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.     

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 effects. 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.     

Properties of the πh_(9/2)  νi_(13/2) band in odd-odd ~(188)Au

A new rotational band has been identified and assigned to 188Au for the first time using the 173Yb(19F,4nγ) reaction at the beam energies of 86 and 90 MeV. This band is proposed to be built on the πh9/2  νi13/2 configuration by comparing the band properties with known bands in neighboring nuclei. The prolate-to-oblate shape transition through triaxial shape has been proposed to occur around 188Au for the πh9/2  νi13/2 bands in odd-odd Au isotopes on the basis of total Routhian surface (TRS) calculations.     

Possible shape coexistence in Ne isotopes and the impurity effect of Λ hyperon

The possible shape coexistence in even-even Ne isotopes and the impurity effects of the sΛand pΛ hyperons are explored employing the multidimensionally constrained relativistic-mean-field(MDC-RMF) model with the PK1 parameter set for the N N interaction and PK1-Y1 for the ΛN interaction. The quadrupole deformation potential energy surfaces(PESs), nuclear deformations, nuclear radii, binding energies, and density distributions of the hypernuclei and core nuclei are examined. The possible shape coexistence in ~(24,26,28)Ne is predicted with small energy differences of 140, 336, and 128 keV, respectively, between the two local energy minima. Different impurity effects of the sΛand pΛ hyperons are revealed. The sΛ hyperon exhibits clear shrinkage effects, which reduce the nuclear size and facilitate a spherical nuclear shape. The prolate pΛhyperon on the 1/2~-[110] orbital renders the nuclear shape more prolate, while the oblate pΛ hyperon on the 3/2~-[101] or 1/2~-[101] orbital renders the nuclei more oblate. Moreover, the Λ hyperon can increase the probabilities of the shape coexistence by reducing the energy differences between the two local energy minima, although the shape coexistence may disappear owing to the vanishment of one energy minimum on the flat energy surface.     

Shape coexistence of superheavy nuclei

Shape coexistence appears in the region of superheavy nuclei. Calculations for the nobelium isotopes have been carried out with the cranking TRS model. It shows that normal deformed and superdeformed prolate shapes coexist. Particularly for the nuclei ^248,250No, the ground states are superdeformed. The kinematic moments of inertia are calculated and they agree well with available experimental results. As rotational frequency increases, the     

偶偶No同位素转动性质研究(英文)

通过总Routhian 面计算方法研究了Z = 102 号元素已实验合成的偶偶248-264No同位素的转动性质。计算的基态形变β2,β4 与前人的计算相符。252,245No 两核基态带的转动惯量特征能得到基本再现。偶偶248-264No同位素转动惯量系统上弯的现象可归因于带交叉。研究还表明,推转时质子与中子顺排有强烈竞争,在较轻的No同位素中j_15/2 中子拆对顺排较为优先,而在较重的No 核中i_13/2 质子顺排更加优先。The rotational properties of the synthesized even-even 248-264No isotopes have been investigated by means of total Routhian surface calculations. The calculated ground-state properties (e.g. β2; β4) are in agreement with previous calculations. The behaviors of moment of inertia of 252,254No are well reproduced by our calculations. The systematic upbending in moment of inertia is attributed to band crossing. It is found that the j_15/2 neutron rotation-alignment is preferred for the lighter No isotopes, but the i_13/2 proton alignment is favored in the heavier ones.     

Triaxial Superdeformed Band and Its Formation Mechanism in Odd-Odd Nucleus ^168Lu

Three-dimensional total Routhian surface calculations are carried out to determine the triaxial superdeformation of odd-odd nucleus ^168Lu. One of the new four rotational bands observed in the experiment is identified as a triaxial superdeformed band, in which the neutron shell correction energy plays a key role and the deformationdriving effect of high j intruder orbital plays an additional role in the formation of triaxial superdeformation shape. Its deformation parameters (ε2, ε4, γ) are derived from the analysis, which can reproduce the experimental assignment.     

Calculation of triaxial superdeformation in <Superscript>174</Superscript>Hf

A two-dimensional Total Routhian Surface (TRS) calculation with the fixed hexadecapole deformation ε4 = 0.03 was carried out for several configurations of 174Hf. Results indicate that the shell corrections have an important contribution to the formation of triaxial superdeformation in 174Hf and some possible configuration assignments are made to the 4 TSD bands experimentally found in 174Hf.     

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.     

Kr同位素的形状共存

用Woods-Saxon推转壳模型对缺中子Kr同位素^70,72,74,76Kr进行了TRS计算. 结果表明, ^70,72Kr的基态为扁椭球, 同时存在着长椭球形变. ^74,76Kr的基态为长椭球, 并与扁椭球形变共存. 另外, 对⁷²Kr的推转计算结果表明, 随着ω的增大, 它的基态由扁椭球变成了长椭球.     

Shape coexistence and evolution in neutron-def icient krypton isotopes

Total Routhian Surface(TRS) calculations have been performed to investigate shape coexistence and evolution in neutron-deficient krypton isotopes72,74,76 Kr. The ground-state shape is found to change from oblate in72 Kr to prolate in74,76 Kr, in agreement with experimental data. Quadrupole deformations of the ground states and coexisting 0+2states as well as excitation energies of the latter are also well reproduced. While the general agreement between calculated moments of inertia and those deduced from observed spectra confirms the prolate nature of the low-lying yrast states of all three isotopes(except the ground state of72Kr), the deviation at low spins suggests significant shape mixing. The role of triaxiality in describing shape coexistence and evolution in these nuclei is finally discussed.     

