Nuclear structure with the dinuclear model

The dinuclear system concept is applied to the explanation of the structure of nuclei. The appearance of a low-lying band with negative parity states near the ground-state band in actinides and other nuclei is described by oscillations of the dinuclear system in the mass-asymmetry coordinate. The results for the parity splitting and electric multipole moments in alternating parity bands of these nuclei are in agreement with experimental data. The ground-state band and the superdeformed band of ⁶⁰Zn are interpreted as being caused by α-particle and Be clusterizations, respectively. Hyperdeformed nuclei are assumed as dinuclear systems which could directly be built up in heavy-ion collisions. Signatures of hyperdeformed states in such reactions could be γ transitions between these states and their decay into the nuclei forming the hyperdeformed nucleus.     

Using molecules to measure nuclear spin-dependent parity violation

Nuclear spin-dependent parity violation arises from weak interactions between electrons and nucleons and from nuclear anapole moments. We outline a method to measure such effects, using a Stark-interference technique to determine the mixing between opposite-parity rotational/hyperfine levels of ground-state molecules. The technique is applicable to nuclei over a wide range of atomic number, in diatomic species that are theoretically tractable for interpretation. This should provide data on anapole moments of many nuclei and on previously unmeasured neutral weak couplings.     

Nuclear shadowing and heavy-ion collisions at high energies

Nuclear shadowing effects for quarks and gluons are calculated using information on diffractive deep inelastic scattering on a nucleon. Role of these effects in interactions of hadrons and nuclei with nuclei at high energies is investigated. A decrease in particle densities for heavy-ion collisions in comparison with the Glauber model is predicted and nuclear modification factors are calculated. Distributions of gluons in nuclei are used to predict suppression of heavy quarkonia. The parameter-free calculation of J/ψ in DAu and AuAu collisions is in a good agreement with recent RHIC data. Predictions for heavy quarkonia suppression in heavy-ion collisions at LHC are formulated.     

Production of unstable nuclei far from the stability line: its scope and limitations

Recent improvements in isotope separators can be utilized along with the availability of a wide range of nuclear species from the heavy-ion fragmentation process to study hyperfine interactions. We have measured the magnetic moments of mirror nuclei using this method at the Lawrence Berkeley Laboratory's Bevalac heavy-ion accelerator. We present the merits, applicability and limitations of the technique.     

TWO TEMPERATURES EMISSION OF RELATIVISTIC α-PARTICLES IN HIGH-ENERGY HEAVY-ION COLLISIONS

We have performed an experimental study of the α-fragments emitted from collisions between emulsion nuclei and heavy-ion projectiles at beam energies beyond 1A GeV. It is shown that the transverse momentum distributions of relativistic α-particles give evidence for two effective temperatures emission in high-energy heavy-ion collisions. The data might take on a new signature for the phase transition from hadron matter to quark matter.     

Hadrons in nuclei

Changes of hadronic properties in dense nuclear matter as predicted by theory have usually been investigated by means of relativistic heavy-ion reactions. In this talk I show that observable consequences of such changes can also be seen in more elementary reactions on nuclei. Particular emphasis is put on a discussion of photonuclear reactions; examples are the dilepton production at ≈1 GeV and the hadron production in nuclei at 10–20 GeV photon energies. The observable effects are expected to be as large as in relativistic heavy-ion collisions and can be more directly related to the underlying hadronic changes.     

THE ROLE OF NUCLEAR STRUCTURE EFFECTS ON THE NUCLEON EXCHANGE PROCESS IN DISSIPATIVE HEAVY-ION COLLISIONS

Based on the model of nucleon exchange,including the nucleon exchange between two nuclei and the particle-hole excitation in a nucleus,this paper discuss the role of the dynamical evolution in nuclear deformation and the shell effects on the nucleon exchange process in dissipative heavy-ion collision.A nice agreement between theoretical results and experimental data has been gotten.     

Quasimolecular nuclear optical potentials

A theory is presented to calculate potentials for the elastic nuclear heavy-ion scattering in a phenomenological way. The density properties of finite nuclei are derived with a schematic ansatz for the interaction energy between nuclear matter. The same interaction energy is applied to the calculation of the real part of the heavy-ion potential, which is of the quasimolecular type. The imaginary part is connected with the outflow time of nuclear matter out of compressed regions of overlapping nuclei. The resulting cross section for the elastic O¹⁶-O¹⁶ scattering reproduces the experiment up to 30 MeV quite well. An effective compression modulus of the S³² compound system can be deduced from the scattering experiment. It results to be about 200 MeV.     

A systematic semi-microscopic analysis of the scattering of oxygen isotopes

A semi-microscopic theory for the scattering of nuclei near closed shells is discussed in detail and applied to the bulk of the presently available experimental data. The results generally indicate that the single-folding model can be used to extrapolate the effective interactions for heavy-ion scattering away from closed-shell systems. We particularly discuss the importance of the imaginary part of the valence interaction and the effects of higher-order reorientation and two-step transfer processes.     

A Possible Origin of e+e- Peaks in Heavy-Ion Collisions

The behavior of a neutral composite particle composed of a positron and an electron in the strong Coulomb field of a nuclear uquasimolecule formed in low-energy heavy-ion collions is examined. A strong attractive interaction between the composite particle and the Coulomb field is found when the combined nuclear charge of two nuclei is sufficiently large, which is possible to lead to the e⁺e^- pair production in heavy-ion collisions.     

S-matrix spin and parity decoherence and damping of coherent nuclear rotation: quantum chaos in dissipative heavy-ion collisions?

