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In this review, we present some general framework of sequential fragmentation, as provided by the newly proposed Fragmentation–Inactivation–Binary model, and to study briefly its basic and universal features. This model includes as particular cases most of the previous kinetic fragmentation models. In particular, we discuss how one arrives in this framework to the critical behaviour, called the shattering transition. This model is then compared to recent data on gold multifragmentation at 600 MeV/nucl.

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Composition of the neutron star matter above nuclear density is discussed within various models of superdense matter. Weak interaction processes, leading to neutrino cooling of dense, hot neutron star interior are reviewed. Neutrino emissivities of hot dense matter are shown to depend dramatically on the composition of matter. Cooling scenarios for young neutron stars, under various assumptions concerning the composition of the neutron star interior, are presented.

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Five possible regimes of nonresonant nuclear fusion reactions in dense stellar matter are briefly reviewed. They are: classical thermonuclear (weak screening) regime; thermonuclear strong screening burning regime; pycnonuclear (zero-temperature) regime; thermally enhanced pycnonuclear burning; and the regime intermediate between the thermo- and pycno-nuclear ones.

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Possible existence of a new decay mode of highly excited nuclear matter is discussed. Experimental data are shown which suggest that a violent nuclear disassembly occurs at matter density considerably smaller than in normal nuclei. Several attempts to find signatures of instantaneous multifragmentation are evaluated. Prediction of various models ranging from statistical to quantum molecular dynamical ones are presented.

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The complete fragmentation of highly excited nuclear systems into fragments of intermediate mass is observed in heavy-ion reactions at relativistic bombarding energies in the range of several hundreds of MeV per nucleon. Similar features are found for peripheral collisions between heavy nuclei and for more central collisions between a heavy and a light nucleus. The partition space explored in multifragment decays is well described by the statistical multifragmentation models. The expansion before breakup is confirmed by the analysis of the measured fragment energies of ternary events in their own rest frame. Collective radial flow is confined to rather small values in these peripheral-type reactions. Many conceptually different models seem to be capable of reproducing the charge correlations measured for the multifragment decays.

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Au on Au collisions at 150, 250 and 400 A MeV were studied with a high granularity detector covering approximately the forward hemisphere in the center of mass. Methods to select and test centrality of collisions are described. A midrapidity source emitting clusters up to neon is found at all energies. An analysis with a quantum statistical model shows that the chemical composition of the source implies surprisingly low freezeout temperatures and entropies. The kinetic energy spectra of the emitted clusters are found to deviate considerably from Boltzmann–Maxwell distributions. Instead, they are compatible with a blast scenario, the energy stored in the blast exhausting about 50% of the available energy. It is suggested that the blast provides the mechanism necessary to understand the cooling and hence the observed clusterization. Consequences of the nuclear blast on other observables are discussed.

abstract

Physics aspects of the energetic heavy-ion reactions, including changes in the bulk properties of matter during reactions and features of transport description, are discussed. Observables such as particle correlations, mean momentum in the reaction plane, light-fragment yields and spectra are reviewed, together with the information these observables provide on size of the emission region, magnitude of nuclear compressibility, production of entropy, and energy of collective expansion.

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When two nuclei collide, a large fraction of the excitation energy is dissipated through the emission of particles before reaching a state of statistical equilibrium. A theory of these processes based on the Boltzmann master equation approach is discussed. It is shown that it allows a comprehensive description of all the processes that may occur at incident energies of some ten MeV/nucleon.

