Evidence for doorway-state fluctuations in the ${}_{}{}^{12}{}_{}{}^{}\mathrm{Si}$ system is presented. It is found that the correlation widths extracted from the fluctuating excitation functions of this reaction and of other cases either measured in our previous work or found in the literature are up to 1 order of magnitude larger than the traditional compound-nucleus widths; moreover, they exhibit a completely different energy and mass-number dependence. All these features are well interpreted within the framework of the statistical multistep compound theory of preequilibrium reactions.

High-spin states of ${}_{}{}^{172}{}_{}{}^{}\mathrm{Os}$ have been investigated by γ-γ coincidence studies. These states were populated by the ${}_{}{}^{144}{}_{}{}^{}\mathrm{Nd}$${(}^{32}$S,4n) reaction using 162-MeV ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ ions. Gamma-gamma coincidence measurements were made with a Compton-suppression spectrometer system. The yrast band was observed up through the ${30}^{+}$ state, and four sidebands were deduced from γ-γ coincidence relationships. A band identified as belonging to ${}_{}{}^{173}{}_{}{}^{}\mathrm{Os}$ was also observed. Results were interpreted using average nuclear field calculations which incorporated the deformed Woods-Saxon potential with its ‘‘universal’’ parametrization, a cranking approximation, and the Hartree-Fock-Bogoliubov method. The calculations indicate the presence of strongly interacting quasiparticle band crossings for 0.2<ħω<0.3, in semiquantitative agreement with experiment. Both the quasiparticle band structures and decline of neutron pairing are discussed.

Energy spectra and angular distributions of projectile-like fragments, ranging from ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ to ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$, have been measured for the 120 MeV ${}_{}{}^{19}{}_{}{}^{}$F${+}^{64}$Ni reaction. Experimental evidence is given for the presence of two dissipative components attributed, on the basis of optimum Q values, to incomplete fusion and deep-inelastic collision mechanisms. Measured Q-value spectra show the dominance of the incomplete fusion mechanism in N and O isotopes production, while deep-inelastic collisions increase with the charge transfer. Furthermore, angular distributions and optimum Q values display larger relative contributions of incomplete fusion with respect to deep inelastic collisions for heavier isotopes of each Z. An incomplete fusion model reproduces the cross sections for most of the channels where this mechanism is prevalent. An attempt to include deep inelastic mechanisms in the same model is presented.

Electron and positron emission spectra produced in heavy-ion collisions with beam energies in the range $E_{\mathrm{lab}=8\mathrm{}–}$100 MeV/nucleon are calculated up to kinetic lepton energies of 50 MeV. Earlier predictions concerning the observability of nuclear stopping times in the range τ=1–10 fm/c by means of the slope of δ-electron spectra are confirmed. However, the effect of time delay is somewhat less pronounced than predicted in first-order perturbation theory.

Complete angular distributions (${\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}=9\mathrm{}\mathrm{°}–}$90°) have been measured for the reaction ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$${(}^{13}$C,α${)}^{22}$Ne in the energy range $E_{\mathrm{c}.\mathrm{m}.\mathrm{}=10.38\mathrm{}–}$13.38 MeV. The data exhibit significant nonstatistical behavior and have been fitted to a linear sum of Legendre polynomials using a least-squares procedure. An ${11}^{\mathrm{-}}$ resonance is identified at $E_x$${(}^{26}$Mg)=34.21 MeV and a possible ${10}^{+}$ at $E_x$${(}^{26}$Mg)=33.71 MeV.

We have measured the mass and kinetic-energy distributions from the spontaneous fission of ${}_{}{}^{258}{}_{}{}^{}\mathrm{Fm}$, ${}_{}{}^{258}{}_{}{}^{}\mathrm{No}$, ${}_{}{}^{259}{}_{}{}^{}\mathrm{Md}$, ${}_{}{}^{260}{}_{}{}^{}\mathrm{Md}$, and ${}_{}{}^{260}{}_{}{}^{}]$. All are observed to fission with a symmetrical division of mass. The total-kinetic-energy distributions strongly deviated from the Gaussian shape characteristically found in the fission of all other actinides. When the total-kinetic-energy distributions are resolved into two Gaussians, the constituent peaks lie near 200 and 233 MeV. We conclude that both low- and high-energy fission modes occur in four of the five nuclides studied. We call this property ‘‘bimodal fission.’’ Even though both modes are possible in the same nuclide, one generally predominates. We offer an explanation for each mode based on shell structures of the fissioning nucleus and of its fragments. The appearance of both modes of fission in this region of the nuclide chart seems to be a coincidence in that the opportunity to divide into near doubly magic Sn fragments occurs in the same region where the second fission barrier is expected to drop in energy below the ground state of the fissioning nucleus. Appropriate paths on the potential-energy surface of deformation have been found by theorists, but no physical grounds have been advanced that would allow the near equal populations we observe traveling each path. We suggest that this failure to find a reason for somewhat equal branching may be a fundamental flaw of current fission models. Assuming the proposed origins of these modes are correct, we conclude the low-energy, but also mass-symmetrical mode is likely to extend to far heavier nuclei. The high-energy mode will be restricted to a smaller region, a realm of nuclei defined by the proximity of the fragments to the strong neutron and proton shells in ${}_{}{}^{132}{}_{}{}^{}\mathrm{Sn}$. We present some concluding remarks on the present state of fission theory and indicate a potential redirection that might be taken.

