We use a simple potential model to calculate low-lying mirror states of ${}_{}{}^{11}{}_{}{}^{}\mathrm{Be}$ and ${}_{}{}^{11}{}_{}{}^{}\mathrm{N}$. We make predictions for energies and widths in ${}_{}{}^{11}{}_{}{}^{}\mathrm{N}$.

The calculation of the spreading width of a compound nuclear reaction caused by a symmetry breaking K-body force acting in an A-body system (K≪A, usually K=2) involves the determination of the local average square matrix element in A-body space. This problem is reduced to finding the global mean square matrix element ${\mathit{v}}^2$ in K-body space. The result is a compact formula for the spreading width which contains ${\mathit{v}}^2$ as an input. Our method is based on the dilute gas approximation for excitons close to the Fermi edge. The relative strength of the contributions of operators with different exciton rank as well as the connection between the energy dependence of the spreading width and the body rank of the underlying interaction are established.

The influence of short-range correlations on the momentum and energy distribution of nucleons in nuclei is evaluated assuming a realistic meson-exchange potential for the nucleon-nucleon interaction. Using the Green-function approach the calculations are performed directly for the finite nucleus ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ avoiding the local density approximation and its reference to studies of infinite nuclear matter. The nucleon-nucleon correlations induced by the short-range and tensor components of the interaction yield an enhancement of the momentum distribution at high momenta as compared to the Hartree-Fock description. These high-momentum components should be observed mainly in nucleon knockout reactions like (e,e’p) leaving the final nucleus in a state of high excitation energy. Our analysis also demonstrates that non-negligible contributions to the momentum distribution should be found in partial waves which are unoccupied in the simple shell model. The treatment of correlations beyond the Brueckner-Hartree-Fock approximation also yields an improvement for the calculated ground-state properties.

We investigate effects of finite core spin in two-neutron halos in the three-body model consisting of two neutrons and a core. The states in the neutron-core subsystem can then have an additional splitting due to the coupling of the neutron and core spins. The connection between the structure of the total system and the states of the neutron-core subsystem depends strongly on this spin splitting. However, the spatial structure is essentially unchanged. The neutron momentum distribution in a nuclear dissociation reaction will consist of a broad and a narrow distribution arising from the two spin split neutron-core virtual states. The large distance behavior is investigated and the conditions for the Efimov effect turn out to be more restrictive. The magnetic moment is equal to the core value independent of spin splitting and energies of the neutron-core states. The excited states of opposite parity depend strongly on the spin splitting. The parameters in our numerical examples are chosen to be appropriate for ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ and ${}_{}{}^{19}{}_{}{}^{}\mathrm{B}$.

The random-phase approximation (RPA) is examined in a boson formalism and special attention is focused on the problem of the violation of the Pauli principle affecting this theory. A mapping technique is discussed and the boson image of a two-body fermion Hamiltonian is constructed. Within the boson space so defined, an extension of RPA is proposed where structure and energy of the ground state, as well as those of the one-phonon states, are analyzed with regard to the role of the spurious components associated with a violation of the Pauli principle. A multistep minimization procedure for the determination of a better ground state is also examined. Numerical tests are performed within the Lipkin-Meshkov-Glick model.

Neutron capture resonances produced in ${}_{}{}^{177}{}_{}{}^{}\mathrm{Lu}$ by thermal neutrons are shown to gamma decay with intensities which are dependent on a ΔK selection rule. The difference between ΔK- forbidden (and ΔK-allowed) transition rates, corrected for the energy dependence, when summed over all forbidden (and allowed) transitions and divided by the number of transitions is 1.37 photons/${10}^7$ neutron captures/${\mathrm{MeV}}^5$ for the forbidden transitions and 5.49 photons/${10}^7$ neutron captures/${\mathrm{MeV}}^5$ for the allowed transitions which gives a ratio between forbidden and allowed transitions of 0.26. If we require that allowed and forbidden transitions only be compared within the same spin and parity group, many transitions are excluded because there are no forbidden transitions to negative parity states. The average values for the forbidden and allowed transition ensembles are then 0.59 and 1.31, respectively, giving a ratio of forbidden to allowed transition intensities of 0.45.

Using the finite-temperature Hartree-Fock-Bogoliubov formalism we analyze the properties of the nuclei ${}_{}{}^{152,154,156}{}_{}{}^{}\mathrm{Dy}$ at the quasicontinuum region from I=0ħ to 70ħ and excitation energy up to approximately 16 MeV. We discuss energy gaps, shapes, moments of inertia, and entropy among others. The role of shape fluctuations is studied in the frame of classical statistics and we find large effects on several observables. A very rich structure is found in terms of excitation energy and angular momentum.

The electromagnetic decay of the nuclei ${}_{}{}^{152,154,156}{}_{}{}^{}\mathrm{Dy}$ is analyzed using microscopic Hartree-Fock calculations at finite temperature. The theoretical collective transition probabilities are implemented in numerical simulations to produce theoretical spectra. Thermal shape fluctuations are also taken into account. The inclusion of these correlation is crucial in order to understand the main features of the collective E2 spectra of these isotopes at different energies. The theoretical calculations suggest a shape change as responsible for the unusual features of the spectrum of the nucleus ${}_{}{}^{154}{}_{}{}^{}\mathrm{Dy}$ at high energy.

