超重Z=113-116元素β~-衰变寿命的计算研究

超重元素结构和性质的研究对于超重核实验的合成具有重要的意义,而超重核素β-衰变寿命是了解超重核素结构的重要性质之一。利用我们提出的远离β稳定线原子核β-衰变寿命的指数规律理论计算公式,对超重区原子核Z=113-116同位素链上β-衰变寿命进行了系统的理论计算和讨论。计算结果与当前普遍采用的宏观-微观模型结果进行了比较,结果表明:该指数计算公式对超重附近原子核寿命的计算结果与宏观-微观模型的结果符合较好。     

超重核素94～102同位素链上的位能曲面研究

采用宏观-微观模型对原子核系数在94～102之间偶偶核素同位链上原子核的位能曲面进行了系统的研究,给出了这些同位素链上原子核的位能曲面图。在此基础上讨论了超重核素的形变随核子数之间的变化规律,研究了该区域可能存在的形状共存现象和超重核素的稳定性。最后对超重核区域原子核的同质异能态进行了讨论。     

奇特原子核电荷半径的理论研究进展

电荷半径是描述原子核基本性质的可观测量之一,对于奇特原子核电荷半径的精确描述是核物理实验和理论研究的前沿课题．影响原子核电荷半径大小的因素有很多,例如形变、对关联、壳闭合效应等,因此需要发展一个统一的理论模型．对于奇特原子核电荷半径的精确描述,一方面可以更深层次地揭示核子-核子有效相互作用,对理论模型参数进行约束;另一方面,可靠的电荷半径数值作为输入参量,对核天体演化研究具有重要意义．本文简要介绍关于奇特原子核电荷半径的理论研究进展,分析了不同理论模型对电荷半径的壳效应和奇偶效应的描述;结合Ca和Rb同位素链电荷半径的变化趋势,分析指出中子-质子关联和自旋-轨道相互作用在精确描述原子核电荷半径中起到了很重要的作用．      

核耗散强度对超重核蒸发剩余截面的影响

尽管目前利用熔合蒸发反应合成超重核的研究陷入停顿,但该反应机制仍是实验室合成新核素的主要方法.为了研究核耗散强度对超重核素合成截面的影响,通过冻结能级密度参数及其在鞍点和基态处的比值,对超重元素Cn、Fl和Lv的7个反应进行了数值计算.计算结果表明重现实验数据所需核耗散强度随超重余核质量数的减小而逐渐减弱.此外,相比于对~(282,283)Cn和~(292,293)Lv的模拟,要重现新质子幻数Z=114对应的超重复合核~(287,288,289)Fl的实验数据则需要增强核耗散强度.上述规律为获取超重核的结构信息提供了一种潜在的核反应学方法.     

超重新核素的研究进展

超重核素合成是当前核物理研究的热点。本文简要回顾和介绍了合成超重核素的实验进展、超重核素的理论研究和当前的一些理论研究近况,主要包括各种相对论平均场模型和宏观-微观模型的计算结果,并分析和比较了各种理论模型在描述超重核性质方面的差异。对超重核素的性质做了总结,在此基础上预言了一些超重核素的性质,对比较容易合成的超重核素的实验提出了建议。     

原子核质量的测量

质量是原子核最基本的性质之一,核质量数据在核物理、核天体物理及核技术应用等多个领域得到广泛应用.原子核质量的测量是核物理一个重要的前沿研究课题.本文简要回顾了核质量测量的发展历史,综述目前国际上的研究现状,并介绍了原子核质量数据表的评估工作.基于兰州重离子加速器大科学装置,我们建立了等时性质谱术,精确测量了一批短寿命原子核的质量.随后介绍了兰州的质量测量工作,讨论了新质量数据对原子核的同位旋对称性和天体X射线暴研究的影响.     