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It is shown how first- and second-order interference effects can be used to measure the extent of chaotic light sources such as stars viewed from a great distance. The same technique can be applied in nuclear physics where the interference effect arises from the quantum statistics of identical particles. The results from an experiment attempting to measure the size of the participant zone in a heavy-ion reaction using bremsstrahlung photons as a probe are presented.

abstract

Results from the experimental program with light ion beams and heavy target nuclei at the CERN SPS could demonstrate the occurrence of an un unprecedented state of high density in hadronic matter. The thermal nature of the hadronic system has been investigated by analyzing spectra and production ratios of hadrons which reveal a large degree of rescattering of primary and secondary hadrons. Thermal photons from elementary quark–gluon interactions are considered a promising signal for the occurrence of a phase transition to the quark–gluon plasma. The predictions for thermal photons from elementary parton interactions are discussed and compared to the thermal emission rate of photons from a hot hadronic gas. Recent results from the photon spectrometers in heavy ion experiments are presented. Production cross sections of \(\pi ^0\) and \(\eta \) mesons are determined and the projectile and target mass dependence is discussed. An upper limit for the single photon yield was determined for central O + Au reactions. Recent S + Au reactions exhibit an excess of photons over the yield expected from hadronic decays. The spectral shape of the expected single photon signal is discussed which might reveal the temperature of hot matter and indicate a phase transition.

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Systematic studies of peripheral nuclear collisions such as the fragmentation of relativistic projectiles up to uranium and uranium fission are reported as well as the preparation of isotopic beams of exotic nuclei, ranging from light neutron-rich drip line nuclei to the fission of exotic nuclei near uranium, for secondary-beam experiments with the fragment separator FRS. Experiments in the experimental storage ring ESR with cooled secondary-beams will be discussed. We will give an outline of the prospects of secondary-beam physics at relativistic energies.

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Several examples of mean-field calculations, relevant to the recent and planned low-spin experimental works, are presented. The perspectives for future studies (mainly related to spectroscopy of exotic nuclei) are reviewed.

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New and unexpected results have been obtained with the Eurogam spectrometer. In the mass 150 region, several excited superdeformed bands have been discovered which show that models implying a scaling of the moment of inertia with mass are difficult to justify locally. The decay-out mechanism has been studied in detail through a systematic investigation of nuclei for which accurate data are available. This study shows that the high-\(N\) intruder configurations play a major role in the deexcitation process. A very weak perturbation on the yrast superdeformed energy levels of \(^{149}\)Gd has been measured and this observation may be interpreted as the remnant of a quantum number associated with a 4-fold symmetry.

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Two applications of heavy-ion induced transfer reactions are discussed here. The structure of the collective bands built upon two quasi-particle excitations excited in the \(^{161}\)Dy(\(^{61}\)Ni, \(^{62}\)Ni)\(^{160}\)Dy; \(^{161}\)Dy(\(^{61}\)Ni, \(^{60}\)Ni)\(^{162}\)Dy reactions was explored using the EUROGAM array at the Daresbury Laboratory. The ability of transfer reactions to populate superdeformed states was investigated by attempting to detect the decay of fission isomers populated by the \(^{239}\)Pu(\(^{117}\)Sn, \(^{118}\)Sn)\(^{238}\)Pu reaction, using a particle detector system within the Oak Ridge Spin Spectrometer.

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This talk gives an overview of selected topics in the physics of \({\mit \Lambda }\) and \({\mit \Sigma }\) hypernuclei.

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With the help of molecular dynamics computer simulations we study the equilibrium configurations and the volume and surface energies at low temperature of large systems of classical interacting particles either under the influence of their mutual long range Coulomb forces and a radial harmonic external confining force or of the short range Lennard–Jones potential. The former is a model for charged particles in ion traps and the latter for clusters. For the Coulomb plus harmonic force, the particles arrange in concentric spherical shells with hexagonal structures on the surfaces. The closed shell particle numbers agree well with those of multilayer icosahedra (mli). A Madelung (excess) energy of \(-0.8926\) is extracted which is larger than the bcc value. The results are compared with those obtained by a simple onion shell model. For the Lennard–Jones force we employ various initial configurations like multilayer icosahedra or hexagonal closed packed (hcp) spheres. Cohesive (volume) and surface energies per particle are extracted and compared to the energies of scaled mli quasicrystals and of spherical scaled crystals with \(N\) up to 36000. It is shown that relaxed mli are the dominant structures for \(N \lt 5000\) and hcp spheres for larger particle numbers. For \(N \lt 22000\), hcp crystals have about the same closed shell numbers as mli quasicrystals but smaller ones for \(N \gt 22000\). The same magic numbers are obtained with other short range Mie potentials. The stable Argon cluster configurations calculated with a realistic pair potential are mli for \(N \lt 750\), hcp for \(750 \lt N \lt 9300\) and face centered cubic (fcc) for \(N \gt 9300\).

