The three-nucleon transfer reactions (α,p) and ${(}^9$Be${,}^6$Li) on ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$ were employed to study the 21.4-MeV state in ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$. This state is of particular interest as it exhibits anomalous behavior in its production via the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(p,${\mathrm{\pi }}^{+}$${)}^{13}$C reaction. A study of the structure of this state via ‘‘conventional’’ reactions serves to elucidate the underlying NN→NNπ production mechanism.

We have searched for three-photon decays produced in 6-MeV/nucleon U+Th, Th+Th, and U+U collisions. We see no evidence for narrow lines corresponding to the electron-positron lines seen by others: in the summed-energy region between 1.2 and 2.0 MeV, we set an upper limit for the cross section of 3×${10}^{\mathrm{-}28}$ ${\mathrm{cm}}^2$ averaged over a target thickness of 1 mg/${\mathrm{cm}}^2$.

The light charged particles emitted from hot ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ compound nuclei, populated at excitation energy ${\mathit{E}}_{\mathit{x}}$=94 MeV and 〈J〉=20.5ħ by the reaction 130 MeV ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ on ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$, have been studied. Energy spectra of protons and alpha particles, measured in coincidence with evaporation residues and with a selection of multiple-alpha chains, have been compared with the predictions of Monte Carlo statistical model calculations. The comparison shows that the level density of hot nuclei with A≤40, needed to account for the measured quantities, is well predicted by the Fermi-gas model using a level-density parameter ${\mathit{a}}_{\mathrm{eff}}$=A/8 ${\mathrm{MeV}}^{\mathrm{-}1}$ up to excitation energy 〈${\mathit{E}}_{\mathrm{th}}$/A〉∼1.7 MeV. In agreement with theory, light hot nuclei do not show the transition from ${\mathit{a}}_{\mathrm{eff}}$=A/8 ${\mathrm{MeV}}^{\mathrm{-}1}$ to ${\mathit{a}}_{\mathrm{eff}}$∼A/13 ${\mathrm{MeV}}^{\mathrm{-}1}$ evidenced in the A∼160 mass region for the same range of excitation energies ${\mathit{E}}_{\mathrm{th}}$/A. The analysis of the alpha-particle spectra shows that the effects associated with the angular-momentum-induced deformations depend on the entrance channel characteristics and, in this case, are very small compared with those evidenced in the past for compound nuclei in the region A=50–70.

The one-neutron pickup reaction ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$${(}^{206}$Pb${,}^{207}$Pb${)}^{234}$U at a laboratory energy of 1394 MeV was used to investigate the influence of collective motion at high spin on the single-particle nature of transfer reactions in the actinide region. Deexcitation γ rays were measured using a particle-particle-γ triple-coincidence method. The decay scheme of the reaction products was identified using p-γ-γ coincidences. Rotational states up to ${28}^{+}$(${30}^{+}$) were seen in ${}_{}{}^{234}{}_{}{}^{}\mathrm{U}$. A comparison of rotational state population in both the p–γ-ray singles and the p-γ-γ coincidences is also made between data from the above reaction and from the reaction ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$${(}^{58}$Ni${,}^{59}$Ni${)}^{234}$U (${\mathit{E}}_{\mathrm{lab}}$=325 MeV). For each system, angular distributions for both inelastic excitation and transfer are presented and one-neutron transfer reaction cross sections as well as grazing angles have been extracted. The reaction cross sections are compared to a recent semiclassical calculation based on ${\mathit{Q}}_{\mathit{g}\mathit{g}}$ systematics. The present study demonstrates the feasibility of using heavy-ion-induced transfer reactions for spectroscopic studies.

