We report quantum Monte Carlo calculations of ground and low-lying excited states for nuclei with $A<~7$ using a realistic Hamiltonian containing the Argonne $v_{18}$ two-nucleon and Urbana IX three-nucleon potentials. A detailed description of the Green's-function Monte Carlo algorithm for systems with state-dependent potentials is given and a number of tests of its convergence and accuracy are performed. We find that the Hamiltonian being used results in ground states of both ${}^6$Li and ${}^7$Li that are stable against breakup into subclusters, but somewhat underbound compared to experiment. We also have results for ${}^6$He, ${}^7$He, and their isobaric analogs. The known excitation spectra of all these nuclei are reproduced reasonably well and we predict a number of excited states in ${}^6$He and ${}^7$He. We also present spin-polarized one-body and several different two-body density distributions. These are the first microscopic calculations that directly produce nuclear shell structure from realistic interactions that fit $\mathrm{NN}$ scattering data.

We studied the resonance behavior of the $\pi \mathrm{NN}$ system in the configuration $J^P{=0\mathrm{}}^{-},$ isospin 0. We applied nonrelativistic Faddeev equations with realistic local potentials for the pion-nucleon and nucleon-nucleon interactions in the $S_{11}$ and ${}^1{S}_0$ channels, respectively. A resonance was found in this specific state; it lies slightly above the $\pi \mathrm{NN}$ threshold and has a mass of 2018 MeV and a width of 1.75 MeV.

The high-spin behavior of ${}^{153}\mathrm{Eu}$ nucleus has been investigated via the ${}^{150}{\mathrm{N}\mathrm{d}(}^7\mathrm{Li},4n\gamma )$ reaction. The level structures of the nucleus built on the ${5/2}^{+}$ ground state and the ${5/2}^{-}$ excited state have been established up to spins ${39/2}^{+}$ and ${43/2}^{-},$ respectively, and are observed to be interleaved through strong $E1\mathrm{}$ transitions. From the $B\left(E1\mathrm{}\right)/B\left(E2\mathrm{}\right)\mathrm{}$ ratios of the high-spin region the intrinsic electric-dipole moment is deduced and is found to be $0.181\pm 0.007$ $e\mathrm{fm}$ and ${\beta }_3$ thus obtained is $\sim \mathrm{0.03.}$ The rotational features and magnetic moments indicate that an octupole correlated deformation has developed with the increasing spin. A theoretical study of the correlation between the ${\beta }_3$ and the band crossing frequency supports the conjecture of octupole deformation at high spin.

Various theoretical approaches to proton emission from spherical nuclei are investigated, and it is found that all the methods employed give very similar results. The calculated decay widths are found to be qualitatively insensitive to the parameters of the proton-nucleus potential, i.e., changing the potential parameters over a fairly large range typically changes the decay width by no more than a factor of $\sim$3. Proton half-lives of observed heavy proton emitters are, in general, well reproduced by spherical calculations with the spectroscopic factors calculated in the independent quasiparticle approximation. The quantitative agreement with experimental data obtained in our study requires that the parameters of the proton-nucleus potential be chosen carefully. It also suggests that deformed proton emitters will provide invaluable spectroscopic information on the angular momentum decomposition of single-proton orbitals in deformed nuclei.

The recently developed variational Wigner-Kirkwood approach is extended to the relativistic mean field theory for finite nuclei. A numerical application to the calculation of the surface energy coefficient in semi-infinite nuclear matter is presented. The new method is contrasted with the standard density functional theory and the fully quantal approach.

Using a single-particle basis with good angular momentum, $\alpha$ decay processes from deformed nuclei are described microscopically. The influence of the quadrupole deformation upon transitions to the ground state and to excited states is studied. It is found that the long-range proton-neutron interaction strongly affects the hindrance factor corresponding to the decay to excited states.

The Dirac structure of the nucleon self-energy in asymmetric nuclear matter cannot reliably be deduced from the momentum dependence of the single-particle energies. It is demonstrated that such attempts yield an isospin dependence with a wrong sign. Relativistic studies of finite nuclei have been based on such studies of asymmetric nuclear matter. The effects of these isospin components on the results for finite nuclei are investigated.

A particle-number conserving approach is presented to solve the nuclear mean-field plus pairing Hamiltonian problem with a realistic deformed Woods-Saxon single-particle potential. The method is designed for the state-dependent monopole pairing Hamiltonian $H{⁁}_{\mathrm{pair}}={\sum }_{\alpha \beta }{G}_{\alpha \beta }{c}_{\alpha }^{†}{c}_{\alpha ¯}^{†}{c}_{\beta ¯}{c}_{\beta }$ with an arbitrary set of matrix elements $G_{\alpha \beta }.$ Symmetries of the Hamiltonians on the many-body level are discussed using the language of $\mathcal{P}$ symmetry introduced earlier in the literature and are employed to diagonalize the problem; the only essential approximation used is a many-body (Fock-space) basis cutoff. An optimal basis construction is discussed and the stability of the final result with respect to the basis cutoff is illustrated in details. Extensions of the concept of $\mathcal{P}$ symmetry are introduced and their consequences for an optimal many-body basis cutoff construction are exploited. An algorithm is constructed allowing to solve the pairing problems in the many-body spaces corresponding to $p\sim 40$ particles on $n\sim 80$ levels and for several dozens of lowest lying states with precision $\sim$(1–2) % within seconds of the CPU time on a CRAY computer. Among applications, the presence of the low-lying seniority $s=0\mathrm{}$ solutions, that are usually poorly described in terms of the standard approximations (BCS, HFB), is discussed and demonstrated to play a role in the interpretation of the spectra of rotating nuclei.