The high-spin yield fraction (HSF) for the fission product ${}_{}{}^{132}{}_{}{}^{}\mathrm{I}_{}^{\mathit{m},}{}_{}{}^{}$g has been measured as a function of fragment emission angle (90° ≥Θ≥10°) in the ${}_{}{}^{237}{}_{}{}^{}\mathrm{Np}$(${\mathrm{\alpha }}_{29\mathrm{M}\mathrm{e}\mathrm{V}}$,f) system. It was seen that the HSF for ${}_{}{}^{132}{}_{}{}^{}\mathrm{I}$ or corresponding fragment (${\mathrm{\approxeq }}^{134}$I) spin initially decreases as emission angle decreases from 90° to ≊45° and then steadily increases at lower angles (Θ<45°). Contrary to the present observation in odd-Z ${}_{}{}^{241}{}_{}{}^{}\mathrm{Am}$ fission, earlier we had observed that fragment spin continuously decreases to a limit with decrease in emission angle from 90° to 20° in even-even ${}_{}{}^{242}{}_{}{}^{}\mathrm{Pu}$ fission. These data have been analyzed in the framework of the collective mode model invoking the effect of single particle spin. It is seen that for an odd-Z or A fissioning nucleus, angular variation of fragment spin could be accounted for on the basis of coupling between the odd nucleon spin (j≥k≊4ħ) projections and spin due to the collective rotational (tilting) degrees. Collective rotational degrees govern fragment spin for even-even fissioning nucleus.

The fragment angular distributions and excitation functions of the fission following complete fusion (FFCF) have been measured after separating them from targetlike-fragment fission (TLFF) for the ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$${+}^{232}$Th system in the bombarding energy range of 84.5 to 106.5 MeV. The fraction of the targetlike-fragment fission was observed to increase with decreasing bombarding energy below the Coulomb barrier. The excitation function for fission following complete fusion reaction agrees well with coupled channel calculations. However, the 〈${\mathit{l}}^2$〉 values derived from the fragment anisotropy data of the FFCF events are found to be much larger than those calculated using the coupled channel transmission coefficient values. The discrepancy between the experimental and calculated 〈${\mathit{l}}^2$〉 values increases as the bombarding energy is decreased below the barrier.

The inclusive parallel momentum distributions of ${}_{}{}^9{}_{}{}^{}\mathrm{Li}$ fragments from the breakup of a secondary ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ beam have been measured at 66 MeV/nucleon over a wide range of targets ${(}^9$Be to ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$). The measurements were performed using a zero-degree fragment separator as an energy-loss spectrometer operating in a dispersion matched mode. Earlier measurements have been extended here to the case of breakup by ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ where a distribution with a width of FWHM=38.1±1.9 MeV/c was observed. Together with a remeasurement of breakup on ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$ (FWHM)=42.8±2.6 MeV/c) a weak dependence of distribution width on target nucleus was observed. A discussion of the nature of the momentum distributions and relationship to the structure of the halo is presented in the light of recent calculations. It is concluded that the ${}_{}{}^9{}_{}{}^{}\mathrm{Li}$ fragment parallel momentum distributions are relatively insensitive to the reaction and reflect the extended neutron distribution of the halo.

Measurements of prompt neutron energy spectra and angular distributions from mass and kinetic energy selected fission fragments were carried out in the thermal neutron fission of ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$. Neutron energy was determined by the time-of-flight technique and fission fragment energy and angle were measured using a back-to-back gridded ionization chamber. The measured angular distributions of neutrons emitted from fragment pairs of various mass and kinetic energy were compared with results of Monte Carlo calculations assuming neutron emission from fully accelerated fragments to determine the component of neutrons which may be emitted in the prescission stage. The calculations were carried out using as inputs the measured center-of-mass neutron energy spectra and multiplicites and assuming isotropic emission of neutrons in the center-of-mass frame of both the fission fragments, and a three source fitting of the angular distributions was done to deduce the component of prescission neutrons. The value of the prescission neutron multiplicity averaged over all fragment masses is found to be 0.25±0.05 (about 10% of the total neutron multiplicity). The present results have been discussed on the basis of the energy damping and time scale of the saddle to scission transition in the thermal neutron induced fission process.

The azimuthal distributions of light particles (Z=1,2) with respect to the entrance channel reaction plane are investigated for Ar+V collisions in order to characterize the modes of collective motion in intermediate energy heavy-ion reactions. At a beam energy of 35 MeV/nucleon, light charged particles are found to exhibit an enhanced emission in the reaction plane which increases with the mass of the detected particle. As the beam energy is increased to 100 MeV/nucleon, the anisotropy nearly vanishes, providing insight into the dynamics of these reactions in a transitional energy regime. The observed anisotropy exhibits signatures of two distinct modes of collective motion: attractive mean-field deflection and rotation of the fused system. A microscopic calculation based on mean-field mediated interactions plus nucleon-nucleon collisions reproduces both forms of collective motion and their associated azimuthal anisotropies. The calculation also suggests that the anisotropy due to mean-field deflection is established during the initial stages of the collision.