abstract

Experimental confirmation of the nucleon quark structure is usually identified with the results of MIT-SLAC inelastic scattering program [1]. In particular, measurements of the cross-sections for the deep inelastic scattering (DIS) of electrons: \[e + p \to e^{\prime } + X\] allowed to study a matter granularity of the order of \(\lambda \lt 0.5\) fermis. From very beginnig DIS of polarized leptons off polarized protons was recognized as an excellent tool for studying of the internal spin structure of nucleons [2]. Already the first studies of the deep inelastic scattering (DIS) of polarized leptons off polarized protons (EMC/CERN and SLAC/Stanford, 1987–88) have shown, that an amount of the proton spin carried by quarks is surprisingly small. This phenomenon was named “the proton spin crisis”. In this lecture the present status of this subject is reviewed. After an introduction to the polarized DIS, the experimental aspects of the proton spin crisis are discussed. Then, some theoretical explanations of this phenomenon are listed. Recent progress in the obtaining polarized particles inside the storage rings as well as development of the polarized internal gas targets made possible to start new generation of experiments. Two such projects using polarized electrons, namely HERMES and SLAC E-143 as well as the proposed studies of the polarized \(p + p\) DIS in the storage ring RHIC are presented. Some ideas about future extensions of such experiments are also discussed. Many facts concerning the subject were learned by the author during his participation in FILTEX/HERMES projects in Heidelberg. Therefore, all members of this group are warmly acknowledged for many discussions of the problems raised in this lecture.

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The potentialities of investigation of nucleus–nucleus collisions on internal beams of the Nuclotron (a specialized superconducting strong-focusing accelerator of nuclei at the LHE) are discussed. Emphasis is made on the importance of the change of beam parameters as a result of ion-internal target interaction. Analytical expressions for the evolution of beam parameters are obtained. The target station, which was used in a first experiment at the Nuclotron, is described. The time change of the ion flux interacting with an internal target, which was controlled by means of target radiation, agrees with theoretical estimations.

abstract

Possible errors in calculations of \(T_{\rm sf}\) of atomic nuclei are discussed. The methods of improving the results are briefly presented.

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The quantitative analysis of scenarios of nonstandard big bang nucleosynthesis requires the detailed knowledge of capture reaction rates on light isotopes, especially for the build-up of nuclei with \(A \geq 12\). With a new setup for fast cyclic activation, capture reaction rates of a variety of isotopes have been measured, especially for the nuclei \(^{22}\)Ne, \(^{14}\)C and \(^{18}\)O. The technique was checked on isotopes of Kr, Ag, Xe and Pt, isomeric ratios were determined and some of the cross sections served as cross section standard for the measurements on \(^{22}\)Ne and \(^{18}\)O.

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Numerical studies of the excitation of 112 fermions in oscillating nucleus-like Woods–Saxon potentials are compared with analogous classical calculations in infinitely deep cavities. For oscillation frequencies such that \(\hbar \omega \) is large compared to the level spacings, and for excitations small compared to the separation energy, a close correspondence is observed. For small frequencies a suppression of the excitation (relative to the classical result) is found.

abstract

In the paper the idea of direct integrals of Hilbert spaces applied to the algebraical generator coordinate method is shown. The rotational- spectrum of \(^8\)Be is obtained within this method.

