Effective boson charges, ${\mathit{e}}_{\mathrm{\pi }}$ and ${\mathit{e}}_{\nu }$, are extracted for isotopic chains of most elements from Z=42 to the actinides from analytic expressions derived in the interacting boson approximation. It is shown that, in valence space models, such effective charges carry an additional, physically intuitive interpretation, beyond the normal one of ensuring agreement of calculated electromagnetic transition rates with experiment. In valence models ${\mathit{e}}_{\mathrm{\pi }}$ and ${\mathit{e}}_{\nu }$ are approximately proportional to the derivatives of M(E2:$0_1^{+}$→$2_1^{+}$) with ${\mathit{N}}_{\mathrm{\pi }}$ and ${\mathit{N}}_{\nu }$, respectively; that is, they are measures of the rate of change of collectivity. This feature allows one to disentangle the separate roles of protons and neutrons in the development of collectivity and exposes subtle effects originating in the valence p-n interaction. The results are striking. While for most elements, ${\mathit{e}}_{\mathrm{\pi }}$>${\mathit{e}}_{\nu }$ as expected, certain regions display anomalously large ${\mathit{e}}_{\nu }$, and, sometimes ${\mathit{e}}_{\nu }$/${\mathit{e}}_{\mathrm{\pi }}$>1. These effects are interpreted in terms of the p-n interaction and, in particular, in terms of its monopole component which acts to shift single particle energies and, thereby, can alter shell gaps and the effective size of the valence space of one kind of particle as a function of the number of the other. Very small values of ${\mathit{e}}_{\nu }$ near midshell are also interpreted in terms of the saturation of collectivity in such regions.

A recent study of the onset of chaos in the low-lying collective states of nuclei, which uses the interacting boson model, is extended to higher spins and/or higher energies by including broken pairs. Spectral fluctuations are studied as a function of the quadrupole-quadrupole interaction between the fermion pair and the core and the pair-breaking interaction that mixes states with different number of fermions. The effects of the Coriolis force are discussed.

It is impossible to determine spins for superdeformed bands by fitting the γ-transition energies alone. It is necessary to introduce a model. By using a variable moment of inertia (VMI) model one can estimate spins but cannot rule out the possibility of a ±ħ uncertainty. Therefore, no objective evidence exists requiring the presence of quantized spin alignment in superdeformed nuclei. An alternative hypothesis that all superdeformed nuclei in a given mass region have the same VMI core, and thus essentially no alignment until high-N Coriolis effects become significant, seems to explain the present data.

A microscopic approach to the alpha decay problem in deformed nuclei is presented. The nuclear wave functions are calculated in the frame of the Nilsson+BCS approximation, making use of a realistic deformed mean field. A large configuration space has been employed in the calculation of the formation amplitude while the penetration process has been treated within the WKB approximation. The calculated widths agree with the experimental data within a factor of about 3. Effects due to deformation are also discussed. Applications are presented for Ra, Rn, and Th isotopes.

We study the pairing energy in the ground state of a system of N particles occupying a symmetric two-level model space with a level degeneracy Ω. Assuming a pairing Hamiltonian, we calculate the energies of the projected BCS states, using the exact, the Kamlah, and the Lipkin-Nogami particle number projection methods. We find that conclusions regarding the quality of the BCS approximation as well as various approximate projection methods, drawn from studying the N=Ω case alone, are not valid in the more general N≠Ω case when the pairing interaction is weak.

Excitation functions have been measured for production of isotopes of Th through Fm in bombardments of ${}_{}{}^{248}{}_{}{}^{}\mathrm{Cm}$ with 231- to 323-MeV ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ca}$ ions and for the production of isotopes of Th through Cm in bombardments of ${}_{}{}^{248}{}_{}{}^{}\mathrm{Cm}$ with 230- to 291-MeV ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ ions, respectively, using radiochemical methods. Upper production cross section limits were established for nuclides that were not positively detected. The experimental data were compared with the results of previous reaction studies in the systems ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$${+}^{248}$Cm and ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$${+}^{248}$Cm. The half-widths of the Gaussian isotopic distributions were about 2.5 mass numbers for above-target elements and 5 to 5.5 mass numbers for below-target elements in all three systems. The majority of the cross section for the production of above-target nuclides was assigned to predominantly quasielastic reactions, whereas below-target nuclides were formed in deeply inelastic and asymmetric quasifission reactions. The maxima of the isotopic distributions were shown by others to closely follow the minimum of the potential energy surface in experiments with ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$, whereas in reactions with ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ and ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ca}$ we found that a transfer of 4 to 5 protons in either direction was required to reach the minimum in potential energy.