Differential cross sections and analyzing powers have been measured for the excitation by 318 MeV protons of states of ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ below 7.2 MeV. The data for those normal-parity excitations for which transition densities are available from electroexcitation measurements are analyzed in terms of medium modifications to the nucleon-nucleon interaction. We find that the empirical effective interaction previously fitted to ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(p,p’) data at the same energy predicts ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$(p,p’) very well. Density-dependent modifications of the effective interaction fitted to data for ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ or ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, either independently or simultaneously, are virtually identical. The density dependence of the empirical interaction is considerably stronger than that of interactions based upon nonrelativistic nuclear matter theory and persists to lower density. The most significant differences are that the empirical interaction has a stronger repulsive core and that absorption is enhanced at high density, contrary to expectations based upon Pauli blocking. We also find substantial suppression of the spin-orbit interaction at low density and enhancement at high density. Nevertheless, the independence of the effective interaction from the target supports the concept of local nuclear matter density. We also find that optical potentials based upon the empirical effective interaction are very similar to Schrödinger-equivalent potentials based upon a relativistic impulse approximation model, suggesting that the empirical density dependence is similar to the equivalent density dependence that arises from elimination of lower components from Dirac wave functions. Finally, the results are compared with global optical potentials from Dirac phenomenology.

Analyzing powers and isotope ratios have been measured for ejectiles with Z≤7 emitted at forward angles in the 200-MeV p→${+}^{\mathrm{nat}}$Ag reaction. The observed analyzing powers are consistent with zero, and thus do not provide evidence for a significant contribution from cluster knockout, or similar direct formation mechanisms. Fragment kinetic-energy spectra above the Coulomb peak are compared with a coalescence calculation. The isotopic composition of the elemental kinetic-energy spectra is found to favor N/Z≥1 nuclei for fragment energies near the exit-channel Coulomb energy, whereas species with N/Z≤1 are more abundant in the high-energy spectral tails. This behavior is consistent with the predictions of an accreting source calculation.

Detailed angular distributions of protons and α particles detected in coincidence with evaporation residues have been measured for the reaction ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$${+}^{28}$Si at 12.4, 19.7, and 30.0 MeV/nucleon. We have separated these angular distributions into pre-equilibrium and evaporation components. The invariant velocity distributions of pre-equilibrium protons are typical for nucleons emitted by jetting processes, while the distributions of pre-equilibrium α particles are typical for particles produced in breakup reactions. The charge and energy balance in the reaction allows us to reconstruct the average properties of the compound nucleus and to deduce the effects of the reaction dynamics. At 12.4 MeV/nucleon only a few pre-equilibrium light particles are emitted prior to fusion, whereas at 19.7 and 30.0 MeV/nucleon hot nuclei are formed in breakup-fusion reactions. All of our results can be fully explained assuming that compound nuclei do not produce evaporation residues if their excitation energy is above 4.3 MeV/nucleon.

Excitation functions for the helium-ion-induced fission of holmium (Z=67) and erbium (Z=68) in the energy range 34–70 MeV were measured using lexan polycarbonate plastic as the fission fragment track detector. By analyzing the data in terms of the statistical model expression for ${\mathrm{\Gamma }}_{\mathit{f}}$/${\mathrm{\Gamma }}_{\mathit{n}}$, the ratio of the fission width to neutron emission width, the fission barriers of the compound nuclei ${}_{69}{}^{169}{}_{}{}^{}\mathrm{Tm}$ and ${}_{70}{}^{171.3}{}_{}{}^{}\mathrm{Yb}$ were determined to be 29.8±3 and 27.8±3 MeV, respectively. The corresponding values for the fission level density parameter were found to be ${\mathit{a}}_{\mathit{f}}$=A/12 and A/13, respectively. The uncertainties shown in the fission barriers allow for inclusion of other values derived from reasonable upper and lower limits of ${\mathit{a}}_{\mathit{f}}$ values of A/8 to A/20. The measured fission barriers compare very well with the shell-corrected liquid-drop barriers of Myers and Swiatecki. The present measurements extend the range of low-Z elements which are away from the closed-shell region and which are studied at these medium energies. The results are compared with similar data available in the literature which bring out some interesting correlations and trends in the fission properties, viz., fission barriers and level density parameters of low-Z elements.

