The angular distributions have been measured for the three-neutron pickup reaction ${(}^3$He, ${}_{}{}^6{}_{}{}^{}\mathrm{He}$) at 74 MeV. The angular distributions measured show a clear dependence on the transferred angular momentum. This feature allows spin-parity assignments, suggesting this reaction to be a useful tool for studying proton-rich nuclei.

The neutron-induced fission cross section of ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$ has been measured from 1 eV to 20 keV using a lead slowing time spectrometer. The cross section was normalized to the ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$(n,f) subthreshold cross section. In the energy region between 1 and 500 eV the fission cross section has a 1/v shape, and has a small peak near 5 keV. By extrapolation of 1/v the thermal fission cross section of 54±6 μb was deduced. The observed 1/v and small-peaked cross sections were interpreted as the fission through the vibrational states in the second well of a triple-humped fission barrier of ${}_{}{}^{233}{}_{}{}^{}\mathrm{Th}$.

Experimental data for the ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$(n,2n${)}^{26}$Al cross section have never been reported in the neutron energy range above 15 MeV, since the detection of the long-lived ${}_{}{}^{26}{}_{}{}^{}\mathrm{Al}$ (half-life of 7.2×${10}^5$ yr) necessitates an intense high-energy neutron source and highly sensitive detection method. We have measured the ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$(n,2n${)}^{26}$Al cross section in the energy range of 14–36 MeV by using a semimonoenergetic neutron beam from the Be(p,n) reaction. The activity of ${}_{}{}^{26}{}_{}{}^{}\mathrm{Al}$ was measured by the accelerator mass spectrometry method and we found that the cross section has a maximum value of 95 mb in the neutron energy range of 20–24 MeV.

Data are presented on the energy and angle dependence of the charge-symmetry superratio R and simple ratios ${\mathrm{r}}_1^{\prime }$ and ${\mathrm{r}}_2^{\prime }$ for ${\mathrm{\pi }}^{\pm }$ elastic scattering from ${\mathrm{H}}^3$ and ${\mathrm{He}}^3$. ${\mathrm{r}}_1^{\prime }$ and ${\mathrm{r}}_2^{\prime }$ were normalized with respect to ${\mathrm{\pi }}^{+}$ d and ${\mathrm{\pi }}^{\mathrm{-}}$ d elastic scattering, which is assumed to have the ratio 1.0. The beam energies are ${\mathrm{T}}_{\mathrm{\pi }}$=142, 180, and 220 MeV, and the scattering angle, ${\mathrm{\theta }}_{\mathrm{L}}$, ranges from 40° to 110°. In all cases measured it is found that R>1, ${\mathrm{r}}_1^{\prime }$≃1, and ${\mathrm{r}}_2^{\prime }$>1. These results provide substantial evidence for charge-symmetry violation. The angular distributions for ${\mathrm{\pi }}^{\pm }$ ${\mathrm{H}}^3$ and ${\mathrm{\pi }}^{\pm }$ ${\mathrm{He}}^3$ elastic scattering also have been measured and comparisons are made with various model calculations. R≡σ(θ)[${\mathrm{\pi }}^{+}$ ${\mathrm{H}}^3$]σ(θ)[${\mathrm{\pi }}^{\mathrm{-}}$ ${\mathrm{H}}^3$]/σ(θ)[${\mathrm{\pi }}^{\mathrm{-}}$ ${\mathrm{He}}^3$]σ(θ)[${\mathrm{\pi }}^{+}$ ${\mathrm{He}}^3$], ${\mathrm{r}}_1^{\prime }$=σ(θ)[${\mathrm{\pi }}^{+}$ ${\mathrm{H}}^3$]σ(θ)[${\mathrm{\pi }}^{\mathrm{-}}$d]/σ(θ)[${\mathrm{\pi }}^{\mathrm{-}}$ ${\mathrm{He}}^3$]σ(θ)[${\mathrm{\pi }}^{+}$d], ${\mathrm{r}}_2^{\prime }$=σ(θ)[${\mathrm{\pi }}^{\mathrm{-}}$ ${\mathrm{H}}^3$]σ(θ)[${\mathrm{\pi }}^{+}$d]/σ(θ)[${\mathrm{\pi }}^{+}$ ${\mathrm{He}}^3$]σ(θ)[${\mathrm{\pi }}^{\mathrm{-}}$d].

