The high-spin level structures of ${}^{96,97,98}\mathrm{Ru}$ $\mathrm{}(Z=44\mathrm{})\mathrm{}$ have been investigated using the ${}^{65}\mathrm{Cu}{(}^{36}\mathrm{S},{pxn)}^{96,97,98}\mathrm{Ru}$ $\mathrm{}(x=4,3,2\mathrm{})\mathrm{}$ reactions. About 130 new transitions have been observed and unambiguously placed in the decay schemes of these nuclei. The level schemes have been extended up to spin $J\approx 22$– $34ħ$, and excitation energies $E_x\approx 20-24$ MeV. Spherical shell model calculations have been performed and theoretical level energies compared with experimental values. Calculations using ${}^{88}\mathrm{Sr}$ as the core give a reasonable agreement for the observed energy levels up to $J<~16ħ$ (the maximum angular momentum possible within this restricted model space). The higher angular momentum states are dominated by the $\nu {(g}_{9/2}{)}^{-1}$ configuration, associated with breaking of the $N=50\mathrm{}$ core. The experimental indications for this “core breaking” are (i) the observation of $\gamma$ rays with energies $E_{\gamma }\approx$ 2 MeV at intermediate spins and (ii) the fragmentation of $\gamma$-ray intensity into a number of branches. A cascade of $E2\mathrm{}$ transitions of nearly equal transition energies has been observed in ${}^{98}\mathrm{Ru}$ after the core breaking $(J>~16ħ)$, possibly manifesting vibrational behavior.

The parities of high-spin bands in the odd-odd nucleus ${}^{72}\mathrm{As}$ have been established by measurements of the angular distributions and linear polarizations of the decay γ rays via the ${}^{62}\mathrm{Ni}{(}^{13}\mathrm{C},p2n)$ reaction at a beam energy of 48.5 MeV. In particular, the parity change determined between the $8^{+}$ and $7^{-}$ states leads to positive parity for the yrast high-spin band. This band and the electromagnetic transition strengths within it are interpreted based on microscopic calculations using the VAMPIR model as arising from the intruder $(\pi g_{9/2}\otimes \nu g_{9/2})$ configuration.

Four new superdeformed bands have been found in the nucleus ${}^{86}\mathrm{Zr}$. The good agreement between experiment and configuration-dependent shell correction calculations suggests that three of the bands have triaxial superdeformed shapes. Such unique features in mass $A\sim 80$ superdeformed bands have been predicted, but not observed experimentally until now. A fourth band in ${}^{86}\mathrm{Zr}$ is interesting due to a fairly constant and unusually high dynamic moment of inertia. Possible interpretations of this structure are discussed.

The quadrupole moments of highly deformed bands in ${}^{134,135}\mathrm{Nd}$ and ${}^{131}\mathrm{Ce}$ have been determined using the Doppler-shift attenuation method. The obtained $Q_0$ values show no clear dependence on the number of occupied $\nu i_{13/2}$ intruder orbitals. Cranked shell model calculations indicate that the charge-quadrupole moments of the highly deformed bands decrease with increasing spin. The expected increase in deformation induced by the $\nu i_{13/2}$ orbital in two bands of ${}^{134}\mathrm{Nd}$ is attenuated by a rotation-induced shrinking effect driving the nucleus towards smaller deformation.

The nucleus ${}^{185}\mathrm{Pt},$ which has a strongly deformed ground state and numerous low-lying rotational bands, is shown to possess low-lying excited states which are nonrotational. This is demonstrated through the absence of rotational excitations associated with two low-spin $(J=\frac{3}{2};\frac{5}{2})$ states at excitations between 500 and 600 keV. The implications of these observations for shape changes and shape coexistence in this region are discussed.

The spectra and electromagnetic transitions of the odd-odd nucleus ${}^{52}\mathrm{Sc}$ are calculated in the nuclear shell model approach, using the full $\mathrm{fp}$ shell basis functions with no truncation. Two of the most used two-body effective interactions in the $\mathrm{fp}$ shell yield quite different nuclear spectra. The energy levels from the two interactions are compared, as well as the magnetic and quadrupole moments and the electromagnetic transitions. The available experimental data, mostly $1^{+}$ levels, are not sufficient to conclude which interaction provides a better fit.

