The spectral shape and multiplicity of neutrons from the reaction of ${}_{}{}^{14}{}_{}{}^{}$N+Ag at E/A=20 and 35 MeV have been measured for neutrons in coincidence with intermediate mass nuclei emitted at 50°, 70°, and 90°. The spectral shape clearly suggests two moving sources. The slower source velocity is about 80% of the center-of-mass velocity for E/A=20 MeV and 65% of the center-of-mass velocity for E/A=35 MeV (9% and 7% of the beam velocity, respectively). The faster source velocity is slightly less than half of the beam velocity for each case. Knowledge of the neutron multiplicity is necessary for models which attempt to explain the low effective temperature which has been determined from recent measurements of excited state populations. The data are also compared to the Boltzmann master equation approach of Harp, Miller, and Berne.

We introduce a new numerical method for calculating continuum excitation probabilities of complex physical systems under the influence of external, time-dependent, and nonperturbative fields. The method utilizes a discretized form of the Hamiltonian on a space lattice and is particularly suited for large scale computations involving many-body systems. We perform a comparative study for a model problem by solving the same time-dependent Schrödinger equation in spherical and cylindrical coordinates. As a realistic example, we apply the method to the problem of prompt nucleon emission in low energy heavy-ion reactions.

The velocities of heavy residues with atomic numbers Z>8 were measured and analyzed in the ${}_{}{}^{28}{}_{}{}^{}$Si${+}^{\mathrm{nat}}$Si reaction at 12.4 MeV/nucleon. The average missing linear momentum transfer in the incomplete fusion processes for this symmetric system lies between 2.5% and 3.5%. The analysis revealed the existence of a fully damped component peaked strongly in the beam direction. The velocity distributions of this component seem to be determined mainly by recoils from secondary emitted particles.

We have measured light-particle energy spectra over a 90° range of angles in the forward hemisphere in coincidence with heavy residues from the reaction ${}_{}{}^{20}{}_{}{}^{}\mathrm{Al}$ at 19.2 MeV/nucleon. A selection on residues with Z≥11 removes the contributions of deep-inelastic scattering and peripheral processes from the fusion-like cross section. With the help of a simple analytic model that includes the coincidence kinematics we are able to describe the data and extract multiplicities, primary-energy distributions, and source velocities for the light particles from fusion-like reactions. The mass difference between the observed fragments and the compound system comes almost exclusively from light particles with Z≤2. The evaporated α particles are more energetic and more numerous than the statistical model implies. The fast α particles have distributions consistent with a fragmentation-fusion picture; however, they account for at most (1/3 of the momentum lost in the incomplete fusion process.

A nuclear projection model is developed for heavy-ion reactions in the sub-Coulomb region. Generalized doorways are introduced as the set of resulting states obtained by coupling the shape resonances to the single and mutual excitation channels. The model is applied to the ${}_{}{}^{12}{}_{}{}^{}$C${+}^{12}$C reaction by treating the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ nucleus as deformed, and the ion-ion optical potential is taken as that of Kondo et al. with a soft repulsive core. The energies and continuum widths of the resonances below and near the Coulomb barrier are calculated and found to be consistent with observation. Intermediate structure is mainly caused by the shape resonances which are fragmented into the various generalized doorways. However, the major strength of the elastic channel remains concentrated around the energy where a potential resonance exists in the elastic channel. Levels are predicted down to 2.91 MeV c.m. and provide a first step in an impending extrapolation of ${}_{}{}^{12}{}_{}{}^{}$C${+}^{12}$C reaction rates to astrophysical energies.

Two- and three-nucleon stripping reactions induced by 480 MeV ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ have been studied on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$, and ${}_{}{}^{54}{}_{}{}^{}\mathrm{Fe}$ target nuclei. Discrete levels are fed with cross sections up to 1 mb/sr for d-transfer reactions and 1 order and 2 orders of magnitude less for 2p- and ${}_{}{}^3{}_{}{}^{}\mathrm{transfer}$ reactions, respectively. These reactions preferentially populate high spin states with stretched configurations. Several spin assignments were known from transfer reactions induced by lighter projectiles at incident energies well above the Coulomb barrier. In the case of two-nucleon transfer reactions, the energy of these states is well reproduced by crude shell model calculations. Such estimates are of use in proposing spins of newly observed states especially as the shapes of the measured angular distributions are independent of the final spin of the residual nucleus.

