The structure of ${}^{43}\mathrm{Sc}$ is investigated by the $\alpha {+}^{39}\mathrm{K}$ orthogonality condition model. The properties investigated are energy spectra, $\alpha$-spectroscopic factors, $E2\mathrm{}$, $M1\mathrm{}$, and $E1\mathrm{}$ transitions. On the whole, the calculated properties are in good agreement with the available experimental data. Low-lying levels are assigned to the weak coupling multiplets based on $\alpha {+}^{39}\mathrm{K}{(3/2\mathrm{}}^{+})$ and $\alpha {+}^{39}\mathrm{K}{(1/2\mathrm{}}^{+})$ cluster configurations and interesting selectivities for $M1\mathrm{}$ and $E1\mathrm{}$ transitions are discussed.

Large amplitude collective motion is investigated for a model pairing Hamiltonian containing an avoided level crossing. A classical theory of collective motion for the adiabatic limit is applied utilizing either a time-dependent mean-field theory or a direct parametrization of the time-dependent Schrödinger equation. A modified local harmonic equation is formulated to take account of the Nambu-Goldstone mode. It turns out that in some cases the system selects a diabatic path. Requantizing the collective Hamiltonian, a reasonable agreement with an exact calculation for the low-lying levels is obtained for both weak and strong pairing force. This improves on results of the conventional Born-Oppenheimer approximation.

Starting from an effective interaction of Skyrme type, a finite rank separable approximation is proposed for the residual particle-hole interaction with the aim to allow one to perform structure calculations in very large particle-hole spaces. The approximation is checked on a specific example by calculating isoscalar quadrupole and isovector dipole modes in a finite nucleus using the random phase approximation. It is found that the finite rank approximation is very accurate in the isoscalar channel and it reproduces reasonably well the isovector channel. The use of the finite rank interaction is illustrated by calculating the evolution of the dipole strength distribution along the Ar isotope chain, from $A=32\mathrm{}$ to $A=52.\mathrm{}$

Conventional theories of nuclear interactions predict a net increase in the distribution of virtual pions in nuclei relative to free nucleons. Analysis of data from several nuclear experiments has led to claims of evidence against such a pion excess. These conclusions are usually based on a collective theory [random-phase approximation (RPA)] of the pions, which may be inadequate. The issue is the energy dependence of the nuclear response, which differs for theories with strong $\mathrm{NN}$ correlations from the RPA predictions. In the present paper, information about the energy dependence is extracted from sum rules, which are calculated for such a correlated, noncollective nuclear theory. The results lead to much reduced sensitivity of nuclear reactions to the correlations that are responsible for the pion excess. The primary example is $(\overrightarrow{p},\overrightarrow{n})$ spin transfer, for which the expected effects are found to be smaller than the experimental uncertainties. The analysis has consequences for deep inelastic scattering experiments as well.

The coupling between the rotational and shape degrees of freedom in soft nuclei is studied using a constrained time-dependent Hartree-Fock approach. The dynamical equations are derived using the time-dependent variational principle on a restricted trial manifold consisting of cranked squeezed states. This procedure is applied to describe the low-lying isovector magnetic excitations observed recently in the $\gamma$-soft nucleus ${}^{134}$Ba. The role of shape softness in the fragmentation mechanism of the low-lying $M1\mathrm{}$ strength is emphasized.

The proper form of the pairing interaction near the drip line is discussed. The relativistic Hartree-Bogoliubov (RHB) theory in coordinate space is used to describe the chain of even-even nickel isotopes reaching from the proton drip line to the neutron drip line. The pairing correlations are taken into account by both a density-dependent force of zero range and the finite range Gogny force. Through the comparisons of the two neutron separation energies $S_{2n},$ the neutron, proton, and matter rms radii, excellent agreement has been found between the calculations with both interactions and the empirical values. The same drip-line nuclei ${}^{100}$Ni have been predicted. The pairing energies, single particle levels in the canonical bases and their corresponding occupation probabilities have turned out to be similar. It is shown clearly that after proper renormalization (e.g., fixing the corresponding pairing energies here), physical observables such as $S_{2n}$ and rms radii remain the same, even within a reasonable region of the interaction strength.