In this paper we study the neutron elastic breakup in reactions initiated by ${}^{11}\mathrm{Be}$. The neutron angular distribution is obtained from a general formalism which can be applied to any heavy-ion transfer to the continuum reaction at intermediate energies. With the same method momentum distributions can be obtained. Our equations can be reduced to the incident free particle limit and the validity of this approximation is discussed. Theoretical results are compared to recent experimental data.

An alternative description of tilted rotation, observed in deformed nuclei, is presented using the projected shell model approach. It is shown that a strong configuration mixing among the projected states is responsible for the appearance of the tilted bands near to, but slightly above, the yrast line in even-even tungsten isotopes. Various tilted bands in ${}^{184}\mathrm{Os}$ are also predicted.

A dynamical valence and sea quark mixing model is shown to fit the baryon ground state properties as well as the spin content of the nucleon. The relativistic correction and the $q^3\leftrightarrow q^{3}q\overline{q}$ transition terms induced by the quark axial vector current $\overline{\psi }\overrightarrow{\gamma }{\gamma }^5\psi$ in this model space is responsible for the quark spin reduction.

Realistic caloric curves are obtained for the ${}^{197}\mathrm{Au}{+}^{197}\mathrm{Au}$ reaction with incident energy ranging from 35 to 130 MeV/nucleon in the dynamic statistical multifragmentation model. It is shown that for the excitation energy 3 to 8 MeV/nucleon, the temperature remains constant in the range 5 to 6 MeV, which is close to the experiment. The mechanism of energy deposition through the tripartition of the colliding system envisaged in this model together with interfragment nuclear interaction are found to play important roles. A possible signature of a liquid-gas phase transition is seen in the specific heat distribution calculated from these caloric curves, and the critical temperature is found to be $\sim$6 to 6.5 MeV.

Fission following the fusion of ${}^6\mathrm{He}$ with a ${}^{209}\mathrm{Bi}$ target has been studied near the Coulomb barrier, at excitation energies of 32 and 34 MeV in the compound system. These new experimental data are in disagreement with previous work which reported an anomalously large fusion-fission yield, when compared with ${}^4\mathrm{He}$-induced fission of ${}^{209}\mathrm{Bi}$ at similar excitation energies. In fact, the ${}^6\mathrm{He}$-induced fusion-fission yield appears to be smaller than that for ${}^4\mathrm{He}$, in qualitative agreement with conventional statistical model calculations.

The analyzing power $A_y$ has been measured for $n$-α scattering at energies of 11.3, 15.7, and 17.1 MeV for laboratory angles ${\theta }_{\mathrm{lab}}=42\mathrm{}°,$ 52°, and 62°. The beam polarization was determined at $E_n=11.3\mathrm{}$ and 15.7 MeV via $n$-α scattering at backward angles where $A_y$ is accurately known. The data were analyzed by means of extensive Monte Carlo simulations. Taking our results together with previously published data by other authors, it is concluded that the $n$-α analyzing power at forward angles is very well described by the phase-shift predictions of Stammbach and Walter over the whole energy range.

We investigate the influence of negative-energy states in proton-proton bremsstrahlung in a fully relativistic framework using the $T$ matrix of Fleischer and Tjon. The contribution from negative-energy states in the single-scattering diagrams is shown to be large, indicating that relativistic effects are important. The rescattering contribution compensates some of the effect, which is shown to be a consequence of a low-energy theorem. The net effect of negative-energy states nevertheless is of the order of 20% at higher energies. We investigate retardation effects in the nucleon-nucleon (NN) interaction by means of a one-pion exchange model, which gives effects of the order of 15% at the pion-production threshold. We furthermore modify the NN $T$ matrix to incorporate some of these effects, and find that on the level of single-scattering contributions they are of the order of 10%. We show predictions at incoming proton energy $T_{\mathrm{lab}}=190\mathrm{}\mathrm{}\mathrm{MeV},$ where high accuracy measurements are being done at KVI, and conclude that even at these relatively low energies off-shell effects in the NN interaction and contributions from negative-energy states clearly show up.

We show how to derive relativistic, unitary, gauge-invariant, and charge-conserving three-dimensional scattering equations for a system of hadrons interacting with an electromagnetic field. In the method proposed, the spectator equations describing the strong interactions of the hadrons are gauged using our recently introduced gauging of equations method. A key ingredient in our model is the on-mass-shell particle propagator. We discuss how to gauge this on-mass-shell propagator so that both the Ward-Takahashi and Ward identities are satisfied. We then demonstrate our gauging procedure by deriving the gauge-invariant three-dimensional expression for the deuteron photodisintegration amplitude within the spectator approach.

