美科学家发现钆147原子核的超形变现象

美科学家发现钆１４７原子核的超形变现象原子核通常被描述为质子和中子粗糙球形凝聚体。但是美国华盛顿大学的季米里奥．Ｇ．萨兰蒂特斯及其合作者发现并证明，某些原子能经受更加急剧的形变，这就是他们首次在钆１４７核子中发现超形变现象。所谓超形变，是两个较小核之...     

协变密度泛函理论对原子核磁矩的研究

原子核磁矩是原子核最重要的物理观测量之一,它反映了原子核结构的重要信息,本文回顾了原子核磁矩的理论研究进展,特别是协变密度泛函理论的研究进展,并分别介绍了其对球形奇A核和形变奇A核磁矩的描述.对球形奇A核,首先以~(16)O和~(40)Ca附近具有LS闭壳核芯加减一个核子的奇A原子核磁矩为例,讨论了奇时间场的贡献.其次,基于点耦合相互作用的协变密度泛函理论,并考虑相应的奇时间场、单π介子交换流、一阶和二阶组态混合效应的修正,研究了jj闭壳核~(208)Pb附近原子核~(209)Pb,~(207)Pb,~(209)Bi和~(207)T1的磁矩.对于形变奇A原子核,以~(33)Mg为例,利用包含时间分量的相对论平均场理论和组态固定的形变约束方法,研究其内禀磁矩.最后,对原子核磁矩的协变密度泛函理论研究进行了展望.     

超形变核态的相对论对称性研究

相对论对称性在原子核的壳层结构及其演化中扮演重要角色.探讨超形变核态的相对论对称性,利用相对论平均场理论计算超形变核态的结合能、单粒子能级,提取单粒子能级的自旋和赝自旋能量劈裂,分析这些能量劈裂与原子核形变及自旋和赝自旋双重态量子数间的关系,进而研究超形变核态的自旋和赝自旋对称性及其随形变变化的规律,结果表明超形变核态的自旋和赝自旋对称性与双重态量子数和形变都相关.     

相互作用玻色子模型中高阶项效应的定性分析

在相互作用玻色子模型中引入了一种新的高阶项,并对过渡区原子核量子相变进行了研究.首先对能量曲面进行分析,结果发现高阶项可以描述原子核基态的三轴形变.接着应用到192Pt核和188 Os核中,计算了电四极B(E2)跃迁值.结果表明高阶项效应十分明显.     

参数空间八极振动的量子化

利用核八极形变最普遍的参数化形式，通过正则量子化程序，导出了参数空间量子化的哈密顿量，可用来分析原子核不同模式的振动，对研究原子核的结构有重要意义。     

描写从球形核到大形变核过渡的简单能量公式

本用一个双参数公式，拟合了从球形核到大形变核的基带能谱，其中参数Ｘ可视为球形度。     

原子核电四极矩与三轴形变参量γ的关系研究

电四极矩是表征核电荷分布偏离球对称程度的重要参数,与核形变参量之间有着必然的联系。但一直以来只给出了电四极矩Q与轴对称形变参量β（或ε）之间的关系。文章从原子核表面在球坐标中用球谐函数展开式出发,导出了原子核电四极矩Q与三轴形变参量γ的关系,并对结果进行了讨论。     

A=100区奇奇核旋称反转及三轴形变对它的影响

将两准粒子加轴对称转子模型扩展到对A=100质量区两个奇奇核^102Rh和^98Rh的旋称反转的研究后，又在此基础上引入原子核的三轴形变．计算结果表明，可能的旋称反转机制(即：低K空间n—p相互作用和科氏力的相互竞争)，对于A=100质量区奇奇核也是适用的．在引入了三轴形变后与轴对称情形下相比较，明显地改进了能谱的振荡特性。     

轻原子核的集体参数

我们用Nilsson波函数计算了轻原子核(从0~(17)—K~(39))的平衡形变及内部电四极矩,并根据Inglis模型,计算了轻核的转动惯量,9_R因子及球形核振动参数B、C。结果表明,形变参数一般较实验小很多。这个结果与以前关于重核计算所得结果不同。计算转动惯量时,如取合理的x值,并用实验的平衡形变,则与实验符合得很好,只有0.4％—30％的误差,至于轻核振动参数,目前还没有肯定的实验结果可以比较,但理论的C值显示出壳层效应,比非旋的结果合理。又,除形变外,其他集体参数对x、μ的改变是敏感的。     

清华大学物理系原子核结构实验研究进展

在清华大学百年校庆之际,我们对近年来清华大学物理系有关原子核结构实验研究的主要进展作一介绍,内容包括在A≈140缺中子核区核的形状驱动效应研究,如扁椭形变带、形状共存等;在A≈110丰中子核区核的多声子γ振动带结构、新手征二重带、新的准粒子带结构研究等;在A≈150丰中子核区核的八极形变研究等.研究成果对原子核结构的理解提供许多新的重要信息.     

核素分类单位区的对称与递变

核素分类中,单个核素与一大片核素的分布具有相似性,均遵守对称与扩张的1,2,4规律.如中子数N36～N38的7核素就是这样一个对称小区,再如以6×8核素区作为一个分布单位区,内含3个递变的6×6核素区,7个这样的单位区递变则形成一个核素分布统一主区域,其中有14个6×6核素区,14个中心排列在差K17与K9,坐标S33与S37四线上,主区域的中心坐标(33,20)是放射核素.核素分类中显示出核素体系的对称性、整体性与数学美.     