The mean and the standard deviation of the prompt gamma-ray multiplicity distribution in spontaneous fission of ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$ have been measured as a function of the charge ratio of the fission fragment pairs. While the variation of the mean multiplicity as a function of charge ratio is found to be nearly structureless, the standard deviation exhibits considerable variations. A statistical model analysis of the data was carried out to determine the contribution of the initial spin distribution widths of the fission fragments to the observed standard deviation of the gamma-ray multiplicity distribution.

The neutron energy spectra and angular distributions have been measured for thick targets of ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$, ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$, and ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ bombarded by 40–60 MeV alpha particles. These data as well as those of other authors have been analyzed in terms of the extended exciton model formalism of nuclear reactions. The model takes into account the emission of neutrons through the single-step direct, multistep direct, multistep compound, and compound-nuclear evaporation processes.

Differential cross sections for the elastic scattering of alpha particles from ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$ have been measured over a wide angular range at a number of energies between 24 and 70 MeV. The present data along with existing data in this energy range have been analyzed using the optical model with both phenomenological and double-folded potentials. The application of the dispersion relation of Mahaux, Ngô, and Satchler allows a reproduction of the observed energy dependence of the real part of the potential. A nearside-farside decomposition of the data clearly reveals large-angle Fraunhöfer oscillations. The inelastic cross sections at 69.5 MeV have also been measured and the deformation lengths obtained from a distorted-wave Born analysis are consistent with values reported in the literature.

The sensitivity of proton-nucleus elastic scattering to different nucleon-nucleon effective interactions is studied within the framework of the nonrelativistic full-folding model. Calculations of the nucleon-nucleus optical potential are made using the free nucleon-nucleon t-matrices generated from the Bonn, Paris, Hamada-Johnston, and Melbourne nucleon-nucleon potentials, whose full off-shell behavior is treated explicitly. Applications are made to p${+}^{40}$Ca elastic scattering at energies of 200, 300, and 400 MeV within the full-folding framework. Calculations using the on-shell tρ model have been made for comparison. Both full-folding and tρ results show comparable sensitivity to the particular choice of effective interaction, demonstrating the importance of a realistic description of the nucleon-nucleon interaction both on and off the energy shell.

In heavy-ion collisions, kaons can be produced from baryon-baryon, meson-baryon, and meson-meson interactions. Simple meson-exchange models are introduced to study kaon production from these processes in the free space. These models are then extended to determine kaon production in hot, dense nuclear matter by taking into account the decreasing hadron masses as a result of the restoration of chiral symmetry and the condensation of kaons. We find that the cross sections for kaon production from all three processes are enhanced. In particular, the effect of decreasing hadron masses on kaon production from the meson-meson annihilation is most significant. In the hydrochemical model for heavy-ion collisions, we demonstrate that the observed enhancement of kaon yield in high-energy heavy-ion collisions can be explained if the medium effect is included.

We extend the same techniques found to be successful in condensed matter physics for deriving Boltzmann transport equations to the relativistic domain to facilitate the study of nonequilibrium phenomena where relativistic effects are important. Although the ensuing equations are discussed in the context of the relativistic heavy-ion system, the discussion is sufficiently general to cover other important physical situations such as those of astrophysical origin. Starting from an arbitrary local quantum field theory, we show how one may construct a Boltzmann transport equation and what the necessary assumptions that go into its construction are. To illustrate these techniques we derive a set of coupled Boltzmann equations with medium-dependent collision terms for relativistic fermions and spin-zero bosons interacting via a Yukawa coupling. We find that the dynamics may be described in terms of the fermion distribution function alone only under the very restrictive condition that the boson fields remain in local equilibrium throughout the collision process. Moreover, we find that one must go beyond the mass-shell constraint to find a physically reasonable boson production mechanism.

