利用SD对壳模型讨论偶偶Mo核的集体性质(英文)

利用SD对壳模型讨论了偶偶Mo核低激发谱的集体性质。发现当SD对按照如下方法来确定，即对于两核子体系，通过对角化表面δ相互作用哈氏量，将SD对取为01^＋态和21^＋态，该模型可以合理的描述偶偶Mo核低激发态的集体性质。The SD-pair shell model was applied to study the even-even^94 Mo-^100 Mo. It is found that with the SD pair determined as 01^＋ and 21^＋ states of a two-valence-nucleon system with a Hamiltonian, which contains the single particle energy term and the Surface-Delta interaction （SDI） between like nucleons, the collectivity of low-lying states can be described reasonably.     

A≈180质量区偶偶核形状相变研究

采用E-GOS方法对质子数在Z=72-78区的偶偶原子核170-184 Hf,170-184W,170-192Os和176-192Pt的集体运动模式和形状相变进行了研究.结果表明,170-184 Hf和170-184 W同位素核的低自旋态趋于SU(3)极限,176-192Pt和170-174Os同位素核是O(6)→U(5)的过渡核,并且基本上都存在角动量驱动的形状相变.     

相对论平均场框架下偶-偶核奇-偶核计算误差的系统研究

在相对论平均场理论框架下, 用NL-3和NL-Z两组相互作用参数研究了4个同位素链²⁸Ni,⁵⁴Xe,⁷⁸Pt,⁹⁴Pu的基态性质. 发现,在Hatree近似下奇A核结合能理论计算值与实验值的相对误差反而普遍比偶偶核小. 这说明用相对论平均场理论,即使不考虑矢量介子的空间分量,仍可以比较可靠地计算奇A核结合能.     

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.     

基于壳模型对力加四极力研究sd和pf壳偶偶原子核

本文在原子核壳模型框架下基于唯象相互作用(对力加四极力)研究sd壳和pf壳的偶偶核低激发集体态。在提取了USDB和GXPF1相互作用的单粒子能量和单极相互作用的基础上,我们用一套统一参数计算重现了球形核和形变核的低激发谱;将对相互作用中的单极成分扣除后可以得到较好的结合能计算结果。同位旋标量的对相互作用对计算结果影响不大。单极相互作用在经验质子—中子相互作用、原子核对称能和Wigner能中产生重要贡献。     

Rn-Th偶偶核的八级形变研究

用推转壳模型在多维形变空间系统研究了Rn-Th偶偶核的基态性质及高自旋情形下的性质, 其中选取的形变自由度为β₂, β₃, β₄和β₅. 计算结果很好的再现了实验提取的转动惯量值. 势能面的研究表明, 随中子数的增加, 基态形状由近球形(N≈130)逐渐演变为八极形变(N≈136)后又发展成为稳定的四极形变(N≥140). 推转计算表明Rn-Th偶偶核的八极形变非常软, 在推转到高自旋情形下, 逐渐变为反射对称形变.     

偶偶变形核的集体激发能谱(Ⅰ)理论公式

本文从Bohr哈密顿量出发, 采用含有一定奇异性的、β可分离变数的集体位能, 转动动能项按sin 3γ展开, 并略去(sin⁴3γ)的高级小量后, 研究了对于轴对称偏离不大的偶偶变形核的能谱性质. 处理过程中不再应用绝热近似. 得到的集体激发谱具有振动-转动带的结构. 在一个振动-转动带中, 转动惯量和形变都不再是常数, 能级也与I(I+1)的规律有不同程度的偏离.     

q变形三参数公式对偶偶核基带的描述

利用q变形三参数公式,计算了锕系和稀土偶偶核基带转动谱,详细分析了拟合参数值呈现出的规律性.结果表明,q变形转动惯量转子模型能够较精确地描述偶偶核基带转动谱.     