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With the advent of high intensity antiproton beams at LEAR ultimate resolution spectroscopy of antiprotonic X-rays became feasible. We describe an experiment that uses the cyclotron trap to produce a high intensity antiprotonic X-ray source. The K\(\alpha \) radiation of antiprotonic atoms is measured with a CCD detector system, while the L\(\alpha \) radiation is analysed with ultimate resolution and high precision by specially optimised doubly focussing crystal spectrometers using two dimensional position sensitive CCD detectors. MC simulations of the experiments, scheduled for 1994, show that new information about the hadronic interaction and a crucial check of our basic understanding can be expected.

abstract

Quadrupole collective states of the pairing-plus-quadrupole hamiltonian acting in a degenerate single-\(j\) shell are determined within the generator coordinate method. The particle-number and angular-momentum symmetries are exactly conserved. The collective space is constructed by acting with the single-particle quadrupole operator on a condensate of monopole fermion pairs.

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The optical potential \(\mathcal {V}\) for heavy-ion scattering is derived from the properties of nuclear matter and the NN cross section. The proximity approximation for the complex energy-dependent \(\mathcal {V}\) is discussed.

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The transformation formula to pseudo-SU(3) space for arbitrary one-body operators is derived using Algebraic Generator Coordinate Method (AGCM). The single-particle energies of the Nilsson and pseudo-Nilsson Hamiltonians are compared.

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In the March’93 the first commissioning run of the Nuclotron, a novel superconducting accelerator of nuclei, has been carried out at the Laboratory of High Energies of the Joint Institute for Nuclear Research. The first experiment on its internal target has been performed already in July. Thus, two accelerators, Synchrophasotron and Nuclotron, having a common injector and a common set of external beam lines, can further provide physics experiments with various beams. Both a brief description of the accelerator facility and of the beams parameters are given in this paper. The main beam lines are also shown.

abstract

Statistical fluctuations in one-body dissipation are considered. A method for calculating the size of such fluctuations is presented, then applied to a specific example. Quantal corrections are discussed.

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The \(^{208}\)Pb + \(^{64}\)Ni reaction at 350 MeV energy was investigated using \(\gamma \)–\(\gamma \) coincidence technique and target radioactivity measurements. The determined distribution of products indicates a dominant role of deep-inelastic collisions. The flow of protons and neutrons between the colliding nuclei is discussed in terms of mass and charge equilibration processes.

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We report particle-exclusive measurements of triple-differential cross sections for positive pious, nucleons and light nuclear fragments in multipli- city-selected collisions of 1 GeV/u \(^{209}\)Bi\(+^{208}\)Pb. The dependence upon the azimuthal angle with respect to the reaction plane is studied as a function of the particle rapidity and transverse momentum. Flow and squeeze-out are clearly established. For the baryonic component both effects increase with increasing mass of the particle. The meson flow is anticorrelated to the baryon flow.

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The average L-shell ionization probabilities in near central collisions were determined from the K\(\alpha \) X-ray satellite yield distributions measured for elements With \(42 \leq Z_{\rm target} \leq 92\) bombarded by N, O, and Ne ions. A comparison of experimental values with Semiclassical Approximation (SCA-HYD) and Classical Trajectory Monte Carlo (CTMC) calculations shows the importance of the electron capture mechanism for reduced velocities \(\eta \simeq 1\). The CTMC calculations of direct ionization plus electron capture axe in agreement with experimental L-shell ionization probabilities.

abstract

For the first time single photons with energies up to 6 times the beam energy per nucleon have been measured in a heavy-ion reaction. The reaction studied was Kr + Ni at 60 A MeV. In the nucleon–nucleon center of mass system the spectra exhibit an exponential shape with an inverse slope parameter \(E_o= 20\) MeV. Bremsstrahlung in individual NN collisions is the origin of the highest energy photons, as for the lower energy ones.

abstract

The properties of the atomic nucleus are investigated from the point of view of selforganization. The transition from low to high level density is traced as a function of the coupling strength between the discrete nuclear states and the environment of decay channels. A redistribution inside the nucleus takes place in a small region around some critical value of the coupling strength. Beyond the critical value, a few relevant short-lived modes exist together with long-lived states (slaving principle of synergetics). In the critical region of the coupling strength, information entropy, calculated from the resonant states in relation to the discrete states of the closed system, is created (maximum information entropy principle). The long lived states are characterized by disorder, which is expressed by a large information entropy. The relevant modes have a high order and take, correspondingly, a small part of the information entropy of the whole system.