Elastic differential, total, and integrated reaction ${\mathrm{\pi }}^{\pm }$${\mathrm{-}}^{40}$Ca cross sections are calculated in a semimicroscopic model for incident energies from 65 to 292 MeV. Kinematical and binding effects, as well as Pauli blocking of Δ decay are calculated exactly on a shell-model basis, whereas shadowing due to multihole channels is represented by means of a phenomenological spreading potential with central and spin-orbit parts. Compared to lighter targets, the central Δ-nucleus potential scales to a very good accuracy with the target mass number. The strength of the potential has smooth energy dependence up to ${\mathit{T}}_{\mathrm{\pi }}$=241 MeV. Below 100 MeV a repulsive S-wave ${\mathrm{\rho }}^2$ term in the optical potential is required in order to fit the experimental angular distribution. At 292 MeV comparison with the measured elastic cross section favors a strongly repulsive spreading potential. The distorted pion wave function is calculated and an interesting focusing effect is observed at low energies. The total ${\mathrm{\pi }}^{\pm }$${\mathrm{-}}^{40}$Ca cross section is partitioned into elastic and reaction parts. Our calculation agrees well with an experimentally extracted ${\mathrm{\pi }}^{+}$${\mathrm{-}}^{40}$Ca elastic-scattering amplitude at θ=0°, but disagrees for ${\mathrm{\pi }}^{\mathrm{-}}$. Finally, a pion ‘‘absorption’’ cross section is calculated and its physical interpretation is discussed.

The spectra of α particles in (n,α) reactions induced on ${}_{}{}^{144,147,149}{}_{}{}^{}\mathrm{Sm}$ by neutrons with energy between ≊12 and 20 MeV are greatly affected by the shell structure of the target nucleus. Semimicroscopical calculations made in the framework of the pickup model, assuming dominance of transitions to neutron-hole states of the residual nuclei and the homology of high-energy states of ${}_{}{}^{144,146}{}_{}{}^{}\mathrm{Nd}$ excited in the reactions induced on the nonmagic ${}_{}{}^{147,149}{}_{}{}^{}\mathrm{Sm}$ isotopes with the low-energy states of ${}_{}{}^{141}{}_{}{}^{}\mathrm{Nd}$ excited in the reaction on the magic ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$ isotope, reproduce satisfactorily the data.

We study the reaction e+A→e’+(A${\mathrm{\pi }}^{\mathrm{-}}$) with the ${\mathrm{\pi }}^{\mathrm{-}}$ bound in the nucleus as a means of producing deeply bound pionic states of heavy nuclei so far unobserved. Although the cross sections found can be rather large, they are overwhelmed by the background from the inclusive (e,e’) reaction, which makes the reaction not well suited for the investigation of these pionic states. However, the ratio of signal to background is much bigger in light nuclei and the reaction could be used to observe pionic states of unstable light nuclei, provided the resolution in the beam and detectors is of the order of the width of the pionic state.

In this paper, the differential cross sections for elastic scattering from ${}_{}{}^{39}{}_{}{}^{}\mathrm{K}$ and ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ are calculated utilizing the optical potential. The importance of the virtual excitation of low-lying vibrational states in predicting the differential cross section is discussed.

We examine the effect of particle compositeness on the importance of ‘‘Z diagrams’’, i.e., virtual particle-antiparticle states appearing in scattering processes. The examples of positronium in QED, and of the nucleon in the QCD-based quark model, are discussed in detail. Generally, if the composite particle consists of N constituents, its Z-diagram amplitude involves creation and annihilation of N constituent-anticonstituent pairs. This process (which we assume to be governed by Coulomb-type interactions with the ‘‘fine structure constant’’ α) must take place in a small volume ∼1/${\mathit{M}}^3$, where M is the particle’s mass; an additional suppression is due to the fact that the created system is electrically (or color) neutral. The composite particle’s Z-diagram amplitude is then suppressed, compared to that for an elementary particle, by at least a factor ${\mathit{f}}_{\mathit{Z}}$∼(${\mathit{q}}^2$/${\mathit{M}}^2$)[${\mathrm{\alpha }}^2$/(${\mathit{M}}^3$${\mathit{R}}^3$)${]}^{\mathit{N}\mathrm{-}1}$, where q is the momentum transfer to the particle, and R the composite particle’s size. The decoupling of the composite Z diagrams at zero momentum transfer is consistent with low-energy theorems.

