基于相对论Hartree-Fock-Bogoliubov近似的新幻数研究（英文）

基于相对论Hartree-Fock-Bogoliubov （RHFB） 近似分别探索了质量-电荷极限下的超重元素与极端中质比下的奇特原子核中的新幻数问题。研究结果表明,赝自旋对称性的守恒和破缺与超重核区球形幻数结构的形成密切相关,并分别决定了中子与质子的新幻数结构。同时,理论模型之间的差异也与之密切相关。在中重奇特核区,RHFB近似很好地再现了Ca 同位素中的新幻数N = 32,34,其中同位旋矢量道中洛伦兹张量耦合扮演了较为关键的角色。以此为例,研究证明了显式考虑交换（Fock） 项的RHFB 近似的可靠性。Recent applications of the relativistic Hartree-Fock-Bogoliubov (RHFB) approach in exploring the new magicities under extreme conditions are presented for the superheavy elements with the limits of mass and charge and for the exotic nuclei with extreme neutron-to-proton ratios. It is found that the emergence of new magic shells in superheavy region is tightly related to the restoration and violation of pseudo-spin symmetry, respectively for the neutron and proton ones, in which the model deviations are indicated and discussed. In medium-heavy exotic nuclei, the occurrence of new magicity N = 32, 34 in Ca isotopes is well reproduced by the RHFB approach, in which the isovector Lorentz tensor couplings are found to play an essential role. The results exemplify that the RHFB approach, which considers the exchange (Fock) terms explicitly, furnishes a new theoretical instrument for advancing relativistic nuclear mean-field approaches.     

原子核单粒子共振态的研究进展

共振是自然界普遍存在的有趣现象。在核物理领域,存在许多奇特现象,共振在其中扮演着重要角色。介绍了近期发展的RMF-CSM、RMF-CGF和RMF-CMR方法及其对原子核单粒子共振态的研究。给出了120Sn,31Ne等核的单粒子共振态的能量和宽度及其随质量数、形变的变化规律,分析了19C,31Ne和39Mg等核的晕形成的物理机制和在N=20附近能级反转的原因。特别是新发展的RMF-CMR方法,在描述稳定核和奇特核方面都取得了成功,支持Zr同位素存在巨晕的预言。Resonance is an interesting phenomenon in nature. In nuclear physics, resonance plays an important role in the formation of many exotic phenomena. This paper introduces the recently developed RMF-CSM, RMFCGF, and RMF-CMR methods and their researches on nuclear single-particle resonances. The energies and widths of the single-particle resonant states in 120Sn and 31Ne and their evolution to mass number and deformation are given. In addition, the physical mechanism of the halo formation in 19C, 31Ne and 39Mg and the cause of energy level inversion near N=20 are analyzed. In particular, the newly developed RMF-CMR approach has been successful in describing stable and exotic nuclei and supports the prediction that Zr isotopes exist in a giant halo.     

Gamma Spectroscopy along N~Z towards 100Sn

A wide range of research topics in different fields of physics can be addressed by study of the self-conjugate N~Z nuclei, such as the np pairing, isospin symmetry, the rp-process and the properties of the electroweak interaction. This contribution focuses on the spectroscopy of N~Z nuclei towards 100Sn. The latest results on the isomeric decay spectroscopy of N~Z nuclei below 100Sn, such as the N =Z+2 nuclides 94Pd and 96Ag, the N~Z nuclide 96Cd and so on are highlighted. New opportunities in in-beam   spectrscopy of N~Z nuclei towards 100Sn, like 90Rh and 92Pd, with radioactive ion beams are discussed.     

