通过破裂反应研究轻丰中子核的集团结构

概括介绍了关于轻丰中子同位素链集团结构的理论模型和通过破裂反应研究该结构的实验方法、 实验装置及物理分析。 The theoretical models of the cluster structures of the light neutron rich nuclei as well as the corresponding physical mechanism and experimental approaches by breakup reaction have been introduced, which may serve as references for possible experimental studies of the cluster structure of light neutron rich nuclei.      

β~--Decay Half-Lives for Waiting Point Nuclei Around N=126

We have systematically analyzed the experimental β--decay half-lives of waiting point heavy nuclei around neutron number N = 126. A new set of parameters for the exponential formula of β~--decay half-lives is proposed. The forbidden transition effects are included in the new set of parameters self-consistently. Theoretical β~--decay half-lives of nuclei around N = 126 are compared with recent theoretical results and experimental data. It is found that the new theoretical results are in better agreement with experimental data. The unknown β~--decay half-lives of some nuclei in this region are predicted for studies on nuclear structure far from stability and the nucleosynthesis in stars.     

α-decay half-lives of superheavy nuclei and general predictions

The generalized liquid drop model (GLDM) and the cluster model have been employed to calculate the α-decay half-lives of superheavy nuclei (SHN) using the experimental α-decay Q values. The results of the cluster model are slightly poorer than those from the GLDM if experimental Q values are used. The prediction powers of these two models with theoretical Q values from Audi et al. (Qaudi) and Muntian et al. (QM) have been tested to find that the cluster model with Qaudi and QM could provide reliable results for Z>112 but the GLDM with Qaudi for Z≤112. The half-lives of some still unknown nuclei are predicted by these two models and these results may be useful for future experimental assignment and identification.     

β-衰变中容许跃迁和禁戒跃迁的衰变规律

在考虑容许跃迁和禁戒跃迁的基础上, 对远离β稳定线附近原子核的β^-衰变寿命进行了系统的研究, 发现对于远离β稳定线的原子核的β^-衰变寿命, 其容许跃迁和禁戒跃迁寿命(T_1/2)与母核的质子数和中子数之间存在指数规律. 利用这个规律, 计算了β^-衰变中的容许跃迁和禁戒跃迁(包括一级禁戒跃迁和二级禁戒跃迁)的衰变寿命, 理论计算结果与实验值符合得很好. 在此基础上, 对于一些核素的β^-衰变寿命进行预言, 这对于核物理和天体物理中β^-衰变研究具有重要意义.     

Electromagnetic moments of unstable nuclei studied with polarized projectile fragments

Phenomenon of ejectile spin polarization in the projectile fragmentation reaction was exploited as a tool to produce polarized radioactive nuclei. The polarized unstable nuclei were subjected to the β-detected NMR meaurements, and the magnetic moments and electric quadrupole moments were determined for several neutron-rich light nuclei. The comparison of the experimental results with theoretical predictions shows that the nuclear moments provide useful test of models for nuclear structure and interaction in the region of light-mass unstable nuclei.     

Long-lived NMR echoes in solids

A new type of long-lived NMR echo in solids with homogeneously broadened dipolar spectra is discussed. The echo can be generated by a simple two-pulse Hahn sequence in solid samples, where dipolar-coupled nuclei have different chemical shifts. We present general considerations and simple theoretical models which explain some features of this phenomenon.     

N=Z原子核性质的研究

论述了N=Z核实验和理论研究的历史和现状在,N=Z,是研究T=0对关联最好的核区,实验表明T=0和n-p对关联起着重要的作用,理论研究知心朋友同时包括T=0和T=1的对关联,是研究它们之间竞争及相变。 The history and current status of the study of N=Z nuclei are reviewed. T=0 n p pairing correlation is expected to play an important role in the structure of the nuclei along N=Z line. Both T=0 and T=1 pairing modes should be included in the theoretical models. Phenomena like possible competition and phase transition between different pairing modes are becoming important issues in nuclear structure.     

IBM-2 calculations of some even-even selenium nuclei

In this study, we determined the most appropriate Hamiltonian that is needed for present calculations of nuclei in the A≅ 80 region by the view of interacting boson model (IBM-2). Using the best-fitted values of parameters in the Hamiltonian, we have calculated energy levels and B(E2) values for a number of transitions in some doubly even Se nuclei. The results were compared with the previous experimental and theoretical data and it is observed that they are in good agreement. The calculations have been extended to Se isotopes with A < 76 for which some B(E2) values are still not known.     

