Radioactive nuclear beams: Present and future

Some results of investigations into a new nuclear-physics field associated with the production of radioactive nuclear beams and physical studies with these beams are presented. The most recent results obtained by studying the structure of nuclei and reaction mechanisms with radioactive nuclear beams are surveyed. Data obtained in Dubna at the DRIBs accelerator complex are presented along with allied results from other research centers. In this connection, existing experimental data on light loosely bound exotic nuclei are discussed. The parameters of DRIBs3, which is a new accelerator complex, are presented, and the physics research program that will be implemented with the aid of new setups, including a high-resolution magnetic analyzer (MAVR) and a 4π neutron detector (TETRA), is described. A collaboration in the realms of employing radioactive nuclear beams at the DRIBs complex together with other accelerator complexes [SPIRAL2 (France), RIKEN (Japan), FAIR (Germany), and RIBF (CIIIA)] on the basis of employing new highly efficient experimental facilities has already led to the discovery of new phenomena in nuclear physics and will make it possible to study in the future new regions of nuclear matter in extreme states.     

Precision mass measurements of neutron halo nuclei using the TITAN Penning trap

Precise atomic mass determinations play a key role in various fields of physics, including nuclear physics, testing of fundamental symmetries and constants and atomic physics. Recently, the TITAN Penning trap measured the masses of several neutron halos. These exotic systems have an extended, diluted, matter distribution that can be modelled by considering a nuclear core surrounded by a halo formed by one or more of loosely bound neutrons. Combined with laser spectroscopy measurements of isotopic shifts precise masses can be used to obtain reliable charge radii and two-neutron-seperation energies for these halo nuclei. It is shown that these results can be used as stringent tests of nuclear models and potentials providing an important metric for our understanding of the interactions in all nuclei.     

Recent progress and new challenges in isospin physics with heavy-ion reactions

The ultimate goal of studying isospin physics via heavy-ion reactions with neutron-rich, stable and/or radioactive nuclei is to explore the isospin dependence of in-medium nuclear effective interactions and the equation of state of neutron-rich nuclear matter, particularly the isospin-dependent term in the equation of state, i.e., the density dependence of the symmetry energy. Because of its great importance for understanding many phenomena in both nuclear physics and astrophysics, the study of the density dependence of the nuclear symmetry energy has been the main focus of the intermediate-energy heavy-ion physics community during the last decade, and significant progress has been achieved both experimentally and theoretically. In particular, a number of phenomena or observables have been identified as sensitive probes to the density dependence of nuclear symmetry energy. Experimental studies have confirmed some of these interesting isospin-dependent effects and allowed us to constrain relatively stringently the symmetry energy at sub-saturation densities. The impact of this constrained density dependence of the symmetry energy on the properties of neutron stars have also been studied, and they were found to be very useful for the astrophysical community. With new opportunities provided by the various radioactive beam facilities being constructed around the world, the study of isospin physics is expected to remain one of the forefront research areas in nuclear physics. In this report, we review the major progress achieved during the last decade in isospin physics with heavy ion reactions and discuss future challenges to the most important issues in this field.     

Laser applications in nuclear physics: Present and future

The use of lasers for nuclear physics research is widespread and growing rapidly. The major impact in nuclear structure research has come from nuclear size and shape determinations for nuclei far from stability via high resolution isotope shift measurements. In addition, systematic data on nuclear magnetic and quadrupole moments have been obtained via the hyperfine splitting resolved in laser fluorescence studies of atomic spectra in both stable and unstable systems. The tunability, high intensity and inherent polarization of laser light can be used to polarize atomic nuclei for nuclear reaction studies. The rapid efficient polarization of unstable nuclei with lasers also presents opportunities for new research in nuclear physics. In this paper the physics of the laser interaction for the studies indicated will be introduced. Some examples of work completed and in progress will be presented primarily from on-line laser studies at charged particle accelerators. Extensions of current research, particularly with respect to possible studies of short-lived nuclei, are discussed and the synergistic effects of certain advances in quantum electronics and nuclear physics described.     

Science with radioactive beams: The alchemist's dream

Nuclear science is being transformed by a new capacity to create beams of radioactive nuclei. Until now all of our knowledge of nuclear physics and the applications which flow from it has been derived from studies of radioactive decay and nuclear reactions induced by beams of the 283 stable or long-lived nuclear species we can find on Earth. Here we describe first how beams of radioactive nuclei can be created. The present status of nuclear physics is then reviewed before potential applications to nuclear physics, nuclear astrophysics, materials science, bio-medical, and environmental studies are described.     