重偶偶核的α结团现象与集体激发的统一描述

本文建立了统一描述重偶偶核的四极集体运动、α结团和八极振动的代数模型U(6)×U(11), 给出了该模型的三种动力学对称性: SU(5)、SU(3)和SO(6). 计算了SU(5)极限下的能谱, 并与²¹⁸Ra核的实验数据进行了比较.     

计算偶偶变形核基态转动惯量的一个简化方法

本文在刚性转动与量子系统集体转动特征基础之上,提出了一个计算偶偶变形核基态转动惯量的有效方法。     

Description of the Pt and Os isotopes in the interacting boson model

Properties of the even-even Pt and Os isotopes are investigated in the framework of the interacting boson approximation, including the neutron-proton degree of freedom. It is shown that the transition between the gamma unstable region of the heavier Pt isotopes towards the more axially symmetric deformed festures of the lighter Os and Pt isotopes can be described very well by the IBA hamiltonian; qualitatively the properties of the transitional region are reproduced by the smooth change of one parameter, χ_ν, which determines the character of the quadrupole-quadrupole interaction. Calculated excitation energies and electromagnetic properties are compared with experiment.     

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     

Shape transition in light Pt isotopes: Magnetic moments and electric quadrupole moment ratios for185,187,189Pt

Nuclear orientation and nuclear magnetic resonance experiments were performed on^{185, 187, 189}Pt isotopes oriented in Fe and single crystal Zn at temperatures down to about 6 mK. The hyperfine splitting frequencies of¹⁸⁵Pt and¹⁸⁷Pt in iron were determined to be 164.9(2) and 261.1(2) MHz, respectively. With the hyperfine field of −126.1(2.5) T, the g-factors are deduced to be |g(¹⁸⁵Pt)|=0.172(3) and |g(¹⁸⁷Pt)|=0.272(5). The spectroscopic quadrupole moment of¹⁸⁷Pt was found to be negative with magnitude similar to that of¹⁸⁹Pt, indicating a predominantly oblate ground state deformation for both isotopes. The spectroscopic quadrupole moment of¹⁸⁵Pt was found to be positive, with the ratio Q(¹⁸⁵Pt)/Q(¹⁸⁹Pt)=−3.6(9), clearly indicating a change to prolate ground state deformation.     

Deformation properties of the neutron-deficient odd-A Pt and Hg nuclei

Nuclear and atomic spectroscopy measurements have provided a great number of data on the neutron-deficient Pt and Hg nuclei. The odd-A Pt and Hg with A<186 have a prolate shape, and the even-even isotopes have a triaxial shape, while the nuclear shape of the odd-A Pt and Hg with A>186 is still an open question. The energy of the low-lying levels and the nuclear moments have been calculated in the framework of a semimicroscopic “axial-rotor + 1 quasiparticle” coupling model. The predictions are compared with the experimental data and discussed. The results strongly suggest a prolate shape for the negative-parity low-lying states of the odd-A ^187–191Pt and ^187–193Hg isotopes.     

相对论平均场理论对Pt同位素形状演化的研究

利用形变约束的相对论平均场理论研究了Pt同位素偶-偶核的形状演化,比较了基态结合能和四极形变的理论计算值和实验值, 分析了这些核的位能曲线、单粒子能级及其随四极形变β₂ 的变化规律,发现从N=88到N=126, Pt同位素的基态变形从球形对称核经X(5)对称性核、演化为具有稳定形变的核,再演化为球形核的变化过程.其中, ^166-172Pt是近球形核, ¹⁷⁴Pt和^192-196Pt位于球形和稳定形变之间,可能具有X(5)对称性, ^176-190Pt具有稳定的变形, ^198-202Pt是近球形核, ²⁰⁴Pt是球形核,这些结果与实验一致.     