A triplet of differently shaped spin-zero states in the atomic nucleus 186Pb

Understanding the fundamental excitations of many-fermion systems is of significant current interest. In atomic nuclei with even numbers of neutrons and protons, the low-lying excitation spectrum is generally formed by nucleon pair breaking and nuclear vibrations or rotations. However, for certain numbers of protons and neutrons, a subtle rearrangement of only a few nucleons among the orbitals at the Fermi surface can result in a different elementary mode: a macroscopic shape change. The first experimental evidence for this phenomenon came from the observation of shape coexistence in 16O (ref. 4). Other unexpected examples came with the discovery of fission isomers and super-deformed nuclei. Here we find experimentally that the lowest three states in the energy spectrum of the neutron deficient nucleus 186Pb are spherical, oblate and prolate. The states are populated by the alpha-decay of a parent nucleus; to identify them, we combine knowledge of the particular features of this decay with sensitive measurement techniques (a highly efficient velocity filters with strong background reduction, and an extremely selective recoil-alpha-electron coincidence tagging methods). The existence of this apparently unique shape triplet is permitted only by the specific conditions that are met around this particular nucleus.     

7核素列的三角形与4线联系

在坐标单位是氘氚结团的正方形核素图中,描述一个线性7核素组成的三角形,其顶点与3边中点都是7核素列的端点;另外,说明开始点核素在坐标S轴上的4列偶奇相间的7核素列统一于关系式:S=a+n H(n=1,2,3,4).可以以上结论为突破点,探索核素体系的本质.     

Nuclear localization and signalling activity of phosphoinositidase C beta in Swiss 3T3 cells.

The hydrolysis of phosphatidylinositol 4,5-bisphosphate (PtdInsP2) is a widespread receptor-coupled signalling system at the plasma membrane of most eukaryotic cells. The existence of an entirely separate nuclear phosphoinositide signalling system is suggested from evidence that purified nuclei synthesize PtdInsP2 and phosphatidylinositol 4-phosphate (PtdInsP) in vitro and that a transient decrease in the mass of these lipids occurs when Swiss 3T3 cells are cultured in the presence of insulin-like growth factor-1 (IGF-1). These IGF-1-dependent changes in inositol lipids coincide with an increase in nuclear diacyglycerol and precede translocation to the nucleus and activation of protein kinase C (refs 5, 6). Circumstantial evidence that links these changes with mitosis comes from the isolation of a 3T3 clone that expresses the type-1 IGF receptor and binds IGF-1 peptide but does not respond mitogenically or show transient mass changes in nuclear inositol lipids. A key question is how IGF-1 initiates the rapid breakdown of PtdInsP and PtdInsP2 in the nucleus. Here we present evidence that nuclei of 3T3 cells contain the beta-isozyme of phosphoinositidase C, whereas the gamma-isozyme is confined to the cytoplasm and that IGF-1 treatment stimulates exclusively the activity of nuclear phosphoinositidase C.     

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.     

濒危植物-半日花(Helianthemum songaricum)的双受精作用及胚和胚乳发育

运用石蜡切片法,对半日花Ｈ．ｓｏｎｇａｒｉｃｕｍ的受精过程,胚及胚乳发育进行了初步观察．受精前,一个助细胞解体,另一助细胞宿存．精核与极核的融合早于精核与卵的融合．受精极核不经过休眠过程,经多次分裂形成核型胚乳．胚乳游离核于球胚晚期开始细胞化．种子成熟后无胚乳．胚胎发育属柳叶菜型．胚柄由一纵列细胞组成并于球胚晚期开始退化．胚的发育经历球形原胚、心形胚、鱼雷形胚及成熟胚各时期．     

原子核幻数与群子结构之间界定

原子核的幻数已被大量实验所证明是一系列的正整数,如有2.8,2.0,2.8,5.0,8.2,12.6等,但从理论上推导这些整数的存在并不是轻易的事情。为此,曾提出过单粒子壳层模型,进一步发展成为自旋轨道耦合模型,成功地推导出上述所有幻数系列并预测了各种核素的自旋角动量。大量的实验也表明实测的核素的自旋角动量与理论预测值之间有相当大的差距。在这种情况下,人们开始倾向于原子核的集团运动的看法,始终未能出现突破性的进展。文中运用作者创立的第四统计力学———JRG群子统计理论的观点,提出了原子核内存在亚结构———核群子的观点,用k、l、n、m等群子参数标定每一个核素,并与幻数比较,凡是具有幻数的核素具有简单的核群子结构,有较明显的界定。     

Electromagnetically induced transparency with resonant nuclei in a cavity

The manipulation of light-matter interactions by quantum control of atomic levels has had a profound impact on optical sciences. Such manipulation has many applications, including nonlinear optics at the few-photon level, slow light, lasing without inversion and optical quantum information processing. The critical underlying technique is electromagnetically induced transparency, in which quantum interference between transitions in multilevel atoms renders an opaque medium transparent near an atomic resonance. With the advent of high-brilliance, accelerator-driven light sources such as storage rings or X-ray lasers, it has become attractive to extend the techniques of optical quantum control to the X-ray regime. Here we demonstrate electromagnetically induced transparency in the regime of hard X-rays, using the 14.4-kiloelectronvolt nuclear resonance of the M?ssbauer isotope iron-57 (a two-level system). We exploit cooperative emission from ensembles of the nuclei, which are embedded in a low-finesse cavity and excited by synchrotron radiation. The spatial modulation of the photonic density of states in a cavity mode leads to the coexistence of superradiant and subradiant states of nuclei, respectively located at an antinode and a node of the cavity field. This scheme causes the nuclei to behave as effective three-level systems, with two degenerate levels in the excited state (one of which can be considered metastable). The radiative coupling of the nuclear ensembles by the cavity field establishes the atomic coherence necessary for the cancellation of resonant absorption. Because this technique does not require atomic systems with a metastable level, electromagnetically induced transparency and its applications can be transferred to the regime of nuclear resonances, establishing the field of nuclear quantum optics.