相对论多组态相互作用方法计算Mg~+离子同位素位移

采用相对论多组态相互作用方法研究了Mg~+离子3s~2S_(1/2)—3s~2P_(1/2)和3s~2S_(1/2)—3s~2P_(3/2)两条跃迁谱线的特殊质量位移系数和场位移因子,并计算了中子数8≤N≤20的Mg~+离子的同位素位移.计算结果与其他理论的计算值符合得比较好,与最新的实验测量结果比较,相对误差在0.13%到0.28%范围,是目前最接近Mg~+离子同位素位移实验测量的理论计算结果.该计算结果可为Mg~+离子同位素位移实验和理论研究提供参考,能够用于Mg~+离子的短寿命同位素的光谱测量实验以及利用Mg~+离子开展幻中子数N=8和N=20附近的奇异原子核特性研究等.所用的计算方法和电子激发模式也可以推广到其他核外电子数为11的多电子体系,用于开展相应的原子光谱结构计算和同位素位移的理论研究.     

Electric monopole transitions and isotope shift of nuclear radii of even Sm isotopes in the interacting boson model

The interacting boson model has been used to calculate the isotope shift in^146–154Sm isotopes. Fitted model parameters have been used for calculation of the monopole strength parameters (EO) and the branching ratios X(EO/E2) for^150–154Sm. Consideration of the effective proton boson number as it reflects the Z=64 subshell closure, is shown to be insignificant in the present calculation.     

A muonic X-ray study of the charge distribution of 144, 148, 150, 152, 154Sm

We report the measurement of the energies of the 4f → 3d, 3d → 2p and 2p → Is muonic atomic transitions in separated isotopes of ^{144, 148, 150, 152, 154}Sm, and that of the 2s → 2p transitions of ¹⁵²Sm as well. Using these transition energies as well as the hyperfine splittings of the 2p levels, we have interpreted our data in terms of a deformed Fermi distribution for the charge density and obtained good fits. A model independent analysis of the isotope shifts in terms of generalized R_h moments has been made and is in good agreement with electronic X-ray and optical isotope shifts. The static quadrupole moments and the isomer shifts of the first excited state of ^{152, 154}Sm have been determined from the 2p hyperfine structure.     

Shape evolution for Sm isotopes in relativistic mean-field theory

The evolution of shape from the spherical to the axially deformed shapes in the Sm isotopes is investigated microscopically in relativistic mean-field theory. The microscopic and self-consistent quadrupole deformation constrained relativistic mean-field calculations show a clear shape change for the even-even Sm isotopes with N = 82-96. The potential surfaces for ¹⁴⁸Sm, ¹⁵⁰Sm and ¹⁵²Sm are found to be relatively flat, which may be the possible critical-point nuclei. By examining the single-particle spectra and nearest-neighbor spacing distribution of the single-particle levels, one finds that the single-particle levels in ¹⁴⁸Sm , ¹⁵⁰Sm, and ¹⁵²Sm distribute more uniformly.     

A study of electromagnetic characteristics of <Superscript>124,126,128,130,132,134,136</Superscript>Ba isotopes performed in the framework of IBA

It was pointed out that the level scheme of the transitional nuclei ^{124,126,128,130,132,134,136}Ba also can be studied by both characteristics (IBM-1 and IBM-2) of the interacting boson model and an adequate point of the model leading to E2 transitions is therefore confirmed. Most of the δ(E2/M1) ratios that are still not known so far are stated and the set of parameters used in these calculations is the best approximation that has been carried out so far. It has turned out that the interacting boson approximation is fairly reliable for the calculation of spectra in the entire set of ^{124,126,128,130,132,134,136}Ba isotopes.     

采用相对论多组态Dirac-Hartree-Fock方法对Mg原子同位素位移的理论研究

利用相对论多组态Dirac-Hartree-Fock方法研究了Mg原子基态到低激发态~1S_0-~1P_1和~1S_0-~3P_1两条跃迁谱线的同位素位移参数,包括正常质量位移系数,特殊质量位移系数和场位移因子,并计算了~(24)Mg,~(25)Mg和~(26)Mg三个稳定同位素的同位素位移.在计算中采用了一种受限制的双电子激发模式,并将同位素位移计算结果与已有的实验测量和理论计算结果进行了对比.结果表明,用本文的研究方法计算的Mg原子同位素位移与其他理论结果和实验测量值十分符合.本文的计算结果可以为~(20-40)Mg同位素位移测量实验提供必要的参考,所用的计算方法也可以应用到其他类Mg体系(核外电子数等于12的离子)等多电子离子的光谱结构计算和同位素位移的研究中.     

First Measurement of the Nuclear Charge Radii of Short-Lived Lithium Isotopes

A novel method for the determination of nuclear charge radii of lithium isotopes is presented. Precise laser spectroscopic measurements of the isotope shift in the lithium 2s → 3s transition are combined with highly accurate atomic physics calculation of the mass dependent isotope shift to extract the charge-distribution-sensitive information. This approach has been used to determine the charge radii of ^8,9Li for the first time.     