The $M1\mathrm{}$ transition and ground state spectra of the even-even ${}^{160–164}\mathrm{Dy}$ and ${}^{156–160}\mathrm{Gd}$ isotopes are calculated within the framework of the microscopic pseudo-SU(3) shell model. A reasonable description of the $M1\mathrm{}$ strength function, including its fragmentation, is obtained with an interaction that includes collective as well as single-particle and pairing terms with the parameters of the theory fit to the energy spectrum and $E2\mathrm{}$ transition strengths.

Quasiparticle-phonon equations of motion are solved starting from a microscopic realistic many-body Hamiltonian. In this microscopic quasiparticle-phonon model (MQPM) the relevant part of the three-quasiparticle Hilbert space may possibly be taken into account even in calculations using large single-particle bases. As an example, the MQPM is applied to the calculation of energy levels and Fermi and Gamow-Teller beta-decay transition amplitudes for transitions between odd-mass ${}^{127-133}\mathrm{Xe}$, ${}^{127-133}\mathrm{I}$, and ${}^{127-133}\mathrm{Cs}$ isotopes. Considering the fully microscopic nature of the MQPM, comparison of its results and data indicates a rather satisfactory agreement between theory and experiment.

An energy-weighted sum rule covering the full $M1\mathrm{}$ scissorslike spectrum is computed in the context of the random phase approximation (RPA) using a separable Hamiltonian. The deformed mean field is derived in Hartree approximation from the quadrupole-quadrupole interaction which is accordingly modified so as to avoid further distortions of the mean field. The main effect of this modification consists in the complete cancellation of the contribution to the sum rule coming from the one-body potential. The resulting sum is almost entirely exhausted once the contribution from the observed low-lying $M1\mathrm{}$ transitions is implemented with the one coming from energy and strength of the high-lying $M1\mathrm{}$ mode, computed in schematic RPA. It also emerges naturally that the $M1\mathrm{}$ transitions of both modes are strictly correlated with the quadrupole collectivity of the ground state.

The ${}^{25}$Mg${(d,}^3$He)${}^{24}$Na reaction has been investigated at 29 MeV incident energy. Spectra were measured at ${\theta }_{\mathrm{lab}}=10\mathrm{}°$ and $18°$. Observations using a split-pole magnetic spectrograph have been made of 56 levels of ${}^{24}$Na in the range of excitation energy between 0 and 7.3 MeV. Most of these have been identified with ${}^{24}$Na levels which have been previously observed by other techniques. From the ratios of the experimental as well as distorted-wave Born approximation (DWBA)-predicted cross sections at the two angles, the population through the pickup of an $l_p=1\mathrm{}$ proton has been established (or confirmed) for the twelve levels at $E_x=3.372\mathrm{}$, 3.745, 3.936, 4.524, 5.192, 5.250, 5.452, 5.846, 5.863, 6.905, 7.084, and 7.246 MeV. Spectroscopic factors were obtained from the comparison of the experimentally measured cross sections at the two angles with the DWBA-predicted cross sections. The experimental values of spectroscopic factors and excitation energies for positive-parity states were compared with the results of a recent, complete $\mathrm{sd}$-shell space, shell-model calculation. In conjunction with the results of various previous works, this comparison leads to the identification of 19 shell-model levels with experimental levels, and thus allows the removal of ambiguities existing in the current literature for the $J^{\pi }$ values of some ${}^{24}$Na states with $E_x<$3.7 MeV.