Magnetic rotation — past,present and future

Magnetic-dipole rotational (MR) bands were discovered about 15 years ago without any theoretical prediction in contrast to the super-deformed (SD) bands which were predicted long ago. First identification of a quasirotational structure as MR band occurred around 1992 although Kr isotopes probably have the first set of data having the signatures of MR bands as shown by us. Our first compilation of MR bands listed 120 MR bands in 56 nuclides which have now grown to more than 180 bands in 80 nuclides. We have observed new MR bands in the A = 130 mass region in ¹³⁷Pr, ¹³⁹Nd and ¹³⁵Ba nuclei. This led to the observation of the smallest MR bands in ¹³⁷Pr, multiple minima in the γ deformation in ¹³⁵Ba, coexistence of band structure based on these minima and band crossing of MR bands in A = 130 region. Some of these results have been reviewed in this paper along with theoretical calculations. There are still a number of questions related to MR bands which have not been fully resolved. The role of neutrons/protons in magnetic rotation still needs to be delineated. Do the MR bands follow the I(I + 1) behaviour? Are these structures as regular as normal rotational bands? How important is the existence of deformation for MR bands? We address some of these questions in this paper.     

Structure and reactions of halo nuclei: An entangled approach

Halo nuclei are characterised by their weak binding, large spatial extent and hence a quite pronounced, yet highly correlated, few-body structure. This is typically in terms of a well-defined core plus one or more valence nucleons. Over the past decade the properties of halo nuclei have been studied theoretically using a range of reaction models, many of which having served us well for half a century or more in the study of less exotic, “mean-field”, nuclei. However, it is now clear that for many reactions with halo nuclei, it is not appropriate to disentangle (factorise out) the structure information from the reaction information. That is, the few-body nature of these systems requires few-body reaction models in which the nuclear structure and reaction mechanisms are necessarily entangled. This talk will briefly review the physical assumptions made by various reaction models, and point to areas where progress is being made to extend their range of applicability in order to provide further insights into halo structure. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: j.al-khalili@surrey.ac.uk     

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.     

Nucleon elastic form factors

The nucleon form factors are still the subject of active investigation even after an experimental effort spanning 50 years. This is because they are of critical importance to our understanding of the electromagnetic properties of nuclei and provide a unique testing ground for QCD motivated models of nucleon structure. Progress in polarized beams, polarized targets and recoil polarimetry have allowed an important and precise set of data to be collected over the last decade. I will review the experimental status of elastic electron scattering from the nucleon along with an outlook for future progress.     

深度学习在核物理中的应用

深度学习是目前最好的模式识别工具,预期会在核物理领域帮助科学家从大量复杂数据中寻找与某些物理最相关的特征。本文综述了深度学习技术的分类,不同数据结构对应的最优神经网络架构,黑盒模型的可解释性与预测结果的不确定性。介绍了深度学习在核物质状态方程、核结构、原子核质量、衰变与裂变方面的应用,并展示如何训练神经网络预测原子核质量。结果发现使用实验数据训练的神经网络模型对未参与训练的实验数据拥有良好的预测能力。基于已有的实验数据外推,神经网络对丰中子的轻原子核质量预测结果与宏观微观液滴模型有较大偏离。此区域可能存在未被宏观微观液滴模型包含的新物理,需要进一步的实验数据验证。     

Reaction mechanisms for light halo nuclei

Current nuclear physics focuses on exploring nucleon matter under extreme conditions, such as those that can be created in modern accelerator laboratories. On the neutron-rich side of stability, radioactive beams have already led to the discovery of halos in nuclei with neutron distributions extending to large distances. Halo nuclei are composite systems with prominent features of few-body correlations, which reveal themselves in various reactions involving these systems. We will discuss experiments that probe a halo structure through studying various reactions involving halo nuclei, with special emphasis on how, from the theoretical point of view, such reactions contribute to our knowledge of the structure and dynamics of the nuclear halo.     

不同理论模型预言合成超重核Z=119~122研究进展

通过双核系统模型与其他模型对$Z\leqslant$118元素的计算结果与实验数据的比较,证明了不同模型预测超重核的产生截面是可靠的。对比分析了不同模型对Z=119和Z=120超重核的预言结果,我们认为合成超重核Z=119和Z=120的最佳弹靶组合分别为反应$^{48}{\rm{Ca}} + ^{{\rm{252}}}{\rm{Es}}$和$^{40}{\rm{Ca}} + ^{{\rm{257}}}{\rm{Fm}}$,并且Z=119新核素很有可能会先于Z=120新核素在实验上被合成。由于实验上Z>100锕系靶的限制,人们正尝试寻找比48Ca更重的弹核来合成超重核Z=121和Z=122,超重核Z=121可以通过反应V+Cf来合成,而超重核Z=122的产生截面已经非常小,要求将来在实验上提高探测及鉴别技术。希望本文的讨论可以在将来为实验及理论核物理工作者们提供一些参考。