核物理中的π介子

在强子层次上,原子核或强子物质的基本组元是核子和介子.弄清这些强子的结构,并由基本原理出发研究它们的性质,是当代核物理的重要课题.在各种介子中,π介子是最轻且最重要的介子.关于自由空间中π介子的结构与性质、核介质内π介子的性质、π 核子相互作用与π 核相互作用等问题,始终受到相当多的关注.π介子在核物理中的作用直接联系着手征对称性,汤川秀树关于π介子的最初概念已经大大发展了.有清楚的实验证据表明,核内存在π介子的集体模式,这种集体模式与以前观测到的所有核集体运动模式截然不同.拟对π 核物理的研究现状及值得进一步研究的主要问题予以简要评述. At the hadronic level, nucleons and mesons are constituents of nuclei and hadronic matter. Understanding the structures of hadrons, finding the physics of how the properties of these particles arise from the first principle, are major interests in modern nuclear physics. Among mesons, the lightest and most important one is certainly the pion, thus it is no accident that its structure, properties (both in free space and in nuclear matter) and interactions with nucleons and nuclei have gotten considerable ...     

Pushing the limits of nuclear stability

Reaching the limits of nuclear stability offers unique opportunities to understand basic nuclear properties. New shell structures close to the driplines can change the existence of neutron-rich nuclei. A new search for ¹⁶Be confirmed the previous limit for particle stable Be isotopes at A=14. Single proton knock-out reactions offer the potential for more sensitive searches of very weakly bound nuclei. In order to extend the knowledge of the neutron dripline beyond Z=8 requires new accelerator developments. The proposed new rare isotope accelerator has the potential to push the limit of the neutron dripline to at least Z=25.     

Nuclear structure studies on halo nuclei by direct reactions with radioactive beams

The investigation of direct reactions with exotic beams in inverse kinematics gives access to a wide field of nuclear structure studies in the region far off stability. The basic concept and the methods involved are briefly discussed. The present contribution will focus on the investigation of light neutron-rich halo nuclei. Such nuclei reveal a new type of nuclear structure, namely an extended neutron distribution surrounding a nuclear core. An overview on this phenomenon, and on the various methods which gave first evidence and qualitative confirmation of our present picture of halo nuclei, is given. To obtain more quantitative information on the radial shape of halo nuclei, elastic proton scattering on neutron-rich light nuclei at intermediate energies was recently investigated for the first time. This method is demonstrated to be an effective means for studying the nuclear matter distributions of such nuclei. The results on the nuclear matter radii of ⁶He and ⁸He, the deduced nuclear matter density distributions, and the significance of the data on the halo structure is discussed. The present data allow also a sensitive test of theoretical model calculations on the structure of neutron-rich helium isotopes. A few examples are presented. The investigation of few-nucleon transfer reactions in inverse kinematics may provide new and complementary information on nuclear structure, as well as astrophysical questions. The physics motivation and the experimental concept for such experiments, to be performed due to momentum matching reasons at low incident energies around 5–20 MeV/u at the new generation low energy radioactive beam facilities SPIRAL, PIAFE, etc., is briefly discussed.     

南开大学奇异性核物理的理论研究

简要介绍了南开大学核物理组在奇异性核物理方面的理论研究工作. 已经完成的工作有核介质内超子平均自由程的理论计算, 奇异性核物理方面已完成的其他4个理论研究课题是, 不同重子杂质对原子核的影响、重味重子超核、核物质内的eta-介子以及K介子原子核的性质.     

Double-strangeness production with antiprotons

The production of double-strangeness by antiproton annihilation in nuclei will be an exciting way to investigate whether the formation of deeply bound antikaonic nuclear clusters occurs. The existence of deeply bound antikaonic nuclear clusters is a lively debated problem in hadron physics today, which can be solved only experimentally. At CERN with the Antiproton Decelerator (AD) and in future with the new FAIR facility at Darmstadt low energy antiprotons are available to perform this type of experiments. The use of antiprotons for the production of double-strangeness was recently discussed by Weise and Kienle and indeed, it would be very challenging to produce and study such “double-strange nuclei” in the view of the prediction of Akaishi and Yamazaki that double-antikaon bound nuclear systems with strangeness (S?=???2) will be formed with binding energies up to 200–300 MeV. Such binding energies might result in an increase of the average density to more than 3 times the average nuclear density. If such dense systems are created, conditions in the phase diagram might be reached where phase transition to kaon condensation or colour superconductivity will occur at low temperature.     

