Isotopes in the light actinide region with N<126, Z≳82 have been produced in the reaction of ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ on ${}_{}{}^{182}{}_{}{}^{}\mathrm{W}$ at beam energies of 164 and 170 MeV. Evaporation residues were selected using an in-flight mass separator, the Argonne Fragment Mass Analyzer, and implanted in a double-sided silicon strip detector. The charge-to-mass ratio of implanted ions, and energies and half-lives of correlated α-decay events have been used to make isotopic identifications. The α decay from the ground state of ${}_{}{}^{204}{}_{}{}^{}\mathrm{Ra}$ has been observed with an α-particle energy of 7.488(12) MeV and a half-life of ${45}_{\mathrm{-}21}^{+55\mathrm{}}$ ms. Previous results concerning the decay of ${}_{}{}^{205}{}_{}{}^{}\mathrm{Ra}$ were also confirmed.

High angular-momentum states in ${}_{}{}^{196,197}{}_{}{}^{}\mathrm{Bi}$ were populated in the reaction ${}_{}{}^{183}{}_{}{}^{}\mathrm{W}$ ${(}^{19}$F,xn) at a beam energy of 108 MeV, and γ rays were detected with the Gammasphere array. Two weakly populated rotational bands, with energy spacings characteristic of superdeformation have been found. Both cascades can be assigned unambiguously to the Bi nuclei; however, their isotopic assignment to ${}_{}{}^{197}{}_{}{}^{}\mathrm{Bi}$ is tentative. The properties of the bands and their possible structures are discussed. Our results represent the first identification of superdeformed bands in a nucleus of the A∼190 mass region with Z≳82.

Evidence of collective octupole excitations built on spherical shell-model states is reported for the N=84 isotones ${}_{}{}^{146}{}_{}{}^{}\mathrm{Sm}$ and ${}_{}{}^{144}{}_{}{}^{}\mathrm{Nd}$. In particular, good candidates for double-octupole excitations, analog to the ${12}^{+}$ state at 3981 keV in ${}_{}{}^{148}{}_{}{}^{}\mathrm{Gd}$, have been identified in both nuclei.

A superdeformed band has been found in the ${}_{}{}^{154}{}_{}{}^{}\mathrm{Dy}$ (N=88) nucleus. The dynamic moment of inertia is identical to that of the yrast superdeformed band of ${}_{}{}^{152}{}_{}{}^{}\mathrm{Dy}$ and the transition energies are similar to those of an excited superdeformed band in ${}_{}{}^{153}{}_{}{}^{}\mathrm{Dy}$. It is proposed that the two valence neutrons above the N=86 shell gap occupy the deformation-driving [514]9/2 orbital.

The reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(${\nu }_{\mathrm{\mu }}$,${\mathrm{\mu }}^{\mathrm{-}}$)X has been measured near threshold using a ${\mathrm{\pi }}^{+}$ decay-in-flight ${\nu }_{\mathrm{\mu }}$ beam from the Los Alamos Meson Physics Facility and a massive liquid scintillator neutrino detector (LSND). In the energy region 123.7<${\mathit{E}}_{\nu }$<280 MeV, the measured spectral shape is consistent with that expected from the Fermi-gas model (FGM). However, the measured flux-averaged inclusive cross section {[8.3±0.7(stat)±1.6(syst)]×${10}^{\mathrm{-}40}$ ${\mathrm{cm}}^2$} is more than a factor of 2 lower than that predicted by the Fermi-gas model and by a recent random phase approximation calculation.

The two-proton stability in even-even nuclei around the doubly magic ${}_{}{}^{100}{}_{}{}^{}\mathrm{Sn}$ is examined by the self-consistent Skyrme-Hartree-Fock-Bogoliubov theory. According to our analysis, the nuclei ${}_{}{}^{98}{}_{}{}^{}\mathrm{Sn}$ and ${}_{}{}^{106}{}_{}{}^{}\mathrm{Te}$ are stable to two-proton decay while ${}_{}{}^{96}{}_{}{}^{}\mathrm{Sn}$ and ${}_{}{}^{104}{}_{}{}^{}\mathrm{Te}$ lie beyond the two-proton drip line.

The few available data for the reactions γp→${\mathit{K}}^0$${\mathrm{\Sigma }}^{+}$ and γn→${\mathit{K}}^{+}$${\mathrm{\Sigma }}^{\mathrm{-}}$ are compared to models developed for the processes γp→${\mathit{K}}^{+}$${\mathrm{\Sigma }}^0$ and γp→${\mathit{K}}^{+}$Λ. It is found that some of these phenomenological models overpredict the measurements by up to a factor of 100. Fitting the data for all of these reactions leads to drastically reduced Born coupling constants.

We remove the sharp separation between multistep compound and multistep direct emission in the Feshbach-Kerman-Koonin (FKK) derivation of preequilibrium processes. In addition to the original multistep compound mechanism, we find a new class of multistep processes arising from linking of the direct and compound chains. There can be additional scatterings in unbound P space before the quasibound compound Q space is entered, or after it is left. We provide a theoretical justification for the presence of P→Q transitions, which are needed to account for experimentally observed preequilibrium spectra. Our formalism is applied to the analysis of the 14 MeV ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$(n,n’) reaction, using modified distorted-wave Born approximation (DWBA) matrix elements which include an inverse S-matrix factor. Since the dominant contribution to multistep compound emission comes from the 2p1h Q stage, the linking of the multistep chains results in flux bypassing this stage, resulting in a reduced multistep compound emission and an increased emission from the compound nucleus.

