It is suggested that the inclusion of the virtual excitation of the soft giant dipole (pygmy) resonance in the calculation of the cross section for very neutron-rich radioactive beam-induced fusion reactions may enhance the formation probability of the heavy compound nucleus produced at low excitation energy.

A set of coupled transport equations for the phase-space distribution functions of nucleons, deltas, and pions is solved with the test particle method to study pion production in relativistic heavy ion collisions. The experimentally observed concave shape of the pion spectra is well reproduced. The mechanism that causes the concave shape of the pion spectra is found to be due to the different contributions of the delta resonance produced during the early and the late stages of the heavy ion collision and due to the energy dependence of the pion and delta absorption cross sections. The dependence of the shape of the pion spectra on beam energy, target and projectile mass, and impact parameter is also studied. An approximate scaling function for the shape parameter of the pion spectra is found.

We present theoretical calculations for data pertaining to Ne on NaF collisions at 45 MeV per nucleon. The calculations use the Boltzmann-Uehling-Uhlenbeck model, modified to incorporate fluctuations. The recent numerical technique developed by Lenk and Pandharipande is applied to test particle propagation in the nuclear mean field. We find that the agreement with experimental data ranges from good to very good.

Results of Glauber model calculations of elastic and inelastic scattering from ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$, and ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$ of pions having energy of 300 to 1200 MeV are presented. Experimental πN phase shifts including l=0 through 5 are used in the calculation. The f wave is important above 300 MeV and the g and h wave above 900 MeV. Effects of spin flip are included. The model reasonably reproduces the 800 MeV/c data of Marlow although the inelastic scattering of the $2^{+}$ of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ requires an enhancement of the quadrupole component consistent with the effective charge. The previously observed anomaly in ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ in which a much larger oscillator parameter was required in pion scattering than in electron scattering disappears at higher energy. The σ(${\mathrm{\pi }}^{\mathrm{-}}$n) to σ(${\mathrm{\pi }}^{+}$n) ratio is found to be appreciably different from expectations based on pion scattering from free nucleons.

The geometric scattering theory and the Wentzel-Kramers-Brillouin (WKB) approximation are used to derive explicit expressions for the dynamic polarization potential induced by Coulomb excitation in heavy-ion collisions involving strongly deformed targets. We build two phase-equivalent potentials with very different radial and angular-momentum behaviors, which are discussed in the context of polarization potentials obtained previously within different frameworks. This correspondence provides a recipe for approximately correcting the deficiencies of the geometric scattering approach, which tends to overemphasize the effects of Coulomb coupling.

We consider a nonlocal quantum field theory, which can be used for the description of a composite particle, such as the nucleon interacting with its virtual pion field. Assuming a global symmetry of the theory, we discuss how to find the corresponding conserved currents. For the case of a U(1) symmetry, we then examine the conditions for second quantization and derive a general Ward-Takahashi identity. The formalism is then applied to the electromagnetic interaction.

The parity- and isospin-forbidden ${\mathrm{\alpha }}_0$ decay from ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}_{}^{\mathrm{*}}{}_{}{}^{}$(${\mathit{J}}^{\mathrm{\pi }}$=$2^{\mathrm{-}}$, T=1, ${\mathit{E}}_{\mathit{x}}$=12.9686 MeV) to ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(g.s.) has been investigated theoretically. Considering various strong and weak interaction models the longitudinal ${\mathit{A}}_{\mathit{L}}$ and the irregular transverse ${\mathit{A}}_{\mathit{b}}$ analyzing powers of the reaction ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$(p→,${\mathrm{\alpha }}_0$${)}^{12}$C have been calculated in the energy range of the $2^{\mathrm{-}}$ resonance in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}_{}^{\mathrm{*}}{}_{}{}^{}$. Energy anomalies for the expected interference effects, relevant for experiments, have been found to be ${\mathit{A}}_{\mathit{L}}$=1.1×${10}^{\mathrm{-}5}$ and ${\mathit{A}}_{\mathit{b}}$=0.9×${10}^{\mathrm{-}5}$ at θ=90° and ${\mathit{A}}_{\mathit{L}}$=1.4×${10}^{\mathrm{-}5}$ and ${\mathit{A}}_{\mathit{b}}$=0.2×${10}^{\mathrm{-}5}$ at θ=150° based on a conservative value of 0.1 eV for the parity-nonconservation matrix element. A proposal for an experimental investigation is sketched.

