A simple method is presented to evaluate the effects of short-range correlations on the momentum distribution of nucleons in nuclear matter within the framework of the Green’s function approach. The method provides a very efficient representation of the single-particle Green’s function for a correlated system. The reliability of this method is established by comparing its results to those obtained in more elaborate calculations. The sensitivity of the momentum distribution on the nucleon-nucleon interaction and the nuclear density is studied. The momentum distributions of nucleons in finite nuclei are derived from those in nuclear matter using a local-density approximation. These results are compared to those obtained directly for light nuclei like ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$.

The experimental data on positive parity, low-lying levels of the even ruthenium isotopes ${}_{}{}^{98-114}{}_{}{}^{}\mathrm{Ru}$ have been analyzed in the framework of the IBA-2 model, with the aim of identifying states having a large mixed-symmetry component. Energies, static and transition electric quadrupole and magnetic dipole moments as well as mixing and branching ratios of the relevant levels have been considered. It appears that the properties of all low-lying levels in these isotopes, for which the comparison between experiment and theory is possible, can be satisfactorily described by the standard IBA-2 model, provided proper account is taken of the presence at low energy of states having a mixed-symmetry character. It seems possible to identify, in each isotope, a few states having such a character, the lowest ones being the $2_3^{+}$ and $3_1^{+}$ levels. Some indications for the presence above the $3_1^{+}$ level of a band of states having $J^{\pi }=5_1^{+}, 7_1^{+}, 9_1^{+}$ and a comparable degree of mixed symmetry are pointed out for the heavier nuclei of the chain.

We have used cranking calculations, based on the total Routhian surface formalism, to investigate the medium spin structure (I<25ħ) of light tellurium isotopes with A≤122. Several energetically favored noncollective oblate (γ=+60°) states, based on the aligned π[(${\mathit{g}}_{7/2}$${)}^2$${]}_{6^{+}}$⊗ν[(${\mathit{d}}_{5/2}$${)}^{\mathit{x}}$(${\mathit{h}}_{11/2}$${)}^{\mathit{y}}$] configuration (x=0,1, y=1-4), are found to coexist with weakly deformed collective structures. Particularly favored ${16}^{+}$ states are predicted for the even Te isotopes, while 39/$2^{\mathrm{-}}$ states are predicted for the odd Te isotopes. The theoretical results are compared to available experimental data.

Microscopic analysis of the quantum (shell) effects related to the presence of the hexadecapole (${\mathit{Y}}_{4\mathrm{\mu }}$; μ=0,2,4) components in the nuclear mean field is performed for the superdeformed nuclei in the mass A ∼ 150 region using the deformed Woods-Saxon potential. No shell effects favoring the ${\mathit{C}}_4$-symmetry are found. The calculations indicate, however, the existence of the ${\mathrm{\alpha }}_{44}$-deformation driving orbitals whose occupation might induce an ${\mathrm{\alpha }}_{44}$-polarization effect. For ${}_{}{}^{149}{}_{}{}^{}\mathrm{Gd}$ and ${}_{}{}^{153}{}_{}{}^{}\mathrm{Dy}$ nuclei, in which the existence of the ${\mathit{C}}_4$-symmetry effects is suspected, properties of several excited particle-hole configuration are analyzed.

A systematic numerical investigation of a recently developed nuclear structure approach is presented which diagonalizes the Hamiltonian in the space of the symmetry-projected Hartree-Fock-Bogoliubov (HFB) vacuum and symmetry-projected quasiparticle excitations with respect to it. The underlying HFB transformation, which is assumed to be time-reversal and axially symmetric, is determined by variation after the projection. The model allows the use of large basis systems. It has been applied to the calculation of energy spectra of several even-even, odd-odd, and odd mass nuclei in the $\mathrm{sd}$ shell with mass numbers reaching from $A=20-30\mathrm{}$. The Chung-Wildenthal interaction has been used. Good agreement with the exact shell model diagonalization and a considerable improvement on a previous approach, where the HFB transformation was significantly more restricted, is obtained.