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The cranked anisotropic harmonic oscillator is examined in the grand canonical ensemble as a simple model of hot and rapidly rotating nuclei. The shape of the nucleus and its phase transitions are studied as functions of temperature and angular momentum of the system. The results are graphically presented and discussed.

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The new isospin dependent formula for the nuclear charge distribution radius \[ R = 1.25\ \left (1-0.2 \frac {N - Z}{A}\right )A^{1/3} \] is proposed. Its parameters are found by the fit of the theoretical mean square radii of even–even nuclei to all the available experimental data on the isotopic shift of the charge radius.

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The neutron rich Ni isotopes have been studied using the quasi- and deep-inelastic reactions in \(^{64}\)Ni bombardments of the thick \(^{208}\)Pb target at 350 MeV. The \(\gamma \)–\(\gamma \) coincidence analysis and half-life measurements provided new spectroscopic information for heavy, A = 64 to 67 Ni isotopes with particular emphasis on the high spin states and the role of the \(g_{9/2}\) neutron orbital.

abstract

The 4\(\pi \) neutron detector ORION was installed at SATURNE laboratory to perform experiments with high energy light- and heavy-ion beams. The first preliminary results are now available. The thermal excitation energy distribution of nuclei produced in high energy proton induced reactions was measured using almost direct approach. Comparison of the experimental results and predictions of the intranuclear cascade (INC) model is presented. The experimentally observed distributions are in fair agreement with the results of the INC model.

abstract

The process of energy dissipation in antiproton–nucleus interactions is studied by multiplicities and energy spectra of \(n, p, d, t, \pi ^{\pm }\) and \(K^{\pm }\) for thirteen targets from carbon to uranium. By these observables the energy transfer to the nucleus and the excitation energy of the equilibrated system was determined by two methods. The results are compared with intranuclear cascade predictions.

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The outcome of the dynamical fission process with prescission particle emission is strongly correlated with the excitation energy and the spin distribution of the initial compound system. We intend to estimate the effect of the deformation of heavy ions in the entrance channel on the spin distribution of the fused system. Classical dynamical calculations with a fluctuating force based on the Langevin equation and one body dissipation have been performed.

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The dynamics of classical motion of a nucleus is investigated. The Hamiltonian consists of harmonic oscillator potential and spin orbit coupling. It is shown that the classical dynamics of the nucleon motion in such a mean field is very rich. The trajectories live in submanifolds with dimensions ranging from 3 to 6, depending on initial conditions and control parameters. This reflects a transition from ordered to chaotic dynamics. The calculated Poincaré sections, Lyapunov exponents, correlation dimensions and power spectra describe quantitatively this transition.

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Processes with high energy dissipation in 30 MeV/\(A\) \(^{32}\)S + \(^{58}\)Ni reaction were studied. Coincidences between three intermediate mass fragments (IMF, \(Z \gt 2\)) were used to investigate the mechanism of the multifragmentation process. The mass and the velocity distributions of one of the three fragments and the angular correlation between two of them were extracted from the experimental data and compared with predictions of two models for the direct statistical multifragmentation and with the simulations of two sequential binary fissions. The results suggest that the measured three-IMF events determine a mixture of the simultaneous and the sequential processes with the significant domination of the latter.

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Using the macroscopic–microscopic model, the masses and quadrupole moments for Cs and Ba isotopes are calculated. It is performed in the six-dimensional deformation space \(\{\beta _{\lambda }\}\), \(\lambda = 2,3,4,5,6,7\). The quadrupole moments are evaluated in single particle, pairing and macroscopic models. The results are compared with the experimental data.