A≈100和130核区手征双重带的描述

利用三轴形变的粒子 转子模型讨论了A≈100和A≈130核区手征双重带.基于粒子空穴组态πh11/2 νh-111/2的计算很好地再现了A≈130核区N=75同中子素的手征双重带实验能谱.通过分析基于组态πg9/2 νg-19/2的约化跃迁几率B(E2)和B(M1)研究A≈100核区可能的手征双重带. The Chiral doublets for nuclei in A≈100 and 130 regions have been studied with the particle-rotor model. The experimental spectra of chiral partner bands for four N=75 isotones in A≈region have been well reproduced by the calculation with the configuration πh_(11/2)νh~(-1)_(11/2). The possible chiral doublets in A≈100 region have been predicted by the particle-rotor model (PRM) with the configuration πg_(9/2) νg~(-1)_(9/2) based on the analysis of the B(M1) and B(E2) transition probabilities.     

转动谱的若干理论及其对超形变带的研究

简述了若干转动谱理论及其对超形变带的应用 ,并用 Bohr- Mottelson的 I(I+1 )展开公式分析了 A=1 90区超形变带的性质和指定了它们的能级自旋 ,用 Harris的ω2 展开公式 J(1) =2α+(4/3 )βω2 +(6 /5 )γω4分析了 A=1 5 0区 Tb和 Dy同位素 2 0条超形变带的性质 ,指定了它们的能级自旋 .对于首次发现的152 Dy(1 )超形变带 ,带首自旋指定为 2 6 h,与实验结果更加符合. The recent developments of rotational spectral theories and its application to superdeformed bands were briefly reviewed. The superdeformed bands in A ≈190 region were analyzed and the spins of energy level were determined by the least square fitting experimental transition energy with the formula of Bohr Mottelson’s I(I+1) expansions. The superdeformed bands in A ≈150 region were analyzed by using the kinematic moments of inertia formula J (1) =2α+(4/3)βω 2+(6/5)γω 4 in...     

Rotational properties of the odd-Z transfermium nucleus 255Lr by a particle-number-conserving method in the cranked shell model

Experimentally observed ground state band based on the 1/2-[521] Nilsson state and the first exited band based on the 7/2-[514]Nilsson state of the odd-Z nucleus ~(255)Lr are studied by the cranked shell model(CSM) with the paring correlations treated by the particle-number-conserving(PNC) method. This is the first time the detailed theoretical investigations are performed on these rotational bands. Both experimental kinematic and dynamic moments of inertia(J~(1)and J~(2)) versus rotational frequency are reproduced quite well by the PNC-CSM calculations. By comparing the theoretical kinematic moment of inertia J~(1) with the experimental ones extracted from different spin assignments, the spin 17/2~-→13/2~- is assigned to the lowest-lying 196.6(5) ke V transition of the 1/2~-[521] band, and 15/2~-→11/2~- to the 189(1) ke V transition of the 7/2~-[514] band, respectively. The proton N = 7 major shell is included in the calculations. The intruder of the high- j low-? 1 j_((15)/2)(1/2~-[770]) orbital at the high spin leads to band-crossings at ω≈0.20( ω≈0.25) Me V for the 7/2~-[514] α =-1/2(α = +1/2) band, and at ω≈0.175 Me V for the1/2~-[521] α =-1/2 band, respectively. Further investigations show that the band-crossing frequencies are quadrupole deformation dependent.     

正常形变带[521]1/2的ΔI=1颤动

系统分析了A≈ 170区正常形变带 [5 2 1]1/ 2 - 中的ΔI =1颤动现象 .根据旋称伙伴带的跃迁能量提取Δ2 Eγ(I) =[Eγ(I) +Eγ(I- 2 ) ]/ 2 -Eγ(I - 1)值 ,表现出旋称相关的规则上下颤动 .其颤动幅度在低自旋端约为 5 0keV ,而后随自旋而增大或减小 ,大体呈抛物线形 .利用改进的ab公式 ,提取了相关的脱耦合系数 .运用Nilsson波函数 ,探讨了原子核集体哈密顿量中高阶微扰项的可能形式 .     

正常形变带[521]1/2的ΔI=1颤动

系统分析了A≈170区正常形变带[521]1/2-中的ΔI=1颤动现象. 根据旋称伙伴带的跃迁能量提取Δ2 Eγ (I)=[Eγ(I)+Eγ(I-2)]/2-Eγ(I-1)值, 表现出旋称相关的规则上下颤动. 其颤动幅度在低自旋端约为50 keV, 而后随自旋而增大或减小, 大体呈抛物线形. 利用改进的ab公式, 提取了相关的脱耦合系数. 运用Nilsson波函数, 探讨了原子核集体哈密顿量中高阶微扰项的可能形式.     