The influence of density dependent meson masses, proposed in many previous papers, on proton-nucleus scattering in the several hundred MeV region is investigated. Introduction of this density dependence is found to remove the nuclear radius discrepancy which persistently occurred in analyses with the nonrelativistic impulse approximation when empirical nuclear densities obtained from electron scattering were employed. Nonlocality, suggested by earlier derivations of the density dependent masses, had to be introduced. Taking the estimated range of nonlocality from the earlier calculations, agreement with experiment was significantly improved by this introduction. Effects on the spin-orbit interaction and imaginary part of the optical model are qualitatively discussed. The density dependent meson masses aid in increasing the strength of the spin-orbit interaction. Preliminary results calculated in a relativistic impulse approximation (IA2) formalism for the spin observables are shown and discussed.

The Coulomb interaction between two protons sequentially evaporated from the same compound nucleus is studied as a possible origin for their measured correlations. This is done in the frame of three-body trajectory calculations with both Coulomb and nuclear forces. The temperature and mass of the emitting nucleus were determined from the measured energy spectra of single protons. The correlation function was found to be very sensitive to the mean time delay between the emissions of the two particles. A value ${\mathrm{\tau }}_0$=(1.0±0.2)×${10}^{\mathrm{-}21}$ s was obtained by comparison of our calculations with the two-proton correlation function measured at backward angles in the reaction ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$${+}^{108}$Ag at 44 MeV/nucleon.

The microscopic nucleus-nucleus Glauber model is combined with the macroscopic model for pairing correlations in order to describe multipair-transfer processes between heavy ions at intermediate energies. Quantitative predictions for multipair transfer cross sections are given at different bombarding energies. Strong destructive interference among different transfer mechanisms is evidenced, leading to cross sections significantly smaller than those obtained when only sequential single-pair transfer is allowed.

The process of heavy-ion fusion followed by compound-nucleus fission is explored in the context of light nuclear systems. Spin- and mass-asymmetry-dependent saddle-point energies are calculated for several nuclei with 40≤${\mathit{A}}_{\mathrm{CN}}$≤80 using the diffuse-surface, finite-nuclear-range model. A simple, double-spheroid approximation to the macroscopic-energy calculation is developed for determining fission barriers and fragment total kinetic energies. Fission cross sections are calculated within a statistical model and compared to experimental results. These comparisons support the idea that nuclear fission is the dominant process responsible for the fully energy-damped yields observed in this mass region.

Using Coulomb distorted waves for the electron wave functions, we investigate (e,e’γ) processes where the nucleus is excited by inelastic electron scattering and the subsequent decay photon is detected in coincidence with the scattered electron with the nonavoidable bremsstrahlung process which must be coherently included. We examine the effects of Coulomb distortion on the resulting cross sections and compare our results with plane-wave analyses and with previous approximate calculations. In addition to examining other calculations, we compare our results with the available data and discuss the possibilities of using this reaction to determine multipole admixtures and extracting transition charge and current distributions for medium and heavy nuclei.

Within the Feshbach formalism we calculate the nucleus-nucleus dynamical polarization potential arising from the coupling of the elastic channel to the collective vibrational states, described by the random-phase approximation. Calculations for the systems ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${+}^{40}$Ca and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$${+}^{40}$Ca show the importance of the high-lying states. They give the main contribution to the real part of the polarization potential at every incident energy, while they dominate the imaginary part only at very high energy. At low energy the absorption is given by the low-lying states. The real and imaginary parts of the potential are shown to obey a dispersion relation. Calculations of elastic cross section give a good description of the experimental data.