We have observed the broad $2^{+}$ member of the $K^{\pi }$${=0\mathrm{}}_4^{+}$ band of ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ with the ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$(${\pi }^{+}$,${\pi }^{+}$’) reaction at $T_{\pi }$=120 and 180 MeV and with ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$(${\pi }^{\mathrm{-}}$,${\pi }^{\mathrm{-}}$’) at $T_{\pi }$=180 MeV. We find an excitation energy of 9.00±0.18 MeV and a width of 0.8 MeV. The B(E2↑) is determined to be approximately 25 to 35 $e^2$${\mathrm{fm}}^4$.

The longitudinal and transverse response functions for the inclusive quasielastic (e,e’) reaction are analyzed in detail. A microscopic theoretical framework for the many-body reaction provides a clear conceptual (nonrelativistic) basis for treating final-state interactions and goes far beyond simple plane-wave or Hermitean potential models. The many-body physics of inelastic final-state channels as described by optical and multiple scattering theories is properly included by incorporating a full complex optical potential. Explicit nonrelativistic and relativistic momentum-space calculations quantitatively demonstrate the importance of such a treatment of final-state interactions for both the transverse and longitudinal response. Nonrelativistic calculations are performed using final-state interactions based on phenomenology, local density models, and microscopic multiple scattering theory. Relativistic calculations span a similar range of models and employ Dirac bound-state wave functions. The theoretical extension to relativistic dynamics is of course not clear, but is done in obvious parallel to elastic proton scattering. Extensive calculations are performed for ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ at momentum transfers of 410, 550, and 700 MeV/c. A number of interesting physical effects are observed, including significant relativistic suppressions (especially for $R_L$), large off-shell and virtual pair effects, enhancement of the tails of the response by the final-state interactions, and large qualitative and even shape distinctions between the predictions of the various models of the final-state interactions. None of the models is found to be able to simultaneously predict the data for both response functions. This strongly suggests that additional physical mechanisms are of qualitative importance in inclusive quasielastic electron scattering.

The results of a comparative study of the ${}_{}{}^{13}{}_{}{}^{}(\mathit{p}\to$,${\pi }^{\pm }$) and ${}_{}{}^{12}{}_{}{}^{}(\mathit{p}\to$,${\pi }^{+}$) reactions at $T_p$=200 MeV and 30°≤${\theta }_{\mathrm{lab}{}^{\pi }\mathrm{\le }150\mathrm{°}}$ are reported. The isospin-dependence of the NN→NNπ processes inside nuclei is investigated by comparing cross sections and analyzing powers for the ${}_{}{}^{13}{}_{}{}^{}(\mathit{p}$,${\pi }^{\pm }$) continuum production to those for corresponding NN→NNπ processes in the free case. The comparison favors the dominance of a quasifree two-nucleon mechanism in nuclear pion production. Relative populations of discrete final states in the ${}_{}{}^{13}{}_{}{}^{}(\mathit{p}$,${\pi }^{\pm }$) spectra are compared, confirming the dominance of the two-nucleon mechanism and suggesting the identification of some high-spin states in the mirror nuclei ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{14}{}_{}{}^{}\mathrm{O}$. Cross-section and analyzing power angular distributions are presented for discrete final states populated strongly in ${}_{}{}^{13}{}_{}{}^{}(\mathit{p}$,${\pi }^{\pm }$) and ${}_{}{}^{12}{}_{}{}^{}(\mathit{p}$,${\pi }^{+}$) up to 24 MeV excitation energy. Cross-section data for a number of ${}_{}{}^{12}{}_{}{}^{}$,13C(p,${\pi }^{+}$) transitions are compared to (p,${\pi }^{+}$) shell-model calculations employing the elementary pp→d${\pi }^{+}$ amplitude along with realistic nuclear wave functions. Isolated anomalous features exhibited by strong ${}_{}{}^{12}{}_{}{}^{}$,13C(p,${\pi }^{+}$) transitions to two highly excited discrete states in ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ are discussed and alternative possible interpretations for these states are presented.