We derive relativistic three-dimensional integral equations describing the interaction of the three-nucleon system with an external electromagnetic field. Our equations are unitary, gauge invariant, and they conserve charge. This has been achieved by applying the recently introduced gauging of equations method to the three-nucleon spectator equations where spectator nucleons are always on mass shell. As a result, the external photon is attached to all possible places in the strong interaction model, so that current and charge conservation are implemented in the theoretically correct fashion. Explicit expressions are given for the three-nucleon bound-state electromagnetic current, as well as the transition currents for the scattering processes ${\gamma }^3$He$\to \mathrm{NNN}$, $\mathrm{Nd}\to \gamma \mathrm{Nd}$, and ${\gamma }^3$He$\to \mathrm{Nd}$. As a result, a unified covariant three-dimensional description of the $\mathrm{NNN}$-$\gamma \mathrm{NNN}$ system is achieved.

The complex Kohn variational principle and the (correlated) hyperspherical harmonics technique are applied to study $N$-$d$ scattering above the deuteron breakup threshold. The configuration with three outgoing nucleons is explicitly taken into account by solving a set of differential equations with outgoing boundary conditions. A convenient procedure is used to obtain the correct boundary conditions at values of the hyperradius of $\approx 100$ fm. The inclusion of the Coulomb potential is straightforward and does not give additional difficulties. Numerical results have been obtained for a simple $s$-wave central potential. They are in nice agreement with the benchmarks produced by different groups using the Faddeev technique. Comparisons are also done with experimental elastic $N$-$d$ cross section at several energies.

Beginning with an effective field theory based upon meson exchange, the Bethe-Salpeter equation for the three-particle propagator (six-point function) is derived. Using the one-boson-exchange form of the kernel, this equation is then analyzed using time-ordered perturbation theory, and a three-dimensional equation for the propagator is developed. The propagator consists of a prefactor in which the relative energies are fixed by the initial state of the particles, an intermediate part in which only global propagation of the particles occurs, and a post-factor in which relative energies are fixed by the final state of the particles. The pre- and post-factors are necessary in order to account for the transition from states where particles are off their mass shell to states described by the global propagator with all of the particle energies on shell. The pole structure of the intermediate part of the propagator is used to determine the equation for the three-body bound state: a Schrödinger-like relativistic equation with a single, global Green’s function. The role of the pre- and post-factors in the relativistic dynamics is to incorporate the poles of the breakup channels in the initial and final states. The derivation of this equation by integrating over the relative times rather than via a constraint on relative momenta allows the inclusion of retardation and dynamical boost corrections without introducing unphysical singularities.

A partial-wave analysis of $\mathrm{NN}$ elastic scattering data has been completed. This analysis covers an expanded energy range, from threshold to a laboratory kinetic energy of 2.5 GeV, in order to include recent elastic $\mathrm{pp}$ scattering data from the EDDA Collaboration. The results of both single-energy and energy-dependent analyses are described.

The low-energy $\pi N$ interaction is investigated with the use of a relativistic isospin-symmetric $\pi N$ model based on scalar-isoscalar and vector-isovector exchanges in the $t$ channel, and the nucleon and Δ-isobar contributions in the $s$ and $u$ channels; the small contributions from the well-established $s$ and $p$ higher (baryon) resonances are also taken into account. In the region of elasticity, the model provides a firm basis for analyzing the experimental data. The analysis of all (recent and old) $\pi N$ measurements between (pion laboratory kinetic energy of) 20 and 100 MeV has been achieved with the implementation of robust statistics. Provided the correctness of the bulk of the experimental data and the completeness of the electromagnetic corrections applied to the scattering problem, this work provides overwhelming evidence for isospin-symmetry breaking of the strong interaction in the $\pi N$ system.

By using a chiral quark cluster model for a system of two nonstrange baryons, we analyze the consequences of the symmetry requirements from the underlying quark structure. Quark Pauli and dynamical correlations are studied putting the emphasis in the different repulsive mechanisms implied in the $\mathrm{NN}$ (nucleon-nucleon) and $\Delta \Delta$ systems. We find an alternative explanation for the short-range repulsion in the $\mathrm{NN}$ system, up to now attributed to the one-gluon exchange potential. A $\Delta \Delta$ interaction, derived from a basic quark-quark potential fitted to the $\mathrm{NN}$ sector, is studied in detail.