Review of Induced Gamma Emission and Gamma-Ray Laser Research

Induced gamma emission with the potential for substantial energy gain is an exciting area of research. This paper reviews related work done internationally, including some that has potential for a gamma-ray laser. This revised version was published online in August 2006 with corrections to the Cover Date.     

Non-Radiative Triggering of Long-Lived Nuclear Isomers

The triggering of long-lived isomeric nuclei by non-radiative excitation to a relatively short-lived mediating state is considered. Coulomb triggering in inelastic scattering of heavy ions, a transfer of triggering energy from resonant electron transitions of atomic shell (NEET) and triggering by capture of a free electron into a bound atomic state (NEEC) are discussed. Cross sections for the above processes of non-radiative triggering are presented and the relative efficiencies of these different triggering mechanisms are discussed. Numerical estimates are presented for the selected isomers. This revised version was published online in August 2006 with corrections to the Cover Date.     

利用双色激光感生光栅光谱法测定^127I的核自旋

本文利用ＮｄＹＡＧ激光倍频光５３２ｎｍ激光分成强度大致相等的两束激光作为泵浦光以２．７３°交叉于碘分子样品室中，两束泵浦光发生干涉在碘分子中选择激发形成了空间正弦分布的激光态分子光栅和基态耗尽型光栅。另一束窄线宽染料激光作为探索光射入到激光感生光栅上，沿着布拉格衍射的方向接收信号光。利用泵浦共振为３２－０Ｒ（５５），探索共振为１３－０Ｐ（５５），Ｒ（５５）和泵浦共振为３２－０Ｐ（５２），探索共振为１３－０Ｐ（５２），Ｒ（５２）的碘分子双色激光感生光栅光谱谱线强度测定了１２７Ｉ的核自旋，测定值为５／２。     

Nuclear Spin Maser Oscillation of 129Xe by Means of Optical-Detection Feedback

We have developed the nuclear spin maser oscillating at a low frequency of 34 Hz with highly polarized nuclear spins of the noble gas element ¹²⁹Xe. The system is advantageous for detecting a small frequency shift of the nuclear spin precession. We are thus planning to apply this system to the search for an atomic electric dipole moment of ¹²⁹Xe. We here report the development of the system and its performance.     

Exotic Isomers in Deformed Atomic Nuclei

Excited states of atomic nuclei can have long half lives, due to the angular-momentum couplings of unpaired nucleons. Such isomeric states provide opportunities for exploring novel nuclear physics, astrophysics and physics at the atomic/nuclear interface. This review focuses on the properties of isomers in deformed nuclei, and emphasises the importance of axial symmetry in preserving the integrity of the K quantum number. A region of neutron-rich nuclei around ¹⁸⁸Hf (Z=72, N=116) is predicted to have exceptional isomer properties, and experimental advances are now opening up this region to detailed investigation. This revised version was published online in July 2006 with corrections to the Cover Date.     

反质子引起的核反应中碎裂机制和粒子产生（英文）

基于兰州量子分子动力学（LQMD） 模型,系统研究了低能反质子引起的核反应中原子核碎裂机制和粒子产生。在LQMD输运模型中,考虑了反重子-重子、重子-重子和介子-重子碰撞可能产生的弹性散射、湮灭反应、电荷交换和非弹性散射。发展了并合模型,用于相空间构造初级碎片产生。处于激发态的碎片退激是基于统计模型描述。研究结果说明超子主要是由于奇异性交换产生;重碎片裂变会导致中等质量区域碎片产额增加;反质子引起的核反应有利于产生s=-2 和s=1 奇特超核,并给出了产生截面。Within the framework of the Lanzhou quantum molecular dynamics (LQMD) transport model, the nuclear fragmentation and particle production induced by low-energy antiprotons have been investigated thoroughly. Production of strange particles in the antiproton induced nuclear reactions is modeled within the LQMD model, in which all possible reaction channels such as elastic scattering, annihilation, charge exchange and inelastic scattering in antibaryon-baryon, baryon-baryon and mesonbaryon collisions have been included. A coalescence approach is developed for constructing the primary fragments in phase space. The secondary decay process of the fragments is described by the well-known statistical code. It is found that the strangeness exchange reactions dominate the hyperon production. A bump structure in the domain of intermediate mass for heavy targets appears owing to the contribution of fission fragments. It has advantage to produce heavier hyperfragments and hypernuclides with strangeness s = -2 (double-Λ fragments) and s = 1 (Λ-fragments) in antiproton induced reactions. The production cross sections are evaluated.     

