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1.
基于Ru (Z = 44) 丰中子同位素中存在最大三轴形变的理论预言和实验证据,综述了近年来Rh (Z = 45),Pd (Z =46), Ag (Z =47), Cd (Z =48)(质子数Z 位于Ru,Z =44 之上)及Zr (Z =40), Nb (Z =41), Mo (Z =42),Tc (Z =43)(质子数Z 位于Ru,Z =44 之下) 的A~ (100~126) 丰中子同位素中关于三轴形变的形状变迁和形状共存系统性研究的重要进展。252Cf 自发裂变瞬发 射线-- 三重符合、特别是新建立的--- 四重符合数据的系统观测和研究,在Ru, Pd, Cd 和Nb 丰中子同位素中显著扩展或首次观测到了一系列能带,为这个核区原子核形状的研究提供了新的、重要的实验数据。联系此前报道的有关进展,使用PES, TRS, PSM, CCCSM 和SCTAC 理论模型计算拟合新的实验数据,在该核区沿同中素和同位素链,并随自旋和激发能变化各自由度,跟踪原子核形状渐进变化,获得了新的系统性研究成果,显著扩展和深化了人们对原子核形状变迁和形状共存的认知。对于Ru 及其上的Rh (Z = 45), Pd (Z = 46), Ag (Z = 47) 和Cd (Z = 48) 丰中子同位素的研究表明:Rh 丰中子核具有比最大值稍小的三轴形变,γ = 28°,并在103{106Rh 同位素链上鉴别出了手征对称破缺;在三轴形变核112Ru和114Pd(N = 68)中发现了三轴原子核的摆动运动,该摆动运动也可能在114Ru (N = 70)中存在;观察到了从具有最大三轴形变的110,112Ru 中手征破缺到稍小三轴形变的112,114,116Pd 中扰动的手征破缺的过渡;在较软的Ag 核中观察到了丰富的谱学结构,在104,105Ag 中鉴别出了可能的手征对称破缺,在较重的115,117Ag 中提出了趋于三轴形变的软度;具有小形变的Cd核的能级结构被解释为准粒子耦合、准转动和软三轴形变;最近的库伦激发的研究提供了Z = 50, N = 82满壳附近122,124,126Cd 核中出现核集体性的实验和理论证据;上述研究成果展现出从Ru中的最大三轴形变(γ=30°,三轴形变极小增益为0.67 MeV), 经具有大三轴形变的Rh核γ=28°),到Pd核中的稍小、但稳定于中等自旋到高自旋区的三轴形变(γ~41°,三轴形变极小增益为0.32 MeV),再经Ag核中的软度,最后到具有很小形变、但仍出现集体性质、包括软三轴形变的Cd核的过渡。对于Pd核转动带交叉系统性的研究揭示了其第一带交叉(νh11/2)2 中子转动顺排的上行驱动,和第二带交叉(πg9/2)2质子转动顺排的下行驱动效应,成功地解释了114Pd 中的三轴摆动运动,并给出了110-118Pd同位素链中理论早已预言、而比早期理论预言更为完整准确的形状渐进变迁和形状共存的图像。根据该核区的系统研究,发现最大三轴形变出现在112Ru,而在相邻的偶Z(Pd)同位素链,三轴形变极小的中心在114Pd, 两者均为N = 68。上述系统性研究沿相邻的Ru和Pd偶Z同位素链,在N =68同中素中鉴别出最大三轴形变,均比理论预言的108Ru 和110Pd 多4个中子。在Z值位于Ru (Z = 44) 之下的Zr (Z = 40), Nb (Z = 41), Mo (Z = 42) and Tc (Z = 43) 丰中子同位素中,Y和Zr核具有很强的轴对称四极形变,而在较重的Zr同位素中出现了自由度;较重的Nb核(A = 104~106) 基态具有中等程度的软三轴形变和强四极形变,随着自旋和激发能的增加,过渡到接近于轴对称的强四极形变;而较轻的Nb核(A≤103) 基态均接近轴对称形状;在Nb同位素链上基态由球形到强四极形变的形状突变发生在100Nb(N = 59),在100-106Nb同位素链中基态的软三轴形变随中子数增加而增加;在Nb核中还观察到关于软三轴形变的形状共存;Mo核具有大的三轴形变,观察到了振动和手征对称破缺;Tc核具有比最大值稍小的三轴形变,γ=26°,并观察到了手征对称破缺。质子数Z从41到48的A~(100~126)丰中子同位素,特别是Pd和Nb 同位素,呈现出关于三轴形变的过渡特征。This paper reviews the systematic investigations and understanding for the shape transitions and coexistence with regard to triaxial deformations in A s 100 to 126 neutron-rich Rh (Z = 45), Pd (Z = 46), Ag (Z = 47), Cd (Z = 48) and Zr (Z = 40), Nb (Z = 41), Mo (Z = 42), Tc (Z = 43) isotopes with Z beyond and below Ru (Z = 44), respectively, in Ru the maximal triaxial deformation having been predicted and deduced. The recent measurements and studies of prompt triple- and four-fold, γ-γ-γ and γ-γ-γ-γ, coincidence data from the spontaneous fission of 252Cf using Gammasphere have yielded considerable expansion and extension or first observation of the bands in Ru, Pd, Cd, and Nb isotopes,which provided important data for the studies of nuclear shapes in this region. Combined with previous investigations, recent systematic studies of the new data well reproduced by PES, TRS, PSM, CCCSM and SCTAC model calculations have traced shape changes along the isotonic and isotopic chains, respectively,and with changing excitations/spins as well, significantly expanding our knowledge of shape transitions/coexistence in nuclei.For the neutron-rich Ru and beyond, Rh, Pd, Ag and Cd isotopes, triaxial deformations γ= 28°,slightly smaller than the maximal value, were deduced in Rh (Z = 45) isotopes, with chiral symmetry breaking proposed