超重核Z=117同位素链的α衰变性质

运用推广液滴模型结合WKB方法对新合成超重核293117和294117及其α衰变链中各核素的半衰期进行系统性分析,论计算到超重核半衰期与实验值符合非好.说明推广液滴模型可以成功研究超重核半衰期.本文还预测了Z=117同位素链未合成超重核α衰变半衰期.计算结果表明在Z=117同位素链中存在比已合成293117和294117更稳定、寿命更超重核.     

利用重离子核反应的碎片截面测量极度丰中子核的对称能

<正>对称能是原子核形成中的重要约束量.丰中子核的对称能对于中子滴线的位置(新同位素产生)、中子皮厚度、低密度核结构和性质、天体物理研究等等具有重要意义.利用重离子核反应产生碎片的截面可以很好地提取丰中子核对称能.但目前这种方法要对多个炮弹碎裂反应进行测量.基于一个修改的Fisher模型(modified Fisher model,MFM),利用单个炮弹碎裂反应即可从其碎片截面提取极度丰中子核的对称能,极大地节约实验测量工作量.     

稳定核素位置分析

<正> 一引言原子核由Z 个质子和N 个中子组成。以N—Z 标绘的核素图(图3)告诉我们,稳定核素Z。聚集成一条线(即β稳定线)。在稳定线两侧是不稳定的放射核素。离稳定线越远核素寿命越短。β稳定性是原子核的重要性质之一,它对于核结构、核反应及远离β稳定线的短寿命核素的研究均有重要意义。它也是检验半经验的原子核质量公式的一个重要判据。Dewdnay在β稳定线的研究方面曾作过有益的工作。但,由于近代     

径向基函数方法在原子核质量预言中的应用

结合径向基函数方法,我们将常用的几种原子核质量模型的精度提高了约10％～40％.留一交叉验证与AME03-11测试表明径向基函数方法是一种非常强大并且实用的工具.考虑径向基函数修正后,原子核质量模型能够更好地描述实验新测量原子核质量的数据.这一工作对于核天体物理、超重核合成及原子核对称能等方面的研究具有很高的应用价值.     

Towards the drip lines of the nuclide landscape

In the paper we review the recent progress of studies in unstable nuclei,mainly affiliated with the facilities of radioactive ion beams in China,including both experimental and theoretical aspects of researches.Many experiments for reactions,decays and structures have been performed targeting better understandings of properties of unstable nuclei.Special experimental measurements related to nuclear astrophysics have been done to seek insights into the processes of syntheses of elements in the universe.Theoretical calculations have provided many useful predictions on the behaviors of unstable nuclei,with model developments.Studies covered many mass regions from light to superheavy nuclei,giving plenty of information about the structures of unstable nuclei,towards the limits of existence of atomic nuclei.     

Shape coexistence and triaxiality in the superheavy nuclei

Superheavy nuclei represent the limit of nuclear mass and charge; they inhabit the remote corner of the nuclear landscape, whose extent is unknown. The discovery of new elements with atomic numbers Z > or = 110 has brought much excitement to the atomic and nuclear physics communities. The existence of such heavy nuclei hangs on a subtle balance between the attractive nuclear force and the disruptive Coulomb repulsion between protons that favours fission. Here we model the interplay between these forces using self-consistent energy density functional theory; our approach accounts for spontaneous breaking of spherical symmetry through the nuclear Jahn-Teller effect. We predict that the long-lived superheavy elements can exist in a variety of shapes, including spherical, axial and triaxial configurations. In some cases, we anticipate the existence of metastable states and shape isomers that can affect decay properties and hence nuclear half-lives.     

Nuclear isomers in superheavy elements as stepping stones towards the island of stability

A long-standing prediction of nuclear models is the emergence of a region of long-lived, or even stable, superheavy elements beyond the actinides. These nuclei owe their enhanced stability to closed shells in the structure of both protons and neutrons. However, theoretical approaches to date do not yield consistent predictions of the precise limits of the 'island of stability'; experimental studies are therefore crucial. The bulk of experimental effort so far has been focused on the direct creation of superheavy elements in heavy ion fusion reactions, leading to the production of elements up to proton number Z = 118 (refs 4, 5). Recently, it has become possible to make detailed spectroscopic studies of nuclei beyond fermium (Z = 100), with the aim of understanding the underlying single-particle structure of superheavy elements. Here we report such a study of the nobelium isotope 254No, with 102 protons and 152 neutrons--the heaviest nucleus studied in this manner to date. We find three excited structures, two of which are isomeric (metastable). One of these structures is firmly assigned to a two-proton excitation. These states are highly significant as their location is sensitive to single-particle levels above the gap in shell energies predicted at Z = 114, and thus provide a microscopic benchmark for nuclear models of the superheavy elements.     