The features of the (p,p’η) reaction are examined for incident proton energies between 0.8 and 1.6 GeV. Reactions are calculated for exclusive transitions in which the continuum proton and η are observed in coincidence. This process should be dominated by transitions N+N→N+N+η involving intermediate excitation of one of the nucleons to an N(1535) isobar. We take phenomenological amplitudes for the process π+N→η+N in the nuclear medium. A theoretical formalism for the reaction amplitudes is derived and examined in detail. Nuclear distortions of the hadrons are estimated in the eikonal approximation. The theoretical cross sections are shown to be dominated by a single production amplitude. This results in the prediction that η production should occur entirely through ΔT=1 non-normal parity nuclear transitions; i.e., that the nuclear states excited should show the spin-isospin characteristics of the exchanged meson. Peak reaction cross sections are predicted to have a strong dependence on the incident proton energy. Expected peak cross sections, for a target like ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, are on the order of 1 μb/${\mathrm{sr}}^2$ MeV.

Total reaction cross sections were measured for 50 MeV ${\pi }^{\pm }$ on Si and Ni, 65 MeV ${\pi }^{\pm }$ on Ni, and 80 MeV ${\pi }^{\pm }$ on C, Ca, Zr, and Pb. Together with similar data measured previously for 50 and 65 MeV ${\pi }^{\pm }$ on several targets, these cross sections were used as constraints in optical-model analysis of the elastic scattering of pions by nuclei. Also analyzing data at 20 and 30 MeV, a pion-nucleus potential was constructed that is strongly linked with the free pion-nucleon interaction, has smooth variation with energy between 0 and 80 MeV, and is capable of describing very well, much better than any potential published so far, all available data on differential and integral cross sections for ${\pi }^{+}$ and ${\pi }^{\mathrm{-}}$ interactions with nuclei.

Resonances were observed in pion-induced double charge exchange (at $T_{\pi }$=292 MeV) on ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$, ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$, ${}_{}{}^{138}{}_{}{}^{}\mathrm{Ba}$, and ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ in the continuum at excitation energies of 8.4, 27.5, 33.2, 38.7, and 44.2 MeV, respectively (Q=-27.4, -32.3, -35.8, -38.4, and -46.0 MeV). An angular distribution was measured for the resonance on ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$ and observed to have a dipole shape. The measured cross sections and the angular distribution agree well with a simple sequential two-step calculation in which the intermediate states arise from single charge exchange to the isobaric analog state and to the giant dipole resonance. Based on their excitation energies, angular distribution for ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$, and cross sections we identify the resonances as the giant dipoles built on the isobaric analog states. The new data together with the recent observation of the resonance in three other nuclei indicate that the excitation energies, widths, and cross sections for these resonances have a simple mass dependence.

Inelastic scattering of 180 MeV ${\pi }^{\mathrm{-}}$ and ${\pi }^{+}$ from ${}_{}{}^{58}{}_{}{}^{}$,60,62,64Ni shows a prominent quadrupole feature near 65$A^{\mathrm{-}1/3}$ MeV, identified as the familiar isoscalar giant quadrupole resonance. For the heavier two isotopes, the ${\pi }^{\mathrm{-}}$ scattering cross sections greatly exceed those for ${\pi }^{+}$, the same effect previously noted in pion scattering on heavy nuclei. Since these four nickel targets contain a range of single-nucleon binding energies, these new data demonstrate the influence of these single-particle effects on the apparent isospin response, increasingly neutronlike for the heavier isotopes.

Neutrino opacities are analyzed in terms of correlation functions for density, spin density, isospin density, and spin-isospin density operators. In a long-wavelength limit appropriate to the scattering of thermal neutrinos in most situations relevant to the supernova, the opacities coming from the neutral current interaction are given in terms of susceptibilities, ∂${\rho }_i$/∂${\mu }_j$, where ${\rho }_i$ are the various densities and ${\mu }_j$ the associated chemical potentials. These susceptibilities are calculated in the framework of a Skyrme interaction, one which has been used in calculations of the hot equation of state, supplemented by spin-dependent terms from other sources. There is a large reduction in the Gamow-Teller part of the cross sections in all of the domains of temperature, proton fraction, and density which were studied. Effects of the screened Coulomb force also cause a large reduction in the opacity arising from the Fermi interaction of the neutrino with protons, in some domains of density and temperature.

