The general features of electron-positron emission from high temperature nuclear matter are discussed. Estimates are made of the production rates arising from incoherent nucleon-nucleon scattering and from two-pion annihilation. It may be possible to infer the pion dispersion relation in hot and dense nuclear matter by measuring the invariant mass distribution of back-to-back electrons and positrons in the center of mass frame in high energy nucleus-nucleus collisions.

The production cross sections for the actinides from ${}_{}{}^{136}{}_{}{}^{}\mathrm{Xe}$ bombardments of ${}_{}{}^{249}{}_{}{}^{}\mathrm{Cf}$ at energies 1.02, 1.09, and 1.16 times the Coulomb barrier were determined. Chemical fractions of the individual actinide elements were prepared and the gamma, alpha, and spontaneous fission activities of the actinide isotopes were measured. The cross section distributions are presented and compared with those from other heavy ion bombardments of actinide targets. Conclusions are drawn as to the utility of these heavy ion bombardments for producing unknown isotopes in the actinide region. It is shown that for new neutron-rich actinide isotopes with atomic numbers smaller than that of the target these very heavy ion bombardments are perhaps the best method of production, and when using the most neutron-rich targets available new neutron-rich isotopes should be produced in quantities sufficient for their identification and study.

The energy spectra and angular distributions of alpha particles and protons emitted from ${}_{}{}^{67}{}_{}{}^{}\mathrm{Ga}$ compound nuclei at excitation energies of 110 to 116 MeV formed in four different reactions have been measured. The populated angular momentum ranges deduced from fusion cross section information correspond to 0–24 ħ for ${}_{}{}^4{}_{}{}^{}\mathrm{Cu}$, 0–38 ħ for ${}_{}{}^{12}{}_{}{}^{}\mathrm{Mn}$, 0–48 ħ for ${}_{}{}^{16}{}_{}{}^{}\mathrm{V}$, and 0–50 ħ for ${}_{}{}^{40}{}_{}{}^{}\mathrm{Al}$. The experimental data are analyzed using the angular-momentum-dependent statistical model and the rotating liquid drop model. Average multiplicities and barriers are extracted for different zones of angular momentum. Comparisons with the models indicate large deformations of the ${}_{}{}^{67}{}_{}{}^{}\mathrm{Ga}$ nuclei at the higher angular momenta and suggest large deformation related increases in the nuclear level density and decreases of emission barriers. The p/α ratio decreases with increasing angular momentum less than expected for spherical emitters at the higher angular momenta. The average α emission barriers are found to be close to those which are calculated for emission from the tips of prolate deformed nuclei such as those predicted by the liquid drop model. The experimental proton barriers appear somewhat smaller than those calculated using the liquid drop model shapes.

Quasielastic yields have been measured for the ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$${+}^{208}$Pb reaction at $E_{\mathrm{lab}{(\mathrm{}}^{28}}$Si)=166 MeV. A coupled-channels analysis was performed on the elastic and inelastic scattering, resulting in a good description of all data except for the angular distribution associated with inelastic excitation of the $3^{\mathrm{-}}$ state in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$. A large fraction of the total reaction cross section was found to be contained in quasielastic single-neutron and single-proton transfer. The one-nucleon transfer data were analyzed using the distorted-wave Born approximation with optical-model parameters deduced from the elastic scattering analysis, and spectroscopic factors taken from the literature. The magnitudes of the single-nucleon transfer cross sections are reproduced to within a factor of 1.6 or better.

A potential consisting of two ellipsoidally deformed Gaussian potentials is suggested to be used for a two-center shell model of deformed and arbitrarily orientated nuclei. The eigenenergies of the two-center Hamiltonian are calculated with a set of Nilsson wave functions concentrated around the individual nuclear centers. The two-center shell model is applied to the system ${}_{}{}^{13}{}_{}{}^{}\mathrm{Si}$, where the ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ nucleus is assumed to have an oblately deformed shape. Consequences for reactions between deformed nuclei resulting from the level diagrams are discussed.

Positron and electron peaks produced by sub-Coulomb barrier heavy-ion collisions are studied in terms of a new neutral particle ($\phi$) production together with its decay into the electron-positron pair. The $\phi$-production cross section is calculated in the semiclassical method, assuming a spinless $\phi$ and ignoring the Doppler broadening. The $\phi$ couplings to charged leptons are two orders of magnitude larger than that expected from their ($g-2\mathrm{}$). The identification of $\phi$ as the axion is ruled out for the minimal standard theory by Weinberg-Wilczek. If we take seriously the small Doppler broadenings of positron and electron peaks observed in the experiment, we cannot retain the origin of the peaks to be due to a particle $\phi$. Other possible origins of the peaks are discussed.

