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.     

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.     

Study of the Superdeformed State of 196Pb in the Relativistic Mean Field Theory

Based on the constrained relativistic mean field (RMF) theory, the superdeformed states of ¹⁹⁶Pb are systematically investigated with four different interactions, TMA, PK1, NL3 and NL-SH. The potential surface, the quadruple deformation of ground and superdeformed states, and the excitation energies of superdeformed states are calculated. The results show that the shape of ¹⁹⁶Pb is oblate for the ground state with deformation β₂≈－0.15, and prolate for the superdeformed states with deformation β₂≈0.60. The calculated excitation energy and the depth of the potential well of the superdeformed state are approximately equal to 4.5MeV and 1.6MeV, respectively. These results are in good agreement with the current experimental data. It indicates that RMF theory can well describe the energy of the band head of superdeformed rotational band in ¹⁹⁶Pb.     

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°.     

Systematic Research on Shapes of Even Even Nuclei Around A～100 Regions With DHF Method

Using modified surface delta interaction, the deformed Hartree-Fock calculations for twenty tWo nuclei: ^102—114Ru, ^102—116Pd and ^104—116Cd are performed.Prolate and oblate configurations are obtained. The calculated results show that there exist form transitions and shape coexistence from mass number 102 to 116, and that the single-particle energy spectra are different not only for different mass number but also for different configurations of nuclei. At the same time, it is also found that the numbers of proton and the 3s_1/2 orbit begining to fill with neutrons play important roles in the shape transitions.     

Influence of 1h11/2 Orbit on the Shapes of Even Even Nuclei Around A～100 Region

Using modified surface delta interaction, the deformed Hartree-Fock calculations for twenty two nuclei such as ^102—114Ru, ^102—116Pd,^104—116Cd etc. are performed in the gds and gdsh configuration space, respectively. Prolate and oblate configurations are obtained. It is shown that there exist shape transitions for the nuclei with the mass number from 102 to 116, the resultant single-particle energy spectrum is changed not only with the mass number but also with the configuration, and the results, by considering the 1h_11/2 orbit, are quite different from those obtained in the gds configuration space. Moreover, the number of protons in the nucleus and filling up the 1h_11/2 orbit, especially with neutrons, play important roles in the single-particle energy spectrum and the shape transition.     

Collective Dand Structures in Doubly Odd 136La Nucleus

Using heavy-ion nuclear reaction and in-beam γ-ray spectroscopy technique,high spin states of ¹³⁶La have been studied. The nuclear reaction used is ¹³⁰Te(¹¹B,5n) with a beam energy 60MeV. The level scheme with three collective band structures has been updated with spin up to 20h. The collective backbending has been observed in $\uppi h_{11/2}\otimes \upnu h_{11/2}$ band. According to the TRS calculations,this backbending is due to the alignment of a pair of h_11/2 neutrons. The signature splitting and inversion for the $\uppi h_{11/2}\otimes \upnu h_{11/2}$ band were also discussed. Other two bands based on $12^-$ and $16^+$ levels were proposed as oblate deformation with $\gamma\approx -60^\circ$. They most probably originate from four- and six- quasiparticle configurations, that is,$\uppi h_{11/2}\otimes\upnu g_{7/2} h_{11/2}^2$ and $\uppi g_{7/2}\otimes\upnu g_{7/2}^2 d_{5/2}h_{11/2}^2$ respectively.     

Ultrahigh Spin Structures in 157,158,159Er

Rotational structures at ultrahigh spin in ^157,158,159 Er have been investigated with the configuration-dependent cranked Nilsson-Strutinsky approach. Configurations of observed bands are assigned and the corresponding deformations are given theoretically. The calculations suggest that one of ultrahigh spin bands in ^158 Er is triaxial highly deformed and the other is normal-deformed, while both ultrahigh spin bands in ^157Er are suggested to be triaxial highly deformed. The possible ultrahigh spin bands in ^159Er are predicted to be triaxial highly deformed and have shape coexistence in the same configuration. The configurations with two neutron holes in the Nose = 4 orbitals and two neutron holes in the h11/2 orbitals in ^159Er are favoured for ultrahigh spin states but unfavoured for band termination, which is similar to ultrahigh spin bands in ^157,15SEr.     

THE SHAPE COEXISTENCE IN 190Hg

The ground state Potential Energy Surface for nucleus ¹⁹⁰Hg was calculated in terms of Nilsson-Strutinsky method with standard κ,μ set and modified one.It is shown that there is a low-lying second minimum in prolate side except the known oblate minimum.The existence of such a prolate minimum,which is different from Total Routhian Surface calculation,may explain the recent observation of extra deformation band in ¹⁹⁰Hg.     

Evidence for shape coexistence in186Pt

High-spin states in¹⁸⁶Pt have been populated by the¹⁸⁸Os (α, 6n) reaction and were investigated with the OSIRIS spectrometer. A shape coexistence at high spins was established in the nucleus¹⁸⁶Pt, which lies on the border between light prolate and heavy oblate Pt nuclei. Two bands corresponding to predominantly prolate shapes and one band of predominantly oblate shape have been observed. For prolate shapes a (π h _9/2)² alignment and for oblate shapesa (vi _13/2)² alignment has been found.     