High spin band structure in 139Nd

High-spin states in 139Nd nucleus have been reinvestigated with the reaction 128Te (16O, 5n) at a beam energy of 90 MeV. The level scheme has been expanded with spin up to 47/2 h. At the low spin states,the yrast collective structure built on the vh(-1)(11/2) multiplet shows a transitional shape with γ≈32° according to calculations of the triaxial rotor-plus-particle model. Three collective oblate bands with γ～-60° at the high spin states were identified for the first time. A band crossing is observed around hw ～0.4 MeV in one oblate band based on the 25/2- level.     

Collective Band Structures and Identification of One-Phonon and Two-Phonon γ-Vibrational Bands in 109Tc

The high spin states of the neutron-rich 109Tc nucleus are reinvestigated by observing prompt γ-rays from the spontaneous fission of 252 Cf. The previously known yrast band based on the 7/2＋ state is updated. A side band built on the 11/2＋ state is expanded and a new band based on the 15/2＋ state is identified. Band crossing in the yrast band occurs around fω≈ 0.36 MeV. This band crossing is associated with the alignment of two h11/2 neutrons according to the cranked shell model calculations. The band based on the 11/2＋ state is proposed as a candidate for the one-phonon γ-vibrational band, and the band built on the 15/2＋ state is proposed as a candidate for the two-phonon γ-vibrational band. Other characteristics for the observed bands are discussed.     

High Spin Band Structure in ^112Ru

Levels in the neutron-rich ^112Ru nucleus have been investigated by observing prompt gamma-rays from the spontaneous fission of ^252Cf with the Gammasphere detector array. The ground state band and the one-phonon γ-vibrational band have been confirmed and extended with spin up to 16h and 15h, respectively. The other two side bands, one proposed as two-phonon γ-vibrational band and the other proposed as two-quasiparticle band, have been observed for the first time. The total-Routhian-surface calculations show that rotational 112 Ru nucleus has triaxial deformation with parameters β2 - 0.27 and γ= -29°. The observed band crossing in the yrast band is due to the alignment of a pair of h11/2 neutrons according to the cranked shell model calculations. The possible configuration for the quasiparticle band has also been discussed.     

基于非对称粒子空穴组态的手征双重带

利用三轴形变的粒子转子模型对基于非对称粒子空穴组态πg–1 9/2 νh11/2和πh–1 11/2 νi13/2等的手征双重带进行了研究.详细分析了转动能谱、角动量随转动频率的变化关系、以及约化跃迁几率B(E2)和B(M1)等性质.发现基于非对称组态的三轴形变原子核也有类似对称组态的手征双重带现象.但它们所对应的最佳三轴形变值从γ=30°变为γ～27°.随着组态中价核子角动量的增加,出现手征双重带的自旋随之增加,简并区间也相应增大     

131La形状共存和带终止

用组态相关推转Nilsson-Strutinsky模型研究了¹³¹La转动带结构性质.对一些特殊组态带的形状共存和带终止做了较为详细的探讨,并把理论计算结果与实验结果进行了比较.理论计算结果表明,¹³¹La是软γ形变核,很多具有不同组态的转动带都有形状共存.实验上测量的¹³¹La的宇称和辛量子数为(π,α)=(+,±1/2)的转动带的组态是[02,8],即组态π(h_11/2)²⊙ν(h_11/2)⁸,其中负辛量子数带几乎达到该带的带终止理论预言值I=41.5h,但是该带对实验上测量带终止不利,因为接近带终止态时能量增加太快.     

High Spin States and Shape Coexistence in 134Ce

high spin states in ¹³⁴Ce nucleus have been studied by using the heavy–ion induced reaction ¹²²Sn(¹⁶O,4n) carried out at china institute of atomic energy. the early level scheme has been extended with spin up to 22. however,our result is different from that in a recent publication,and the magnetic rotation bands reported there have not been confirmed. our observed level structures may be interpreted as shape coexistence. the 10+ state at the backbending with h_11/2 quasineutron configuration has an oblate deformation with an asymmetry parameter γ≈–60°(lund convention),and the 10+ isomer is a yrast trap of prolate deformation with γ≈–120°,whereas the other signature partner bands with h_11/2 and g_7/2 proton configuration probably have a prolate deformation with γ≈0°.     