超重原子核与新元素研究

当前,原子核物理研究的一个重要前沿是探索原子核的电荷与质量极限,研究超重原子核与超重元素的性质,以及合成超重原子核。20世纪60年代,基于量子壳效应,理论预言质子数为114、中子数为184的原子核及其相邻核具有较长的寿命,甚至可能是稳定的,形成一个超重稳定岛。这个理论预言促进了重离子加速器及相关探测设备的建造,推动了重离子物理的发展。到目前,已经合成到了118号元素,填满了元素周期表的第7行。然而,合成更重的超重元素或包含更多中子的超重原子核面临着很多挑战,需要理论与实验密切结合,探索超重原子核的性质与合成机制,以登上超重稳定岛。文章概要评述超重原子核与新元素研究。首先介绍超重原子核与超重元素研究的背景及理论预言,包括超重核存在的根源、理论预言的概况等。之后简要给出实验合成超重核取得的主要进展和新元素命名情况。关于合成更重的超重元素面临的挑战,文章将针对利用重离子熔合蒸发反应合成超重核的截面低、所合成的超重核缺中子等情况展开讨论。最后评述近年来超重原子核结构性质、衰变、裂变与合成机制等方面的理论研究进展,包括超重核区的幻数和超重岛的位置,超重核的稳定性,利用重离子熔合蒸发反应合成超重核的三步过程及其复杂性,利用多核子转移合成超重核的探索,等等。The exploration of charge and mass limits of atomic nuclei and the synthesis of long-lived or stable superheavy nuclei (SHN) are at the frontier of modern nuclear physics. In the 1960s, based on the stability originating from quantum shell effects, the possible existence of an island of stability around 298114 was predicted. This prediction advanced the construction of heavy ion accelerators and detectors and the development of heavy ion physics. So far, superheavy elements (SHE) with Z up to 118 have been synthesized via heavy ion fusion reactions in laboratories. Recently the IUPAC/IUPAP Joint Working Party (JWP) concluded that criteria for the discovery of new elements have been met for those with Z=113, 115, 117 and 118. Therefore the seventh period of the periodic table of elements is completed. To synthesize even heavier elements or more neutron-rich SHN by using heavy ion fusion reactions, one confronts many challenges. More efforts should be made to study the properties of SHN both experimentally and theoretically. In this short review on the study on SHN and SHE, we will first introduce the background and theoretical predictions of SHN, including the origin of the possible existence of SHN and the predicted island of stability of SHN, etc. Then we will present progresses made up to now concerning the synthesis of SHN and the naming of the four new elements. As for the challenges nuclear physicists confront in synthesizing even heavier SHEs, we will detail those connected with heavy ion fusion-evaporation reactions, namely, the tiny cross sections to produce SHN and the fact that only neutron-deficient SHNs can be synthesized. Finally we will discuss some theoretical progresses on the study of SHN, including the structure of SHN and proton and neutron magic numbers after 208Pb, the stability and the synthesis mechanism of SHN as well as what we should focus on in the future.     

等时性质量谱仪中N=Z核质量测量的方法探索

N=Z核的质量数据对于研究rp-和νp-过程至关重要。此外,N=Z原子核的质量数据将会帮助我们解决与核结构有关的许多关键问题。结合碎片分离器的等时性质谱仪（Isochronous mass spectrometry,IMS）是十分快速有效而且高分辨的质量测量工具。由于N=Z核的m/q值非常接近,目前国际上的储存环质量谱仪CSRe/IMP和ESR/GSI还无法实现对N=Z核运用飞行时间谱进行鉴别,因而无法对它们进行质量测量。在日本理化学研究所的仁科加速器中心新建了专用的等时性质谱仪（IMS）,即稀有放射性同位素储存环"Rare-RI Ring"（R3）,以确定短寿命的放射性原子核的质量,其目标质量相对精度为10-6。R3质谱仪与高分辨的碎片分离器BigRIPS的组合,运用束流线的高分辨的离子鉴别,使得R3上的IMS方法对N=Z核进行质量测量成为可能。本文设计了专用的等时性束流光学设置,模拟了124Xe的主束经过碎裂反应产生的N=Z核在束流线中穿过各焦平面的径迹、能量、速度等信息,同时检验了这些次级束在环内的飞行时间相对于动量的变化关系。模拟的结果表明:当储存环的等时性光学设置在某一个N=Z核时,所有其它N=Z核在环内的回旋时间也与动量弥散无关,说明了这些核也满足等时性条件。基于N=Z核的这种等时性的特点,本文对R3上刻度N=Z核的方法也进行了讨论。     

