Nuclear chart in covariant density functional theory with dynamic correlations: From oxygen to tin

Nuclear masses of even-even nuclei with the proton number 8≤Z≤50(O to Sn isotopes)from the proton drip line to neutron drip line are investigated using the triaxial relativistic Hartree-Bogoliubov theory with the relativistic density functional PC-PK1.Further,the dynamical correlation energies(DCEs)associated with the rotational motion and quadrupole-shaped vibrational motion are taken into account by the five-dimensional collective Hamiltonian(5DCH)method.The root-mean-square deviation with respect to the experimental masses reduces from 2.50 to 1.59 MeV after the consideration of DCEs.The inclusion of DCEs has little influence on the position of drip lines,and the predicted numbers of bound even-even nuclei between proton and neutron drip lines from O to Sn isotopes are 569 and 564 with and without DCEs,respectively.     

缺中子Np新核素的α衰变研究

合成远离稳定线的新核素、探索原子核存在的极限是目前核物理研究的重要课题。在中子壳N=126的最丰质子一侧,极端缺中子的超铀核素处于质子滴线和中子壳的交叉位置,合成和研究该核区核素对研究N=126壳结构的演化性质具有重要意义。基于兰州重离子加速器上的充气反冲核谱仪装置(SHANS),利用36,40Ar+185,187Re熔合蒸发反应,合成了极缺中子的219,220,223,224Np新核素,在中子壳N=126附近首次建立了Np同位素链的$ \alpha$衰变系统性,获得了N=126壳效应在Np同位素链中依然存在的实验证据。依据单质子分离能的系统性分析,确定了Np同位素链中质子滴线的位置,219Np也成为目前已知的最重的质子滴线外核素。此外,基于实验测量的反应截面,并与理论模型的计算结果相比较,讨论了进一步合成该核区其它新核素218,221,222Np的可行性。     

轻核区双中子滴线核的研究

运用形变相对论平均场（RMF）理论系统地研究了轻核区的元素O, Ne, Mg, Si, S, Ar和 Ca及Ni。 计算了这8个元素的偶 偶核基态的一些性质, 如结合能、 四极形变、 平均每核子结合能以及双中子分离能等。 计算中采用了NL3参数组, 并用BCS方法处理对关联。 限于篇幅, 文中只给出O和Mg元素的计算结果。 RMF理论计算的结果和实验值基本一致。 从双中子分离能的分析可知, RMF理论计算的各元素的双中子滴线核分别为 30O, 38Ne, 42Mg, 52Si, 54S, 60Ar, 80Ca和98Ni。 最后简单讨论了Ca和Ni同位素中的中子幻数情况。 The ground state properties of even even O, Ne, Mg, Si, S, Ar, Ca and Ni isotopes were studied with the self consistent deformed relativistic mean field theory with NL3 parameter set. The calculated results of O and Mg isotopes were presented in detail. The calculated binding energies and the two neutron separation energies were in good agreement with experimental values. By examining the two neutron separation energies, it was suggested that 30O, 38Ne, 42Mg, 52Si, 54S, 60Ar, 80Ca and 98Ni are the two neutron drip line nuclei. We also briefly discussed the possible changes of neutron magic numbers in Ca and Ni isotopes. Key words: relativistic mean field; drip line nucleus; two neutron separation energy     

Mass prediction of proton-rich nuclides with the Coulomb displacement energies in the relativistic point-coupling model

The masses,one-and two-proton separation energies of proton-rich nuclei with Z = 20-55,are computed using the measured masses of mirror neutron-rich nuclei and the Coulomb displacement energies calculated from the relativistic point-coupling model.The implications for the proton drip lines,candidates for two-proton emitters,as well as the impact on the astrophysical rp-process are discussed.     

Proton magic even-even isotopes and giant halos of Ca isotopes with relativistic continuum Hartree-Bogoliubov theory

We study the proton magic O, Ca, Ni, Zr, Sn, and Pb isotope chains from the proton drip line to the neutron drip line with the relativistic continuum Hartree-Bogoliubov (RCHB) theory. Particulary, we study in detail the properties of even-even Ca isotopes due to the appearance of giant halos in neutron rich Ca nuclei near the neutron drip line. The RCHB theory is able to reproduce the experimental binding energiesE _b and two neutron separation energiesS _2n very well. The predicted neutron drip line nuclei are²⁸O,⁷²Ca,⁹⁸Ni,¹³⁶Zr,¹⁷⁶Sn, and²⁶⁶Pb. Halo and giant halo properties predicted in Ca isotopes withA>60 are investigated in detail through analysis of two neutron separation energies, nucleon density distributions, single particle energy levels, and the occupation probabilities of energy levels including continuum states. The spin-orbit splitting and the diffuseness of nuclear potential in these Ca isotopes, as well as the neighboring lighter isotopes in the drip line Ca region and find certain possibilities of giant halo nuclei in the Ne−Na−Mg drip line nuclei are also studied.     