Non-yrast states and shape co-existence in light Pt isotopes

Low-lying states in the even-even light platinum isotopes ¹⁷⁶Pt, ¹⁷⁸Pt, ¹⁸⁰Pt and ¹⁸²Pt have been populated using β⁺ /EC decay from parent gold nuclei, created in (HI,xn) reactions. State energies, spins and parities and γ-ray branching ratios were determined using γ-ray and electron spectroscopy. Whereas non-yrast states were observed in ¹⁷⁸Pt, ¹⁸⁰Pt and ¹⁸²Pt, none were seen in ¹⁷⁶Pt. The excitation energies of the observed states are analysed in terms of a band-mixing model, yielding the moments of inertia of the unperturbed bands. Branching ratios and ground-state-band quadrupole moments are calculated and compared with experimental values. The results indicate that the two lowest-lying 0⁺ states in each of the light Pt isotopes are formed from the mixing of two intrinsic states of different deformation, and other low-lying states can be described as admixtures of rotational states built on these intrinsic states, and on γ-vibrational states.     

Charge radii and shape transitions in short-lived Hg,Au and Pt isotopes

The hyperfine structure and the isotope shift of very neutron-deficient Au and Pt isotopes have been determined at the on-line isotope separator ISOLDE/CERN by resonance ionization mass spectroscopy combined with pulsed-laser induced desorption of the implanted radioactive sample. The changes of the mean-square charge radii were determined for the isotopes¹⁸⁴Au (T_1/2=53 s) and¹⁸³Au (T_1/2=42 s) as well as for 15 isotopes of platinum in the range between¹⁹⁸Pt (stable) and¹⁸³Pt (T_1/2=6.5 min). The strong deformation of¹⁸⁵Au (|β₂|≃0.25) persits down to¹⁸³Au. In¹⁸³Pt nearly the same value of |β₂| is reached but the deformation is build up rather smoothly in contrast to the neighbouring isotopes of gold and mercury. The magnetic moment of¹⁸³Pt was found to be μ₁=+0.51(3)μ _N .     

Rotational Bands of Some Neutron Deficient Odd-A Pt Isotopes in Particle-Triaxial-Rotor Model

Theoretical calculations are performed for neutron deficient Pt isotopes ^177pt and ^175,173,171 Pt in the particletriaxial-rotor model with variable moment of inertia. The obtained energy spectra agree with experimental data quite well. The calculated results indicate that all these nuclei are in triaxial rotation with ^177pt; being in prolate and ^175,173,171pt in oblate. Several levels are predicted for the 13/2^＋ band in ^169pt.     

The spin(6) scheme and electromagnetic transitions in 191Ir and 193Ir

The Coulomb excitation of natural Ir and Pt targets has been measured with protons and α-particles of energies between 5.0 and 6.0 MeV. Accurate γ-ray angular distributions were taken to determine the relative yields of observed γ-rays. Using ¹⁹⁴Pt as standard the reduced electric quadrupole transition probabilities to the ground states from Coulomb excited levels in the Ir and Pt isotopes were determined. Other B(E2) and B(M1) values were determined from the decay schemes obtained and from mixing ratios deduced from γ-ray angular distributions or from previously measured internal conversion coefficients. The detailed sets are compared with calcula- tions based on the Spin(6) scheme, which predicts several symmetries in ¹⁹¹Ir and ¹⁹³Ir. The possible existence of wider supersymmetry multiplets in this region of nuclei is examined on the basis of comparison of electromagnetic properties of Ir nuclei with those of Pt and Os isotopes.     

ON THE νi13/2PAIR IN EVEN Pt ISOTOPES

A systematic analysis on the νi_13/2 pair in the even Pt isotopes has been carefully done. Comparisons between the experimental data and Nilsson cranked model results with different parameters κ,μ show. 1)An improved κ,μ set, which can nicely fit the ¹⁸⁵Au data, seems also applicable in Pt isotopes too. 2)The νi_13/2 alignment only could not explain the big up-bend phenomenon in ¹⁸⁴Pt,πh_9/2 alignment must be taken into considevation as well. 3) Deviations between experimental data and theoretical calculations indicate that dimensional potential energy surface calculation of ε₂, ε₄ and γ, is needed.