原子核基态性质的系统研究

在Skyrme-Hartree-Fock-Bogoliubov（SHFB）理论框架下,利用SkOP1,SkOP2,SKC和SKD 4套新的Skyrme相互作用参数系统地研究了Ca,Ni,Sn和Pb同位素链上原子核的结合能、电荷半径等基态性质,并重点讨论了丰中子Ca核的新中子幻数以及Pb的同位素位移现象。通过与实验数据和SLy5相互作用参数的结果对比,发现这4套相互作用参数都能很好地再现结合能的实验数据,其预言精度比SLy5要高。对于丰中子Ca核,只有SKC和SKD相互作用参数能够再现N=28处的壳效应,而对于实验上发现的新幻数N=32和34,所有的相互作用参数均不能再现这一结果。对于电荷半径,发现所有的相互作用参数均不能很好地预言Ca同位素链电荷半径的演化规律以及Pb的同位素位移现象。另外,还将这些相互作用参数推广至远离β稳定线原子核的单粒子能级结构研究,发现其不适用于描述其随同位旋的演化行为。因此,为了更好地描述远离β稳定线原子核的宏观性质及单粒子能级,建议在拟合Skyrme相互作用参数时,除自旋-轨道耦合项包括合理的同位旋依赖外,还要考虑张量力成分。The nuclear ground state properties of Ca, Ni, Sn and Pb isotopes, such as the binding energies, the charge radii, are studied systematically by 4 sets of new Skyrme parametrizations SKC, SKD, SkOP1 and SkOP2 in the framework of the Skyrme-Hartree-Fock-Bogoliubov (SHFB) method. The new magic numbers of neutronrich Ca isotopes and the isotopic shift of Pb isotopes are discussed emphatically. By the comparisons between the calculations and the experimental data and results from the SLy5 interaction parametrization, it is found that the experimental binding energies can be reproduced accurately by all parametrizations. The calculated accuracies of SKC, SKD SkOP1 and SkOP2 parametrizations are higher than the ones of SLy5 parametrization. For the neutron-rich Ca nuclei, the shell effect of N=28 can be reproduced by the SKC and SKD parametrizations, but the magic numbers at N=32 and 34 are not found by the calculations of all the parametrizations. For the charge radii, the experimental evolution tendency of Ca isotopes and isotopic shift of Pb isotopes can not be reproduced by all the parametrizations. In addition, all Skyrme parametrizations are extended to study the structure of the nuclei far from the β stability line, it is shown that the single-particle energy evolutions with the isospin are not suitable for being studied by these parametrizations. Thus the tensor force component should be considered besides the isospin dependence in spin-orbit coupling term when the Skyrme interaction parametrizations are fitted.     

丰中子锰同位素的壳模型计算

利用球形壳模型和投影壳模型两种方法对Z≤28,N=40附近pf壳的丰中子核素的结构进行了一系列的研究。以丰中子的锰同位素为例讨论了对奇奇核58,60Mn的两种壳模型计算结果。结果显示,两种理论方法都很好地再现了58,60Mn实验上观测到的从低激发到高自旋态的能级。在对这两个同位素由中子g_9/2轨道闯入所产生的负宇称转动带进行描述时,两种理论计算也得到了一致的结果。通过对比,阐明了两种壳模型方法及其采用的有效相互作用在该丰中子核区的适用性,特别强调了中子g_9/2轨道的激发对于pf壳Z≤28丰中子核素结构的重要性。Recently,we have carried out a series of studies on the structures of pf shell neutron-rich nuclei around N=40 using the spherical shell model and the projected shell model respectively.As an example,these two types of shell model calculations for the neutron-rich odd-odd isotopes 58,60Mn are discussed in this paper.The results show that both the calculations reproduce the observed experimental energy levels from the lowexcitation states to the high-spin ones in 58,60Mn.Consistent results are also obtained by these two theoretical calculations when describing the negative-parity rotational band derived from the intruder neutron g_9/2 orbital in both isotopes.Through comparison,we show the applicability of these two shell model methods and the adopted effective interactions in the present neutron-rich mass region.The significance of the excitations from neutron g_9/2 orbital to the structures of the neutron-rich nuclei in pf shell with Z≤28 are especially emphasized in this paper.     

大型壳模型计算中的截断效应对132Sn附近丰中子空穴核能级结构的影响

以双幻核132Sn以及附近的空穴核131Sn,130Sn,131In,130In,130Cd为例,研究了大型壳模型计算中的截断效应对该核区能级结构以及电四极跃迁的影响,其中截断包括了有无中子跨壳激发,以及限制轨道粒子数两种情况。计算结果表明,只有在允许质子跨壳激发的情况下才能给出130In与实验相符的基态能级,而允许两个中子的跨壳激发则会改善132Sn的低激发能级结构。此外中子壳芯激发也会对该核区空穴核的低激发能级有一定的影响,相应低能态之间的电四极跃迁则更加敏感地反映出了空间截断效应的影响。With two different truncations, i.e., neutron core-excitation truncation and orbital particle-number truncation, the research is studied at the truncation effects in shell-model calculations by the hole nuclei of 130Sn, 131Sn, 130In, 130In and 130Cd. We found that the right ground state of 130In needs proton core-excitation in shell model space, and allowing two neutron core-excitations will promote the low-lying states in 132Sn. The neutron core-excitations will also slightly affect the low-lying levels of hole-nuclei close to 132Sn, and the values of BE2 between the corresponded low-lying states reflect more obviously to the neutron core-excitations.     