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.     

Spin-dependent γ softness or triaxiality in even-even~(132-138) Nd nuclei

The properties of γ instability in rapidly rotating even-even132-138 Nd isotopes have been investigated using the pairing-deformation self-consistent total-Routhian-surface calculations in a deformation space of(β2, γ,β4). It is found that even-even134-138 Nd nuclei exhibit triaxiality in both ground and excited states, even up to high-spin states. The lightest isotope possesses a well-deformed prolate shape without a γ deformation component.The current numerical results are compared with previous calculations and available observables such as quadrupole deformation β2 and the feature of γ-band levels, showing basically a general agreement with the observed trend ofγ correlations(e.g. the pattern of the odd-even energy staggering of the γ band). The existing differences between theory and experiment are analyzed and discussed briefly.     

Experimental Study of High-Spin States in Deformed Odd-Odd 180 Ir

High spin states in deformed odd-odd ¹⁸⁰Ir have been investigated using the ¹⁵⁴Sm (³¹P, 5nγ)¹⁸⁰Ir reaction through the measurements of excitation functions at 150, 155, 160, 165 and 170 MeV beam energies, K X-γ and γ-γ coincidences at 160 MeV. A new level scheme composed of 5 rotational bands has been established. According to the band structure characteristics and the deduced in band B(M1)/B(E2) ratios, the quasiparticle configurations and spin and parity have been proposed to the observed bands. The neutron AB crossing is observed at hω_c≈0.26 MeV for the π1/2^－[541]⊙ν1/2^－[521] and π1/2^－[541]⊙ν5/2^－[512] bands. This AB crossing frequency is close to that in the ν5/2^－[512] band of ¹⁷⁹Os indicating the loss of intruder nature of the π1/2 - orbit. Gradual alignment gain in both the π9/2^－[514]⊙ν7/2⁺[633] and π9/2^－ν5/2^－[512] bands is observed which is similar to the low spin anomaly in alignment in the πh_11/2,πd_5/2 and πi_13/2 bands of neighboring Ir and Re isotopes. Different alignment properties have been discussed in the framework of cranked shell model, and a larger quadrupole deformation is suggested for the bands with π9/2^－[514] orbit involved.     

Particle-number conserving analysis for the 2-quasiparticle and high-K multi-quasiparticle states in doubly-odd 174,176Lu

Two-quasiparticle bands and low-lying excited high-K four-, six-, and eight-quasiparticle bands in the doubly-odd ^{174, 176}Lu are analyzed by using the cranked shell model (CSM) with the pairing correlations treated by a particle-number conserving (PNC) method, in which the blocking effects are taken into account exactly. The proton and neutron Nilsson level schemes for ^{174, 176}Lu are taken from the adjacent odd-A Lu and Hf isotopes, which are adopted to reproduce the experimental bandhead energies of the one-quasiproton and one-quasineutron bands of these odd-A Lu and Hf nuclei, respectively. Once the quasiparticle configurations are determined, the experimental bandhead energies and the moments of inertia of these two- and multi-quasiparticle bands are well reproduced by PNC-CSM calculations. The Coriolis mixing of the low-K (K=|Ω₁-Ω₂|) two-quasiparticle band of the Gallagher-Moszkowski doublet with one nucleon in the Ω = 1/2 orbital is analyzed.     

Single Particle Schr dinger Fluid and Moments of Inertia of Deformed Nuclei

We have applied the theory of the single-particle Schrodinger fluid to the nuclear collective motion of axially deformed nuclei. A counter example of an arbitrary number of independent nucleons in the anisotropic harmonic oscillator potential at the equilibrium deformation has been also given. Moreover, the ground states of the doubly even nuclei in the s-d shell ²⁰Ne,²⁴Mg,²⁸Si,³²S and ³⁶Ar are constructed by filling the single particle states corresponding to the possible values of the number of quanta of excitations n_x,n_y, and n_z. Accordingly, the cranking-model, the rigid-body model and the equilibrium-model moments of inertia of these nuclei are calculated as functions of the oscillator parameters ω_x,ω_yand ω_z which are given in terms of the non deformed value ω00 , depending on the mass number A, the number of neutrons N, the number of protons Z, and the deformation parameter β. The calculated values of the cranking-model moments of inertia of these nuclei are in good agreement with the corresponding experimental values and show that the considered axially deformed nuclei may have oblate as well as prolate shapes and that the nucleus ²⁴Mg is the only one which is highly deformed. The rigid body model and the equilibrium model moments of inertia of the two nuclei ²⁰Ne and ²⁴Mg are also in good agreement with the corresponding experimental values.     

