Pairing correlations in rotating nuclei are discussed within the Lipkin-Nogami method. The accuracy of the method is tested for the Krumlinde-Szymański R(5) model. The results of calculations are compared with those obtained from the standard mean field theory and particle-number projection method, and with exact solutions.

We have investigated the odd-A Tc isotopes in the mass 100 region using the neutron-proton interacting boson-fermion model. The calculation is based on the validity of the Z=38 subshell closure. The results for the energy spectra and electromagnetic transitions are compared with experimental data and with results from other calculations which considered Z=50 as a valid closed shell for Tc isotopes.

We derive in-medium nucleon-nucleon (NN) cross sections in a microscopic model. Our calculations are based upon the Bonn NN potential and the Dirac-Brueckner approach for nuclear matter. We consider energies up to 300 MeV (in the laboratory frame) and densities up to twice nuclear matter density. Our results deviate substantially from cross section parametrizations that are commonly used in the nuclear medium.

We compare the static approximation to the Hubbard-Stratonovich representation of the partition function with the order parameter representation based on the Landau theory of phase transitions and we find that the two expressions for the partition function are very similar if we choose the expectation value of the potential for the order parameter of the system. This choice for the order parameter has certain advantages above choosing the BCS energy gap for the order parameter in that it generalizes naturally for momentum-dependent pairing interactions and that it remains well defined in exact treatments. In a simple ${\mathit{i}}_{13/2}$-model calculation different choices for the order parameter are compared with the exact grand canonical and with the static path integral results.

The analyses of low-energy (<150 eV) total neutron-atom cross sections, giving the best current but contradictory values for the charge radius of the neutron at present, are reconsidered. It is confirmed that the discrepancy between previous estimates of the crucial electron scattering length is due to different treatments of resonance contributions. In particular the discrepancy arises because the ${\mathit{b}}_{\mathit{n}\mathit{e}}$ value is not extracted via the energy dependence of the atomic form factor but is essentially determined from the difference between the neutron-atom total cross sections above 1 eV and the zero energy value given by the coherent scattering length. A consistent resonance analysis of available data favors a value of the neutron charge radius which is less negative than the corresponding Foldy value.

A semimicroscopic algebraic ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${+}^{12}$C cluster model is applied to describe the structure of the ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ nucleus. The spectrum of the T=0 states is analyzed in terms of this configuration with ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ clusters allowed to occupy their $0^{+}$(0.0 MeV), $2^{+}$(4.439 MeV), and $4^{+}$(14.038 MeV) states. About a hundred experimental levels below ${\mathit{E}}_{\mathit{x}}$≃16 MeV are assigned to model bands. A large number of observed reduced E2 transition probabilities are reproduced fairly well indicating the approximate realization of SU(3) dynamical symmetry. The spectrum of molecular resonances is also described reasonably well. E2 transitions within this region are found to be significantly weaker than what has been predicted by other models.

We argue on general grounds that nearly identical bands observed for superdeformation and less frequently for normal deformation must be explicable in terms of a symmetry having a microscopic basis. We assume that the unknown symmetry is associated with a Lie algebra generated by terms bilinear in fermion creation and annihilation operators. Observed features of these bands and the general properties of Lie groups are then used to place constraints on acceptable algebras. Additional constraints are placed by assuming that the collective spectrum is associated with a dynamical symmetry, and examining the subgroup structure required by phenomenology. We observe that requisite symmetry cannot be unitary, and that the simplest known group structures consistent with these minimal criteria are associated with the Ginocchio algebras employed in the fermion dynamical symmetry model. However, our arguments are general in nature, and we propose that they imply model-independent constraints on any candidate explanation for identical bands.

The systematic behavior of the fragmentation of the low energy octupole state over a wide range of mass regions is well reproduced using a U(5)→SU(3) transition in the context of the interacting boson approximation. However, the octupole fragmentation in the even-A Pt isotopes deviates strongly from both the systematic behavior of other nuclei and the U(5)→SU(3) calculations. This anomalous behavior can be explained in terms of the O(6) nature of the stable Pt isotopes. It is concluded that anomalously large fragmentation of the low energy octupole state is a signature of nuclei conforming to the O(6) dynamical symmetry.