Light charged particles from the reactions 247 and 337 MeV ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$${+}^{\mathrm{nat}}$Ag have been measured in singles and in coincidence with fission-like products. Most of the ${}_{}{}^1{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ in coincidence with fusion-fission and quasifission can be accounted for by evaporation from the composite nucleus or by the fragments. Multiplicities are determined for ${}_{}{}^1{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ in association with evaporation residues, fusion-fission, and quasifission. The probability for composite nucleus emission decreases with increasing spin zone of the emitter and gives a view of the role of emitter lifetime. The ratio of composite-nucleus multiplicities for quasifission/fusion-fission is about 1/2 ((1/4) for 337 MeV ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ (247 MeV ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$) which implies a similar ratio for the lifetimes of the respective composite nuclei between thermalization and scission. Energy spectra and angular distributions of particles (in coincidence with fusion-fission and quasifission) are consistent with emission from a strongly distorted nuclear system en route toward scission. Prethermalization emission of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ is observed at 10° in comparable amounts for peripheral collisions (quasifission and fusion-fission) and for central collisions.

We have measured coincidences between ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^1{}_{}{}^{}$,2,3H or a second ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ (large-angle correlations) in the reactions 247 and 337 MeV ${}_{}{}^{40}{}_{}{}^{}$Ar${+}^{\mathrm{nat}}$Ag. These coincidences are dominated by reactions leading to evaporation residues with spins of about 0–70ħ. Large values of the angle-integrated double and triple coincidence cross sections indicate that many particle evaporation chains involve 2 or 3 protons and/or 2 or 3 alphas. The angular and energy distributions are well described by an evaporation model with Hauser-Feshbach coupling. However, one must employ effective evaporation barriers for ${}_{}{}^1{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ that are strongly reduced compared to empirical fusion barriers. The barrier reduction required for ${}_{}{}^2{}_{}{}^{}\mathrm{H}$ is rather small, and for ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ no barrier reduction is needed. Evaporation calculations that include emitter deformation do not give a satisfactory explanation for these results. We suggest a new aspect of composite nucleus excitation and evaporation-like decay. A hot, very diffuse nuclear surface may be formed that promotes evaporative decay prior to its relaxation. The low barriers for ${}_{}{}^1{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ reflect the radial extent of this transitory, diffuse surface.

The ground-state rotational band of ${}_{}{}^{161}{}_{}{}^{}\mathrm{Dy}$ has been investigated through multiple Coulomb excitation with a beam of 250-MeV ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$. γ-ray branchings and E2/M1 mixing ratios were determined up to the ${(25/2\mathrm{}}^{+}$ state by measurements of γ-ray angular distributions and γ-γ angular correlations. Nuclear lifetimes of levels up to I=(25/2 have been measured using the Doppler-shift recoil-distance method. Considerable signature dependence was observed for ΔI=1 M1 transition probabilities. ΔI=1 E2 transition probabilities were found to decrease significantly as a function of spin. The results are compared with a microscopic model calculation based on the angular momentum projection method.

Elastic and inelastic scatterings of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$, and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ projectiles on ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ have been studied at corresponding bombarding energies to the scattering in regions of the vicinity of the strong absorption radius. Optical model and microscopic double-folding model analyses have been performed in order to define the nature of the optical potential depending on the projectiles. The analysis by the optical model calculations showed that the shallow potential ($V_R$=10 MeV) was not adequate for reproducing both the measured elastic and inelastic angular distributions, and a spin-dependent noncentral potential for the scattering systems ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$${,}^{14}$N${+}^{28}$Si was indispensable for obtaining the similar central potentials for all four projectiles. Analysis by the microscopic double-folding calculations supported the results of the optical model calculations.

Dispersions around mean values of one-body observables are obtained by restoring classical many-body correlations in Vlasov and Landau-Vlasov dynamics. This method is applied to the calculation of fluctuations in mass, charge, and linear momentum in heavy-ion collisions. Results are compared with those obtained by the Balian-Veneroni variational principle in semiclassical approximation.

The spectroscopy of neutron-rich isotopes of ${}_{}{}^{67}{}_{}{}^{}\mathrm{Ni}$ and ${}_{}{}^{68}{}_{}{}^{}\mathrm{Ni}$ is studied using the quasi-elastic transfer reactions ${(}^{14}$C${,}^{16}$O) and ${(}^{14}$C${,}^{17}$O) on a ${}_{}{}^{70}{}_{}{}^{}\mathrm{Zn}$ mass separated target. The structure of these exotic nuclei is investigated in the framework of a microscopic collective model based on the Hartree-Fock-Bogoliubov theory. Gogny’s two-body effective interaction is used. Collective excited states of ${}_{}{}^{68}{}_{}{}^{}\mathrm{Ni}$ are obtained by solving the Bohr Hamiltonian in which inertia parameters are calculated in the cranking approximation. Spin and parity assignments to observed excited levels are suggested on the basis of information deduced from this analysis. This assignment is further checked by comparing measured angular distributions to predictions. Predictions of the level structure of ${}_{}{}^{70}{}_{}{}^{}\mathrm{Ni}$ and ${}_{}{}^{78}{}_{}{}^{}\mathrm{Ni}$ isotopes are given. A more precise test of the $0^{+}$ wave functions is provided by the calculation of monopole operator of the $0_1^{+}$→$0_2^{+}$ transition in ${}_{}{}^{68}{}_{}{}^{}\mathrm{Ni}$. An impressive agreement is obtained between the measured and calculated half-life.