in 103-106Rh; onset of wobbling motions were identified in 112Ru and 114Pd (N =68),and probably also in 114Ru (N =70); evolution from chiral symmetry breaking in 110,112Ru with maximal triaxial deformations to disturbed chirality in 112,114,116Pd with less pronounced triaxial deformations was proposed; rich nuclear structure was proposed in soft Ag isotopes with possible chiral doubling structure suggested in 104,105Ag, and softness towards triaxial deformation proposed in heavier 115,117Ag;quasi-particle couplings, quasi-rotations and soft triaxiality were suggested in Cd (Z =48) isotopes with small deformations; onset of collectivity was recently suggested in 122,124,126Cd in the vicinity of Z =50 and N = 82 closed shells by studies of Coulomb excitations; shape evolutions from maximal triaxial deformations in Ru (γ=30°, with triaxial minimum energy gain of 0.67 MeV), through Rh with large triaxial deformations ( γ=28°), to less pronounced triaxiality in Pd (with triaxial minimum energy gain of 0.32 MeV), then soft triaxiality in Ag, and finally to slightly deformed Cd isotopes but with emergence of collectivity and soft triaxiality were proposed. The systematic studies of the band crossings in Pd revealed up-rising drivings of the first band crossings caused by (νh11/2)2 and down-sloping drivings of the second band crossings by (πg9/2)2, explained the onset of wobbling motions in 114Pd,and showed a long-sought picture of shape evolution and coexistence in the Pd isotopic chain which is more complete but complex than earlier predictions. Based on the systematic studies in the mass region,maximal triaxial deformation is found to be reached in 112Ru and less-pronounced triaxiality centered at 114Pd, both for N =68, four neutrons more than predicted in earlier theoretical calculations.In the neutron-rich Zr (Z =40), Nb (Z =41), Mo (Z =42) and Tc (Z =43) isotopes with Z just below Ru, large quadrupole deformations of axially symmetric shapes were deduced in Y and Zr isotopes, with emergence of the degree of freedom having been suggested for heavier Zr isotopes; medium triaxial deformations were deduced for the ground states of heavier (A > 104) Nb isotopes, and, with increasing excitations and spins, evolution from medium triaxial deformations with strong quadrupole deformations at ground states to nearly axially-symmetric shapes were deduced; light Nb isotopes (A6103) have near axially-symmetric shapes with strong quadrupole deformations; combining with the identification of onset of strong quadrupole deformation at 100Nb in the Nb isotopic chain, an increase of soft triaxiality with increasing neutron number was proposed in 100-106Nb. Shape coexistence with regard to soft triaxiality is also proposed in Nb isotopes; large triaxial deformations, vibrations and chiral doublets were proposed in Mo isotopes; chiral doubling and large triaxial deformations (γ ~26°) slightly smaller than the maximal triaxiality were suggested in Tc isotopes.The neutron-rich nuclei with Z ranging from 41 through 48 and A ~100 to 126, especially the Pd and Nb isotopes are thus found to be transitional nuclei with regard to triaxiality.  相似文献   
2.