Microscopic study of electromagnetic properties and band spectra of neutron deficient ~(133,135,137)Sm

A microscopic high spin study of neutron deficient and normally deformed ~(133,135,137)Sm has been carried out in projected shell model framework.The theoretical results have been obtained for the spins,parities and energy values of yrast and excited bands.Besides this,the band spectra,band head energies,moment of inertia and electromagnetic transition strengths are also Predicted in these isotoPes.The calculations successfully give a deeper understanding of the mechanism of the formation of yrast and excited bands from the single and multi-quasi particle configurations.The results on moment of inertia predict an alignment of a pair of protons in the proton(1 h_(11/2))~2 orbitals in the yrast ground state bands of ~(133-137)Sm due to the crossing of one quasiparticle bands by multi-quasiparticle bands at higher spins.The discussion in the present work is based on the deformed single particle scheme.Any future experimental confirmation or refutation of our predictions will be a valuable information which can help to understand the deformed single particle structure in these odd mass neutron deficient ~(133-137)Sm.     

Shape Coexistence and Band Termination in Doubly Magic Nucleus 40Ca

Shape coexistence and band structure near yrast line of the Z=N doubly magic nucleus ⁴⁰Ca have been investigated by the configuration-dependent cranked Nilsson-Strutinsky approach. The observed normal deformed and superdeformed bands are explained and the terminating states are confirmed by the calculations. The transition quadrupole moment Q_t of the calculated superdeformed band is in good agreement with the observed one at high spin. There is shape coexistence within the same configuration. Possible normal deformed and superdeformed bands with rotation around the intermediate axis in several interesting configurations of ⁴⁰Ca are discussed. Possible favored superdeformed band terminations in ³⁸Ca and ³⁸Ar are predicted. The experimental results in ³⁸Ar are discussed simply.     

Criteria of the Spin Assignment of Rotational Band

Based on the very general properties of the rotational band of axially symmetric nucleus, some rules of the I variation of the kinematic and dynamic moments of inertia are obtained, which may serve as the effective criteria of the spin assignment of rotational band. Extensive analysis of large amount of ro tational bands (below bandcrossing) of normally deformed eveneven nuclei whose spins were established shows that these rules do hold without exception. The spins of the yrast superdeformed bands of even-even nuclei in the actinide region (fission isomeric bands), and in the A～190, 150 regions are analyzed also. The spin of the lowest observed level of the yrast superdeformed band in ¹⁵²Dy is determined to be I₀ = 26, rather than I₀ = 22 or 24.     

Highest spin reached in the superdeformed well in the A≈190 mass region

The high efficiency of the new-generation of γ-arrays as EUROGAM or GAMMASPHERE makes reachable the fission limit in angular momentum of the nuclei populated by means of heavy ion reactions in the A ≈ 190 mass region. This is established by the strong correlation between the fissility parameters Z ²/A and the spin values of the state of highest energy observed in the yrast superdeformed bands.     

Yrast feeding and multiplicity of gamma transitions in the reaction 124Sn(28Si, 5n) 147Gd at 139, 146 and 152 MeV

The population of high-spin yrast and near yrast states of ¹³⁴⁷Gd and the associated multiplicity of feeding transitions have been studied in the ¹²⁴Sn (²⁸Si, 5n) reaction at 139, 146 and 152 MeV. The yrast feeding is found to be independent of the initial angular momentum distribution and very weak for states of spin greater than 30 ħ. The average multiplicity of γ-transitions is found to increase with increasing beam energy. The experimental results are interpreted in terms of collective excitations within rotational bands that channel the γ- decay towards the known oblate single-particle yrast states below ~30 ħ.     

The rotational quasi-continuum in specific configurations: high-K states and superdeformation

The analysis of the fluctuations of the counts of unresolved γ-γ energy spectra can extend our knowledge of the rotational motion at high angular momentum and excitation energy above the yrast band. Detailed studies of the rotational quasi-continuum built on specific intrinsic nuclear configurations are here discussed. First, the validity of the K-selection rules in the quasi-continuum region is investigated in the case of the normal deformed nucleus ¹⁶³Er. The γ cascades feeding into low-K and high-K bands are analyzed studying variance and covariance of the spectrum fluctuations. Low-K bands are found to be fed by a much larger effective number of cascades than high-K bands, while the covariance between pairs of gated spectra shows that the cascades feeding into low-K bands are different from those feeding into high-K bands. These findings suggest a persistence of K-selection rules in the region of excitation energy and angular momentum probed by the rotational decay of ¹⁶³Er. As a second case, the existence of a rotational quasi-continuum in the super deformed well of ¹⁴³Eu is discussed. An intense bump of rotationally correlated transitions is observed to develop as function of fold in the high spin region of gated spectra. Fold distribution, angular anisotropies, moment of inertia and life time show that the bump consists of fully damped super deformed transitions. This gives experimental evidence of damped rotational motion up to several MeV excitation energy above the super deformed yrast line.