For a wide range of incident energy ($E_{\mathrm{lab}=40\mathrm{}–}$170 MeV) and target mass number (A=12–208), projectile breakup effects in elastic scattering of ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ have been investigated in the microscopic coupled-channel framework; coupling with ${}_{}{}^6{}_{}{}^{}\to \mathit{\alpha }$+d breakup process is taken into account by the method of coupled discretized continuum channels. ${}_{}{}^6{}_{}{}^{}\mathrm{target}$ interactions are provided by folding of the M3Y effective nucleon-nucleon potential with nucleon densities of colliding nuclei. The calculation reproduces well experimental data of elastic scattering for all the targets and incident energies investigated, without any renormalization of the folding real potential. The breakup effect is found to depend little on the energy and target, which is shown by calculating dynamical polarization potentials induced by the breakup process. The dynamical polarization potential has a repulsive real part with strength of about 40% of the folding potential, the imaginary part being negligible, which explains well the empirical reduction factor of the single-channel double-folding model. The origin of repulsive nature of the breakup effect is discussed.

In this paper we examine first the contributions of various reaction mechanisms to ‘‘clean’’ fission of ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ projectiles incident on nuclear emulsion at E/A≊1 GeV. ‘‘Clean’’ fission designates events in which fission occurs but no other charged particle tracks are observed. The examined reaction mechanisms are able to account for only about half of the observed cross section for clean fission. Evidently, charged-particle emission is more strongly suppressed in grazing collisions than our modified soft spheres model can account for. Also examined are the mechanisms for $F_1$-type events in which fission is accompanied by a small-angle singly or doubly charged particle. We present results of a Monte Carlo code yielding angular and linear momentum distributions following hot-spot nucleon emission or following a nucleon-nucleon quasielastic collision in the grazing passage of the heavy nuclei.

A nonrelativistic distorted wave Born approximation analysis, using a phenomenological effective proton-nucleon interaction to generate both optical and transition potentials, is made of new 500 MeV (p→,p’) data for excitation of low-lying states in ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$, and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$. The data, differential cross section and analyzing power angular distributions for 5°≤${\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}\mathrm{\le }30\mathrm{°}}$, are well described using this effective interaction. Calculations using the impulse approximation to generate the optical and transition potentials do not adequately describe the data. As a further test of the 500 MeV empirical effective interaction, model-dependent neutron transition densities are deduced for excitations which are expected to be purely isoscalar, such as the first $3^{\mathrm{-}}$ states of ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$. These are found to be qualitatively similar in strength and overall shape to the renormalized (×N/Z) model-independent proton densities determined from analysis of (e,e’) data. Model-dependent neutron transition densities are also deduced for other excitations and are in reasonable agreement with results of analyses of other hadron plus nucleus scattering data. These results indicate that the 500 MeV isoscalar effective interaction is better than the free proton-nucleon scattering amplitudes (impulse approximation) as a starting point for analysis of (p,p’) data aimed at detailed extraction of neutron transition densities and other nuclear structure information.

Data for inelastic pion scattering from ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ at $T_{\pi }$=164 MeV, exciting the lowest $2^{+}$, $3^{\mathrm{-}}$, and $1^{\mathrm{-}}$ states, were analyzed by distorted-wave impulse approximation and coupled-channel calculations using transition densities derived from shell model calculations. Coupled-channels effects were found to be relatively unimportant for the $2^{+}$ and $3^{\mathrm{-}}$ states, but non-negligible for the excitation of the $1^{\mathrm{-}}$ state. Nevertheless, the inclusion of multistep excitation paths is not sufficient to generate a fit to the $1^{\mathrm{-}}$ data with the shell model wave functions. Major modifications are needed in the radial dependence of the neutron and proton parts of the transition density for the $0^{+}$→$1^{\mathrm{-}}$ one-step process.

The lifetime of negative muons has been measured in 50 elements plus 8 isotopes. For light elements the accuracy of 2 to 3 ns is a significant improvement over most previous measurements. In heavier elements the accuracy is 1 to 2 ns, which is comparable to, or better than, previous results, with reasonable agreement in most cases. For ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$, Sc, Dy, and Er there were no previous data. The total capture rates have been deduced and compared to various calculations.

