Theoretical Study on N = 126 Shell Evolution

The nuclei around magic number N = 126 are investigated in the deformed relativistic mean field (RMF) model with effective interactions TMA. We focus investigations on the N = 126 isotonic chain. The N = 126 shell evolution is studied by analyzing the variations of two-neutron (proton) separation energies, quadruple deformations, single particle levels etc. The good agreement of two-neutron separation energies between experimental data and calculated values is reached. The RMF theory predicts that the sizes of N = 126 shell become smaller and smaller with the increasing of proton number Z. However, the N = 126 shell exists in our calculated region all along. According to the calculated two-proton separation energies, the RMF theory suggests ²²⁰Pu is a two-proton drip-line nucleus in the N = 126 isotonic chain.     

对超重核基态性质的系统性研究

对有限力程小液滴模型计算的质子数z=101—130超重核同位素链核的基态性质进行了系统的分析，通过对这些同位素链中处于裂变稳定线上核的平均结合能、四极形变、单质子分离能、双质子分离能和a衰变能等性质的系统研究，显示了质子数Z=108，114，126和中子数N=162，180，196时壳幻数的存在，同时可以看到Z=127之后超重核的基态性质还需要进一步研究。The calculated data by the Finite Range Droplet Model (FRDM) for the ground state properties of super-heavy nuclear isotope chains from Z=101 to Z=130 are analyzed in a global systematic way. Some quantities of the super-heavy nuclei which lie on the line of stability agains fission, such as the mean binding energy, deformation, single and double proton separation energy, as well as the α decay energy indicate the existence of the shell closure positions at Z=108, 114 and 126 and N=162...     

香港大学在束伽玛谱学研究与新一代伽玛探测器阵列(英文)

探索原子核的壳层演化,验证奇特核的幻数结构是香港大学核物理研究的重要方向。目前,科研团队利用在束伽玛谱学技术已经研究了30Ne的N=20幻数消失和78Ni（Z=28,N=50）附近原子核的双幻数结构,而即将开展的53,56Ca在束伽玛谱学实验会对新幻数N=34的定量研究,以及到N=40核的壳层演化提供重要的数据。下一步的研究目标是探索100Sn（N=Z=50）的奇特结构,特别是研究它的第一个2+激发态与其邻近原子核的低激发态性质。100Sn处于质子滴线以及核天体快质子俘获路径上,因此,它的幻数结构及其临近原子核单粒子性能研究将会极大增强对核力和核合成机制的认识。为了进一步提高物理实验统计,香港大学在数量上增加了30% NaI（Tl）晶体从而全面升级了DALI2伽玛探测阵列。此外,为了探索远离稳定线核区的新物理,开展更高精度在束伽玛谱学实验,香港大学与中国科学院近代物理研究所、中国原子能科学研究院计划合作研制基于溴化镧晶体的新一代伽玛探测器阵列。这套阵列主要在兰州重离子加速器（HIRFL）和将来建成的强流重离子加速器（HIAF）等大科学装置上开展实验,从而在奇特核研究方面取得大量重要的成果,促进科研人员全面认识、理解核力以及天体核合成过程。Exploring the evolution of shell closures and examining the magicity of extremely exotic nuclei are the main research interests of HKU (University of Hong Kong) experimental nuclear physics group. The group has employed in-beam gamma-ray spectroscopy technique to investigate the vanishing of N=20 magicity in 30Ne (N=20) and the strong magicity in nuclei around 78Ni (Z=28, N=50). The approved future's experiment on spectroscopy of 53,56Ca, proposed by HKU, will give quantitative information for the "magic index" of N=34 and shell evolution toward N=40. The next goal is to investigate the structure of 100Sn (N=Z=50), particularly the energy of the first 2+ state, and the low-lying states in the neighboring nuclei. 100Sn lies on the proton drip-line and on the astrophysical rp-process path. Characterizing the magicity of 100Sn and the nature of single-particle states in its neighboring nuclei is therefore essential to the fundamental understanding of nuclear forces and nucleo-synthesis. To significantly increase the data statistics for our physics goals, HKU group has prepared the upgrade of gamma-ray spectrometer DALI2 with 30% more NaI(Tl) detectors integrated into a new array configuration. On the other hand, next significant insights into the structure of nuclei would require new gamma-ray detection array capable for higher precision gamma-ray spectroscopy. HKU group in collaboration with IMP and CIAE therefore proposes to construct a new-generation gamma-ray detection array based on the novel scintillator LaBr₃(Ce) to explore the new physics in nuclei far from the valley of stability. Utilizing the radioactive beams at the Chinese large-scale facilities such as the Heavy Ion Research Facility in Lanzhou (HIRFL) in IMP and the future's High Intensity heavy-ion Accelerator Facility (HIAF), this novel LaBr₃(Ce) array would lead to a significant boost to the frontiers of exotic-nuclei research, which will guide scientists towards the comprehensive and even beyond-traditional understanding of nuclear forces and nucleosynthesis.     