The different neutron numbers of ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ca}$, and ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$ are only partly reflected in the target-like reaction products. Based on a simple model, excitation energies and the maxima of the excitation functions were calculated and compared with the actual data. The yields for production of the below-target elements Th, U, and Pu were found to be two orders of magnitude smaller in the reaction of ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ with ${}_{}{}^{248}{}_{}{}^{}\mathrm{Cm}$ than with ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$. The differences for production of above-target elements were largest between the reactions of ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ca}$ and ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$ ions with ${}_{}{}^{248}{}_{}{}^{}\mathrm{Cm}$. Differences in below-target yields have been attributed either to losses of reaction products due to prompt fission, and/or to dynamic effects due to fusion hindrance. The data for above-target elements seem to confirm the presence of a strong isospin driving force, which in combination with favorable reaction energies results in surprisingly high yields in reactions with ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ca}$ projectiles.

The results of momentum distribution measurements at 0° for projectile-like fragments produced by several intermediate-energy beams and separated using the A1200 beam-analysis device are described. The most detailed measurements were performed for neutron-rich fragments from the reaction of ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ (E/A=80 MeV) projectiles with ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ and ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$ targets. The analysis of the centroids and widths of the parallel momentum distributions of the fragments indicated that no ‘‘pure’’ fragmentation occurs, but rather, along with fragmentation, direct stripping and/or pickup channels contribute significantly to the production mechanism, especially for fragments close in mass to the projectile. Apart from nucleon-removal products, nuclei with a net number of nucleons picked up from the target were observed with momentum distributions peaked at velocities considerably lower than that of the beam. These distributions are consistent with momentum conservation and the previously established feature of lower energy transfer reactions that the excitation energy is preferentially given to the nucleon acceptor.

Angular distributions for elastic and inelastic proton transfer in the ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}$${+}^{12}$C system were measured at the incident ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ laboratory energy of E=344.5 MeV. From a distorted-wave Born approximation analysis, proton spectroscopic factors in ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ were extracted and compared with values obtained previously at lower energies. Contributions from two-step processes were taken into account in the analysis.

Excitation functions were measured radiochemically for the ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ti}$(n,α${)}^{45}$Ca and ${}_{}{}^{50}{}_{}{}^{}\mathrm{Ti}$(n,α${)}^{47}$Ca reactions over the neutron energy range of 12.6 to 19.6 MeV. Use was made of low-level anticoincidence ${\mathrm{\beta }}^{\mathrm{-}}$ counting in the radioactivity measurement of ${}_{}{}^{45}{}_{}{}^{}\mathrm{Ca}$ and of high-resolution γ-ray spectroscopy in the case of ${}_{}{}^{47}{}_{}{}^{}\mathrm{Ca}$. Statistical model calculations taking into account preequilibrium effects described the proton emission well; the calculated ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ emission results were, however, consistently lower than the experimental data, both as regards emission spectrum and excitation function. Inclusion of direct three-nucleon pickup component in the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ emission calculation improved the agreement between theory and experiment.

Experimental results are presented on the charge, velocity, and angular distributions of intermediate mass fragments (IMFs) for the reaction Fe+Au at bombarding energies of 50 and 100 MeV/nucleon. Results are compared to the quantum molecular dynamics (QMD) model and a modified QMD which includes a Pauli potential and follows the subsequent statistical decay of excited reaction products. The more complete model gives a good representation of the data and suggests that the major source of IMFs at large angles is due to multifragmentation of the target residue.

The disappearance of directed, collective nuclear motion (‘‘flow’’) away from the interaction region of heavy-ion collisions has been observed using the Lawrence Berkeley Laboratory Streamer Chamber. We find that flow vanishes at a beam energy near 50 MeV/nucleon for the ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$${+}^{139}$La system and near 60 MeV/nucleon for the ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$${+}^{93}$Nb system. The disappearance of flow may be understood as resulting from a balance between attractive and repulsive scattering strengths. Full calculations with the Boltzmann-Uehling-Uhlenbeck model show that the disappearance of flow is sensitive to the assumed nuclear equation of state (EOS) and to the in-medium scattering cross section (${\mathrm{\sigma }}_{\mathit{N}\mathit{N}}$). Also, in the ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$${+}^{93}$Nb system, the purely attractive contribution to the reduced flow does not appear to be strongly sensitive to the EOS assumptions.

A formalism calculating the cross sections of intermediate-energy proton direct capture populating continuum states has been developed. The transition amplitude includes two terms corresponding to potential-scattering to potential-scattering transitions and potential-scattering to resonance-scattering transitions, respectively. The model is compared with available experimental data of the ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}$(p,${\gamma }_{19}$${)}^{12}$C reaction, and the results show that within the reasonable parameter limit the direct capture mechanism is able to account for a major feature of the measured data, and, in the present case, the contributions from the two terms are of the same order of magnitudes. The physical significance of the results is discussed.

