Bubble nuclei

These are shells in the single-particle spectrum of a bubble nucleus. The shell-corrected deformation energies, calculated with Strutinsky's theory of renormalization, show that ³⁶Ar, ⁸⁴Se, ¹³⁸Ce, ²⁰⁰Hg in their ground or low-lying excited states are bubble nuclei with a small hole in the interior while ¹⁷⁴Yb and ²⁵⁰104 have secondary minima in the bubble degree of freedom.     

Complete destruction of heavy nuclei by hadrons and nuclei

The total disintegration is considered of nuclei with atomic weights ～100 and 200 by high energy hadrons and He⁴, C¹² nuclei with a momentum of 4.5 GeV/c per nucleon. It is shown that mainly nucleons are emitted, and there is no residual nucleus the mass of which is comparable to that of the primary nucleus. The probability of total disintegration is considered as a function of projectile energy and mass. The multiplicity, energy and emission angle of particles are considered as well. It is shown that the density of nuclear matter in the overlap zone of colliding nuclei exceeds the usual one by a factor of ～4. A comparison is made with interaction models. A conclusion is drawn of the collective interaction mechanism (perhaps, of the shock wave type) of particle ejection from the target nucleus at the first stage of interaction and of explosive decay of the residual nucleus at the next one.     

Dripline nuclei

A review of some recent experimental studies of dripline nuclei is given. The main emphasis is devoted to light nulcei and especially to the occurrence of halo states.     

Pseudorapidity configurations in collisions between gold nuclei and track-emulsion nuclei

A method of parametrically invariant quantities is developed for studying pseudorapidity configurations in nucleus-nucleus collisions involving a large number of secondary particles. In simple models where the spectrum of pseudorapidities depends on three parameters, the shape of the spectrum may differ strongly from the shape of pseudorapidity configurations in individual events. Pseudorapidity configurations in collisions between gold nuclei of energy 10.6 GeV per nucleon and track-emulsion nuclei are contrasted against those in random stars calculated theoretically. An investigation of pseudorapidity configurations in individual events is an efficient method for verifying theoretical models.     

Potential of interaction between nuclei and nucleon-density distribution in nuclei

Nuclear-interaction potentials that are calculated by using Skyrme forces within the extended Thomas-Fermi approximation and Hartree-Fock-Bardeen-Cooper-Schrieffer theory are studied in detail. It is shown that the nuclear component of the potential simulating the interaction between nuclei grows with increasing number of neutrons in colliding isotopes and with increasing diffuseness parameter of the density distribution in interacting nuclei. An increase in the diffuseness parameter of the density distribution in interacting nuclei leads to a decrease in the height of the barrier between the nuclei and to an increase in the depth of the capture well and in the fusion cross section. It is shown that the diffuseness parameter calculated for the nuclear component of the potential at large distance between interacting nuclei by using Skyrme forces exceeds the diffuseness parameter of the nucleon-density distribution in these nuclei by a factor of about 1.5. Realistic values of the diffuseness parameter of nuclear interaction between medium-mass and heavy nuclei fall within the range a ≈ 0.75–0.90 fm.     

Generalized shells in nuclei: Hartree-Fock calculations for bubble nuclei

Hartree-Fock calculations in the bubble degree of freedom have been performed on a variety of spherical nuclei. Of particular importance are incipient bubble configurations in ³⁶Ar, ⁶⁸Se, ⁸⁴Se, ¹⁰⁰Sn, ¹¹⁶Ce, ¹³⁸Ce and ²⁰⁰Hg, each of which possesses a binding energy which is comparable to that of the normal spherical closed-shell configuration. The densities of the above nuclei display strong deviations from a uniform shape, and give rise to depletions in the nuclear interior. These nonuniformities are due both to the absence of low angular momentum states in otherwise normally occupied spherical shells, and also to strong self-consistency effects. The nonuniformities in the mass density are further enhanced for nuclei whose neutron and proton densities have depressions or peaks at approximately the same distance from the center of the nucleus. A depression of the central density is most pronounced in the nuclei ³⁶Ar, ¹³⁸Ce and ²⁰⁰Hg. Interior depletions of the density are associated with the relatively higher energies of low angular momentum single-particle levels as compared to high angular momentum single-particle levels. This effect can give rise to moderately large gaps at the Fermi surface. Finally, it is shown that in a bubble configuration, the spin-orbit splitting of low lying doublets is sometimes reversed, and that this effect is especially pronounced for levels with low angular momentum.     