The single particle inclusive reactions ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${+}^{12}$C→x+anything (3≤Z≤6) have been studied at 250 MeV/nucleon at nine production angles from 0° to 4°. Production cross sections for most isotopes (Z>2) were determined. The longitudinal and transverse momentum distributions were constructed. The results at this energy are compared to the data at other energies and to the model of Friedman. It appears that, after the Coulomb effects are separated, there is very little energy dependence in the fragmentation process.

The spectra of $\alpha$ particles emitted from narrow windows of angular momentum with $28\hslash \le J_{\mathrm{av}}\le 34\hslash$ show systematic deviations from spectra calculated using the statistical model as the spin of the emitter increases to values for which strong deformations are predicted. The barrier reduction and the enhancement of the level density needed to reproduce the experimental spectra have been determined.

Transfer reaction cross sections for the systems ${}_{}{}^{46}{}_{}{}^{}$,48,50Ti${+}^{208}$Pb at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}$=243 MeV have been measured with single mass and charge resolution using a magnetic spectrograph and a gas-filled focal-plane detector. The angle and excitation energy ranges studied in this experiment covered both quasi-elastic and deep-inelastic processes. The total reaction cross sections are dominated by transfer reactions with neutron transfer being the strongest transfer mode. Wilczyński plots for individual reaction channels have been generated showing a gradual transition from quasi-elastic reactions to deep-inelastic processes. While macroscopic models cannot explain the element distributions observed in this experiment, a simple model based on a random walk in the N-Z plane gives good agreement for the reaction strength and the measured energy spectra.

Effects induced by a nuclear stratosphere upon statistical particle emission processes are discussed. The calculations are based on the compound nucleus emission model and they include the formation of a nuclear stratosphere. This degree of freedom is accounted for by effective potentials for particle emission channels. The radial dependence of these potentials is adjusted in order to reproduce the temperature-dependent shape evolution of nuclear radial distribution functions. Results are discussed for ${}_{}{}^1{}_{}{}^{}\mathrm{H}$${/}^4$He emission rates from the compound nucleus ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$.

The local-density approximation to the delta-hole model is investigated. Features learned from work on the momentum-space approach to the pion-nucleus optical potential are incorporated into the model. In the limit of no delta-nucleus interaction, we are able to examine the reliability of the approximations of the model by comparing it to a model-exact momentum-space calculation. The model provides a numerically efficient approach to studying delta dynamics in the nucleus.

A low-energy neutrino-electron elastic scattering experiment using an imaging water Cerenkov detector has been proposed to determine ${\sin }^2$${\mathrm{\theta }}_{\mathrm{W}}$ to an accuracy of about 1%. I discuss the nuclear physics complications that arise from charged-current reactions on oxygen isotopes.

Pion-γ angular correlations have been measured both in and out of the reaction plane for the reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(π,π’${)}^{12}$${\mathrm{C}}^{\mathrm{*}}$($2^{+}$, 4.44 MeV), ${}_{}{}^{12}{}_{}{}^{}$${\mathrm{C}}^{\mathrm{*}}$${\to }^{12}$C(g.s.)+γ. Data are presented at a pion momentum transfer of q=0.47 ${\mathrm{fm}}^{\mathrm{-}1}$ for incident pion energies of 116, 140, 162, 180, and 226 MeV and at q=0.85 ${\mathrm{fm}}^{\mathrm{-}1}$ for energies of 116, 162, and 226 MeV. A detailed description of the experimental setup together with the applied test procedures and of the data analysis is given. The data are compared to predictions of the Δ-hole model and its static limit.

A general formula for the coefficient of internal conversion in an intense laser field, which is valid for all atomic electron shells, is deduced in a simple nonrelativistic model. For special shells, for which internal conversion without the laser is energetically forbidden but which have an energy defect relatively small compared to the laser photon energy, the presence of the laser radiation is essential. Cases such as the 4s(1/2 shell internal conversion of the E1 transition of the isomeric state ${}_{}{}^{183}{}_{}{}^{}\mathrm{W}_{}^{\mathrm{m}}{}_{}{}^{}$ ($E_{\gamma }$=544 eV, τ=5.3 s, J${=(11/2\mathrm{}}^{+}$) and the 5d(3/2, 5d(5/2 shell internal conversions of the E3 transition of the isomeric state ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}_{}^{\mathrm{m}}{}_{}{}^{}$ ($E_{\gamma }$=73.5 eV, τ=26 min, J${=(1/2\mathrm{}}^{+}$) are numerically investigated in the small momentum approximation.