Nuclear Spin Alignment of 12,13B Produced in Heavy Ion Collisions

The nuclear spin alignments of the β-emitting fragments ¹²B(I ^π=1⁺, T _1/2=20.2 ms) and ¹³B(I ^π=3/2⁻, T _1/2=17.4 ms) produced in the 100A-MeV ¹³C, ¹⁵N + ⁹Be collisions respectively have been observed for the first time detecting asymmetric β-ray emission from these nuclei. By means of the spin manipulation technique based on the hyperfine interaction of B isotopes in TiO₂, both the polarization P and the alignment A were determined reliably. The obtained P and A were significantly smaller than the expectation from the kinematical model. From the fact that the quenching factors for P and A are almost the same, there may be some depolarization mechanism in the collision process itself. This revised version was published online in September 2006 with corrections to the Cover Date.     

自旋极化的同位旋非对称核物质性质

利用Skyrme有效相互作用,采用核子–核子相互作用参数SKM*和SⅢ对自旋极化的同位旋非对称核物质的特性和状态方程进行了研究,讨论了非对称核物质的磁化率随密度的变化关系及其同位旋依赖性.结果表明:在Skyrme Hartree Fock框架内,同位旋非对称核物质会发生从非极化态到极化态的相变,而且发生相变的临界密度随同位旋非对称度增大而降低.另外,还与微观BHF(Brueckner Hartree Fock)的理论预言进行了比较和讨论.     

三自旋体系核自旋单重态的制备与单重态二维谱的实现

核自旋单重态是一种特殊的自旋状态,其寿命远长于相应自旋的横向和纵向弛豫时间,能够被用于研究分子的慢扩散、慢运动、特征信号选择等过程.目前单重态的研究主要集中于孤立的两自旋体系.而本文以N-乙酰基天冬氨酸（NAA）分子中由亚甲基和次甲基的三个氢原子核构成的三自旋体系为研究对象,将亚甲基中的两个氢核制备成单重态.利用优化控制和数值计算方法,分别设计了包含和不包含次甲基氢核耦合的单重态制备脉冲,结果发现,不考虑次甲基氢耦合设计的优化脉冲,其在实际三自旋体系中的单重态制备效率会显著下降.另外,我们以单重态为起点,实现了针对次甲基和亚甲基的信号选择COSY谱和NOESY谱,结果表明基于单重态的二维谱能够有效避免谱峰重叠现象,提高谱图分辨率,并有助于提高分子结构解析的准确性.     

Nuclear Spin Alignment and Alignment Correlation Terms in Mass A = 8 System

The pure nuclear spin alignments of ⁸Li and ⁸B were produced from the nuclear spin polarization applying the β-NMR method. The alignment correlation terms in the β-ray angular distribution were observed to test the G parity conservation in the nuclear β decay.     

Search for γ-Emission from Isomeric Nuclei Induced by MeV Electron Beams

In this paper we study the nuclear transitions induced by incident electrons having an energy of several MeV's. We measured the cross sections for the excitation of isomeric nuclear states by 7.7 MeV electrons. The cross sections were 1.2 μb for ^111m Cd, 5.5 μb for ^113m In and 7.0 μb for ^115m In. The peak activation rates were 1.8×10⁻¹² s⁻¹ for ^111m Cd, 8.1×10⁻¹² s⁻¹ for ^113m In and 1.0×10⁻¹¹ s⁻¹ for ^115m In, for a peak power of the electron beam of 1.8×10⁶ W cm⁻². Then we describe for the first time the results of a series of experiments in which samples containing the isomeric nuclei ^166m Ho and ^186m Re have been irradiated with MeV electron beams. An upper limit of 17 mb has been determined for the cross section of electron-induced γ-emission from ^166m Ho and an upper limit of 2.2 mb has been determined for the cross section of electron-induced γ-emission from ^186m Re. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Gamma Resonance Problem of Long-Lived Nuclear Isomers

A review is given of the studies relating to the problem of γ-resonant (Mössbauer) excitation of long-lived nuclear isomers. The theoretical estimates of possible γ-line broadening are presented. Earlier experiments are described with ^107mAg and ^109mAg isomers using polycrystalline samples of pure Ag and Ag-Pd alloys. The results of these experiments did not contradict the theoretical predictions. The series of papers using Ag single-crystal γ-sources is reviewed. Their results were interpreted as indications of a rather small ^109mAg γ-line broadening, which cannot be explained by modern theory. The results of the last experiments by ITEP group with ^109mAg are also presented. These data may be coordinated with results of other research, if one takes into account the Zeeman splitting of the γ-spectra by Earth's magnetic field.     