以Fe作为弹核研究合成超重核的黏连截面

超重元素的研究是目前核物理和核化学领域的前沿课题之一,随着实验设备的不断完善和各种理论模型的不断发展,人们在合成超重核的研究上取得了非常大的进展。Fe作为弹核探讨形成超重核的黏连截面,主要采用两步模型来研究超重核的形成过程。主要核反应过程具体分为2步:第1步是指弹靶的黏连阶段,第2步是指弹靶形成复合核阶段。这2个阶段的动力学过程都可以用带随机力的朗之万方程来描述,并且这2个阶段是各自独立的,即可以分别来讨论这2个阶段。主要讨论黏连阶段,根据给出的58Fe+248Cm与58Fe+208Pb激发能与黏连截面的实验值,重新拟合出以Fe作为弹核与锕系中系列核形成超重核的黏连截面的最佳C与ΔB值,及C与ΔB值对拟合出的E*-σ曲线的影响、角动量和激发能等因素对黏连截面的影响。     

Discovery of 40Mg and 42Al suggests neutron drip-line slant towards heavier isotopes

A fundamental question in nuclear physics is what combinations of neutrons and protons can make up a nucleus. Many hundreds of exotic neutron-rich isotopes have never been observed; the limit of how many neutrons a given number of protons can bind is unknown for all but the lightest elements, owing to the delicate interplay between single particle and collective quantum effects in the nucleus. This limit, known as the neutron drip line, provides a benchmark for models of the atomic nucleus. Here we report a significant advance in the determination of this limit: the discovery of two new neutron-rich isotopes--40Mg and 42Al--that are predicted to be drip-line nuclei. In the past, several attempts to observe 40Mg were unsuccessful; moreover, the observation of 42Al provides an experimental indication that the neutron drip line may be located further towards heavier isotopes in this mass region than is currently believed. In stable nuclei, attractive pairing forces enhance the stability of isotopes with even numbers of protons and neutrons. In contrast, the present work shows that nuclei at the drip line gain stability from an unpaired proton, which narrows the shell gaps and provides the opportunity to bind many more neutrons.     

复合核裂变与微观裂变理论进展

核裂变过程是一个复杂的大幅度的量子多体动力学过程,对其理论描述一直是一个挑战.为了描述实验上的裂变可观测量,理论上发展了一些半唯象与近似的模型,但这些模型依赖唯象的参数.从有效核力出发发展微观的裂变理论,原则上无需自由参数,但要达到定量计算的阶段还很困难.本文介绍了复合核裂变的理论进展,特别讨论了微观计算复合核存活概率在超重核合成研究中的关键影响.此外比较了绝热和非绝热的微观裂变动力学模型.其中绝热裂变模型对低激发裂变的实验可观测量能较好描述,而非绝热动力学模型对深入研究裂变机制非常有用.本文分析了核裂变理论的问题和挑战,意识到裂变过程极其复杂,并展望了裂变理论的发展方向.     

Recent progress in theoretical nuclear physics related to large-scale scientific facilities

Several large-scale scientific facilities(LSSF) are running and several others are under construction in China.Recent progress made by Chinese scientists in theoretical study of nuclear physics related to these facilities is reviewed.The emphasis is put on those topics covered in the issue entitled Special Topics on Some Theoretical Nuclear Physics Aspects Related to Large-scale Scientific Facilities(in Sci China Ser G-Phys Mech Astron,Vol.52,No.10,2009).