The $\Delta I=1\mathrm{}$ staggering in odd superdeformed nuclei in the $A\sim 190$ region is systematically investigated. Most of the signature partners in this region show large-amplitude staggerings. The behavior is analyzed and parametrized in the conventional collective model. The spins of the signature partner pairs are assigned in a modified $\mathrm{ab}$ expression.

All the data available for the ground rotational bands of even-even actinide nuclei and rare-earth nuclei (with band crossing spins $I_c>~16$) are studied in terms of the staggering parameter, introduced in the discussion of superdeformed bands. Evidence of $\Delta I=4\mathrm{}$ bifurcation ($\Delta I=2\mathrm{}$ staggering) is observed in many cases. We study theoretically this bifurcation phenomenon in terms of the interacting boson model (IBM) by using the variation before projection (VBP) method. In our theoretical framework, the staggering phenomenon is found to originate from the finite boson number effect. The IBM explains the opposite signs of the staggering patterns between two neighboring nuclei, which are found experimentally. We perform also the full diagonalization of the IBM Hamiltonian and obtain consistent results with the VBP method. By introducing the $g$ bosons, we are able to reproduce even irregular or localized staggering patterns in the $\Delta I=4\mathrm{}$ bifurcation spectrum observed in some data.

We use the generator coordinate method to study the ${}^{12}$C($n,\gamma {)}^{13}$C and ${}^{12}$C($p,\gamma {)}^{13}$N reactions, as well as the ${}^{13}$C and ${}^{13}$N spectroscopy. The ${}^{12}$C wave functions are defined by three $\alpha$ particles in a regular triangle of size $R_C.$ Different configurations are considered, in order to analyze clustering effects. It is shown that spectroscopic properties of ${}^{13}$C and ${}^{13}$N are sensitive to the ${}^{12}$C wave function; reasonable agreement with experiment is found with $R_C$ values minimizing the ${}^{12}$C binding energy. The present study supports the suggestion of a halo structure for the 1/2${}^{+}$ excited state in ${}^{13}$C. The neutron and proton capture cross sections are in good agreement with experiment. Finally, we analyze distortion effects in the ${}^{12}\mathrm{C}+n$ wave functions.

We investigate the BCS treatment of neutron-proton pairing involving time-reversed orbits. We conclude that an isospin-symmetric Hamiltonian, treated with the help of the generalized Bogolyubov transformation, fails to describe the ground state pairing properties correctly. In order for the $\mathrm{np}$ isovector pairs to coexist with the like-particle pairs, one has to break the isospin symmetry of the Hamiltonian by artificially increasing the strength of the $\mathrm{np}$ pairing interaction above its isospin-symmetric value. We briefly discuss the prescription how to choose the coupling constant of this auxiliary isospin-breaking pairing force.

In order to study light unstable nuclei systematically, we propose a new method, the antisymmetrized molecular dynamics plus Hartree-Fock (AMD+HF) method. This method introduces the concept of the single particle orbits into the usual AMD. Applying the AMD+HF method to Be isotopes, it is found that the calculated lowest intrinsic states with plus and minus parities have rather good correspondence with the explanation by the two-center shell model. In addition, by active use of the single particle orbits extracted from the AMD wave function, we construct the first excited $0^{+}$ state of ${}^{10}\mathrm{Be}.$ The obtained state appears in the vicinity of the lowest $1^{-}$ state. This result is consistent with the experimental data.

Taking ${}^{94}\mathrm{Mo}{(d,d}^{\prime }{)}^{94}\mathrm{Mo}{(2\mathrm{}}_1^{+})$ at 13.2 MeV incident energy as an example, a discussion is made about the influence of known experimental uncertainties in the primary data on the precision of the $B\left(E2\mathrm{}\right)\mathrm{}$ and $B\left(\mathrm{IS}2\mathrm{}\right)\mathrm{}$ values, extracted in Coulomb-nuclear interference (CNI) measurements in a correlated way. The reflexes of judicious variations of three optical model parameters (around the global prescription) on the extracted values are also examined. The good quality of the data obtained with the S. Paulo Pelletron-Enge-Spectrograph facility is shown to allow for a 2–3% statistical uncertainty level for these quantities, within a distorted-wave Born approximation-deformed optical model approach. The accuracy of relative values of the ratio $B\left(E2\mathrm{}\right)/B\left(\mathrm{IS}2\mathrm{}\right),$ which may be linked to the ratio of proton to neutron quadrupole moments, is argued to be of similar order.