Properties of Zr isotopes near the neutron drip line and beyond it

The properties of neutron-rich Zr isotopes up to the neutron drip line and beyond it have been investigated on the basis of the Hartree-Fock method with the Skyrme forces (Ska, Sly4), taking into account the deformation. By the example of chains of Zr isotopes, good agreement is shown for the two-neutron separation energies and mean-square radii with the known results of Hartree-Fock-Bogolyubov calculations with the Sly4 forces. For the extremely neutron-rich Zr isotopes, states with very large deformation parameters (β ≈ 0.4?0.45) of neutron and proton density distributions can be realized. Beyond the neutron drip line with respect to emission of two neutrons, the existence of ^150,152Zr isotopes, which are stable with respect to one-neutron emission, is predicted.     

Excited states in128Ba

A group of proton emitters of Au, Ir, Re, Ta has been identified by means of mass values derived from the experimental data. The proton drip line has been determined. It is shown that on the boundary of the proton stability the values of proton pairing energies increase by about 50% as compared with the isotone nuclei near the betastability line.     

Shell-model calculations for the properties of nuclei with A = 86–100 near the proton drip line

Extensive shell-model calculations in the mass range A = 86–100 on the neutron-deficient side of the nuclear chart are performed. The complete spectra of all isotopes are computed and compared to experimental excitation energies where available. Beta decay half lives are evaluated with both free and effective Gamow-Teller operators. The binding energies are obtained using a five parameter fit in addition to the shell-model energies. From the binding energies we deduce the proton drip line.     

Properties of Zr hypernuclei in deformed Skyrme Hartree-Fock approach

Properties of the even-N Zr isotopes and their corresponding single-Λ and double-Λ hypernuclei are studied in the deformed Skyrme-Hartree-Fock approach. Binding energy, the two-neutron separation energies, radii are studied from beta-stable zone to the neutron drip line in this paper. The neutron drip line nuclei predicted with SLy4 and SkI4 interactions are 122Zr and 138Zr, respectively. The neutron drip line of single-Λ and double-Λ hypernuclei are Λ139Zr and 2Λ142 Zr with SkI4 interaction, respectively. The predicted hyperon drip line hypernuclei with 80Zr and 138Zr cores are 20Λ100Zr and 50Λ188Zr, respectively.     

A theoretical description of energy spectra and two-neutron separation energies for neutron-rich zirconium isotopes

Very recently the atomic masses of neutron-rich Zr isotopes, from ⁹⁶Zr to ¹⁰⁴Zr, have been measured with high precision. Using a schematic Interacting Boson Model (IBM) Hamiltonian, the evolution from spherical to deformed shapes along the chain of Zr isotopes, describing at the same time the excitation energies as well as the two-neutron separation energies, can be rather well reproduced. The interplay between phase transitions and configuration mixing of intruder excitations in this mass region is succinctly addressed.     

New isotopes,secondary reactions and spectroscopy for medium-mass nuclei at the proton drip line

This paper reviews two experiments performed at GSI and GANIL. Using a primary beam of ⁵⁸Ni at 650 MeV/nucleon impinging on a beryllium target, production cross sections of proton-rich fragments from projectile fragmentation have been measured at the projectile-fragment separator FRS at GSI. The production rates measured demonstrate that counting rates much higher than expected can be obtained at the proton drip line. The results from spectroscopy measurements show that no Thomas-Ehrmann effect is present in our data which means that the decay energies and masses can be well predicted by using e.g. the IMME. The secondary reactions evidence a slight increase of the interaction cross sections when approaching the proton drip line. Finally, in an experiment performed at the SISSI/LISE facility at GANIL using a ⁷⁸Kr primary beam, we have observed the 5 new isotopes ⁶⁰Ga, ⁶⁴As, ^69,70Kr, and ⁷⁴Sr. However, we have not found any evidence for ⁶⁹Br which was reported to be observed with a few counts at MSU. These new findings change our understanding of the path and of the ending point of the rp process.     

Shape transitions in proton-rich Ho and Tm isotopes

Total Routhian Surface (TRS) calculations have been performed for even-even nuclei along proton drip line to study nuclear ground-state deformations, as well as the odd proton nuclei Ho and Tm isotopes. The drip line nuclei show the expected shape transition with the shell e?ects. Ground-state shape changes from prolate to oblate at 143Ho and 145Tm in these two isotopes, which is due to the γ instability around N =76.     