The issue of spin-isospin strength is addressed from the perspective of the information that is available about one-nucleon spectral functions. Both the effect of ground-state correlations and of the coherence by random-phase-approximation correlations are then incorporated in a natural way. The results for ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$ and ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$ are confronted with those obtained by earlier methods, which have been criticized recently. It is shown that ground-state correlations produce a large amount of strength in the first 20 MeV above the main peaks of the Gamow-Teller and spin-dipole resonances. They also yield for these nuclei with rather large neutron excess considerable (n,p) strength, therby increasing the total (p,n) strength by 25–30 %. In spite of this, the strength within the hitherto analyzed energy domains is not enhanced by these correlations. It is argued that a large amount of quasifree background that is assumed in the analysis of charge exchange reactions consists of broad distributions of genuine charge exchange strength.

We investigate the effects of the single-particle potential insertions in the effective interaction by comparing energy spectra obtained from different treatments of these insertions as a function of the size of the no-core model space. The Brueckner reaction matrix used in the first calculation includes the single-particle insertions in ladder diagrams to all orders, while the Brueckner reaction matrix used in the second calculation only keeps the single-particle potential term in the lowest-order ladder diagram. The two calculations yield almost identical ground-state energies and low-lying excitation spectra for ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ for large enough no-core model spaces, indicating that the effects of the single-particle potential insertions in second- and higher-order ladder diagrams are small. We explain the reason for the diminishing role of these insertions with increasing size of the model space. We also show that, through a standard method of instilling a single center-of-mass wave function into all low-lying states, the spurious center-of-mass kinetic-energy term shifts the energies of all the low-lying states by nearly a constant and, therefore, has little effect on the excitation spectrum.

Two-nucleon spectroscopic amplitudes are investigated using cross-section measurements and tensor analyzing powers for the ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$(d→,α${)}^{56}$Co and ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ti}$(d→,α${)}^{46}$Sc reactions. Angular distributions of cross sections, and analyzing powers ${\mathit{A}}_{\mathit{y}}$, ${\mathit{A}}_{\mathit{x}\mathit{x}}$, and ${\mathit{A}}_{\mathit{y}\mathit{y}}$, were measured in steps of 5° from 10° to 65° at a bombarding energy of 22 MeV. Data were analyzed using full finite-range DWBA calculations including a realistic α-particle wave function. The L-mixing ratios for several strong unnatural-parity transitions have been determined from comparison of calculations with analyzing power data. These ratios are compared to predictions of shell-model calculations to deduce predominant two-nucleon configurations.

A position sensitive neutron detector was used to measure the differential cross sections of 14.8 MeV (or 14.7 MeV) neutrons scattered from ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$, Pb, Ni, Fe, Cr, Al, and O between 2.5° and 16° and that of 12 MeV neutrons from ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ and Fe. The data were corrected for neutron flux attenuation, multiple neutron scattering, and finite geometry with a Monte Carlo simulation. The angular distributions are analyzed with a spherical optical model or coupled channels model (code ecis79) and a set of global optical model parameters were obtained at ∼14.8 MeV neutron energy for mass number between 27 and 238. The measured and calculated results are compared and discussed.

The photofission cross section of ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$ was measured in the energy range 250–1200 MeV using a monochromatic tagged photon beam and a parallel-plate avalanche detector. The ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$ nuclear photofissility was obtained by measuring simultaneously and in the same energy range the photofission cross section of ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ and assuming a photofissility equal to one for ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$. It was found that, contrary to the case for heavier actinides, the ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$ photofissility value does not saturate up to 1200 MeV. Rather, it lies between 0.6 and 0.8, and shows a weak energy dependence: it increases by about 15% over an interval of 1 GeV. A comparison of these experimental findings with the predictions of an intranuclear-cascade Monte Carlo calculation is given.

The multiplicities of p and α particles detected in coincidence with fragments emitted in fully relaxed collisions in the reactions of 18.5A MeV ${}_{}{}^{136}{}_{}{}^{}\mathrm{Xe}$${+}^{48}$Ti have been measured for different exit channel mass asymmetries. A kinematic source analysis of the spectra and angular distributions of the light particles has been used to separate the total multiplicities into prescission and postscission contributions. From these results, the excitation energies at scission are determined using an empirical technique based upon previous measurements of light charged particle multiplicities observed in coincidence with evaporation residues. These excitation energies are found to decrease from ∼400 MeV to 110 MeV as the fragment mass asymmetry, ${\mathit{A}}_{\mathit{H}}$/${\mathit{A}}_{\mathit{L}}$, varies from 4.8 to 1.0. A corresponding increase of the mean lifetime of the scissioning nucleus from ∼5×${10}^{\mathrm{-}22}$ s to ∼1×${10}^{\mathrm{-}20}$ s is derived using calculated statistical model decay widths. The extent to which this variation of lifetime with mass asymmetry may be attributed to completely damped deep inelastic collisions or to dynamic delays in the decay of a compound nucleus is discussed as is the need for inclusion of dynamics in the deexcitation calculations for hot nuclei. Observed three fragment events are also discussed.

