Angular distributions of fast neutrons from the (γ,n) reactions on ${}_{}{}^{159}{}_{}{}^{}\mathrm{Tb}$ and ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$ were measured. Gamma sources in the 7–11.4 MeV range were obtained from (n,γ) reactions using thermal neu- trons. Pronounced asymmetries around 90° were observed for the angular distributions of photoneu- trons leading to the ground and a few excited states, in both the spherical ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$ and the deformed ${}_{}{}^{159}{}_{}{}^{}\mathrm{Tb}$ nuclei. These asymmetries indicate strong and similar E1-E2 interference effects in the two nuclei. The direct-semidirect model was modified to be used for target nuclei with one proton outside an even-even core. From a detailed comparison of the data with calculations using the modified direct-semidirect model, the contributions of different partial waves are estimated. Contributions of the compound nucleus process are included, and are shown to affect to some extent the calculated angular distribution’s energy dependence.

Measurements of alpha spectra in the (n, α) reactions induced on ${}_{}{}^{90}{}_{}{}^{}$,91Zr at 14.3 and 18.15 MeV incident neutron energy are presented. A microscopic calculation of these spectra has been made using both pick-up and knock-on theories, and in both cases only one overall normalizing factor, which is the same for the two target nuclei and incident energies and all the considered transitions, appears as a free parameter in the calculation. Pick-up calculations provide a very satisfactory reproduction of the data. Knock-on calculations reproduce many qualitative features of the measured spectra, but do not allow a fully satisfactory reproduction of them. While the results obtained do not exclude knock-on contributions to these reactions, their presence is not established.

Neutron scattering differential cross sections were measured for ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$, ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$, and ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$ at 14.1 MeV. Optical model calculations were performed using the coupled-channel formalism for deformed nuclei as given by Tamura. Several microscopic and phenomenological optical model potentials were tested for these heavy nuclei: (i) a folding optical model potential using the microscopic nucleon-nucleon effective interaction of Jeukenne, Lejeune, and Mahaux with deformed nuclear density distributions (these calculations are addressed in the text as semimicroscopic optical model potentials), (ii) global phenomenological optical model potentials optimized for the actinide region, and (iii) neutron potentials derived from 35 MeV proton optical potentials using the Lane formalism. The total cross sections calculated from these optical model potentials at 14.1 MeV are also compared with measurements in the literature. The semimicroscopic calculations reproduce reasonably well the measured angular distributions with only two free parameters used to optimize fits to the data. The calculations carried out with optical potentials inferred from proton data give good agreement with the neutron data, an agreement which is similar to that between calculational results using neutron global potentials optimized for this mass region and the measured data.

The real part of the optical-model potentials for neutrons and protons with energy E=11 MeV and for targets with mass numbers 40≤A≤76 are calculated from two versions of a nuclear matter approach. The theoretical results are compared with compilations of empirical properties associated with phenomenological optical-model potentials for protons with energy 9≤E≤12 MeV and for neutrons with energy 8≤E≤15 MeV. Particular attention is paid to the difference between the neutron and proton optical potentials, to the dependence of the theoretical results on the density distributions of the protons and of the neutrons in the target nucleus, and to the role played by the density dependence of the effective interaction. Good agreement between calculated and empirical properties is obtained when one uses the neutron and proton density distributions of the self-consistent extended Thomas-Fermi model, and a recent version of the nuclear matter approach. The root mean square radius of the proton optical potential is larger than that of the neutron potential; it is shown that this has a twofold origin, namely the existence of a neutron excess in the surface tail on the one hand, and the difference between the density dependence of the isoscalar and isovector components of the effective interaction on the other hand.

The real part of the optical-model potential for 35 MeV protons on target with mass number 10<A<80 is calculated from several versions of the nuclear matter approach. All these versions yield good agreement with the dependence upon A of the volume integral of the empirical optical potential, but only several of these versions reproduce the dependence upon A of its root mean square radius. The versions which predict a sizable increase of the potential radius and diffuseness with increasing A are those which take into account the inaccuracy of the nuclear matter approach in the tail of the potential surface. The agreement with the empirical values of the potential radius and diffuseness is best when one introduces between the radial shapes of the proton and neutron density distributions a difference similar to the one predicted by recent theoretical models. The potential radius and diffuseness are also calculated for 11 MeV protons.

Level densities and primary E1 and M1 transition strengths recently obtained from extensive studies in fifteen light and medium odd-odd nuclei (20≤A≤80) are analyzed. The level densities are parametrized in terms of the constant temperature Fermi gas and the Bethe formulae; both models provide equally good fits to the experimental results. Empirical relationships between their parameters and simple expressions for the extension of level densities and γ-ray strength functions into the region of noncomplete level schemes are proposed. For nuclei with A≳46 the E1 strengths agree very well with the predictions of the electric giant dipole resonance model; for the lighter nuclei the E1 strengths are stronger than the giant dipole resonance prediction because of direct neutron capture. The observed mass and energy dependence of M1 strengths seems to indicate some influence of the magnetic giant dipole resonance; however, the M1 spectra are strongly structured by nonstatistical effects, in particular in the sd shell.

