The photofission cross section of ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$ was measured in the 5.8–12 MeV energy range with an average photon energy resolution of 600 eV. Intermediate structure was observed at 5.91, 5.97, and 6.31 MeV. The experimental fission probability and various properties of the intermediate structure were compared with calculated values based on a double-humped fission barrier as well as a triple-humped one. The results favor, though not decisively, the presence of a shallow third well in the barrier. Certain features of both barriers, a rather high first hump and a deep secondary well, are quite different from those predicted by current theoretical barrier calculations.

The pionic fusion reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${(}^3$He, ${\pi }^{+}$${)}^{15}$N has been observed at 181.4 MeV bombarding energy by detection of the ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$ recoil ions using magnetic, time-of-flight, and energy loss analysis. The angle-integrated cross section for population of a broad group of unresolved ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$ excited states in the 6.5–10.5 MeV excitation energy range is 1.3±0.3 nb. The angular distribution of the pions corresponding to this group of excited states is fairly isotropic, with perhaps some peaking in the forward direction. The cross section for population of the ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$ ground state is ≤0.07 nb.

The full polarization structure of the reaction π+N→π+N+γ is established. In the case of a coplanar geometry the number of reaction amplitudes reduces by a factor of 2; hence this geometry is strongly recommended. In that case the polarization structure is formally identical to that of pion photoproduction. The best formalism for this case is one in which the nucleons are described in the transversity frame and the photon in the helicity frame. The experimental program needed to determine the reaction amplitudes is analyzed, and sets of experiments which determine the amplitudes are given. Although the correspondence between the reaction amplitudes of this process and those for off-shell pion-nucleon elastic scattering cannot be made model independently, it can be made for any particular model which describes the way the off-shell process is embedded in the bremsstrahlung reaction.

Surface response model results for quasielastic nucleon-nucleus scattering are compared to recent intermediate energy (p,p’) spectra. The energy and target dependences of the quasielastic peak, as well as the dependence on momentum transfer, are quite accurately described by this model. Discrepancies at large energy and momentum transfers are ascribed to multistep processes, and they become more significant at lower beam energies. Shell structures of finite nuclei, which are not contained in the model, are the main source of the discrepancies at small momentum transfers.

The relativistic three-body equations for the bound-state problem proposed by the authors are solved for the πNN system, in particular for the states with total isospin zero and two. In the case of isospin zero, only one bound state is found which corresponds precisely to the deuteron and whose wave function is quite similar to those of phenomenological models. In the case of isospin two, the most favorable configuration to possess a bound state is with total angular momentum two and positive space parity. There is experimental evidence, however, that the state is unbound; that means that it will appear as a resonance of spin two and isospin two which we call the 4,4 resonance since it is the analog to the well-known 3,3 resonance in the πN system which has spin (3/2) and isospin (3/2). .AE

500 MeV p→+p elastic and quasielastic, and p→+n quasielastic, analyzing powers ($A_y$) and spin-rotation-depolarization parameters ($D_{\mathrm{SS}}$, $D_{\mathrm{SL}}$, $D_{\mathrm{LS}}$, $D_{\mathrm{LL}}$, $D_{\mathrm{NN}}$) were determined for center-of-momentum angular ranges 6.8°–55.4° (elastic) and 22.4°–55.4° (quasielastic); liquid hydrogen and deuterium targets were used. The p→+p elastic and quasielastic results are in good agreement; both the p→+p and p→+n parameters are well described by current phase shift solutions.

A relativistic calculation of photon-nucleon elastic scattering in the energy range from 0 to 450 MeV in the laboratory is presented. It includes explicit contributions from s- and u-channel nucleon intermediate states, t-channel neutral pion states, and s-channel delta resonance states. Other processes are implicitly included via energy-dependent parameters in the resonance process. Comparison with experiments show an improvement over similar nonrelativistic approaches.

The first experimental observation of nuclear deexcitation via an electronic-bridge mechanism has been reported recently by us. We observed deexcitation of the 30.7-keV ($T_{1/2}$∼13.6 yr) isomeric level of ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$ via an inelastic electronic-bridge mechanism involving initial-state L electrons and final-state $N_5$, or higher, electrons. In this work we report a general theoretical analysis of nuclear deexcitation via the inelastic electronic-bridge mechanism. Our estimate of the matrix element is based on solving the inhomogeneous Dirac equation for the external nuclear Coulomb field. Relativistic effects are allowed for and the external field is included in all orders. Specific calculations for ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$ agree, within a factor of 4, with the experimental result.