趋向统一发展的团簇科学

团簇科学在发展过程中，从原子核物理、凝聚态物理和量子化学等引入许多概念和方法，构成团簇研究的中心议题，逐渐形成一门介于原子分子物理和凝聚态物理之间的交叉学科．文章就团簇结构和性质研究的某些最新进展进行了评述，并与原子核和量子点等的性质进行了比较．     

Instabilities in nuclear matter and finite nuclei

Spinodal instability in nuclear matter and finite nuclei is investigated. This instability occurs in the low-density region of the phase diagram. The thermodynamical and dynamical analysis is based on Landau theory of Fermi liquids. It is shown that asymmetric nuclear matter can be characterized by a unique spinodal region, defined by the instability against isoscalar-like fluctuation, as in symmetric nuclear matter. Everywhere in this density region the system is stable against isovector-like fluctuations related to the species separation tendency. Nevertheless, this instability in asymmetric nuclear matter induces isospin distillation leading to a more symmetric liquid phase and a more neutron-rich gas phase.     

Nuclear pairing: New perspectives

Nuclear pairing correlations are known to play an important role in various single-particle and collective aspects of nuclear structure. After the first idea by A. Bohr, B. Mottelson, and D. Pines on similarity of nuclear pairing to electron superconductivity, S.T. Belyaev gave a thorough analysis of the manifestations of pairing in complex nuclei. The current revival of interest in nuclear pairing is connected to the shift of modern nuclear physics towards nuclei far from stability; many loosely bound nuclei are particle-stable only due to the pairing. The theoretical methods borrowed from macroscopic superconductivity turn out to be insufficient for finite systems such as nuclei, in particular, for the cases of weak pairing and proximity of continuum states. We suggest a simple numerical procedure of exact solution of the nuclear pairing problem and discuss the physical features of this complete solution. We show also how the continuum states can be naturally included in the consideration bridging the gap between the structure and reactions. The path from coherent pairing to chaos and thermalization and perspectives of new theoretical approaches based on the full solution of pairing are discussed.     

Dissolution of shell structures in exotic nuclei

Nuclear many-body theory is used to study nuclear matter and finite nuclei at extreme isospin. In-medium interactions in asymmetric nuclear matter are obtained from (Dirac-) Brueckner theory. Neutron skin formation in Ni and Sn isotopes is investigated in relativistic DDRH theory with density dependent meson-nucleon vertices. Applications to light nuclei are discussed with special emphasis on pairing and core polarization in weakly bound nuclei. The calculations show that shell structures are dissolving when the driplines are approached.     

Dirac-Brueckner-Hartree-Fock calculations for isospin asymmetric nuclear matter based on improved approximation schemes

We present Dirac-Brueckner-Hartree-Fock calculations for isospin asymmetric nuclear matter which are based on improved approximations schemes. The potential matrix elements have been adapted for isospin asymmetric nuclear matter in order to account for the proton-neutron mass splitting in a more consistent way. The proton properties are particularly sensitive to this adaption and its consequences, whereas the neutron properties remains almost unaffected in neutron-rich matter. Although at present full Brueckner calculations are still too complex to apply to finite nuclei, these relativistic Brueckner results can be used as a guidance to construct a density-dependent relativistic mean-field theory, which can be applied to finite nuclei. It is found that an accurate reproduction of the Dirac-Brueckner-Hartree-Fock equation of state requires a renormalization of these coupling functions.     

Lead beam experiments at the CERN SPS

The acceleration in 1986 of¹⁶O beams to 200 GeV/nucleon at the CERN SPS created a new frontier of particle and nuclear physics, namely the study of high energy density systems with hundreds of quarks and gluons created in the central collisions of nuclei with heavy targets. In order to produce the largest piece of “quark matter”, beams as heavy as²⁰⁸Pb are needed. The Lead-Injector Project that would provide them is presented. Possible experimental approaches to extract the physics from collisions with thousands of produced particles are discussed.     