气体喷嘴反冲传输技术是继“跑兔”装置之后发展和完善起来的适合于短寿命核素研究的一种快速而有效的在线脱束方法。 它能够将短寿命核反应产物传输至远离高辐射区的低本底场所进行收集和测量。 该技术已在加速器和反应堆上得到了广泛的应用, 是一种研究核反应、 核谱学和合成与鉴别新元素、 新核素的一种不可缺少的基本实验技术和工具。 描述了气嘴系统的结构、 基本原理、 设计要求以及它的主要特性, 特别是对系统的气体动力学机制以及各种参数对系统特性的影响等进行了讨论。 最后, 综述了它在核物理、 核化学以及质谱学等领域的应用情况, 并且给出了几个应用的典型例子。 The gas jet recoil transport technique is developed and improved as a new rapid and effective on line and off beam method following “rabbit” apparatus in the study of short lives nuclei. It can transport the short half life nuclear reaction products far from high radioactive area for collection and measurement at low background area. This technique has been widely used in the researches with accelerator and reactor. It is indispensable basic experimental technology and tool applied to nuclear reaction, spectroscopy, as well as synthesis and identification of new elements and nuclei. The basic principle, structure, design requirement and main characteristics of gas jet system are described in this paper, especially the mechanism of gas dynamics and the effect of several parameters on the system properties are discussed. Finally, the applications of this technique in several fields such as nuclear physics, nuclear chemistry and mass spectroscopy etc. are comprehensively represented. Several typical applications are also illustrated.  相似文献   
3.
利用能量为 90— 1 0 5MeV的16 O束流 ,通过197Au( 16 O ,4n)反应研究了2 0 9 Fr的高自旋态能级结构 .进行了γ射线的激发函数、γ γ延迟符合及γ射线的角分布测量 .首次建立了由 2 1条γ射线构成的2 0 9Fr的能级纲图 ,其中包括一个半寿命为 ( 52± 2 0 )ns的同质异能态 .基于2 0 9Fr与2 0 8Rn低位能级结构的相似性 ,用一个h9/ 2 价质子与2 0 8Rn激发态的弱耦合解释了2 0 9Fr的低位能级结构 .  相似文献   
4.
罗亦孝 《物理》1998,27(7):403-408
远离稳定线原子核的实验研究(Ⅱ)罗亦孝(中国科学院近代物理研究所,兰州重离子加速器国家实验室,兰州730000)42丰质子轻稀土核素的合成和衰变性质研究421轻稀土区质子滴线Z=0743N+116附近新β缓发质子先驱核的合成和研究[16—1...  相似文献   
5.
6.
兰州重离子加速器冷却储存环   总被引:2,自引:0,他引:2  
 兰州重离子加速器(HIRFL)由用作注入器的扇聚焦回旋加速器(SFC)和分离扇回旋加速器(主加速器SSC)组成,是加速中、低能重离子束流的回旋加速器系统.  相似文献   
7.
本文简介HIRFL上中、低能重离子物理基础和应用研究的主要进展;着重介绍三个方面的研究:中能HIC和热核性质的研究,远离稳定线核的合成和研究,重离子束应用,并概述近期实验研究规划的初步建议。 The experimental studies and achievements recently made at the Heavy Ion ResearchFacility of Lanzhou(HIRFL) are reviewed with an emphasis on the three research fields: the study of intermediate energy heavy ion collision and properties of hot nuclei, the synthesis and study of nucleifar from stability, and the applications of heavy ions. A research program for the near future is alsobriefly introduced.  相似文献   
8.
远离稳定线丰中子核素的合成和其衰变性质及核结构研究在过去几年中得到了迅速的发展,已成为原子核物理最为活跃的前沿领域之一。本文综述各质量区丰中子远离核的生成和鉴别,重点讨论丰中子远离核奇异衰变性质和核结构研究的重要进展,并简要介绍丰中子远离核研究在天文物理学中的重要作用。  相似文献   
9.
利用能量为75—95MeV19F束流,通过反应128Te(19F,5nγ)142Pm研究了双奇核142Pm的高自旋态能级结构.实验中进行了γ射线的激发函数、γ射线单谱和γγ符合测量.建立了激发能达7030.0keV的142Pm的能级纲图,其中包括新发现的25条γ射线和13个新能级.基于实验测量的γ跃迁各向异性度,建议了142Pm能级的自旋值.  相似文献   
10.
利用16O重离子束轰击142Nd和147Sm同位素靶分别生成153Er和157Yb.借助氦喷嘴带传输系统和X-γ、γ-γ符合测量方法分离鉴别核素并测量其衰变性质.首次建立了153Er和157Yb的EC/β+衰变纲图.从中指认出153Ho的一个新三(准)粒子态和两个新单粒子态,指认出157Tm的一个新的同质异能态和一条新转动带.低位能级系统分析表明:在Ho和Tm这两条奇A核的同位素链中基态形状的转变区都在中子数86和88之间.  相似文献   
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