A general method to evaluate fluctuations of the semiclassical one-body Wigner function is presented both in the equilibrium and nonequilibrium framework. The model is valid far away from critical points, where the Boltzmann-Nordheim-Vlasov equation represents a good approximation of the average Wigner function. A first application of the model in momentum space is shown in comparison with different analytical results. An extension to realistic phase space calculations of heavy ion collisions is straightforward and numerically feasible. In this case, together with fluctations coming from the scattering processes, mean field fluctuations are automatically included. The role of Landau damping is discussed.

We analyze angular momentum effects in heavy-ion-induced fission in terms of the statistical model, including collective effects in the nonadiabatic approach and avoiding all the usual numerical approximations and free parameters but one. We find that the strong increase of the fission probability along with the increasing compound nucleus spin is responsible for several observable effects such as the increase of the fission cross section and the decrease of the multiple-chance fission contribution, with the increase of the projectile mass. It is shown that the fission is particularly sensitive to the fusion cross section and its spin distribution. This feature can be used to determine the latter two from the measured fission cross section.

The average spin of fission fragment at specific mass asymmetry has been obtained as a function of emission angles in the ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ (${\mathrm{\alpha }}_{39.1\mathrm{M}\mathrm{e}\mathrm{V}}$,f) system from radiochemically determined independent isomeric yield ratios of ${}_{}{}^{132}{}_{}{}^{}\mathrm{I}$. The fragment average spin is seen to decrease from 11.2ħ to 6.5ħ with change in emission angle from 90° to 20°, due to the angle-dependent tilting component over and above the statistical wriggling, bending, and twisting components as per the collective mode model. Effects of entrance channel parameters and multichance fission are also discussed.

A multiple-scattering series for describing the quasielastic peak in nucleus-nucleus collisions is derived using the high-energy optical model. The effects of multiple knockout of target nucleons and internal excitation of the projectile are studied and found to be important for large energy loss and momentum transfers in inclusive α${\mathrm{-}}^4$He scattering at 7 GeV/c. An approximate evaluation of higher-order inelastic collision terms is considered for forward-peaked wave functions and is demonstrated to be accurate.

A quasiclassical Pauli potential is used to simulate the Fermi motion of nucleons in a molecular dynamical simulation of heavy ion collisions. The thermostatic properties of a Fermi gas with and without interactions are presented. The inclusion of this Pauli potential into the quantum molecular dynamics (QMD) approach yields a model with well defined fermionic ground states, which is therefore also able to give the excitation energies of the emitted fragments. The deexcitation mechanisms (particle evaporation and multifragmentation) of the new model are investigated. The dynamics of the QMD with Pauli potential is tested by a wide range of comparisons of calculated and experimental double-differential cross sections for inclusive p-induced reactions at incident energies of 80 to 160 MeV. Results at 256 and 800 MeV incident proton energy are presented as predictions for completed experiments which are as yet unpublished.

We examine the essentials of the pion capture reaction (${\mathrm{\pi }}^{\mathrm{-}}$,p) with the pion captured directly into an atomic orbit. The reaction is a promising candidate for the population of the 1s or 2p atomic levels of medium to heavy nuclei. These levels have never been observed, but rather reliable theoretical calculations indicate that they have relatively small widths. One reason for interest in these levels is that they give a direct measurement of the threshold pion-nucleus amplitude, which has a bearing on questions such as chiral-symmetry breaking in the nuclear medium and the anomalously small level shifts and widths of some of the more deeply-bound pionic atoms. The differential cross section for the process is calculated using the distorted-wave impulse approximation. It is found that for medium-mass nuclei and incident pion beams of 20–50 MeV cross sections of the order of microbarns, well within the capability of present meson factories, can be expected. The related process (${\mathrm{\pi }}^{\mathrm{-}}$,n) is also studied.

A detailed study of the mechanism of emission of pions and protons in the forward and backward hemispheres in 4.5A GeV/c silicon-emulsion interactions has been carried out. For this purpose, a random sample comprising 1024 interactions caused by silicon nuclei is analyzed to examine the behavior of the emission characteristics of pions and protons emitted in the forward and backward hemispheres. The values of the forward-backward ratio and the asymmetry parameter as a function of the number of heavily ionizing particles are determined. The behavior of the angular distributions of pions and protons in the backward hemisphere and multiplicity correlations is also investigated. The results yield quite interesting information regarding the mechanism of production of pions and protons in the backward hemisphere.

Inclusive cross sections for high energy interactions at 0.9, 2.3, 3.6, and 13.5 GeV/nucleon of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ with C, CR-39 (${\mathrm{C}}_{12}$${\mathrm{H}}_{18}$${\mathrm{O}}_7$), ${\mathrm{CH}}_2$, Al, Cu, Ag, and Pb targets were measured. The total charge-changing cross sections and partial charge-changing cross sections for the production of fragments with charge Z=6 and Z=7 are compared to previous experiments at 60 and 200 GeV/nucleon. The contributions of Coulomb dissociation to the total cross sections are calculated. Using factorization rules the partial electromagnetic cross sections are separated from the nuclear components. Energy dependence of both components are investigated and discussed.