Previously observed positive and negative parity states of ${}_{}{}^{105}{}_{}{}^{}\mathrm{Ag}$ have been interpreted using a particle-rotor model. Experimental energies and transition properties have been compared to those predicted by the calculation. The results show that this simple model with very few parameters can explain successfully most of the structure of ${}_{}{}^{105}{}_{}{}^{}\mathrm{Ag}$. Most members of the multiplets resulting from the coupling of R=0, 2, and 4 excitations of the core to $g_{9/2}$, $f_{5/2}$, $p_{3/2}$, and $p_{1/2}$ orbitals have been identified.

The thermal response of states of approximate angular momentum in ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ with $J^{\pi }$${=8\mathrm{}}^{+}$ has been calculated in the finite temperature restricted Hartree-Fock approximation. Full angular momentum projection has been circumvented by the use of constraints on the total angular momentum J${^}^2$ and the z component J${^}_z$. States with an abnormal occupation of the single particle orbitals at T=0 exhibit a discontinuity in the thermal response of their variational energy.

Trinucleon charge densities and charge form factors are calculated in impulse approximation for a large set of wave functions obtained from solving the Faddeev equations for diverse combinations of four two-body force models and three three-nucleon force models. The three-nucleon forces improve the form factor predictions in the region of the secondary maximum slightly, but the experimental data are still substantially higher than the theoretical predictions, while the positions of the theoretical first diffraction minimum and secondary maximum are too high.

The branching ratios of the collective levels in ${}_{}{}^{128}{}_{}{}^{}\mathrm{Xe}$ were discussed in the framework of the proton-neutron interacting boson model . It is shown that the experiment is only consistent with rather small M1 admixtures among the low-lying collective levels. These small M1 matrix elements imply strong constraints on the proton-neutron interacting boson model Hamiltonian.

The M1 γ decay of the 709-keV $1^{+}$ state of ${}_{}{}^{30}{}_{}{}^{}\mathrm{P}$ to the 677-keV $0^{+}$ level has been measured to be (1.25±0.23)×${10}^{\mathrm{-}3}$ relative to the ground-state branch. From this result, the known lifetime of the 709-keV level, and the strength of the analogous ${}_{}{}^{30}{}_{}{}^{}\mathrm{S}$ ${\beta }^{+}$ decay, the M1 width, and the ratio of the orbital and spin parts of the M1 matrix elements are deduced.

A $1^{+}$ level at 5210 keV was observed in ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ca}$, using the (γ,γ’) reaction. The measured M1 strength to the ground state was found to be small, B(M1)↑=0.15±0.06 ${\mu }_{\mathrm{N}{}^2}$, indicating that the M1 strength is probably spread over a wide excitation energy range. In addition, a mixed E2-M1 transition to an excited state was observed, and its B(E2)↓ was determined to be 4.2±0.8 $e^2$ ${\mathrm{fm}}^2$.

The elastic and inelastic (4.44 MeV, $2^{+}$) scattering of 608 MeV ${}_{}{}^{16}{}_{}{}^{}$O${+\mathrm{}}^{12}$C has been measured up to 36° in the c.m. frame. Although the angular distributions are strongly dominated by far side contributions, this feature does not remove the continuous ambiguity in the optical model parameters. The calculated value for ${\sigma }_R$, 1337±22 mb, agrees with nuclear transparency predictions.

We correct the sign of relativistic corrections to the anomalous part of the magnetic moment computed from the Dirac approach to the nucleon-nucleus problem.

A method for calculating main parameters of Gamow-Teller resonance relaxation, namely total width, proton escape widths, and resonance mixing phase, is formulated within the framework of the model of interacting and independently damping quasiparticles. Calculations of the values indicated are carried out for the set of rigid spherical nuclei with the model parameters taken from independent data.

Using an abrasion-ablation collision model, which includes contributions from frictional-spectator interactions and electromagnetic dissociation, analyses of the sensitivities of predicted fragmentation cross sections to the choice of a particular abrasion formalism are made using both geometric and optical potential abrasion models. Most cross section differences obtained using the two abrasion models are less than the present experimental uncertainties, suggesting that either abrasion model is suitable for estimating isotopic and elemental fragment distributions.