Study of Signature Inversion in the πi13/2 νi13/2Bands of Odd Odd Nuclei

High-spin states in odd-odd nuclei of ^176,178Ir and ¹⁸²Au have been studied experimentally using heavy-ion- induced fusion-evaporation reactions and standard in-beam γ-ray spectroscopic techniques. Rotational bands built on the πi_13/2 νi_13/2 configuration have been observed. In addition, on the basis of level spacing systematics, spin assignments have been proposed for the πi_13/2 νi_13/2 band in ¹⁸⁴ Au,which was reported without spin assignments in previous study. It is pointed out that the πi_13/2 νi_13/2 bands in ^176,178Ir and ^182,184Au present a low-spin signature inversion. In the theoretical framework of 2-quasiparticle plus rotor model with p- n residual interaction, the signature inversion phenomenon in the πi_13/2 νi_13/2 bands has been discussed qualitatively. Theoretical investigations have been performed for the πh_9/2 νi_13/2 and πi_13/2 νi_13/2 bands using the cranked shell model. It is found that the signature inversions in both configurations can be well reproduced using the pairing and deformation self-consistent cranked Wood-Saxon calculations.     

DISCOVERY OF MULTIPLE,COLLECTIVE BAND STRUCTURES IN NUCLEI WITH A=60—80

Recent studies of levels in even-even ^68,70,72Ge,^70,72,74Se,^74,76,78,80Kr and ⁶⁵Ga and ⁷⁴Br have led to the discovery of a wide variety of different collective band structures.These include bands built on near spherical ground states and excited more well de-formed shapes that may include triaxial shapes,rotation-aligned bands built on thesame orbital （g_（9/2））² for both protons and neutrons,RAL negative parity bands witheven and odd spins,and ΔI=1 γ-type vibrational bands in even-even nuclei.As recent as 1974,a survey of the energy level in the even-even Ge and Se iso-topes^[1] revealed little was known above a spin of 4⁺ （see for examples Figs.1 and 2 of Ref.1）.With the exception of the unusally low-lying excited 0⁺ states in ^70,72Ge,first discovered in ⁷²Ge in 1948 at Vanderbilt^[2],the theoretical treatment of thesenuclei was limited primarily to some variation of the vibrational model.However,very recently there has been a surge of information on nuclei in this region that hasrevealed fascinating new features and also provided new insight into the excited 0^+’states.Particularly striking are the multiple,independent and highly collective bandstructures which we have discovered in our in-beam γ-ray spectroscopy studies fol-lowing heavy-ion induced reaction.Evidence for and the theoretical understandingof the richness of the collective band structures that are found in our studies of^68,70,72Ge （Refs.3—6）,^70,72,74Se （Refs.7—13） and ^74,76,78,80Kr （Refs.14—18）,as illustratedby the at least seven different bands found in our studies of the levels of ⁶⁸Ge ⁷⁴Se,and ⁷⁶Kr （Figs.1—3）,are described in this paper.These multiple structures includethe following:a) coexistence of ground bands built on near-spherical shapes andexcited bands with larger deformation built on O^+′ band heads;b) bands with 8⁺ band heads interpreted as rotation-aligned,RAL,bands built on both neutron and/orproton （g_（9/2））² quasiparticle configurations coexisting with the ground-state band;c)RAL neutron and proton odd-parity bands formed from coupling of a g_{（9/2 ）}quasipar-ticle and a p_（1/2）,p_（3/2） or f_（5/2）,quasiparticle with the core;d) ΔI=1 even-parity bands,which are best characterized as gamma-vibrational bands;and e) additional bandswhose nature are presently not known.     

Measurement of 125Ba High Spin States

The high spin states of ¹²⁵Ba populated via the ¹⁰⁹Ag(¹⁹F,3n) reaction are measured by using a BGO Compton suppressed HPGe detector array.The negative and positive parity bands built respectively on the h_11/2 and g_7/2 neutron hole states are extended to 35/2^－ and 23/2⁺.Backbending occurs in both signature branches of the negative band at the frequencies close to that of the ¹²⁴Ba yrast band.An onset of backbending in the positive band has been seen.     

Collective Band Structures in Neutron-Rich Odd-A 145,147Ce Nuclei

Through study of the prompt r-rays emitted in the spontaneous fission of ²⁵²Cf, high spin states of neutron-rich odd-A ^145,147Ce nuclei have been investigated. The levels in ¹⁴⁷Ce have been extended. A collective band in ¹⁴⁵Ce have been identified for the first time. The results from the particle rotor model calculations indicate that the yrast bands in ¹⁴⁵Ce and ¹⁴⁷Ce originate from vi_13/2 orbital coupling and the ground states of ¹⁴⁵Ce and ¹⁴⁷Ce originate from (vh_9/2,vf_7/2) and vh_9/2 configiration, respectively. No obvious octupole deformation was observed in these two isotopes, but a side band obtained in ¹⁴⁷Ce may show some octupole correlations.     

Rb晕带signature反转的机理

将角动量投影壳模型应用到84Rb核，对组态为πg9/2νg9/2的正宇称晕带和组态为π(p3/2,f5/2)νg9/2的负宇称晕带理论计算和实验结果进行了比较，特别是对正宇称晕带中的signature反转机理进行了探讨.角动量投影壳模型计算显示正宇称晕带中的signature反转是原子核随自旋增加形状发生变化的信号，其间原子核从低自旋的长椭球通过三轴形变变到高自旋的扁椭球.此外，还确定了此两带的原子核形状.