Mixed Symmetry States in Even—Even ^96—108Mo Nuclei

Excitation energies and electromagnetic transition strengths in even-even ^96-108Mo nuclei have been described systematically be using the proton-neutron interacting boson model (IBM-2).It appears that the properties of low-lying levels in these isotopes,for which the comparison between experiment and theory is possible,can be satisfactorily described by the IBM-2 model,provided proper account is taken of the presence at low energy of states having a mixed-symmetry character.It seems possible to identify,in each isotope,a few states having such a character,the lowest ones being either 22^ or 23^ levels.It is found that these nuclei are in the transition from U(5) to SU(3).     

Laser-atomic-beam spectroscopy in Sm: Isotope shifts and changes in mean-square nuclear charge radii

A systematic investigation of the isotope shifts of all natural Samarium isotopes was performed in 15 lines of the Sm I spectrum using the laser-atomic-beam technique. The observed lines correspond to transitions between the ground configuration 4f ⁶6s ² and the upper configurations 4f ⁶6s6p and 4f ⁵5d6s ². In one line a contribution of hyperfine-structure second-order effects to the isotope shift of the odd isotopes could be demonstrated. The measured isotope shifts have been separated in all lines into field shift and mass shift contributions assuming the specific mass shift to be zero in pures ²-sp transitions. From the field shift of the pures ²-sp transitions the changes in mean-square nuclear charge radii, δ<r ²>, have been evaluated for all natural Sm isotopes (in fm²): [144, 148] 0.517(27); [148, 150] 0.303(16); [150, 152] 0.423(22); [152, 154] 0.230(12); [147, 148] 0.152(8); [148, 149] 0.092(5). There is good consistency with recent muonic x-ray measurements of the changes in the Barrett nuclear charge radii,δR _k , of the even Sm isotopes.     

Isotope shift in the Ca I resonance line and changes in mean-square nuclear charge radii of the stable Ca isotopes

The isotope shift of all stable Ca isotopes was studied in the Ca I resonance line. Enriched isotopes were used in an atomic beam, passing through the center of a spherical Fabry-Perot interferometer. The measured isotope shifts were separated into mass shift and field shift by comparing the optical isotope shift with δ〈r ²〉 values derived from recent muonic x-ray measurements. The results are discussed together with known data on the isotope shift in the Ca I intercombination line and data from Hartree-Fock calculations. The following mean values are obtained for the change in nuclear charge distribution δ〈r ²〉 [fm²]∶ [40, 42] 0.23(3); [40, 43] 0.13(3); [40, 44] 0.28(4); [40, 46] 0.14(7); [40, 48] 0.00(2).     

Structural evolution in the neutron-rich nuclei ¹⁰⁶Zr and ¹⁰⁸Zr

The low-lying states in 1??Zr and 1??Zr have been investigated by means of β-γ and isomer spectroscopy at the radioactive isotope beam factory (RIBF), respectively. A new isomer with a half-life of 620 ± 150 ns has been identified in 1??Zr. For the sequence of even-even Zr isotopes, the excitation energies of the first 2? states reach a minimum at N = 64 and gradually increase as the neutron number increases up to N = 68, suggesting a deformed subshell closure at N = 64. The deformed ground state of 1??Zr indicates that a spherical subshell gap predicted at N = 70 is not large enough to change the ground state of 1??Zr to the spherical shape. The possibility of a tetrahedral shape isomer in 1??Zr is also discussed.     

Ground-state properties of neutron-deficient platinum isotopes

The hyperfine structure splitting and the isotope shift in the =266 nm transition of Pt isotopes within the mass range 183 A 198 have been determined by Resonance Ionization Mass Spectroscopy (RIMS) in combination with Pulsed-Laser Induced Desorption (PLID). The Pt isotopes were obtained at the on-line isotope separator ISOLDE-3/CERN as daugthers of the primarily produced Hg isotopes. Magnetic moments, quadrupole moments, and changes in the mean-square charge radii are deduced and compared with results of a particle-triaxial rotor model and mean field calculations. Good agreement with experimental data (including nuclear level schemes and transition probabilities) can only be obtained if triaxial shape is admitted. The calculations yield a smooth transition in the shape of odd-A Pt nuclei from a slightly deformed, nearly oblate¹⁹⁵Pt via triaxial^197-187Pt to a strongly deformed nearly prolate¹⁷⁷Pt.Dedicated to P. Armbruster on the occasion of his 60th birthday     

Isotopieverschiebung der natürlichen geraden und ungeraden Sm- und Nd-Isotope

The isotope shift of the natural isotopes of Sm and Nd was investigated by a digital recording Fabry-Perot spectrometer using highly enriched samples. By the accuracy achieved in the measurements it was possible to verify earlier results indicating different relative isotope shifts for lines with positive and negative displacements, and to show that also lines with the same sign of the displacement may have different relative isotope shifts. It is shown that these non-constant relative isotope shifts can be explained for the even isotopes by the different contributions of the mass and volume effect to the isotope shifts in the different lines, but this explanation seems only to be partly valid for some distances between even and odd isotopes. The size of the mass effect is estimated and its influence especially on the results of the odd-even staggering is considered. The odd-even staggering is compared to earlier results for Hg. The estimation of the mass effect shows that the results forδ〈r ²〉 determined from the measured isotope shifts without correcting for the mass effect may be considerably wrong. Nevertheless it is possible by a suitable combination of the measured distances to calculate a quantity which only depends on nuclear properties and which therefore enables to check the known theories of the volume dependent isotope shift also without calculating the probability density of thes-electrons at the nucleus.     