Tensor force effect on the exotic structure of neutron-rich Ca isotopes

The structure of neutron-rich Ca isotopes is studied in the spherical Skyrme-Hartree-Fock-Bogoliubov(SHFB) approach with SLy5,SLy5+T,and 36 sets of TIJ parametrizations.The calculated results are compared with the available experimental data for the average binding energies,two-neutron separation energies and charge radii.It is found that the SLy5+T,T31,and T32 parametrizations reproduce best the experimental properties,especially the neutron shell effects at N=20,28 and 32,and the recently measured two-neutron separation energy of ~(56)Ca.The calculations with the SLy5+T and T31 parametrizations are extended to isotopes near the neutron drip line.The neutron giant halo structure in the very neutron-rich Ca isotopes is not seen with these two interactions.However,depleted neutron central densities are found in these nuclei.By analyzing the neutron mean-potential,the reason for the bubble-like structure formation is given.     

First observation of medium-spin excitations in the <Superscript>138</Superscript>Cs nucleus

The Penning trap mass spectrometer JYFLTRAP, coupled to the Ion Guide Isotope Separator On-Line (IGISOL) facility at Jyv?skyl?, was employed to measure the atomic masses of neutron-rich ^70-73Ni and ^{73, 75}Cu isotopes with a typical accuracy less than 5keV. The mass of ⁷³Ni was measured for the first time. Comparisons with the previous data are discussed. Two-neutron separation energies show a weak subshell closure at ⁶⁸ ₂₈Ni₄₀ . A well established proton shell gap is observed at Z = 28 .     

Exact treatment of pairing correlations in Yb isotopes with covariant density functional theory

The effects of pairing correlation in Yb isotopes are investigated by covariant density functional theory with pairing correlations and blocking effects treated exactly by a shell model like approach(SLAP). Experimental one- and two-neutron separation energies are reproduced quite well. The traditional BCS calculations always give larger pairing energies than those given by SLAP calculations, particularly for the nuclei near the proton and neutron drip lines. This may be caused because many of the single particle orbits above the Fermi surface are involved in the BCS calculations, but many of them are excluded in the SLAP calculations.     

Decay Experiments on N∼Z nuclei: The role of Masses, Q Values and Separation Energies

By using heavy-ion induced fusion-evaporation reactions at the on-line mass separator of GSI, decay properties of neutron-deficient isotopes between ⁵⁶Ni and ¹⁰⁰Sn were investigated. Recent experimental results will be presented and discussed, with particular emphasis on the role of masses, Q values and separation energies. This revised version was published online in July 2006 with corrections to the Cover Date.     

Neutron single-particle structure of molybdenum isotopes within the dispersive optical model

The evolution of neutron single-particle spectra in molybdenum isotopes was calculated on the basis of the dispersive optical model over the region extending from stable isotopes to the neutron drip line. The question of how the dependence of surface absorption on the neutron–proton asymmetry and the weakening of spin–orbit interaction affect the single-particle spectra in question is studied. The results agree with the concept according to which the shell effect becomes weaker near the neutron drip line.     

The surface diffuseness and the spin-orbital splitting in relativistic continuum Hartree-Bogoliubov theory

The relativistic continuum Hartree-Bogoliubov (RCHB) theory, which is the extension of the relativistic mean field and the Bogoliubov transformation in the coordinate representation, has been used to study tin isotopes. The pairing correlation is taken into account by a density-dependent force of zero range. The RCHB theory is used to describe the even-even tin isotopes all the way from the proton drip line to the neutron drip line. The contribution of the continuum which is important for nuclei near the drip-line has been taken into account. The theoretical S_2n as well as the neutron, proton, and matter rms radii are presented and compared with the experimental values where they exist. The change of the potential surface with the neutron number has been investigated. The diffuseness of the potentials in tin isotopes is analyzed through the spin-orbital splitting in order to provide new way to understand the halo phenomena in exotic nuclei. The systematic of the isospin and energy dependence of these results are extracted and analyzed.     

An improved single-particle basis for nuclear structure studies far from stability

A new single-particle basis is proposed for use in weakly bound nuclei far from the valley of beta stability.The basis, obtained by applying a local-scaling point transformation to the states of a harmonic oscillator potential, can be tailored to have the correct asymptotic properties for weakly bound systems.We first present a test of the basis and then apply it in Hartree-Fock-Bogolyubov calculations of the even Mg isotopes, from the proton drip line to the neutron drip line.