Nucleon self-energies from the pion-ring series are studied in the relativistic mean-field theory of linear σ model with the ω meson and the Δ. Near the Fermi surface of nuclear matter, the pion rings generate attractive scalar and vector potentials of 10–15 % of the nucleon mass. These strongly energy-dependent potentials cause the nucleons to have a significant probability to be in a collective N-hole or Δ-hole configuration.

The modification of the internal structure of nucleons inside the nucleus is investigated within the context of a constituent quark model, in which quarks interact forming bound clusters that act as nucleons. The elastic form factor, the momentum distribution, the correlation function, and the Coulomb sum rule are calculated. The contribution to these structure functions arising from nucleon degrees of freedom is identified by means of an impulse approximation, in which the quark structure of nucleons is assumed to be unaffected by other nucleons, and the dynamics of nucleons is given by an effective theory, extracted from our quark model. The effect of the modification of the nucleon is found to be noticeable on the elastic form factor at large momentum transfer, and on the Coulomb sum rule. A cluster approximation is also used to study the extent to which these effects are due to exchange of quarks.

We have improved a simple and rapid method of calculating expectation values of operators in states of good angular momentum projected from a hedgehog baryon state introduced by Birse et al. We have included the contributions of quantum mesons, while in the original method only classical meson fields were included. The method has been applied to models where the mean-field approximation does not include loop terms. Hence, for reasons of consistency, contributions of quantum loops to the matrix elements have been dropped. The symmetry of the hedgehog state under grand reversal (the combined operation of time reversal and ${\mathit{e}}_2^{\mathit{i}\mathrm{\pi }\mathbf{I}\mathrm{^}}$, where I^ is the isospin operator) introduces remarkable simplification in the calculation of matrix elements of operators which do not contain time derivatives of meson fields. The quantum meson contributions turn out to be 3/2/〈B‖J${\mathrm{^}}^2$‖B〉 times the classical meson-field contributions, with ‖B〉 being the hedgehog state. Such operators are encountered in the calculation of nucleon magnetic moments, ${\mathit{g}}_{\mathit{A}}$(0) and ${\mathit{g}}_{\mathrm{\pi }\mathit{N}\mathit{N}}$(0)/2M. Calculation of charge radii involves operators containing time derivatives of meson fields and requires the knowledge of wave functions of quantum mesons. Proper nonperturbative treatment, even though at the tree level, requires that these wave functions describe the motion of the mesons in the potential generated by the baryon. Fortunately, because of the neglect of the loop terms, one needs only the even-parity, grand-spin-1 states which are purely pionic. The Goldberger-Treiman relations, an exact result for the model, serves as a partial test of the method of calculation discussed here. This has been used to demonstrate the remarkable improvement in the results produced by the inclusion of quantum effects of the mesons.

The high-mass dilepton production on nuclear targets observed by the E772 Collaboration is analyzed by the constituent quark model. We show that the constituent quark model even without the nuclear shadowing improvement agrees better with the existing data on nuclear targets not only in the inelastic-scattering process, but also in the Drell-Yan process. Further, the QCD improvement for the partonic shadowing model is made. It is found that both the ${\mathit{Q}}^2$ dependence of the shadowing strength and the momentum loss due to the annihilation of the shadowed sea quarks evidently depress the distributions of nuclear sea components in the antishadowing region.

The neutron-capture cross sections for ${}_{}{}^{86,87}{}_{}{}^{}\mathrm{Sr}$ have been measured by the neutron-time-of-flight technique from 100 eV to 1 MeV. Maxwellian-averaged capture cross sections have been determined for stellar temperatures ranging from kT=10 to 100 keV. At kT=30 keV we obtain 70±4 and 97±5 mb for ${}_{}{}^{86}{}_{}{}^{}\mathrm{Sr}$ and ${}_{}{}^{87}{}_{}{}^{}\mathrm{Sr}$, respectively. These cross sections are combined with other existing data to deduce values for the stellar neutron density and temperature during s-process nucleosynthesis and to analyze the viability of the ${}_{}{}^{87}{}_{}{}^{}\mathrm{-}_{}^{87}{}_{}{}^{}$Sr chronometric pair as a means to determine the age of the Galaxy.