The ${}_{}{}^9{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^9{}_{}{}^{}\mathrm{Li}$ mirror nuclei are studied in a microscopic α${+}^3$He+p+p and α${+}^3$H+n+n four-cluster model using the stochastic variational method. The ${}_{}{}^7{}_{}{}^{}\mathrm{-}_{}^7{}_{}{}^{}$Li and ${}_{}{}^8{}_{}{}^{}\mathrm{-}_{}^8{}_{}{}^{}$Li mirror subsystems are also investigated with the same effective interaction. The calculated ground-state energies, the radii, and the densities of the nucleons are in good agreement with the experimental data. The magnetic and quadrupole moments, except for the magnetic moments of ${}_{}{}^8{}_{}{}^{}\mathrm{B}$ and ${}_{}{}^8{}_{}{}^{}\mathrm{Li}$, are also reproduced well. The quadrupole moments of ${}_{}{}^9{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ are predicted to be -5.04 e${\mathrm{fm}}^2$ and -6.11 e${\mathrm{fm}}^2$. A possibility of the existence of neutron (proton) halo structure is studied.

Proton momentum distributions of the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$, and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ nuclei are calculated by a model using the natural orbital representation and the experimental data for the momentum distribution of the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ nucleus. The model allows realistic momentum distributions to be obtained using only hole-state natural orbitals (or mean-field single-particle wave functions as a good approximation to them). To demonstrate the model two different sets of wave functions were employed and the predictions were compared with the available empirical data and other theoretical results.

The combined effect of an octupole and hexadecapole term, when added to a strongly deformed axial harmonic oscillator potential, is carefully studied. The problem is nonintegrable, which calls for a thorough classical analysis in order to understand the quantum mechanical results. Shell structure which is found for particular combinations of the deformation parameters are explained in terms of dominant classical periodic orbits. Using the ‘‘removal of resonances’’ method as an approximation, explicit expressions in terms of the deformation parameters are obtained for effective winding numbers, which in turn generate the quantum shell structure. A mutual cancellation of the octupole and hexadecapole deformation in prolate superdeformed systems has been discovered. Strongly oblate deformed potentials can yield shell structure only when even higher multipoles are added while prolate potentials can support shell structure for arbitrary higher multipoles.

A fully covariant approach to a density dependent hadron field theory is presented. The relation between in-medium NN interactions and field-theoretical meson-nucleon vertices is discussed. The medium dependence of nuclear interactions is described by a functional dependence of the meson-nucleon vertices on the baryon field operators. As a consequence, the Euler-Lagrange equations lead to baryon rearrangement self-energies which are not obtained when only a parametric dependence of the vertices on the density is assumed. It is shown that the approach is energy-momentum conserving and thermodynamically consistent. Solutions of the field equations are studied in the mean-field approximation. Descriptions of the medium dependence in terms of the baryon scalar and vector density are investigated. Applications to infinite nuclear matter and finite nuclei are discussed. Density dependent coupling constants obtained from Dirac-Brueckner calculations with the Bonn NN potentials are used. Results from Hartree calculations for energy spectra, binding energies, and charge density distributions of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{40,48}{}_{}{}^{}\mathrm{Ca}$, and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ are presented. Comparisons to data strongly support the importance of rearrangement in a relativistic density dependent field theory. Most striking is the simultaneous improvement of charge radii, charge densities, and binding energies. The results indicate the appearance of a new ‘‘Coester line’’ in the nuclear matter equation of state.

The tilted-axis cranking approach is investigated in a simple model. Band-crossing frequencies, gains in alignments, and quadrupole moments along the yrast line are studied as functions of the tilting angle.

A study of the reaction ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$${(}^{20}$Ne${,}^{19}$Ne n) at 48A MeV has been performed at the GANIL facility. The inclusive excitation spectrum above 12 MeV excitation is dominated by a broad structureless bump. Calculations performed in the framework of the Bonaccorso-Brink model predict that the absorption process (transfer+inelastic breakup) dominates over the elastic breakup process. Comparison of the neutron multiplicity calculated in a statistical model with the measured one confirms a significant contribution of the direct processes (elastic and inelastic breakup). The neutron yield to the ground state of the ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$ is maximal in the forward direction. Comparisons with calculated neutron angular distributions show the effect of the final state interaction.