From a compilation of the real parts of phenomenological optical-model potentials which yield very good fits to the differential cross sections, it is concluded that in the cases of protons and neutrons on ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ and of protons on ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ the radial shape of the potential varies rapidly with energy for bombarding energies smaller than 20 MeV. The potential half-depth radius decreases with increasing energy, while the surface diffuseness tends to increase with energy. This empirical energy dependence is stronger than the one calculated in the framework of a theoretical nuclear matter approach.

The cross section for emitting high energy gamma rays in heavy-ion collisions is calculated in a model based on the Boltzmann-Uehling-Uhlenbeck equation. The elementary production cross section is assumed to be neutron-proton bremsstrahlung. Comparison is made with experimental data at bombarding energies from 20 to 84 MeV/nucleon. The calculations are found to roughly reproduce the energy spectrum, bombarding energy dependence, and angular distribution. From the numerical analysis we conclude that the production of high-energy γ rays is limited to the very early stage of the collision.

The amplitude of ion-ion scattering, described, e.g., by an optical potential, separates into a ‘‘surface-wave’’ part (which, as shown before, may give rise to resonances) and a ‘‘geometrical-ray’’ part. The amplitude as alternately expressed here by the Wentzel-Kramers-Brillouin approximation resolves into an externally reflected ‘‘barrier wave’’ and into ‘‘internal’’ or ‘‘penetrating rays’’ that undergo an internal reflection together with possible additional multiple reflections. Our numerical calculations show that resonances also occur in the penetrating rays, which take place when a characteristic equation is satisfied. The geometrical meaning of the latter is determined by the optical path length of penetration being an integer multiple of π, plus a 1/2π caustic phase jump, and an extra phase shift due to barrier penetration.

Small angle cross sections for the reactions ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${(}^{16}$O,α${)\mathrm{}}^{28}$Si and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${(}^{16}$O${,}^8$Be${)}^{24}$Mg leading to ground states and first excited states of residual nuclei are reported for $E_{\mathrm{c}.\mathrm{m}.\mathrm{}\mathrm{\sim }12}$ to 20 MeV. Angular distributions are measured for all four exit channels at about forty energies in the neighborhood of resonancelike features. Resonant l values are inferred from both ${\alpha }_0$ and ${}_{}{}^8{}_{}{}^{}$${\mathrm{Be}}_0$ angular distribution and results are compared with other work. The distribution of maxima test shows that cross section maxima in the excitation functions are distributed randomly and that there is a low probability for any resonances in the energy range covered. Statistical model calculations with proper energy level densities and angular momentum conservation reproduce all the general features attributed to heavy-ion resonances.

Excitation functions for fission were measured for ${}_{}{}^{58,64}{}_{}{}^{}\mathrm{Ni}$ beams incident on the even ${}_{}{}^{112-124}{}_{}{}^{}\mathrm{Sn}$ targets at energies extending from well below to about 1.5 times the Coulomb barrier. Fission was identified by kinematic coincidence between fission fragments. Angle integrated fission cross sections were obtained from angular distributions taken at several energies for all systems. From these and the previously measured cross sections for evaporation residues, we obtain the total fusion cross sections and fission probabilities over the energy range $150\lesssim E_{\mathrm{c}.\mathrm{m}.\mathrm{}}\lesssim 240$ MeV. The competition between particle evaporation and fission in the compound nuclei is compared to statistical model calculations. A good description of the data for all 14 systems is achieved with the use of a single set of parameters. The model includes fission barriers with finite range and nuclear diffuseness effects, and partial-wave distributions for fusion that are qualitatively consistent with those from microscopic reaction model calculations. The fusion excitation functions are analyzed in terms of the dynamical fusion model of Swiatecki et al. Within this model we extract new values for the "extra-push" parameters.

Elastic scattering angular distributions for ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$, and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ were measured for projectile energies between 10 and 35 MeV/nucleon. Total reaction cross sections were extracted by an optical model analysis and compared to the prediction of the Glauber model. This comparison suggests that the nucleus-nucleus total reaction cross section at intermediate and high energies is governed by the nucleon-nucleon cross section.

The interaction cross sections of medium and high energy nucleus-nucleus scattering are studied with the Glauber model and Hartree-Fock-type variational calculation. The interaction cross sections so obtained nicely satisfy the additivity relationship, which in turn suggests the existence of a nuclear interaction radius in nucleus-nucleus scattering. With the calculated interaction cross sections, the nuclear interaction mean free path of a high energy nucleus in emulsion is studied, and the results agree very well with experimental data. It is found that the interaction radius of the projectile nucleus can also be determined from an emulsion experiment.

The reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${(}^{19}$F,α${)}^{27}$Al was studied over the same energy range, $E_{\mathrm{c}.\mathrm{m}.\mathrm{}=16\mathrm{}–22}$ MeV, where previous elastic and inelastic measurements were found to exhibit large back angle oscillatory motion. Excitation functions and angular distributions were measured for a number of alpha particle groups. These excitation functions do not show a strong correlation among themselves, nor do they correlate strongly with the elastic and inelastic scattering data. The angular distributions for two resolved states and two unresolved groups have the same average slope without any discernible pattern. Hauser-Feshbach calculations are structureless and the calculated angular distributions have a much smaller slope than the data. Overall, we conclude that within the present study it has not been possible to identify unequivocally any resonances in the ${}_{}{}^{12}{}_{}{}^{}$C+ ${}_{}{}^{19}{}_{}{}^{}$F system.

Assuming the sequential decay of particle unstable primary fragments for light fragment production and the direct two body decay for heavy fragment production, we analyze the apparent temperature (the inverse logarithmic slope of kinetic energy distributions) of fragments in the breakup of spectator residues. Unlike other models it is independent of the projectile energy. Mass numbers obtained for the particle unstable primary fragments in the reactions of projectile proton and targets of Kr, Ag, and Xe are in the range 14–18.

High energy photons may be produced in nuclear reactions by several mechanisms, including bremsstrahlung from the potential field or from nucleon-nucleon collisions. Using infinite and semi-infinite nuclear matter approximations, we obtain simple expressions for the rates. Nucleon-nucleon collisions provide the more important mechanism for both proton-induced and heavy-ion induced reactions, except for the highest energy photons. The photon cross section calculated with a zero range np interaction agrees well with measurements on proton-induced reactions. For heavy-ion reactions, the initial np collisions only account for a third of the measured cross section. The disagreement may be due to an inadequacy of the infinite matter or the zero range approximations, or it may be that multiple collisions are important.

The photonuclear cross sections for ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{234}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{237}{}_{}{}^{}\mathrm{Np}$, and ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$ have been measured from threshold up to 18 MeV. The source of radiation was the monoenergetic photon beam from the annihilation in flight of fast positrons. The branching among the neutron-producing reaction channels was determined by measuring the photofission prompt neutron multiplicities ν${¯}_p$. One interesting result is the complete absence of any (γ,2n) cross section for ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$ and ${}_{}{}^{234}{}_{}{}^{}\mathrm{U}$. The values of ν${¯}_p$(E) for ${}_{}{}^{234}{}_{}{}^{}\mathrm{U}$ agree with those measured with neutrons incident on ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$. The parameters of the giant dipole resonance deduced from the total photonuclear cross sections show that these nuclei have large static deformations, as expected. The integrated photofission cross sections are large (as are the absolute fission probabilities), and account for 60% to 80% of the total photonuclear absorption strength.

Fission barriers calculated from the rotating liquid drop model with finite-range corrections based on scaling of the nonrotating finite-range model of Krappe et al. are compared with results explicitly calculated for rotating systems with the finite-range effect included. The scaling method is shown to give excellent agreement with the calculated barriers, confirming earlier conclusions on effective fission barrier heights based on the scaling procedure.

The reaction ${}_{}{}^2{}_{}{}^{}\mathrm{H}$(γ,pp)${\pi }^{\mathrm{-}}$ has been studied using a monochromatic photon facility, for photon energies between 345 and 465 MeV, using two proton range telescopes. Previously reported data have been reanalyzed, bringing to bear new information. Neither result shows any evidence of a dibaryon resonance as previously reported. Both are consistent with the same conventional rescattering calculations.

Neutron spectra identified by final nuclear states have been measured for stopped ${\pi }^{\mathrm{-}}$ capture in ${}_{}{}^{165}{}_{}{}^{}\mathrm{Ho}$. Neutron time of flight, with a resolution of 20% at 100 MeV, was collected in coincidence with the rotational γ-ray transitions in the even-even Dy isotopes. The inclusive spectrum was also measured in coincidence with pionic x rays, and agrees with previous singles measurements. The neutron spectra for individual final states show sharp cutoffs at characteristic energies, and, in some cases, the structure in the high energy component of the spectra is resolved. A Monte Carlo program based on the hybrid exciton model was developed, suitable for computing the inclusive and exclusive neutron spectra. The program gives a good fit to the measured inclusive spectrum. A different set of model parameters had to be used to reproduce the features of the spectra identified by the final nuclear states, and the fit was less satisfactory, indicating the need for an improvement in the preequilibrium approach which was not apparent in the past application to the inclusive spectra.