The microscopic optical model potential is investigated in its full form starting from the nonlocal two-body effective force. It is found that the nonlocality causes an effective repulsion in the nuclear interior which produces a so called wine-bottle shape which characterizes the optical model potential at intermediate energy. Its relationship to the relativistic approaches based on the Dirac equation is discussed.

Hypernuclei are studied in the mean-field approximation to an extended σ-ω (Walecka) model. The baryon current in systems with one Λ hyperon added to a closed-shell core of nucleons is calculated by treating the linear response of the core to the Λ in a local density approximation. The core is modified through the mixing of positive- and negative-energy nucleon wave functions and the result is a significant nucleonic contribution to the baryon current. This relativistic effect could be directly observable in measurements of the magnetic moments of hypernuclei with a deeply bound Λ.

Scattering of 362 MeV polarized protons from ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ to the ground, $3^{\mathrm{-}}$ (3.74 MeV), $2^{+}$ (3.90 MeV), and $5^{\mathrm{-}}$ (4.49 MeV) states has been studied from 3° to 65° in the laboratory. Measured values of dσ/dΩ and $A_y$ are compared with standard relativistic and nonrelativistic calculations using transition densities from random-phase-approximation calculations and electron scattering data.

The relative cross sections for exciting particular states in the (p,${\pi }^{+}$) reaction near threshold are calculated with the shell model assuming dominance of the elementary p+p→d+${\pi }^{+}$ reaction. Results from the plane-wave approximation show that strongly excited states for ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ targets can be accounted for in this manner.

The neutron-neutron scattering length $a_{\mathrm{nn}}$ is determined from the low energy part of the neutron spectrum of the reaction ${\pi }^{\mathrm{-}}$d→nnγ with pions at rest. Since neutrons are detected in coincidence with the photon, the kinematics is completely determined. We obtain $a_{\mathrm{nn}=\mathrm{-}18.7\pm 0.6}$ fm, in agreement with a result of a previous experiment based on the analysis the photon spectrum.

Elastic cross sections for the scattering of positive and negative pions from ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ were measured at 30 MeV incident pion energy. Statistical errors of ±3% and normalization errors of ±6% were achieved. These data appear to confirm the theoretical construct that the physics which explains anomalously small shifts and widths in pionic atoms would be manifested in low energy pion-nucleus elastic scattering. The data show good agreement with the cross sections calculated assuming s and p partial waves are anomalous. Here anomalous refers to partial waves that are calculated from an optical potential which reproduces anomalously small level shifts and widths in pionic atoms. Conventional optical potentials do not agree as well with both the ${\pi }^{+}$ and ${\pi }^{\mathrm{-}}$ data. Various conventional possibilities such as a larger neutron radius than proton radius in the nuclear density were tried, but these did not result in good agreement with the data.

We obtain the band condition for relativistic quarks moving in one-dimensional periodic potentials using the transfer matrix method. Using a strong electrostatic type of potential in the Dirac equation does not give confining properties, while Lorentz scalar potentials do. We give an analytic form for the wave function which results when the potential is taken to a delta function limit, and discuss the discrepancy between this result and that obtained by ‘‘solving’’ the Dirac equation for a delta function potential.

The β decay of ${}_{}{}^{39}{}_{}{}^{}\mathrm{Cl}$, produced in the ${}_{}{}^{37}{}_{}{}^{}\mathrm{Cl}$(t,p${)}^{39}$Cl reaction at $E_{\mathrm{t}}$=3.1 MeV, has been investigated with a Ge-NaI(Tl) Compton-suppression γ-ray spectrometer. Nineteen γ-ray transitions were observed, including 10 previously known. Precision energy measurements were carried out on six of the strongest lines. In the proposed decay scheme a weak new β-ray branch is established to the 2950-keV level of ${}_{}{}^{39}{}_{}{}^{}\mathrm{Ar}$, and the populations of ${}_{}{}^{39}{}_{}{}^{}\mathrm{Ar}$ levels at 2093 and 2433 keV are accounted for by γ-ray decays from higher excited states. Spin-parity assignments are given.

A spherical shell-model calculation of the odd- and even-parity states of ${}_{}{}^{39}{}_{}{}^{}\mathrm{Ar}$ is made in a full sdpf model space. The calculation includes absolute binding energies and energy spectra, single-neutron spectroscopic factors, and electromagnetic and beta decay observables. Agreement with experiment is fairly good. Comparison is hampered by incomplete experimental knowledge and by the presence of low-lying intruder states.