Masses of nuclei

The study of masses of the different nuclear species is basic to the whole of nuclear physics. Because of the interchangeability of mass and energy the details of energy absorption or release are identical with mass differences or changes in the masses of participating nuclei. The systematic trends in mass value reflect therefore changes in the nuclear binding energy. It is one of the primary tasks of nuclear theory to explain the total binding energy of a lump of nuclear matter. The systematic trends in mass differences are also of basic importance in evolving models to describe the formation of the elements in our galaxy.     

Peripheral interactions of relativistic 14N nuclei with emulsion nuclei

The results of investigation of the dissociation of the 2.86-A-GeV/c ¹⁴N nucleus in an emulsion are presented. The cross sections for various fragmentation channels are given. The invariant approach to analysis of fragmentation is used. The momentum and correlation characteristics of the α particles for the ¹⁴N → 3α + X channel in the laboratory system and c.m.s. of three α particles are examined. The results obtained for the ¹⁴N nucleus are compared with similar data for the ¹²C and ¹⁶O nuclei.     

Molecules in nuclei

The possible existence of analogues of atomic molecules within nuclei is considered in the context of the neutron-rich beryllium and carbon isotopes, where the underlying α cluster structure is believed to produce a multi-centred potential in which valence neutrons move. The generation of molecular wave-functions is examined and the link with the deformed harmonic oscillator and the Nilsson single-particle level scheme traced. Experimental evidence for the existence of molecular exotic cluster structures is reviewed particularly the nature of spectroscopic information provided by break-up reaction measurements. To cite this article: M. Freer, C. R. Physique 4 (2003).     

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.     

Charm in nuclei

The cooled antiproton beam at the HESR of the upcoming FAIR facility in combination with the PANDA detector will open a new comprehensive program in hadron physics. In this contribution we focus on the perspectives to study the properties of charmed hadrons in nuclear matter in antiproton-nucleus collisions. The theoretical predictions for medium modifications of mesons with both open and hidden charm are reviewed. Various proposed approaches to access their in-medium masses and widths experimentally are critically discussed. In particular, the concept to determine the J/ψ-nucleon dissociation cross section in a measurement of antiproton induced J/ψ production from different target nuclei is described. Finally, the results of first detailed simulation studies on the identification of this reaction channel in di-leptonic J/ψ decays at PANDA are presented.     

Fast helium nuclei in interactions induced by very heavy nuclei

Fast helium nuclei emitted in interactions between heavy cosmic ray nuclei (12≦Z≦26) and photoemulsion nuclei at energies >1 GeV/nucleon have been studied. Comparisons with interactions where the incident particles are protons, pions or light nuclei reveal some characteristic features of nucleus-nucleus interactions. The frequency of fast target helium nuclei is much larger and the high energy tail of the energy spectrum of these helium nuclei is more pronounced in nucleus-nucleus interactions than in proton-nucleus and pion-nucleus interactions. The number of helium nuclei emitted depends on the size and disintegration of the interacting nuclei. In order to explain our experimental data several possible production mechanisms have to be considered. Some characteristics of the emission of multiply-charged projectile fragments have-also been studied.     

Photoabsorption on nuclei

We calculate the total photoabsorption cross section on nuclei in the energy range from 300 MeV to 1 GeV within the framework of a semi-classical phase space model. Besides medium modifications like Fermi motion and Pauli blocking we focus on the collision broadening of the involved resonances. The resonance contributions to the elementary cross section are fixed by fits to partial wave amplitudes of pion photoproduction. The cross sections for NR → NN, needed for the calculation of collision broadening, are obtained by detailed balance from a fit to NN → NNπ cross sections. We show that a reasonable collision broadening is not able to explain the experimentally observed disappearance of the D₁₃(1520)-resonance in the photoabsorption cross section on nuclei.     

原子核中的结团运动

结团的形成是原子核物理中最有趣的现象之一。单粒子运动、集体运动和结团(集团)运动是原子核中核子的三种主要运动模式。如何描述原子核中这种复杂的结团关联运动一直是核物理中一个极为重要的问题。文章简要介绍了原子核中的结团现象,结团模型的发展历史,以及α凝聚的相关研究进展。     

Anomalous carbon nuclei

Results are presented from a bubble chamber experiment to search for anomalous mean free path (MFP) phenomena for secondary multicharged fragments (Z _f =5 and 6) of a¹²C beam at 4.2 GeV/c per nucleon. A total of 50,000 primary interactions of carbon with propane (C₃H₈) were treated. Approximately 6,000 beam fragments with charges Z _f =5 and 6 were analyzed in detail to search for an anomalous decrease of MFP. The anomaly is observed only for secondary carbon nuclei. The experiment has been performed at the Laboratory of High Energies, JINR.     