Faddeev-type configuration-space three-body scattering equations are solved for selected two-body- and two-body-plus-three-body-potential model Hamiltonians to obtain absolute predictions for the nucleon-deuteron scattering lengths ${}_{}{}^2{}_{}{}^{}$${\mathit{a}}_{\mathit{n}\mathit{d}}$,${}^4$${\mathit{a}}_{\mathit{n}\mathit{d}}$, ${}_{}{}^2{}_{}{}^{}$${\mathit{a}}_{\mathit{p}\mathit{d}}$, and ${}_{}{}^4{}_{}{}^{}$${\mathit{a}}_{\mathit{p}\mathit{d}}$. Convergence for these zero-energy scattering parameters as a function of the number of NN-potential partial waves included in the calculation is attained for the first time. Kohn variational estimates provide a measure of the precision of our numerical results. The nd predictions agree well with the measured values. The pd predictions differ substantially from accepted experimental values which are extrapolated from measurements made above 400 keV.

Lower limits on the mean lives of the charge-nonconserving (CNC) processes, ${}_{}{}^{127}{}_{}{}^{}\mathrm{I}$+${\mathit{e}}_{\mathit{K}}$${\to }^{127}$${\mathrm{I}}^{\mathrm{*}}$+ν, leading to the first (second) excited state of ${}_{}{}^{127}{}_{}{}^{}\mathrm{I}$, were obtained as τ>0.58(0.56)×${10}^{23}$ yr by searching for the γ decay from the first (second) excited state of ${}_{}{}^{127}{}_{}{}^{}\mathrm{I}$. Upper limits on the ratios of the CNC strengths to the charge-conserving ones through the weak boson and photon mediating processes are obtained as ${\mathrm{\epsilon }}_{\mathit{W}}^2$<11×${10}^{\mathrm{-}25}$ and ${\mathrm{\epsilon }}_{\gamma }^2$<4.8×${10}^{\mathrm{-}40}$.

The partial neutron capture cross section of ${}_{}{}^{175}{}_{}{}^{}\mathrm{Lu}$ to the isomer ${}_{}{}^{176}{}_{}{}^{}\mathrm{Lu}_{}^{\mathit{m}}{}_{}{}^{}$ has been measured at kT=25 keV via the activation technique. Systematic uncertainties were carefully evaluated by two independent methods for determination of the induced activities and by variation of the relevant experimental parameters. The final cross section of 1135±30 mb was derived from six different activations. With this result, the production of the long-lived ground state ${}_{}{}^{176}{}_{}{}^{}\mathrm{Lu}_{}^{\mathit{g}}{}_{}{}^{}$ (${\mathit{t}}_{1/2}$=41 Gyr) by s process neutron captures would not be sufficient to account even for the observed lutetium abundance. Consequently, other mechanisms, e.g., thermally induced transitions from the isomer to the ground state must have enhanced the yield of ${}_{}{}^{176}{}_{}{}^{}\mathrm{Lu}_{}^{\mathit{g}}{}_{}{}^{}$ during the s process.

The back-angle yields of the oxygen and carbon particles from the ${}_{}{}^{31}{}_{}{}^{}\mathrm{P}$${+}^{16}$O reaction have been measured at ${\mathit{E}}_{\mathrm{lab}}$${(}^{31}$P)=135.6 MeV by using reverse kinematics. Comparison with similar data for the ${}_{}{}^{35}{}_{}{}^{}\mathrm{Cl}$${+}^{12}$C reaction forming the same compound nucleus at the same excitation energy and with a very similar spin distribution shows very small entrance-channel dependence of back-angle yields. These results are in contrast to a similar study of the reactions ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$${+}^{12}$C and ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$${+}^{16}$O. It is evident that the oxygen and carbon yields from the ${}_{}{}^{31}{}_{}{}^{}\mathrm{P}$${+}^{16}$O and ${}_{}{}^{35}{}_{}{}^{}\mathrm{Cl}$${+}^{12}$C reactions have a predominantly compound nucleus origin in contrast to those from the ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$${+}^{12}$C and ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$${+}^{16}$O reactions. Possible connection of this nonequilibrium entrance channel dependence with the presence of nuclear molecular resonances is discussed.