Investigation of special features of the neutron and proton shell structure of the isotopes 90,92,94,96Zr

The neutron and proton single-particle energies and the occupation probabilities for the valence states of the even-even isotopes ^90,92,94,96Zr are determined by matching data on nucleon-stripping and nucleon-pickup reactions on the same nucleus. The data obtained in this way suggest the magicity of the number N = 56 for Z = 40. The single-particle energies of all bound neutron and proton states in the ^90,92,94,96Zr nuclei are described within the experimental errors on the basis of the dispersive optical model.     

Enhanced core polarization in (70)Ni and (74)Zn

The reduced transition probabilities B(E2;0(+) --> 2(+)(1)) of the neutron-rich (74)Zn and (70)Ni nuclei have been measured by Coulomb excitation in a (208)Pb target at intermediate energy. These nuclei have been produced at Grand Accélérateur National d'Ions Lourds via interactions of a 60A MeV (76)Ge beam with a Be target. The B(E2) value for (70)Ni(42) is unexpectedly large, which indicates that neutrons added above N=40 strongly polarize the Z=28 proton core. In the Zn isotopic chain, the steep rise of B(E2) values beyond N=40 continues up to (74)Zn(44). The enhanced proton core polarization in (70)Ni is attributed to the monopole interaction between the neutron in the g(9/2) and protons in the f(7/2) and f(5/2) spin-orbit partner orbitals. This interaction could result in a weakening of magicity in (78)Ni(50).     

A pilgrimage through superheavy valley

We searched for the shell closure proton and neutron numbers in the superheavy region beyond Z = 82 and N = 126 within the framework of non-relativistic Skryme–Hartree–Fock (SHF) with FITZ, SIII, SkMP and SLy4 interactions. We have calculated the average proton pairing gap Δ_p, average neutron pairing gap Δ_n, two-nucleon separation energy S _2q and shell correction energy E _shell for the isotopic chain of Z = 112–126. Based on these observables, Z = 120 with N = 182 is suggested to be the magic numbers in the present approach.     

Properties and structure of N=Z nuclei within relativistic mean field theory

The axially deformed relativistic mean field theory with the force NLSH has been performed in the blocked BCS approximation to investigate the properties and structure of N=Z nuclei from Z=20 to Z=48.Some ground state quantities such as binding energies, quadrupole deformations, one/two-nucleon separation energies, root-mean-square (rms) radii of charge and neutron, and shell gaps have been calculated.The results suggest that large deformations can be found in medium-heavy nuclei with N=Z=38-42.The charge and neutron rms radii increase rapidly beyond the magic number N=Z=28 until Z=42 with increasing nucleon number, which is similar to isotope shift, yet beyond Z=42, they decrease dramatically as the structure changes greatly from Z=42 to Z=43.The evolution of shell gaps with proton number Z can be clearly observed.Besides the appearance of possible new shell closures, some conventional shell closures have been found to disappear in some region.In addition, we found that the Coulomb interaction is not strong enough to breakdown the shell structure of protons in the current region.     

偶-偶超重核基态性质的理论研究

在形变的相对论平均场模型下采用NL Z2,TMA两套参数对一些偶 偶核基态性质进行了系统的计算,并将理论计算的结合能、α衰变能与已知的实验数据进行了对比分析.结果发现两方面的数据能够比较好地吻合,从而验证了相对论平均场模型对超重核研究是可行的.同时在计算中给出了未知核素基态性质的计算结果,可供以后在理论或实验上研究超重核时参考. The ground state properties of the even even nuclei with proton number Z=94-104 have been systematically calculated in the deformed relativistic mean field (RMF) theory with two sets of force parameters, TMA and NL Z2. Comparing the calculated binding energies and alpha decay energys with the experimental ones, it is found that theoretical results are in good agreement with experimental data. The reliability of the RMF model for even even superheavy nuclei has been tested by this comparison...     

有效液滴模型对超铅区结团放射性的研究

利用有效液滴模型计算了超铅区结团放射半衰期.在计算Gamow势垒穿透因子时采用了碎块体积不守恒以及有效惯性系数因子,并用有效的核半径常数公式代替原来的经验公式.理论计算得到的结团放射半衰期和实验值符合得很好,其半衰期对数值的均方差只有0.895.理论结果表明,有效液滴模型能充分反映N=126和Z=82的壳效应,并且在奇数结团25Ne,29Mg中出现了明显的奇偶质量摆动现象.另外,理论计算得到的结团半衰期基本符合盖革-努塔尔定律,并基于理论结果得到了一些关于盖革-努塔尔定律的有意义的结论.     

Heavy element research at GSI — Recent results and perspectives

The nuclear shell model predicts that the next doubly magic shellclosure beyond ²⁰⁸Pb is at a proton number between Z=114 and 126 and at a neutron number N=184. The outstanding aim of experimental investigations is the exploration of this region of spherical ‘Superheavy Elements’. This article describes the experiments that were performed recently at the GSI SHIP. They resulted in an unambiguous identification of elements 110 to 112. They were negative so far in searching for elements 113, 116, and 118. The measured decay data are compared with theoretical predictions. Some aspects concerning the reaction mechanism are also presented.     

