HI-13串列加速器上核结构在束γ谱学研究：现状及展望

主要介绍HI-13串列加速器的现状, 升级工程BRIF以及计划中的BRIFF-Ⅱ, 在束γ谱学研究的现状与将来核结构研究的展望.     

141Nd激发态的在束γ谱学研究

通过130Te(16O,5nγ)141Nd反应布居了141Nd的高自旋态能级. 对反应产生的在束γ射线进行了γ射线单谱和γ-γ符合测量. 建立了激发能达7614.5keV的141Nd能级纲图,新发现了12条γ射线和15个能级. 基于实验测量的γ跃迁各向异性,建议了141Nd部分能级的自旋值. 用一个h11/2价中子空穴与142Nd核芯晕态的耦合可以定性地解释141Nd的能级结构.     

Particle-core coupling in 141Nd

High-spin states in 141Nd have been studied using in-beam γ-ray spectroscopic techniques via the 130Te(16O, 5nγ)141Nd reaction. The level scheme of 141Nd has been extended up to an excitation energy of 7614.5 kev including 12 new γ rays deexciting 15 new levels. According to particle-vibrator coupling and semi-empirical shell model calculations, the level structure of 141Nd can be well interpreted by coupling an h11/2 neutron-hole to the respective excited states in 142Nd core.     

Dipole bands in nucleus ~(139)Pm

High-spin states in nucleus 139Pm have been studied using the reaction 116Cd(27Al,4n)139Pm.Two dipole cascades have been found.Spin and parity assignments were based on the Directional Correlation of Oriented Nuclei(DCO) ratios and systematic behavior in neighboring odd-proton nuclei.The level structures of 139Pm are compared with those of the N =78 isotone 141Eu in which two dipole bands have been confirmed as magnetic rotational bands.The close similarity between them suggests that the dipole bands in 139...     

Lifetimes of High Spin States in an Odd-Proton Nucleus 129Cs

Lifetimes of high spin states in 129Cs axe measured using the Doppler shift attenuation method. The high spin states of 129 Cs axe populated following the fusion evaporation reaction 124 Sn（UB, 6n）129 Cs at a beam energy of 65 MeV. The reduced transition probabilities B（E2） and the transition quadrupole moments Qt in the negativeand positive-paxity bands are deduced. The experimental results indicate that the Qt values of the negative parity band are smaller than those of the positive parity bands, probably due to different γ-deformation driving effects of different proton orbitals. The Qt values exhibit a considerable increase near the band crossing region in these bands. This behavior demonstrates that nuclear shape changing results from the neutron or proton alignments. The signature splitting of the πh11/2 and πg7/2 bands shows the opposite changing trend after backbending due to the h11~2 neutron and h11/2 proton alignments, respectively.     

205Po激发态研究

本工作利用重离子熔合蒸发反应¹⁹⁶Pt(¹³C, 4n)²⁰⁵Po布居了²⁰⁵Po核的高自旋态,¹³C束流能量为72 MeV。扩展了²⁰⁵Po的能级纲图,新建了3个退激序列,新发现了19条γ射线。$^{203,,205,,207}{rm{Po}}$的晕态结构与大规模壳模型的计算结果进行了比较,壳模型计算使用的组态空间包含相同的质子和中子轨道,包括0h_9/2, 1f_5/2, 2p_3/2, 2p_1/2, 1g_9/2。理论计算结果很好地再现了实验数据。     

近球形核94Nb的高自旋态研究

通过重离子熔合蒸发反应⁸²Se(¹⁸O, p5n)⁹⁴Nb布居了⁹⁴Nb的高自旋态,实验中使用的¹⁸O束流由中国原子能科学研究院的HI-13串列加速器提供,束流能量为82和88 MeV。在前人工作的基础上发现了13条新的γ跃迁并调整了部分能级的摆放位置,将⁹⁴Nb的自旋推至24⁽⁻⁾,激发能至10.6 MeV,结合DCO比值和线极化测量对部分能级的自旋、宇称进行了指定。在质子π(1f_5/2, 2p_3/2, 2p_1/2, 1g_9/2)和中子(2p_1/2, 1g_9/2, 2d_5/2, 1g_7/2)空间下将⁹⁴Nb的能级结构与壳模型计算结果进行了比较,并探讨了⁹⁴Nb的中子质子激发机制。