核物质对称能的高密行为研究

同位旋物理的主要任务之一是通过放射性核束引起的核反应来探索介质中有效核子-核子相互作用的同位旋依赖性,尤其是同位旋相关的核物质状态方程, 即密度依赖的核物质对称能。由于对称能,尤其是其高密行为,对核物理学和天体物理学具有重要意义,密度依赖的对称能在过去10年一直是中能重离子物理研究领域的主要焦点之一。近年来,低密对称能的研究已经取得了重要进展, 而对称能的高密行为仍然很不确定。在理论方面,人们提出了许多对高密对称能敏感的观测量。 实验方面, 关于对称能高密行为研究的实验计划已经展开,世界各地正在建造的放射性核束装置为对称能的高密行为研究提供了新的机遇。基于IBUU输运模型综述了研究对称能高密行为的一些敏感观测量及其最新进展, 以及所面临的挑战与机遇。One of the major tasks of studying isospin physics via heavy ion collisions with neutron rich nuclei, is to explore the isospin dependence of in medium nuclear effective interactions and the equation of state of neutron rich nuclear matter, i.e., the density dependence of nuclear symmetry energy. Because of its great importance for understanding many phenomena in both nuclear physics and astrophysics, the study of the density dependence of nuclear symmetry energy has been the main focus of the intermediate energy heavy ion physics community during the last decade. Nowadays significant progress has been achieved in studying the low density behavior of nuclear symmetry energy, but the high density behavior of nuclear symmetry energy is still very uncertain. Theoretically, a number of observables have been proposed as sensitive probes to the high density behavior of nuclear symmetry energy. With new opportunities provided by the various radioactive beam facilities being constructed around the world, studies of the high density behavior of nuclear symmetry energy is expected to be one of the main forefront research areas in nuclear physics in the near future. In this report, based on the transport model IBUU we have reviewed the major progress achieved in studying the high density behavior of nuclear symmetry energy and discussed future challenges in this field.     

Finite nuclei to nuclear matter: a leptodermous approach

The liquid drop model (LDM) expansions of energy and incompressibility of finite nuclei are studied in an analytical model using Skyrme-like effective interactions to examine, whether such expansions provide an unambiguous way to go from finite nuclei to nuclear matter, and thereby can yield the saturation properties of the latter, from nuclear masses. We show that the energy expansion is not unique in the sense that, its coefficients do not necessarily correspond to the ground state of nuclear matter and hence, the mass formulas based on it are not equipped to yield saturation properties. The defect is attributed to its use of liquid drop without any reference to particles as its basis, which is classical in nature. It does not possess an essential property of an interacting many-fermion system namely, the single particle property, in particular the Fermi state. It is shown that, the defect is repaired in the infinite nuclear matter model by the use of generalized Hugenholtz–Van Hove theorem of many-body theory. So this model uses infinite nuclear matter with well defined quantum mechanical attributes for its basis. The resulting expansion has the coefficients which are at the ground state of nuclear matter. Thus a well defined path from finite nuclei to nuclear matter is found out. Then using this model, the saturation density 0.1620 fm⁻³ and binding energy per nucleon of nuclear matter 16.108 MeV are determined from the masses of all known nuclei. The corresponding radius constant r₀ equal to 1.138 fm thus determined, agrees quite well with that obtained from electron scattering data, leading to the resolution of the so-called ‘r₀-paradox’. Finally a well defined and stable value of 288±20 MeV for the incompressibility of nuclear matter K_∞ is extracted from the same set of masses and a nuclear equation of state is thus obtained.     

Laser spectroscopy — Recent results and prospects for lighter nuclei

Atomic physics methods have provided important information about the electromagnetic properties of the nuclear ground states. In recent years the experimental effort has been directed towards optical high resolution spectroscopy of very high sensitivity, giving access to short-lived nuclides very far from stability. A few of these new techniques based on collinear laser spectroscopy are presented with their latest results. They are suitable for an extension of the experiments to the region of lighter nuclei.     

Methods for organizing the interaction of circulating particle beams with internal targets in nuclear physics experiments at synchrotrons and storage rings

The first methods for using internal targets and their further development for organization of nuclear physics experiments at synchrotrons and storage rings are reviewed. With these methods, new results are obtained and discoveries are made in physics of interactions of elementary particles and nuclei. Current uses of various internal targets and circulating particle beams in ongoing and projected research in particle physics, relativistic nuclear and spin physics, and physics of interactions of exotic and radioactive nuclei and for producing fluxes of secondary particles (mesons, neutrons, exotic and radioactive nuclei, etc.) for physics experiments are described.