The excitation functions for production of nineteen isotopes of At, Po, Bi, Pb, and Tl in the interaction of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ with ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ between 57 and 97 MeV incident energy have been measured with the activation technique. The analysis of these data allows one to estimate the cross sections for complete fusion of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and incomplete fusion of ${}_{}{}^8{}_{}{}^{}\mathrm{Be}$ and α fragments with gold, and shows the presence of preequilibrium emissions at incident energies only slightly higher than the Coulomb barrier acting between ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$.

The multidetector AMPHORA was used to investigate the reaction of 35 MeV per nucleon ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ ions with a ${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{Cu}$ target. For 150 000 events corresponding to peripheral and midperipheral collisions, it was possible to reconstruct the primary projectilelike fragments and to calculate event by event the center of mass and the excitation energy. Comparison with a percolation simulation (charge moments, critical exponent) and a momentum ellipsoid analysis are presented and commented. No evidence for a change in disintegration mechanism with increasing excitation energy is found.

Non-charge-exchange inclusive cross sections have been measured at 500 MeV incident pion energy at quasifree scattering kinematics for both positive and negative pion charges. Peaks identified with quasifree knockout are seen at momentum transfers from 314 to 724 MeV/c. The widths and sizes of the peaks seen are consistent with the knockout of single nucleons from the nuclear surface. The data are consistent with no softening of the pion quasifree response at high momentum transfer, in contrast to the result seen in 500-MeV pion charge exchange data.

The response function of nuclei in the quasielastic region at large momentum transfer (q≤10 ${\mathrm{fm}}^{\mathrm{-}1}$) is measured for a series of nuclei, ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$, and ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$, up to large values of the Bjorken scaling variables x<2.5.

The differential cross section for the reaction ${}_{}{}^2{}_{}{}^{}\mathrm{H}$(γ,p)n has been measured at several center-of-mass angles ranging from 50° to 143° for photon energies between 0.8 and 1.8 GeV. The experiment was performed at the SLAC-NPAS facility with the use of the 1.6 GeV/c spectrometer to detect the high energy protons produced by a bremsstrahlung beam directed at a liquid deuterium target. Contributions from concurrent disintegration by the residual electron beam were determined by measuring the proton yield without the Cu photon radiator. At angles not very far from 90°, the energy dependence of the cross sections is consistent with predictions of scaling using counting rules for constituent quarks. At least one theoretical calculation based on a meson-baryon picture of the reaction is able to reproduce the magnitude and energy dependence of the 90° cross section. The angular distribution exhibits a large enhancement at backward angles at the higher energies.

The effects of proximity to a diabolic point on neutron transfer in nuclear physics is explored using the reactions ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$ ${(}^{156}$Gd, ${}_{}{}^{154}{}_{}{}^{}\mathrm{Gd}$) ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ (presumed diabolic case) and ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$ ${(}^{156}$Gd, ${}_{}{}^{158}{}_{}{}^{}\mathrm{Gd}$) ${}_{}{}^{204}{}_{}{}^{}\mathrm{Pb}$ (nondiabolic case) at a laboratry bomdarding energy of 888 MeV. Deexcitation γ rays were measured using a particle-particle-γ triple-coincidence method. A comparsion of the spin distributions from each of the above reactions was used to search for a suppression of the γ-ray yields that has been predicted within the cranked Hartree-Fock-Bogoliubov model for diabolical pair transfer. The latest calculations agree with the results of this experiment. The influence of diabolical pair transfer is more subtle than expected for the case of sharp backbending nuclei such as ${}_{}{}^{154}{}_{}{}^{}\mathrm{Gd}$. No clear evidence for diabolical pair transfer was observed within the sensitivity range of this experiment, nor was it possible to unambigously place the diabolical point between ${}_{}{}^{154}{}_{}{}^{}\mathrm{Gd}$ and ${}_{}{}^{156}{}_{}{}^{}\mathrm{Gd}$.