The particle decay ensuing from the reactions 86.0 MeV ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{148}{}_{}{}^{}\mathrm{Sm}$ and 239.1 MeV ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$ + ${}_{}{}^{100}{}_{}{}^{}\mathrm{Mo}$ was studied. These reactions each form ${}_{}{}^{164}{}_{}{}^{}\mathrm{Yb}$ compound nuclei excited to ≊ 54 MeV. Particle decay from compound nucleus producing reactions was selected by gating on the gamma-ray fold and the angular region of the particle emission. While there are no discernable differences in the dominant decay channels between the two reactions, there are fewer deuterons from the more symmetric system. This difference can be interpreted two ways: as a suppression of the emission of energetically expensive clusters during the time required for shape equilibration (which is predicted to be longer for the more symmetric entrance channel), or as an enhancement of the emission of energetically expensive clusters from the more asymmetric system at the very early stage of the collision when the initial energy deposited is only available to a reduced number of nucleons. The first explanation is identical to that used in recent high energy photon work while the second could be identified as the result of the emission of clusters on the multistep compound branch leading to the fusion of the low energy heavy ions. If the first explanation is adopted, the observed suppression is larger than predicted by a standard statistical decay model coupled to a dynamical fusion model, but consistent with work using high energy photons as a probe of fusion dynamics.

Measurement of various moments of the angular momentum distribution in fusion reactions of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$${+}^{115}$In has been carried out at near- and below-barrier energies using a multielement BGO multiplicity detector set-up. Fusion events were selected using the alpha particle evaporation events at backward angles with respect to the beam direction. It is found that for the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${+}^{115}$In reaction, the moments of the l distribution match well with the calculations based on the one-dimensional barrier penetration model, whereas in the case of the ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$${+}^{115}$In reaction, the experimental values are higher than the predictions of the above theoretical calculations, and could be explained by incorporating the coupling of projectile deformation in the barrier penetration calculations. The present work brings out the role of projectile deformation in enhancing the higher moments of the fusion l distribution around barrier energies.

A differentially pumped windowless ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ gas target was used to measure angle averaged excitation functions for binary decay of the ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$${+}^{20}$Ne reaction into low-lying states of ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$${+}^{20}$Ne, ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$${+}^{24}$Mg, and ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$${+}^{16}$O, and for binary decay of the ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$${+}^{20}$Ne reaction into low-lying states of ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$${+}^{20}$Ne and ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$${+}^{16}$O. The ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$${+}^{20}$Ne measurements span the region of excitation energy in ${}_{}{}^{48}{}_{}{}^{}\mathrm{Cr}$ from 50.6 to 67.7 MeV ${(}^{28}$Si beam energies from 87.2 to 128.2 MeV). The reaction ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$${+}^{20}$Ne was investigated over a region in ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ti}$ from 48.75 to 71.0 MeV ${(}^{24}$Mg beam energies from 70.8 to 119.75 MeV). Angular distribution measurements were made for ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$${(}^{28}$Si${,}^{24}$Mg${)}^{24}$Mg at excitation energy=56.22 MeV and for ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$${(}^{24}$Mg${,}^{16}$O${)}^{28}$Si at excitation energy=53.02 and 57.75 MeV. Both systems display evidence of statistically significant correlated resonance phenomena, but the resonances are dominated by spins comparable to the grazing angular momenta of the respective entrance channels, and are not analogs of the molecular configurations that dominate the ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$${(}^{24}$Mg${,}^{24}$${\mathrm{Mg}}^{\mathrm{*}}$${)}^{24}$${\mathrm{Mg}}^{\mathrm{*}}$ reactions.

Fusion excitation functions were obtained for ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{70,72,73,74,76}{}_{}{}^{}\mathrm{Ge}$ at energies from about 4 MeV below to 15 MeV or more above the Coulomb barrier. The barrier parameters extracted from the data agree within 2% with those obtained from the systematics for fusion above the barrier. Low-energy enhancements are observed whose behavior is explained within the context of simple model calculations by assigning appropriate degrees of freedom to the respective reaction partners. These degrees of freedom are consistent with those used in similar analysis of different data sets where either the same projectile or the same targets were used. An analysis of the barrier distributions is made which supports the previous conclusions.