For a relativistic particle moving in the presence of mean scalar and vector fields, the energy at second order in the scalar field is shown to contain two contributions in general. One is a momentum-dependent repulsive interaction satisfying a low-energy theorem pointed out by Wallace, Gross, and Tjon. The other does not vanish at zero momentum and involves a ‘‘polarizability’’ of the particle by the scalar field. The first of these contributions is independent of the details of the structure of the particle and the couplings of its constituents to the external fields. The appearance of such a piece in the central nucleon-nucleus potential thus would support the existence of strong scalar fields in nuclei, without requiring the use of a Dirac equation for the nucleon.

It is shown that the SU(3) symmetry for low-lying states of the fermion dynamical symmetry model is essentially preserved even for highly nondegenerate spherical single-particle energies. The breaking of SU(3) symmetry by single-particle energy terms in heritage-0 configurations for either normal deformation or superdeformation occurs only through an indirect Pauli effect and is significant only when the spherical single-particle splitting within shells is artificially large relative to that observed experimentally.

Single-nucleon spectra in the fast rotating nuclei are shown to exhibit some special orbits that appear to be insensitive to nuclear rotation. It is suggested that the special orbits play an essential role in explaining the appearance and structure of the identical bands discovered in the superdeformed region. It is suggested that identical bands appear whenever the nucleonic orbit approaches the separatrix, i.e., a line dividing regions of different coupling schemes in a rotating mean field.

Low-multipolarity magnetic transitions in ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ were excited by 180° inelastic electron scattering. Measurements were made in the excitation energy range of 9 to 14 MeV, at low momentum transfers corresponding to q values of 0.3 to 0.5 ${\mathrm{fm}}^{\mathrm{-}1}$. Multipolarities and transition strengths were determined in a model-independent analysis for all the observed transitions and compared with previous published and unpublished electron scattering data. The experimental M1 strength distributions are compared with configuration-mixing shell-model calculations.

The hyperfine magnetic fields present at ${}_{}{}^{194}{}_{}{}^{}\mathrm{Pt}$, ${}_{}{}^{196}{}_{}{}^{}\mathrm{Pt}$, and ${}_{}{}^{198}{}_{}{}^{}\mathrm{Pt}$ nuclei implanted into polarized, ferromagnetic Gd at 92 K were measured using the ion-implantation perturbed angular correlation (IMPAC) technique following Coulomb excitation. The present measured precession for ${}_{}{}^{194}{}_{}{}^{}\mathrm{Pt}$ agrees with earlier work, but that for ${}_{}{}^{196}{}_{}{}^{}\mathrm{Pt}$ does not. Our data imply a static field strength for Pt in Gd at 92 K of -38±5 T, which is ∼50% of the magnitude obtained in the only previous measurement. It is likely that the hyperfine field for Pt in Gd has an anomalous dependence on temperature, similar to that observed for Os in Gd.

A nuclear self-absorption measurement was carried out on the nucleus ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ with a bremsstrahlung photon-beam endpoint energy of 4.2 MeV. For a number of states, commonly used as calibration standards in photon-scattering (NRF) experiments, the self absorption was measured. Thereby the level widths and lifetimes were determined absolutely. In addition it was found that the level energy of the 2212.01-keV level deviates from the literature value.

The ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$${(}^{117}$Sn, ${}_{}{}^{118}{}_{}{}^{}\mathrm{Sn}$${)}^{238}$Pu reaction at a beam energy of 630 MeV has been used to attempt populating the 0.5 ns fission isomer in ${}_{}{}^{238}{}_{}{}^{}\mathrm{Pu}$. The measured cross section for prompt fission of ${}_{}{}^{238}{}_{}{}^{}\mathrm{Pu}$ populated by neutron transfer is (6±2) mb while the cross section for prompt fission of ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$ excited by inelastic scattering is (1.7±1.0) mb. A single candidate delayed fission event was observed, corresponding to the population of a fission isomer, most probably in ${}_{}{}^{238}{}_{}{}^{}\mathrm{Pu}$, with a cross section of (80±80) nb. The heavy-ion induced transfer reaction shows no enhancement of the ratio of delayed to prompt fission, compared to light-ion induced reactions.

Collective motion for the reverse reaction system ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$${+}^{27}$Al below 100 MeV/nucleon is studied via the quantum-molecular-dynamics approach. The azimuthal distribution of nucleons and the semiquantitative calculation of rotational observables contribute to the analysis of collective rotation. The collective rotation becomes weaker with increasing beam energy, and fades out at a higher energy. Quantitative comparison between calculation and data is also performed by taking into account the fluctuation of experimental reaction plane determination.

Measurements of neutron total cross sections are both extensive and extremely accurate. Although they place a strong constraint on theoretically constructed models, there are relatively few comparisons of predictions with experiment. The total cross sections for neutron scattering from ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ are calculated as a function of energy from 50 to 700 MeV laboratory energy with a microscopic first-order optical potential derived within the framework of the Watson expansion. Although these results are aleady in qualitative agreement with the data, the inclusion of medium corrections to the propagator is essential to correctly predict the energy dependence given by the experiment. In the region between 100 and 200 MeV, where off-shell tρ calculations for both ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ overpredict the experiment, the modification due to the nuclear medium reduces the calculated values. Above 300 MeV these corrections are very small and depending on the employed nuclear mean field tend to compensate for the underprediction of the off-shell tρ results.

The relativistic momentum-space optical model is extended to include the correct invariant normalization of the target wave function. We find that this correction is important for both pion and ${\mathit{K}}^{+}$ scattering from the deuteron at energies approaching 1 GeV but is insignificant for heavier targets in this energy range.