We have measured α-particle spectra at different laboratory angles from the fusion reaction ${}^{28}{\mathrm{S}\mathrm{i}+}^{51}\mathrm{V}$ at 140 MeV. These spectra deviate at higher energies from the statistical model calculations using rotating liquid drop model values of the moment of inertia. In order to explain the experimental spectra, changes were required in the moments of inertia corresponding to deformation, which suggests dynamical effects on the deexcitation process for charged-particle emission. The comparison of decay times with formation times implies that light charged particles are preferentially emitted prior to the full relaxation of the compound nucleus. Statistical models and dynamical calculations have been employed in an attempt to interpret the experimental data. The results were compared with the ${}^{28}{\mathrm{S}\mathrm{i}+}^{27}\mathrm{Al}$ system studied earlier in order to understand the symmetric and asymmetric entrance channel effects in the formation of the compound system.

The population and decay of excited states in ${}^{24}\mathrm{Mg}$ has been investigated through the ${}^{12}{\mathrm{C}(}^{16}{\mathrm{O},}^{12}{\mathrm{C}}^{12}\mathrm{C})\alpha$ and ${}^{12}{\mathrm{C}(}^{16}{\mathrm{O},}^8{\mathrm{Be}}^{16}\mathrm{O})\mathrm{\alpha }$ reactions, at beam energies of 75, 85, and 115 MeV. The fragments from the breakup of the ${}^{24}\mathrm{Mg}$ nucleus were detected in coincidence, permitting a study of both the excitation energies and the spins of the fissioning states. These measurements indicate a series of states in ${}^{24}\mathrm{Mg}$ between 20 and 40 MeV with spins ranging from $J=4\mathrm{}$ to 14 $ħ$. The results are discussed in the context of the ${}^{12}{\mathrm{C}+}^{12}\mathrm{C}$ quasimolecular scattering resonances and other ${}^{24}\mathrm{Mg}$ breakup reactions.

Excitation function and isomeric cross-section ratios for the production of ${}^{183}{\mathrm{Os}}^{m,g}$ by ${}^7\mathrm{Li}$-induced reactions on ${}^{181}\mathrm{Ta}$ are obtained from the measurements of the residual activities by the conventional stacked-foils technique from threshold to 50 MeV. The excitation function and isomeric cross-section ratios for nuclear reaction ${}^{181}\mathrm{Ta}{(}^7\mathrm{Li}{,5n)}^{183}{\mathrm{Os}}^{m,g}$ are compared with the theoretical statistical model calculation by using the ALICE/91, STAPRE, and CASCADE codes. In the energy range of the present measurement the excitation functions are fitted fairly well by both the geometry dependent hybrid (GDH) model and the hybrid model of Blann with initial exciton number $n_0=7\mathrm{}$ ($n_n=4,$ $n_p=3,$ $n_h=0\mathrm{}$) using the ALICE/91 code. The experimental isomeric cross-section ratios are also reproduced fairly well by the calculation using the STAPRE code. However, the CASCADE code calculations slightly underpredict the cross section but reproduce the shape. In general, the statistical model under a suitable set of global assumptions, can reproduce the excitation function as well as isomeric cross-section ratios.

We have studied the two reactions ${}^{12}\mathrm{C}({\pi }^{+},pp)$ and ${}^{12}\mathrm{C}({\pi }^{+},ppp)$ in one experiment, using the CHAOS spectrometer at TRIUMF, at incident pion energies of 200, 240, and 280 MeV. In both cases, we are able to distinguish between reaction mechanisms involving only the detected protons, and those in which additional nucleons must have participated, on the basis of missing momentum. In the case of ${}^{12}\mathrm{C}({\pi }^{+},ppp)$, we identify events due to the two step process of ${\pi }^{+}p$ quasielastic scattering followed by two-nucleon absorption. Estimates are made for the total cross sections for the various absorption mechanisms.