A simple method to estimate proton and two-proton separation energies of proton-rich nuclei is presented that is sufficiently accurate to allow the prediction of suitable candidates for observable diproton decay. The method is based on the systematics of measured particle separation energies. Predictions for proton-rich nuclei with $Z=18\mathrm{}-24$ are compared with the results of previous calculations.

Results from a 4$\pi$ solid angle measurement of the reaction ${\pi }^{+4\mathrm{}}$He$\to \mathrm{pppn}$ at incident pion energies of $T_{{\pi }^{+}}=$ 70, 118, 162, 239, and 330 MeV are presented. Integrated cross sections are given for the reactions where three nucleons participate, leading to energetic $\mathrm{}\left(\mathrm{ppp}\right)\mathrm{}$ or $\mathrm{}\left(\mathrm{ppn}\right)\mathrm{}$ final states, and for states where four nucleons are involved $\mathrm{}\left(\mathrm{pppn}\right)\mathrm{}$. The two three-nucleon absorption modes were investigated in particular, and an energy dependent isospin ratio of the cross sections of ${\sigma }_{\mathrm{ppn}}$/${\sigma }_{\mathrm{ppp}}$=3.6$\pm$1.3, 2.6$\pm$0.5, 1.8$\pm$0.3, 1.4$\pm$0.2, and 1.8$\pm$0.6 was determined from 70 to 330 MeV. The differential cross sections were described by a complete set of eight independent variables and compared to simple cascade and phase space models. From this analysis the contributions from initial state interactions to the multinucleon absorption cross sections were found to be more important at higher pion energies, while those from final state interactions are stronger at lower energies. However, both mechanisms combined were found to account for not more than one-third of the total $\mathrm{pppn}$ multinucleon yield. The remaining strength is reasonably well reproduced by phase space models, but shows a dependence on the incident pion's orbital angular momentum. The isospin structure of the $\mathrm{}\left(\mathrm{ppp}\right)\mathrm{}$ and $\mathrm{}\left(\mathrm{ppn}\right)\mathrm{}$ final states is not understood, nor are some structures in their distributions. The four-nucleon yield $\mathrm{}\left(\mathrm{pppn}\right)\mathrm{}$ was found to be weak (1–8 % of the total absorption cross section) and shows no evidence for a “double-$\Delta$” excitation.

Data for the elastic scattering of 27.8 MeV polarized ${}^6\mathrm{Li}$ from ${}^4\mathrm{He}$ and new data for the ${}^6\mathrm{Li}\to \alpha +d$ sequential breakup have been analyzed using the coupled-channels (CC) method with potentials derived via the cluster-folding (CF) procedure. The three low-lying $T=0\mathrm{}$ resonant excited states of ${}^6\mathrm{Li}$ as well as nonresonant continuum states were taken into account in the calculations by means of the continuum-discretized coupled-channels (CDCC) method. No adjustable parameters were used. The analysis shows a dominant role of the projectile breakup into $\alpha +d$ in the ${}^6{\mathrm{L}\mathrm{i}+}^4\mathrm{He}$ elastic scattering. The deuteron transfer process is found to be of less importance. The calculations reproduce the values of the differential cross section for the sequential breakup channels at forward scattering angles. Predictions for the direct breakup near the ${}^6\mathrm{Li}\to \alpha +d$ breakup threshold are made.

Excitation functions for one- and two-nucleon transfer in ${}^{28}$Si + ${}^{68}$Zn system have been measured at energies below the Coulomb barrier. The experiment was carried out by detecting the forward recoiling targetlike nuclei using the recoil mass separator, HIRA. With a pulsed beam, the time-of-flight of the recoils was measured and used to resolve the $M/q$ ambiguity. This enabled the determination of the two-nucleon transfer yields. The role of one- and two-nucleon transfer in the sub-barrier fusion cross-section enhancement has been investigated. It turns out that the coupling of the positive $Q$-value two-neutron transfer channel results in a significant contribution to the enhancement. Coupling to both the transfer and the inelastic channels is able to explain the observed enhancement.

Measurements of neutron multiplicity distributions of 1.94 to 5.0 GeV/$c$ proton-, antiproton-, pion-, kaon-, and deuteron-induced spallation reactions on thin (few mm thick) and thick (35–40 cm thick) targets are presented. The 4$\pi$ neutron detector employed for the first time to measure neutron multiplicity distributions from thick targets is described. Results for thin and thick targets are compared with intra- and internuclear cascade model calculations.

Spectra, angular distributions, and cross sections have been measured for $Z=3\mathrm{}–14$ fragments produced in 200-MeV ${}^4\mathrm{He}$-induced reactions on ${}^{\mathrm{nat}}\mathrm{Ag}$ and ${}^{197}\mathrm{Au}$ targets. In addition, isotopic yields were measured at forward angles. Two-component moving-source fits have been performed on the data to evaluate the relative contributions of nonequilibrium and equilibrium emission mechanisms. At forward angles, the complex fragment yields are dominated by nonequilibrium emission, with IMF energies extending from the emission barrier to momenta in excess of the incident beam. Backward of 90° the yields are nearly isotropic and exhibit spectra consistent with emission from an equilibrated composite nucleus.