In the framework of the statistical theory of nuclear reactions we calculated the fission probability ${\mathit{P}}_{\mathit{f}}$ of the ${}_{}{}^{153}{}_{}{}^{}\mathrm{Tb}$, ${}_{}{}^{158}{}_{}{}^{}\mathrm{Er}$, ${}_{}{}^{159}{}_{}{}^{}\mathrm{Dy}$, ${}_{}{}^{175}{}_{}{}^{}\mathrm{Hf}$, ${}_{}{}^{179}{}_{}{}^{}\mathrm{Ta}$, ${}_{}{}^{186}{}_{}{}^{}\mathrm{Os}$, and ${}_{}{}^{188}{}_{}{}^{}\mathrm{Os}$ nuclei with a mass number A=150–200 produced by heavy-ion reactions. Starting from the spectra of the single-particle levels as determined by Nix and Möller, and utilizing a formalism we developed, we determined the excitation energy dependence of the effective level density parameters for the fission and the neutron emission channels. The agreement between the fission probability calculations and the experimental data was reached when a nonadiabatic estimate of the collective effects was used to calculate the nuclear level density. In the fission process at high excitation energies induced by ions heavier than the α particle, an energy dependence of the effective fission barrier has to be used.

Using an explicit analytical expression of the s-wave S matrix for a typical short-range potential barrier we correlate the classical orbiting and corresponding quantum-mechanical barrier states. These are compared with the results of earlier works on this problem and some additional interesting features, such as dependence of width on height of the barrier and spacing between the levels of the barrier region resonances, are pointed out. On this basis, a four-parameter barrier region resonance model is introduced in the analysis of resonances in heavy ion scattering. The model is then applied to fit satisfactorily the large number of resonances observed in ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${+}^{12}$C and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${+}^{16}$O systems. The present model directly relates the nucleus-nucleus potential barrier generated by the effective nucleus-nucleus potential to heavy ion resonances.

Distributions of transverse energy, forward energy, and ${\mathit{dE}}_{\mathit{T}}$/dη from 60A GeV and 200A GeV ${}_{}{}^{16}{}_{}{}^{}\mathrm{induced}$ and 200A GeV ${}_{}{}^{32}{}_{}{}^{}\mathrm{induced}$ nuclear collision with C, Al, Cu, Ag, and Au are presented. The energy, projectile, target, and centrality dependences are shown and discussed within a simple Glauber spectator-participant model. Two universal parametrizations of the ${\mathit{dE}}_{\mathit{T}}$/dη distributions are presented together with various estimates of the nuclear stopping power and attained energy densities. An upper limit for ${\gamma }_{\mathrm{direct}}$/${\mathrm{\pi }}^0$ in central collisions of 200A GeV ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$${+}^{197}$Au is derived.

We have calculated ground-state properties of nuclear matter in a simple string-flip quark model in one dimension. Special emphasis was placed on the transition from hadron to quark matter and to the response of the system to color fields. Numerical simulations involving a large number of quarks were carried out for two- and three-quark clusters. This in turn enabled us to investigate the hadron-to-quark transition through the study of finite-size effects. The concept of a sudden-quark potential was introduced as an example of a generic response of the medium to color fields. We have argued that this response might be relevant to the propagation of a rapidly moving quark-antiquark pair (e.g., J/ψ meson) through the medium.

A measurement of the total cross section for η-meson photoproduction from light nuclei will determine the isotopic spin dependence of 〈${\mathit{S}}_{11}$‖${\mathit{j}}_{\mathit{e}\mathit{m}}$‖N〉. This acts as a test of models of ${\mathrm{SU}}_6$ breaking. Effects due to the subthreshold Roper resonance are computed and found to be small compared to an isoscalar ${\mathit{S}}_{11}$ signal.

The ${(}^6$Li${,}^6$He) reaction was studied on the nuclei ${}_{}{}^{37}{}_{}{}^{}\mathrm{Cl}$ and ${}_{}{}^{71}{}_{}{}^{}\mathrm{Ga}$ at ${\mathit{E}}_{6\mathrm{L}\mathrm{i}}$=156 MeV at extreme forward angles including zero degree. Gamow-Teller strength and the corresponding B(GT) values were extracted. It is shown that these measurements provide an alternative method to calibrate solar neutrino detectors.