We have deduced the coherent scattering amplitude of ${}_{}{}^{46}{}_{}{}^{}\mathrm{Ca}$ as 3.55±0.21 fm by measuring the neutron-diffraction patterns of calcite enriched to 32% in ${}_{}{}^{46}{}_{}{}^{}\mathrm{Ca}$. We have employed this value in calculating the direct-capture cross sections of the primary electric-dipole γ transitions in ${}_{}{}^{47}{}_{}{}^{}\mathrm{Ca}$ using optical-model potentials with physically realistic parameters. The calculated cross sections agree reasonably well with measurements showing that thermal-neutron capture by ${}_{}{}^{46}{}_{}{}^{}\mathrm{Ca}$ is controlled largely by a simple direct mechanism.

The breakup of ${}_{}{}^{25}{}_{}{}^{}\mathrm{Mg}$ has been studied using a beam of 180 MeV ${}_{}{}^{25}{}_{}{}^{}\mathrm{Mg}$ with a ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ target. The main reaction channels investigated are the near-symmetric breakup into ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${+}^{13}$C and symmetric breakup into ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${+}^{12}$C following neutron transfer to the target. The symmetric breakup into two ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ nuclei is observed to occur from states at high excitation in ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$. The yield is, however, about two orders of magnitude smaller than that observed in a similar experiment using a ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ beam.

An average resonance capture study of ${}_{}{}^{124}{}_{}{}^{}\mathrm{Te}$ was carried out by bombarding samples of ${}_{}{}^{123}{}_{}{}^{}\mathrm{Te}$ with 2- and 24-keV neutron beams. The complete set of $0^{+}$, $1^{+}$, $2^{+}$ states disclosed by the experiment is consistent with the data of Robinson, Hamilton, and Snelling, demonstrating that there are no undetected states of these spins (especially $0^{+}$ states) below about 2500 keV. In particular, proposed $0^{+}$ levels at 1156 and 1290 keV are ruled out. This impacts various attempted interpretations in terms of intruder states, U(5), and O(6) symmetries.

It is shown that quantum hadrodynamics as a formal field theory has a much richer infrared structure at high energies than previously realized. This arises from large vertex corrections due to vector meson exchange. By selectively summing all leading and nonleading logarithms, it is demonstrated that the infrared structure of the theory may in fact overwhelm the corresponding ultraviolet divergences arising from the Landau poles. Since competing infinites can thus be found, caution is urged in the use of any nonperturbative summation, especially one that emphasizes merely one sector of the theory.

If a Goldstone symmetry is also explicitly broken, amplitudes are expected to be nonanalytical functions of the symmetry-breaking parameter and, consequently, of the induced mass of the Goldstone bosons. It is argued that the low-energy theorem for pion photoproduction on a nucleon, which yields the leading terms of the amplitude expanded in the physical pion-nucleon mass ratio, is not affected by this mechanism.

The energy dependence of the total cross section for πd→pp below 1 GeV pion laboratory kinetic energy is described using a form similar to a previous parametrization of that energy dependence below 330 MeV. Measured angular distributions for the reaction below 1 GeV were fitted using a Legendre polynomial expansion. The energy dependences of the coefficients of the expansion have been fitted with a semiempirical form, giving a simple parametrization for the energy dependence of the differential cross sections for the reaction below 1 GeV.

Accuracy and stability of single-particle resonance parameters under changes of a ‘‘resonance wave function’’ are examined in the context of a projection technique. Implications for their use in nuclear structure calculations are discussed.

Relativistic heavy ion charge-exchange reactions yield fragments (ΔZ=+1) whose longitudinal momentum distributions are downshifted by larger values than those associated with the remaining fragments (ΔZ=-1,-2, . . .). Kinematics alone cannot account for the observed downshifts; therefore, an additional contribution from collision dynamics must be included. In this work, an optical model description of collision momentum transfer is used to estimate the additional dynamical momentum downshift. Good agreement between theoretical estimates and experimental data is obtained.

In the framework of an l-window model for complete fusion reactions within a sharp cutoff approximation, the problem of the maximum excitation energy which can be deposited in a compound nucleus is discussed. Predictions about the spin distribution of the compound nucleus are compared with the conclusions of a recent analysis of the ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$${+}^{28}$Si fusion reaction.