Doubly magic properties in superheavy nuclei

A systematic study of global properties of superheavy nuclei in the framework of the Liquid Drop Model and the Strutinsky shell correction method is performed. The evolution equilibrium deformations, TRS graphs and α-decay energies are calculated using the TRS model. The analysis covers a wide range of even-even superheavy nuclei from Z =102 to 122. Magic numbers and their observable influence occurring in this region have been investigated. Shell closures appear at proton number Z =114 and at neutron number N =184.     

Shell structure and shapes of superheavy nuclei

Shell structure and shapes of superheavy nuclei are discussed. Both deformed and spherical nuclei are considered. Theoretical results obtained for even-even nuclei with the proton numberZ=82–120 and neutron numberN=126–190 are examined.     

Analysis of the single-particle energies of 1<Emphasis Type="Italic">f</Emphasis> and 2<Emphasis Type="Italic">p</Emphasis> proton states in <Superscript>64,66,68</Superscript>Zn nuclei by the mean field model with dispersive optical potential

Single-particle proton energies near the Fermi energy in ^64,66,68Zn are analyzed using the mean field model with dispersive optical potential. Good agreement is obtained between the calculated energies and experimental data. The set of parameters of the dispersive optical potential is compared with the set found for neighboring ^58,60,62,64Ni with the magic number Z = 28.     

Ground-state properties of neutron magic nuclei

A systematic study of the ground-state properties of the entire chains of even–even neutron magic nuclei represented by isotones of traditional neutron magic numbers N = 8, 20, 40, 50, 82, and 126 has been carried out using relativistic mean-field plus Bardeen–Cooper–Schrieffer approach. Our present investigation includes deformation, binding energy, two-proton separation energy, single-particle energy, rms radii along with proton and neutron density profiles, etc. Several of these results are compared with the results calculated using nonrelativistic approach (Skyrme–Hartree–Fock method) along with available experimental data and indeed they are found with excellent agreement. In addition, the possible locations of the proton and neutron drip-lines, the (Z, N) values for the new shell closures, disappearance of traditional shell closures as suggested by the detailed analyzes of results are also discussed in detail.     

相对论平均场模型对奇-偶超重核基态性质的系统研究

在形变的相对论平均场模型下,采用NL-Z2,TMA两套参数对质子数为103—109的奇–偶核基态性质进行了系统的计算,并将理论计算的结合能、α衰变能与已知的实验数据进行对比,发现两者符合得很好,肯定了相对论平均场模型对超重核研究的可靠性,同时对未知核素基态性质的计算结果可供未来的超重核理论和实验研究参考.     

Neutron separation energy for heavy and superheavy nuclei

The neutron separation energy is calculated within a macroscopic-microscopic approach for nuclei with proton and neutron numbers, Z=82?128 and N=126?190, respectively. The results are compared with existing experimental and other theoretical data.     

用宏观-微观模型系统计算偶-偶超重核基态性质

用宏观--微观模型系统计算了Z=94—112偶偶超重核的基态性质. 其中宏观部分基于液滴模型, 微观部分采用改进的谐振子势. 理论计算的结合能、α衰变能 与已知的实验数据符合, 理论计算结果也与Moller的计算结果符合很好.这肯定了宏观--微观模型对超重核性质研究的可靠性和稳定性. 对一些未知核素基态性 质的预言可为将来的实验研究提供理论参考.     

Isoscalar giant monopole resonance for drip-line and super heavy nuclei in the framework of relativistic mean field formalism with scaling calculation

We study the isoscalar giant monopole resonance for drip-lines and super heavy nuclei in the framework of relativistic mean field theory with a scaling approach. The well known extended Thomas-Fermi approximation in the nonlinear σ-ω model is used to estimate the giant monopole excitation energy for some selected light spherical nuclei starting from the region of proton to neutron drip-lines. The application is extended to the super heavy region for Z=114 and 120, which are predicted by several models as the next proton magic numbers beyond Z=82. We compared the excitation energy obtained by four successful force parameters NL1, NL3, NL3*, and FSUGold. The monopole energy decreases toward the proton and neutron drip-lines in an isotopic chain for lighter mass nuclei, in contrast to a monotonic decrease for super heavy isotopes. The maximum and minimum monopole excitation energies are obtained for nuclei with minimum and maximum isospin in an isotopic chain, respectively.     

Shell structure of new magic nuclei: Systematics of features

Investigation of the structure of the upper shells of new magic nuclei revealed an empirical regularity with the following characteristic feature: closed proton and neutron subshells, with identically large total angular momenta (j = j coupling), are located near the Fermi energy and there is a closed subshell with j = 1/2 above one of them. The properties of the nuclei exhibiting this feature of closed upper proton and neutron subshells have been investigated in detail. Quantitative manifestation of the new magicity effects, depending on the occupancy of the corresponding subshells with nucleons, has been analyzed. Several nuclei have been found, which, obviously, also have magic properties, and all classical, new magic, and nonmagic oxygen isotopes ^14–48O have been considered from the new point of view.