The charge and mass of the projectile-like fragments produced in the 15-MeV per nucleon ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$${+}^{209}$Bi reaction were determined for products detected near the grazing angle. Neutron number-charge (N-Z) distributions were generated as a function of the total kinetic energy loss and parametrized by their centroids, variances, and correlation coefficients. Although the initial system is very asymmetric, after the interaction, a drift of the charge and mass centroids toward further asymmetry is observed. The production of projectile-like fragments is consistent with a tendency of the projectile-like fragments to retain the projectile neutron-to-proton ratio 〈N〉/〈Z〉≃1. The correlation coefficient remains well below 1.0 for the entire range of total kinetic energy lost. Predictions of two nucleon exchange models, Randrup’s and Tassan-Got’s, are compared to the experimental results. The models are not able to reproduce the evolution of the experimental distributions, especially the fact that the variances reach a maximum and then decrease as function of the energy loss. This behavior supports the hypothesis that some form of projectile-like fragmentation or cluster emission is perturbing the product distribution from that expected from a damped mechanism.

The fragmentation of E/A=40 MeV ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ projectiles into exit channels containing only p, d, t, ${}_{}{}^3{}_{}{}^{}\mathrm{He}$, α, ${}_{}{}^6{}_{}{}^{}\mathrm{He}$, ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$, and ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ fragments has been investigated. Relative shifts between the average longitudinal velocity of each fragment type were measured with ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$ and ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ targets. A post-breakup Coulomb acceleration component of these shifts was isolated. Its magnitude indicates that the projectile broke up while in near contact with the target. On the other hand, correlations between projectile fragments indicate that a significant fraction of these fragments are produced by the sequential decay of long- and short-lived unstable intermediates. A fully sequential decay process, although consistent with the experimental relative angle distributions, fails to reproduce the correlation function. Thus, a picture emerges of a prompt breakup step producing stable and unstable particles with the subsequent decay of the latter extending over a long time period.

Fusion excitation functions for the reactions ${}_{}{}^{144,148,154}{}_{}{}^{}\mathrm{Sm}$ and ${}_{}{}^{186}{}_{}{}^{}\mathrm{W}$ + ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$ + ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ have been measured with high precision, both in the cross sections and the small energy intervals, thus allowing meaningful fusion barrier distributions to be extracted. In this representation it is clearly seen that the excitation functions are not smooth and featureless; each is unique and is shown to depend on the details of the structure of the interacting nuclei. The effects of excitation of the collective single phonon states in ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$ are evident. For the ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ projectile, the role of additional coupling to neutron stripping channels with positive Q values can be seen. As expected, the barrier distributions associated with ${}_{}{}^{154}{}_{}{}^{}\mathrm{Sm}$ and ${}_{}{}^{186}{}_{}{}^{}\mathrm{W}$ are dominated by deformation effects. However, the data appear to display sensitivity to additional couplings, even though they involve relatively weak inelastic and transfer channels.

The multiplicities of prescission protons and α particles in the reaction ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$${+}^{232}$Th at 104, 110, 116, and 118 MeV have been measured. The observed multiplicities are much larger than the prediction of the statistical model without the introduction of fission delay. An analysis of the prescission proton and α data along with that for neutrons (measured earlier) has been made using deformed optical model and deformation-dependent particle binding energies. Simultaneous fits to the charged particle and neutron data required a total fission time scale in the range of (25–80)× ${10}^{\mathrm{-}21}$ s. For this system, the mean kinetic energies of the prescission particles are insensitive to the division of the total delay time into presaddle and postsaddle components; however, the neutron and charged particle multiplicity data are sensitive to the deformation of the saddle-to-scission emitter. The analysis shows that postsaddle emission takes place close to the scission point.

We report excitation function for the reaction ${}_{}{}^{130}{}_{}{}^{}\mathrm{Te}(p, n){}_{}{}^{130}{}_{}{}^{}\mathrm{I}$ in the energy range ≈4-18 MeV. The measurements were done employing stacked foil activation technique and enriched isotope. To the best of our knowledge this excitation function has been reported for the first time. The theoretical analysis of the excitation function has been done employing both the semiclassical as well as quantum mechanical descriptions of the preequilibrium emission. In general, theoretical calculations agree well with the experimental data.