Shape coexistence in light se isotopes: evidence for oblate shapes

Lifetimes of states in the ground-state bands of (70)Se and (72)Se were measured using the recoil-distance Doppler shift method. The results deviate significantly from earlier measurements, requiring a revision of the conclusions drawn from a recent Coulomb excitation experiment concerning the shape of (70)Se. The new results lead to a coherent picture of shape coexistence in the neutron-deficient selenium and krypton isotopes. The coexistence and evolution of oblate and prolate shapes in this mass region is for the first time consistently described by new Hartree-Fock-Bogolyubov-based configuration-mixing calculations which were performed using the Gogny D1S interaction.     

On the Difference of High Spin Band Structure Between I and Ce Isotopes

It has been predicted that in nuclei with Z=52－56,there are many low-lying oblate and prolate rotational bands.Experimental investigation has been carrying out for the high spin band structure in serial I and Ce isotopes recently.It is found along with the prolate bands,there do exist oblate bands for proton h_11/2,g_7/2 and d_5/2,configurations in I.The band termination (non-collective oblate shape) was found in ^119,121I as well.All the prolate band structure was found in Ce.Further theoretical calculation was done with newly fitted Nilsson κ and μ parameters.Results show that the absolute values of shell energy and self-consistent pairing energy for oblate shape are always lager for I than for Ce.Besides,the band head oblateprolate energy difference is much in favor of oblate shape for I than for Ce.All these results are related to the existence of an oblate 54 gap in proton single particle diagram.     

Coexisting structures in 119I

High-spin structures of ¹¹⁹I have been studied by using ¹³C and ¹⁵N induced reactions. In all, fifteen ΔI = 1 or 2 bands belonging to ¹¹⁹I were found. No evidence was found for bands with collective oblate shape, instead, all the observed rotational bands were interpreted to possess a collective prolate shape. A rich tapestry of noncollective states of both negative and positive parity was observed. Based on TRS calculations various configurations at β₂ ≈ 0.17 and γ = 60° were assigned to these states.     

Magic gaps and intruder levels in triaxially superdeformed nuclei

Nuclear shell model calculations based on a modified harmonic-oscillator potential result in amazingly stable triaxial nuclear shapes. Major gaps in the single-particle energy spectra at proton number 71 and neutron number 94 combine constructively at low and intermediate rotational frequencies. At high frequencies, gaps at proton number 72 and neutron number 97 combine in an equally favourable way. The sizes of the gaps may be as large as 35% of the values for the gaps at the classical magic numbers 50 and 82 at spherical shape. The dependence on the positions of the intruder levels in forming the gaps is discussed. Experimentally observed rotational bands in lutetium (Z = 71) and hafnium (Z = 72) appear in isotopes and frequency ranges, which are consistent with the gaps in the theoretical single-particle energy spectra.     

Structure of 72,74Se at high spin

Lifetimes of high spin states up to { }=22⁺ in the yrast positive parity bands have been measured to investigate the shape evolution with increasing spin in ^{72, 74}Se. The Q _t values derived from these measurements indicate that prolate shape stabilizes for ⁷²Se, while a triaxial shape develops for ⁷⁴Se at higher spins. Comparison of the observed trend in Q _t with spin for ^{72, 74}Se with that of the corresponding kryptones isotones emphasizes the stability provided by N=38 prolate shell gap even at high rotational frequency.     

188Pb形变和形状共存的研究

用角动量投影壳模型研究了188Pb核素的形状共存. 实验数据经过计算结果的分析,指出188Pb的低能激发态存在着对应于不同内部粒子组态的球形基态、扁椭球和长椭球三种形状的共存;预言了质子h9/2两粒子-两空穴扁椭球带;指出长椭球带是两种多粒子-空穴激发组态的混杂,并导出了混合系数. 由这些系数,可以说明中子i13/2破对引起的顺排对长椭球带的影响是一个渐进过程;并指出了2+态的能量范围在804-880keV.     

101Pd的能级结构研究以及与其邻近核素的系统性对比

在本工作中，我们主要研究了101Pd核中$ \nu_{11/2} $带的能级结构，并与临近同位素相对应的能级结构进行了对比。研究发现在Pd同位素链，即$ N\!= \!Z\! =\! 50 $的壳附近，三轴形变的演变符合很好的系统性，即从小的不稳定形变逐渐演变为稳定的长椭形变。同时，我们也做了总势能面(TRS)随着原子核转动频率以及中子数变化的系统计算，结果也支持该核区不稳定三轴形变演化的规律。     

Electromagnetic properties and shapes of ground states in Pt−Au−Hg region

We present a comprehensive calculation of odd-A isotopes of Pt, Au and Hg in the mass region 177≤A≤195. Two nuclear models have been used. The particle-triaxial rotor model with modified oscillator s.p. potential (PTR-MO) yielded deformation parameters ε₂ and γ as a result of fitting to a wide range of experimental data. Also, mean field calculations based on the Woods-Saxon potential with Strutinsky shell corrections were performed to predict deformation parameters β₂, β₄ and γ form Total Routhian Surfaces (TRS). Subsequent PTR calculation using these deformation parameters and Woods-Saxon s.p. potential (PTR-WS) yielded ground state properties of all nuclei in question in very good agreement with experiment. The deformation parameters ε₂ and β₂ showed the same general trend as a function of neutron number. The fitted parameter γ from (PTR-MO) calculation indicated a smooth change from prolate (N≈100) to oblate shape (N≈115) via triaxial in Pt, Au and Hg. The value of γ extracted from TRS calculations predicts a smooth change in Pt isotopes but much sharper change in Au and Hg nuclei.