High-energy γ-ray spectra were measured following the reactions ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$${+}^{92}$Mo and ${}_{}{}^{50}{}_{}{}^{}\mathrm{Ti}$${+}^{60}$Ni forming the compound nucleus ${}_{}{}^{110}{}_{}{}^{}\mathrm{Sn}$ at the same excitation energy of 56 MeV. The angular momentum gated γ-ray spectra from both reactions can be described by standard statistical model calculations. The influence of particle and γ-ray decay during the formation time is found to be small in both reactions. This result is consistent with predictions from dissipative dyanmics calculations.

Central heavy-ion collisions in the (nearly) symmetric entrance channels ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$${+}^{27}$Al, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$${+}^{45}$Sc, ${}_{}{}^{87}{}_{}{}^{}\mathrm{Kr}$${+}^{93}$Nb, and ${}_{}{}^{129}{}_{}{}^{}\mathrm{Xe}$${+}^{139}$La have been systematically studied at many intermediate beam energies. The relative sizes of the three largest fragments in the central events are studied using new variables defined from charge Dalitz plots. Autocorrelations between these variables and the method used to select the central events are investigated. Also described are the hidden constraints on these variables that are imposed by definition. For increasing beam energies, the average values of these variables imply transitions from sequential binary disassembly to multifragmentation at beam energies of ∼50 and ∼30 MeV/nucleon in the ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$${+}^{45}$Sc and ${}_{}{}^{129}{}_{}{}^{}\mathrm{Xe}$${+}^{139}$La entrance channels, respectively. Similar trends are observed for the central ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$${+}^{27}$Al and ${}_{}{}^{87}{}_{}{}^{}\mathrm{Kr}$${+}^{93}$Nb reactions.

We have measured the zero-degree cross sections for proton inelastic scattering to the $1^{+}$, T=0 (12.7 MeV) and $1^{+}$, T=1 (15.1 MeV) states in ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ at 65, 100, 200, 300, and 400 MeV. The ratios of cross sections [dσ/dΩ($1^{+}$,T=0)]/[dσ/dΩ($1^{+}$,T=1)] at 0 ° are compared with the calculations in the distorted wave approximation using various effective nucleon-nucleon interactions. The experimental ratios are found to be smaller than the theoretical predictions. It was found that the experimental results were better described by modifying the isovector tensor terms of the effective interactions.

Pion-induced double charge exchange (${\mathrm{\pi }}^{+}$,${\mathrm{\pi }}^{\mathrm{-}}$) on ${}_{}{}^{76,78,80,82}{}_{}{}^{}\mathrm{Se}$, leading to the double isobaric analog states (DIAS) and the ground states of ${}_{}{}^{76,78,80,82}{}_{}{}^{}\mathrm{Kr}$, has been studied at a laboratory angle of $5^0$ and incident pion kinetic energy of 293.2 MeV. Cross sections for these transitions have been extracted, and those for the DIAS are compared to two simple models of pion double charge exchange.

The population of excited states in ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ and ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ has been investigated through the reactions ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${(}^{16}$O${,}^{12}$${\mathrm{C}}^{12}$C)α and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${(}^{16}$O${,}^{12}$${\mathrm{C}}^{16}$O)α, at beam energies of 80.5 and 99 MeV. The heavy-ion fragments from the breakup of the ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ and ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ nuclei were detected in coincidence, permitting a study of both the reaction kinematics and the spins of the fissioning states. These measurements indicate a series of states in ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ between 25 and 32 MeV with spins ranging from J=10 to 14 ħ. Evidence was also found for the breakup of ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ into ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ from states between 27 and 29 MeV.

Proton and α-particle energy spectra were measured in coincidence with evaporation residues from 252 and 295 MeV ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$${+}^{112}$Sn fusion reactions. Residues were separated from the beam using an electrostatic deflector and detected with surface barrier detectors. Light charged particles were detected with arrays of NaI detectors. Statistical model calculations based on standard parameter choices reproduce the spectra from the cold, low spin ${}_{}{}^{170}{}_{}{}^{}\mathrm{Pt}_{}^{\mathrm{*}}{}_{}{}^{}$ system. The effects of employing different methods of calculating transmission coefficients were explored. The optical model, ingoing wave boundary condition model, and a simple one-dimensional barrier penetration model from a fusion systematics analysis produce comparable satisfactory predictions. The Hill-Wheeler approximation for transmission coefficients gives unrealistic results for protons.

Quantum tunneling under the influence of an environment with nearly degenerate spectrum is considered. We first give a general derivation of the zero point motion formula in the sudden tunneling limit. The effects of a finite excitation energy of the environment are then considered by a perturbation method. Examples of linear oscillator coupling and rotational coupling show that the finite excitation energy can be represented by a dissipation factor and reduces the tunneling probability estimated in the limit of sudden tunneling. These examples clearly show that the applicability of the sudden tunneling approximation is governed by the details of the coupling as well as the relative time scales of the tunneling and the environmental degrees of freedom. We discuss some applications to heavy-ion fusion reactions.