Description of the two-humped mass distribution of fission fragments of mercury isotopes on the basis of the multidimensional stochastic model

The dynamical model proposed earlier for describing fusion-fission reactions is applied to describing the two-humped mass distribution of fission fragments of mercury isotopes. In this model, the calculation of the time evolution of collective coordinates of the system is broken down into two stages. The first stage is that within which the projectile approaches the target nucleus, while the second is that of the evolution of the system formed after the touching of the projectile and target nuclei. The dynamical evolution of the system within both stages of the calculation is described on the basis of Langevin equations. The shell structure of colliding nuclei is taken into account at either stage of the calculation. Mass distributions are calculated for fragments originating from the fission of the mercury isotopes ^{190, 184}Hg formed in the fusion-fission reactions ⁴⁸Ca + ¹⁴²Nd → ¹⁹⁰Hg and ⁴⁰Ar + ¹⁴⁴Sm → ¹⁸⁴Hg. The process in which the isotope ¹⁸⁰Hg undergoes fission from the ground state is also calculated. The results obtained in this way are compared with the results of previous theoretical calculations and with available experimental data.     

Cd偶同位素集体能谱与价质子空穴激发特性

采用以玻色子展开和MJS(ModifiedJancovici-Schiff)代换为基础的微观IBM-2方案,用直接对角化的计算方法,研究^108—118Cd偶同位素集体能谱.计算结果与实验能谱作了比较,并对近满壳偶偶核中价质子空穴激发特性及影响能谱结构的因素作了讨论.     

Uncertainty evaluation of the isotope shift factors for 2s2p~(3,1)P_1~o–2s~2 ~1S_0 transitions in B Ⅱ

Accurate isotope shift factors of the 2s2p~(3,1)P_1~o–2s~2 ~1S_0 transitions in B II, obtained with the multi-configuration Dirac–Hartree–Fock and the relativistic configuration interaction methods, are reported. We found a linear correlation relation between the mass shift factors and the energies for the transitions concerned, considering all-order electron correlations. This relation is important for estimating the uncertainty in the calculation of isotope shift factors. These atomic data can be used to extract the nuclear mean-square charge radii of the boron isotopes with halo structures or to resolve the high precise spectroscopy of B II in astronomical observation.     

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.     

Dynamic microscopic basis for IBM-2: A new approach

A dynamic approach, based on deformed Hartree-Fock solution of a nucleus, is suggested for obtaining correlated identical nucleon pair wave function for neutrons and protons. Expressions for single pair energies and two pair interaction matrix elements amongst the neutron and proton pairs in the microscopic fermion basis are presented. These matrix elements define the IBM-2 Hamiltonian through Marumori mapping. The entire procedure is illustrated by obtaining the IBM-2 spectra of²⁰Ne,⁴⁴Ti,⁶⁰Zn and⁹⁴Mo and comparing them with shell model (SM) and/or experimental results. The Yrast levels given by our calculations match well with those of the SM and the experimental results for all the four nuclei, while the non-Yrast levels do not barring the case of⁹⁴Mo. This is due to the loss of isospin symmetry for light nuclei in IBM-2. These results are discussed in detail.     

Experimental and theoretical investigation of the isotope shift of the 4D level in atomic potassium

Doppler-free two-photon laser spectroscopic measurements in the deep red spectral region have been performed on the transition 4² S _1/2→4² D _J in the naturally abundant isotopes 39 and 41 of atomic potassium. The 4D level isotope shift, ?81±12 MHz was obtained by combining the current results with data from Rydberg-state spectroscopy. Many-body perturbation theoretical calculations of the specific mass shift in the measured state are also presented. With the use of Brueckner orbitals the value ?70 MHz was obtained in substantial agreement with the experimental result.     

Structure analysis of 159Sm and properties of odd-mass neutron-rich nuclei in mass-160 region

Recent fission experiment data provide interesting structure information for neutron-rich nuclei in the mass A ∼ 160 region. We apply the projected shell model to study the strongly-deformed, neutron-rich Sm isotopes. We perform calculations for rotational bands up to spin I = 20 (29/2) for even-even (odd-neutron) Sm isotopes, and analyze the band structure of low-lying states with quasiparticle excitations. Emphasis is given to rotational bands based on one-quasiparticle (1-qp) configurations in the odd-mass ¹⁵⁹Sm. The ¹⁵⁹Sm result is discussed together with those of the even-even isotopes ^158,160Sm. New bands in ¹⁵⁹Sm based on neutron 1-qp 1/2⁻ and 5/2⁺ configurations are predicted. Electromagnetic transition probabilities are discussed.