We extend the statistical reaction with memory approach to study off-diagonal spin and parity S-matrix energy autocorrelation in dissipative heavy-ion collisions. It is suggested that S-matrix spin and parity decoherence results in (i) damping of the coherent nuclear rotation and (ii) is a manifestation of quantum chaos in dissipative heavy-ion collisions.     

Polarization in heavy-ion reactions

A series of experiments is described in which beta-ray asymmetry has been used to determine polarization of heavy-ion reaction products¹²B and the present status of the studies of polarization phenomena in heavy-ion reactions is reviewed. A large amount of angular momentum sustained by the two colliding nuclei gives rise to polarization phenomena of reaction products. Coupling between the degrees of freedom accompanying the intrinsic and the relative motions is investigated from the systematic behaviour of polarization of reaction products disclosed by the experiments.     

Resonances: Population of low-level density regions?

A simple explanation based primarily on the binding energies of nuclei in the entrance channel and level densities calculated with the shell model is proposed to explain the occurence of resonances in heavy-ion reactions for sd-shell nuclei.     

An analysis of parity violating nuclear effects at low energy

We present an analysis of parity violating nuclear effects at low energy which attempts to circumvent the uncertainties due to the weak and strong nucleon-nucleon interactions at short distances. Extending Danilov's parametrization of the parity violating nucleon-nucleon scattering amplitude, we introduce six parameters: one for the long range contribution due to the pion exchange and five for the shorter range contributions. This choice gives an accurate representation of parity violating effects in the nucleon-nucleon system up to a lab energy of 75 MeV. For calculations in nuclei, we derive an effective two-body potential in terms of the parameters. The analysis of presently measured effects shows that they are consistent, and, in particular, that the circular polarization of photons in n + p → d + γ is not incompatible with the other measurements. It does not imply a dominant isotensor component.     

Heavy-ion total reaction cross sections

A one-parameter expression has been found which predicts with a smaller χ² than previous expressions, the total reaction cross sections for a large number of heavy-ion systems covering a wide energy range. The expression uses an interaction radius which is a sum of the equivalent uniform matter radii of the interacting nuclei plus and energy-dependent term.     

Parity non-conserving effects in neutron-nucleus scattering at thermal energies

The contribution of the neutron-nucleus component to parity non-conserving effects in neutron-nucleus scattering at thermal energies is considered for several nuclei. The wave function relative to the neutron-nucleus component incorporates for the first time physics which is usually accounted for by optical potential models (strength function and existence of a finite potential scattering length). Different models aiming to reproduce these quantities are developed. Some way to use directly information available from optical model wave functions is also proposed. The various results so obtained show that it is impossible to account for several parity non-conserving effects observed in ⁸¹Br, ¹¹¹Cd, ¹¹⁷Sn and ¹³⁹La with a single weak neutron-nucleus force, as it should be if the dominant parity admixture was taking place at the level of the neutron-nucleus component. Furthermore, its strength is too large compared to usual expectations. The only explanation left to account for these effects assumes that the dominant parity admixture takes place at the level of the compound nucleus.     

Simple estimates for Fermi jets

The phenomenon of Fermi jets is investigated in the approximation of two colliding potential wells filled with degenerate Fermi gases of nucleons. A model is formulated which largely bypasses the explicit treatment of the relative motion of the nuclei, assumed to be governed by the window friction mechanism. Formulae for the velocity distributions and differential cross sections for neutrons and protons jetting through either target or projectile are derived. The numerical results are investigated systematically over a wide range of nuclear reactions. It is shown that the net linear momentum carried away by Fermi jets accounts for only a rather minor fraction of the observed missing momentum in typical heavy-ion fusion reactions.     

Nuclear spin dependent atomic parity violation,nuclear anapole moments and the hadronic axial neutral current

Left-right asymmetries in atomic transitions, depending upon the nuclear spin, could be a source of information on the neutral hadronic axial current. We show that the relevant electroweak parameter can be extracted from experiment by measuring hyperfine component ratios which do not involve the knowledge of the atomic wave function. In the standard electroweak model, the parity violating electron-nucleus interaction associated with the hadronic axial neutral current is accidently suppressed and, as a consequence, dominated by the electron interaction with the nuclear anapole moment, which describes the effect of the parity violating nuclear forces on the nucleus electromagnetic current. One of our objectives was to identify the various physical mechanisms which determine the size of the nuclear anapole moments. As an important step, we have established a simple relation between the anapole moment and the nuclear spin magnetization. From this relation it follows that the computation of the anapole moment can be reduced to that of one-body operators. The basic tool is a unitary transformationW which eliminates the one-body parity violating potential from the nuclear hamiltonian. It generalizes, to more realistic situations, a procedure used by F.C. Michel in the case of constant nuclear density. The fact that the transformationW does not commute with the residual spin-dependent nucleon-nucleon interaction can be accounted for — within some approximation — by a renormalization of the effective coupling constants which appear in the one-body reduction of the two-body parity violating nucleon-nucleon interaction induced by meson exchange. A particular attention was paid to nuclear correlation effects. They are treated semi-empirically in the independent pair approximation. The nuclear anapole moments of⁸⁵Rb,¹³³Cs, and²⁰⁹Bi have been evaluated for three sets of parity violating meson-nucleon coupling constants, taking into account configuration mixing effects in a semi-empirical way. We suggest a possible strategy to disentangle the axial neutral current from the anapole moment contribution. It requires experiments, accurate to few tenths of a percent, performed on several heavy nuclei. The results should be collected in a two-dimensional plot involving a suitably chosen set of variables (X, Y). In an ideal situation — small theoretical uncertainties —the points corresponding to various nuclei should fall on a straight line which crosses the lineX=0 at a point the ordinate of which is the sought for axial coupling constant.