Inelastic interactions of fast nucleons with nuclei and fission of nuclei

The cross section for the fission of actinide nuclei that is induced by fast neutrons is considered as a fraction of the cross section for inelastic nucleon interaction with nuclei. In turn, inelastic nucleon interaction with a nucleus is treated as scattering on intranuclear nucleons. It is shown that this interaction model describes satisfactorily the cross section for the inelastic interaction of 60- to 2200-MeV nucleons for a broad set of nuclei and that the energy dependence of the cross section for the fission of actinide nuclei that is induced by 400- to 1000–MeV protons replicates the energy dependence of the cross section for inelastic interactions with respective nuclei. From the model used, it follows that the cross sections for proton-nucleus interactions exceed cross sections for respective neutron-nucleus interactions in the energy range extending up to 550 MeV; at higher energies neutron cross sections are larger than proton cross sections.     

Photofission of nuclei with allowance for wriggling vibrations of fissioning nuclei

It is confirmed that one source of the large relative orbital momenta L of fragments in spontaneous and stimulated low-energy nuclear fission is quantum transverse zero-point wriggling vibrations of the fissioning system near its scission point. The angular distributions of fragments of low-energy photofission of actinide nuclei, calculated using the quantum theory of fission, are compared. Vibrations are allowed for by using parameter C _w determined by Nix and Swiatecki. Agreement between the experimental and theoretical angular distributions for ²³⁴U, ²³⁶U, ²³⁸U, ²³⁸Pu, ²⁴⁰Pu, ²⁴²Pu nuclei is observed. The strong sensitivity of the theoretical angular distributions for ²³⁸Pu, ²⁴⁰Pu, ²⁴²Pu nuclei toward the choice of parameters of transient fissioning states at the external and internal fission barriers is demonstrated.     

Exotic nuclei in astrophysics

Recently the academic community has marked several anniversaries connected with discoveries that played a significant role in the development of astrophysical investigations. The year 2009 was proclaimed by the United Nations the International Year of Astronomy. This was associated with the 400th anniversary of Galileo Galilei??s discovery of the optical telescope, which marked the beginning of regular research in the field of astronomy. An important contribution to not only the development of physics of the microcosm, but also to the understanding of processes occurring in the Universe, was the discovery of the atomic nucleus made by E. Rutherford 100 years ago. Since then the investigations in the fields of physics of particles and atomic nuclei have helped to understand many processes in the microcosm. Exactly 80 years ago, K. Yanski used a radio-telescope in order to receive the radiation from cosmic objects for the first time, and at the present time this research area of physics is the most efficient method for studying the properties of the Universe. Finally, the April 12, 1961 (50 years ago) launching of the first sputnik into space with a human being onboard, the Russian cosmonaut Yuri Gagarin, marked the beginning of exploration of the Universe with the direct participation of man. All these achievements considerably extended our ideas about the Universe. This work is an attempt to present some problems on the evolution of the Universe: the nucleosynthesis and cosmochronology from the standpoint of physics of particles and nuclei, in particular with the use of the latest results, obtained by means of radioactive nuclear beams. The comparison is made between the processes taking place in the Universe and the mechanisms of formation and decay of nuclei, as well as of their interaction at different energies. Examples are given to show the capabilities of nuclear-physics methods for studying cosmic objects and properties of the Universe. The results of investigations in nuclear reactions, induced by radioactive nuclear beams, make it possible to analyze the nucleosynthesis scenario in the region of light elements in a new manner.     

Halo and skin nuclei

The changes in nuclear structure far from the stability line are reviewed for light nuclei. The basic concepts of neutron and proton skins and neutron halos are presented with several experimental data. Signatures of new mode of collective excitation as consequences of such exotic structures are also shown. These changes of structure point to the need for the detailed study of single-particle orbitals for unstable nuclei. Such recent studies, in particular, the spectroscopic information of halo states, are reviewed. Changes of neutron orbital ordering away from the stability line are observed from such studies. Its most profound implication has emerged in the change of magic numbers. An over view of magic number variation is presented. To cite this article: I. Tanihata, R. Kanungo, C. R. Physique 4 (2003).