The formation probabilities of deeply bound states of ${\pi }^{\mathrm{-}}$ from hypernuclear weak decay are calculated. The best candidate for detecting narrow 1s and 2p ${\pi }^{\mathrm{-}}$ bound states is ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$, where the signature, a sharp peak in a proton spectrum, attains a strength, which may be within the future experimental reach.

First-order Kerman-McManus-Thaler nuclear optical potentials for intermediate energy protons are constructed from realistic meson-exchange models of the nucleon-nucleon interaction including off-shell effects. At 200 MeV the full model developed by the Bonn group is employed, while at 500 MeV a simplified version with delta resonance inelasticity is used. The resulting off-shell effects on the nuclear scattering spin observables are found to be substantial.

Tensor polarization, $t_{20}$, of elastic electron-deuteron scattering is calculated with the resonating group method applied to the six-quark system. We stress the role of baryon size for short-range nuclear correlations, such as the short-range repulsion due to the color magnetic interaction, through the six-quark dynamics. Correct sizes of the delta-nucleon mass splitting and the binding energy of the deuteron are the restrictions imposed on the model Hamiltonian for each different choice of the three-quark cluster size b. An interesting scaling behavior for $t_{20}$ is observed with regard to the momentum transfer q and b, for different models of the medium-range attractive force. An asymptotic equation predicted by the perturbative quantum chromodynamics, i.e., ${\lim }_{\mathrm{q}\to \mathrm{\infty }}$${\mathrm{t}}_{20}$(q)=const, is examined within the present framework, and the momentum transfer for this condition turns out to be quite large, q=4–6 GeV/c. Magnetic effects are seen to be important at large q.

Using separable potentials in a coupled-channel Lippmann-Schwinger equation, we investigate the motion of poles on the different Riemann sheets and their observable effects as the coupling strength is varied. Only in the weak-coupling limit can one determine in which uncoupled channel the pole originated by the sheet on which it lies. Cusp structure versus resonance peak as one crosses a threshold is found to depend on the distance of the pole from the physical sheet. Resonance poles in each uncoupled channel can produce double-loop Argand plots similar to those seen in πN $P_{11}$ amplitude analysis.

Inverse scattering theory for the uncoupled channels of neutron-proton systems is developed from both the Gel’fand-Levitan and Marchenko fundamental equations. A most practical form of that theory is deduced by starting with a rational function representation of the phase shift data. By using Padé approximants for the exponential function $e^z$, rational function representations for the scattering, Jost and spectral functions result. They facilitate accurate numerical solutions of both fundamental equations and from which local, energy-independent channel potentials are obtained. The Reid soft-core potential phase shifts when used as input data give potentials in excellent agreement with the original. Inversion potentials have also been generated by using as input empirical phase shifts and also those from the Paris and Bonn meson exchange interactions. Results are computed for the ${}_{}{}^1{}_{}{}^{}\mathrm{S}_0^{}{}_{}{}^{}$, ${}_{}{}^3{}_{}{}^{}\mathrm{P}_0^{}{}_{}{}^{}$, ${}_{}{}^3{}_{}{}^{}\mathrm{P}_1^{}{}_{}{}^{}$, ${}_{}{}^1{}_{}{}^{}\mathrm{D}_2^{}{}_{}{}^{}$, and ${}_{}{}^1{}_{}{}^{}\mathrm{P}_1^{}{}_{}{}^{}$ channels specifically and the potentials are transformed into central, tensor, spin-orbit, and quadratic spin-orbit radial form factors.

We have studied the levels of ${}_{}{}^{143}{}_{}{}^{}\mathrm{Pr}$ populated in the beta decay of ${}_{}{}^{143}{}_{}{}^{}\mathrm{Ce}$ using singles and Compton suppression gamma-ray spectroscopy techniques. We determined a value of 33.10±0.05 h for the half-life of ${}_{}{}^{143}{}_{}{}^{}\mathrm{Ce}$. In contrast to previous studies, we find no evidence for low-energy negative-parity levels in the decay of ${}_{}{}^{143}{}_{}{}^{}\mathrm{Ce}$ to ${}_{}{}^{143}{}_{}{}^{}\mathrm{Pr}$. In addition we have performed calculations in the framework of the interacting boson-fermion model, which compare well with the level structure of ${}_{}{}^{143}{}_{}{}^{}\mathrm{Pr}$. These calculations have been extended to the heavier Pr isotopes.