The impact parameter dependence of light charged particle $(p,d,t,\alpha )$ emission has been studied using an impact parameter selection based on coincident detection of residues or fission fragments. The energy spectra at twelve angles between $20°$ and $150°$ have been fit by a multiple moving source parametrization. The angle and energy integrated preequilibrium proton multiplicities decrease with increasing impact parameter in qualitative agreement with a Fermi jet calculation. The preequilibrium $d/p$ and $t/p$ multiplicities increase slowly with increasing impact parameter and are nearly identical at the two bombarding energies. The preequilibrium $\alpha /p$ ratio shows a less consistent dependency on impact parameter but decreases significantly with increasing bombardment energy. A calculation of the $d/p$ and $t/p$ multiplicity ratios with a transport model incorporating complex particle emission is quite successful in reproducing the absolute magnitude, impact parameter dependence, and bombarding energy dependence of the experimental total multiplicities.

The polarization degrees of freedom in photoinduced two-nucleon knockout from finite nuclei are studied. It is pointed out that they open good perspectives to study the dynamics of dinucleons in the medium in detail. The $(\gamma ,pp)$ and $(\gamma ,pn)$ angular cross sections, photon asymmetries, and outgoing nucleon polarizations are calculated for the target nuclei ${}^{16}$O and ${}^{12}$C and photon energies ranging from 100 up to 500 MeV. It is investigated to which degree the two-nucleon emission reaction is dominated by photoabsorption on ${}^3{S}_1\mathrm{}(T=0\mathrm{})\mathrm{}$ proton-neutron and ${}^1{S}_0\mathrm{}(T=1\mathrm{})\mathrm{}$ proton-proton pairs in the nuclear medium. The calculations demonstrate that dominance of $S$-wave photoabsorption in the $(\gamma ,pn)$ channel does not necessarily imply that the reaction mechanism is similar to what is observed in deuteron photodisintegration.

In light of recent developments in fission studies such as slow saddle to scission motion and spin equilibration near the scission point, the theory of fission fragment angular distribution is examined and a new statistical prescission point model is developed. The conditional equilibrium of the collective angular bearing modes at the prescission point, which is guided mainly by their relaxation times and population probabilities, is taken into account in the present model. The present model gives a consistent description of the fragment angular and spin distributions for a wide variety of heavy and light ion induced fission reactions.

We discuss the effects of multiphonon excitations on heavy-ion fusion reactions at energies near and below the Coulomb barrier, focusing especially on the role of anharmonicities. We carry out a systematic study of those effects on the excitation function of the fusion cross section and on the fusion barrier distribution, by using the vibrational limit of the interacting boson model. We also analyze the recently measured high-precision data of the ${}^{16}$O + ${}^{148}$Sm fusion reaction with this model and discuss the anharmonic properties of the quadrupole as well as the octupole vibrations in ${}^{148}$Sm. Negative and positive static quadrupole moments are deduced for the first 2${}^{+}$ and 3${}^{-}$ states in ${}^{148}$Sm, respectively. It is shown that the fusion barrier distribution strongly depends on the sign of the quadrupole moments, suggesting that subbarrier fusion reactions offer an alternative method to extract the static quadrupole moments of phonon states in spherical nuclei.

We use a simplified model which is based on the same physics as inherent in most statistical models for nuclear multifragmentation. The simplified model allows exact calculations for thermodynamic properties of systems of large number of particles. This enables us to study a phase transition in the model. A first order phase transition can be tracked down. There are significant differences between this phase transition and some other well-known cases.

We study the eikonal model for the nuclear-induced breakup of Borromean nuclei, using ${}^{11}\mathrm{Li}$ and ${}^6\mathrm{He}$ as examples. The full eikonal model is difficult to realize because of six-dimensional integrals, but a number of simplifying approximations are found to be accurate. The integrated diffractive and one-nucleon stripping cross sections are rather insensitive to the neutron-neutron correlation, but the two-nucleon stripping does show some dependence on the correlation. The distribution of excitation energy in the neutron-core final state in one-neutron stripping reactions is quite sensitive to the shell structure of the halo wave function. Experimental data favor models with comparable amounts of $s$ and $p$ waves in the ${}^{11}\mathrm{Li}$ halo.