emission from not fully accelerated fission fragments are taken into account. The unexpected long prescission lifetimes can be explained as long transition times to the scission point caused by a large two-body viscosity. Under this assumption the viscosity parameter of the highly excited nuclei has been determined in a first approximation to μ≊0.1 TP. The results might be understood also assuming a mixture of a two-body and one-body friction.