2,6-双(三甲基锡)-4,8-双(2-乙基己氧基)苯并[1,2-b∶4,5-b']二噻吩的合成与多核NMR研究

以苯并[1,2-b∶4,5-b´]二噻吩-4,8-二酮为原料合成了一种聚合物太阳能电池材料的单体2,6-双(三甲基锡)-4,8-双(2-乙基己氧基)苯并[1,2-b∶4,5-b´]二噻吩. 通过多核1D和2D NMR技术（包括1D ¹H、¹³C、¹¹⁹Sn、¹¹⁷Sn NMR、DEPT、选择性1D TOCSY及2D¹H-¹H COSY、gHSQC、gHMBC）表征了目标分子结构,完成了 ¹H、¹³C、¹¹⁹Sn 与¹¹⁷Sn NMR化学位移归属,并探讨了该化合物的NMR谱线特征.     

∧超核中单粒子谱的自旋及赝自旋对称性研究(英文)

原子核中单粒子谱的自旋和赝自旋对称性对核结构的研究具有重要意义。本文基于相对论平均场理论,以132Sn,_∧133Sn,及_2∧134Sn为例,研究了∧超核中单∧谱和单中子谱的自旋和赝自旋对称性。研究发现,单∧谱的自旋对称性保持得相当好,与实验观测一致;而其赝自旋对称性只是近似保持,与核子谱的情况类似。此外,还研究了∧超子对中子谱的杂质效应,发现∧超子使中子谱的自旋对称性变差,赝自旋对称性变好。Spin and pseudospin symmetries in the single-particle spectra of atomic nuclei are of great significance for the study of nuclear structure. In this work, taking 132Sn, _∧133Sn, and _2∧134Sn as examples, the spin and pseudospin symmetries in ∧ hypernuclei are studied by using the relativistic mean-field model. For the single-∧ spectra, results show that the spin symmetry maintains well while the pseudospin symmetry is approximately conserved. Besides, as impurities, the ∧ hyperons worsen the spin symmetry of single-neutron spectra while improve the pseudospin symmetry.     

Isospin Dependence in Nuclear Multifragmentation Within Site Percolation and Nucleation Pictures

The isospin dependence, recently observed in Sn + Sn reactions at 40 MeV/nucleon, is discussed within the framework of two simple nuclear multifragmentation models, namely the site percolation and the nucleation-evaporation models. It is shown that both the models are able to discriminate between ¹¹²Sn+ ¹¹²Sn and ¹²⁴Sn+ ¹²⁴Sn reactions. The nucleation-evaporation model succeeds to reproduce nicely the experimental data, but the site percolation model fails in doing that, even if the cluster noncompactive effect is taken into account. The calculations indicate that the data are originated mainly from a single source.     

Pair Excitations in Even-Even Nuclei

A charge exchange term is added to the n-p effective interaction in treating eveneven nuclei with shape coexistence. The energy spectra and some of the E2 transition rates are calculated for ^112,114Cd, ^114,116Sn and ^118,120Te nuclei. The inclusion of this new term helps to improve an agreement with experimental data.     

Generalization of α-Decay Cluster-Model to Nuclei Near Spherical and Deformed Shell Closures

The cluster model of a-decay is extended to the regions around doubly magic spherical nucleus ^208Pb and around deformed shell closure ^270Hs, respectively. The effects of spherical shell closures (N=126 and Z=82) on α-decay are investigated by introducing an N-dependent α-preformation factor and a Z-dependent one inspired by a microscopic model. Good agreement between the theoretical a-decay half-lives and the measured ones is obtained for the spherical nuclei near the doubly magic nucleus ^208Pb, where the nuclear shell effect is included in the expression of α-preformation factor. The cluster model is also generalized for the decay of deformed nuclei. The branching ratios of α-decays from the ground state of a parent nucleus to the ground state (0^ ) of its deformed daughter nucleus and to the first excited state (2^ ) are calculated in the framework of the cluster model. The results indicate that a measurement of α spectroscopy is a feasible method to extract the information of nuclear deformation of superheavy nuclei around the deformed nucleus ^270Hs.