A=135核区N=79的同中异位素高自旋结构研究

摘要: 对清华大学在束γ谱实验组近年来在A=135缺中子核区N=79的同中异位素 135Ba, 137Ce和 139Nd的高自旋态实验研究进行了介绍。 实验是在中国原子能科学研究院HI 13串列加速器上用在束γ的实验技术、 分别通过重离子核反应 130Te(9Be, 4n), 124Sn(18O, 5n), 128Te(16O, 5n)进行的。 实验结果扩展了这3个核的高自旋态能级纲图。 研究表明, 这3个核的低自旋态结构均起源于 νh-111/2空穴与其偶偶核芯的耦合。 用粒子 转子模型对其结构进行了计算, 得到这3个核的形变参量γ值均稍大于30°, 为偏向于扁椭的三轴形变, 从而可看出Ba, Ce和Nd 3个同位素链在低自旋态下由长椭边到扁椭边的形状转变都发生在中子数N=77—79之间。 对于中等自旋态下一些能级的组态进行了指定与系统学比较。 在高自旋态下, 在 137Ce中发现一条γ≈－60°的扁椭形变带, 在 139Nd中则发现3条这样的扁椭形变带, 对这些扁椭形变带的起源及结构特性进行了讨论。 The progress of research on the high spin states at N=79 isotopes 135Ba, 137Ce and 139Nd in A=135 neutron deficient region by the research group of Tsinghua University has been reviewed. The experiments were carried out by using in beam γ ray spectroscopy technology and heavy ion nuclear reactions 130Te(9Be, 4n), 124Sn(18O, 5n) and 128Te(16O, 5n) at China Institute of Atomic Energy (CIAE). The high spin level schemes of these nuclei have been expanded. The results indicate that the lower spin states of these nuclei originated from νh-111/2 hole state coupling with the neighboring even even nucleus cores. All the deformation parameters γ values of these three isotones are larger than 30°, which indicates that they have triaxial deformation with oblate side. The prolate oblate transition in Ba, Ce and Nd isotopic chains indeed happens between N=77 and N=79. Through systematical comparison with the neighboring isotones, the configurations for some middle spin state levels have been assigned. At the high spin states, one oblate band in 137Ce and three ones in 139Nd with γ≈ -60° were discovered. The origination and structural character of these oblate bands have been discussed.     

自旋极化的对称核物质和中子物质的性质

利用Skyrme有效相互作用对自旋极化的同位旋对称核物质和中子物质的特性进行了研究.用4种核子-核子相互作用参数SⅢ,SKM,SLy230a和SLy230b,分别描绘了核物质状态方程曲线.可以发现不论使用哪一种参数,在自旋极化的同位旋对称核物质和中子物质中都存在着磁化相变转换点.另外还对磁化系数进行了计算,给出了磁化系数比率随密度的变化关系,由于无限不连续点的存在,进一步肯定了在Skyrme-Hartree-Fock理论框架内两种物质会出现磁化相变转换点.     

三种脉冲序列制备核自旋单重态效率的比较

核自旋单重态的制备和检测在化合物分子的相关分析中具有重要的应用价值和广阔的应用前景.本文以三肽分子AGG（Ala-Gly-Gly）中两个质子构成的一组孤立的自旋耦合体系为研究对象,利用三组基于不同原理的脉冲序列,分别对该体系制备了核自旋单重态;并分别测定和比较了三种方法制备核自旋单重态的效率及其寿命.研究结果表明,对于同一分子的同一自旋耦合体系中的质子,使用不同的脉冲序列制备得到的核自旋单重态的寿命并不会有明显差异,但基于不同脉冲制备核自旋单重态的效率差异相对较大.     

核自旋单重态的制备及其转化效率和寿命的影响因素分析

长寿命核自旋单重态（LLS）因具有寿命较长这一特性而具有广泛的应用前景.本文在一个三肽样品（alanylglycylgcine,AGG）的水溶液中,对结构中离手性碳较远的二自旋体系进行核自旋单重态的制备,并探究了样品浓度、温度、射频发射中心位置、自旋体系之间的J耦合常数,以及磁场不均匀性五个因素对LLS的转化效率及其寿命的影响.实验结果表明,核自旋单重态的转化效率和寿命均不受样品浓度以及磁场不均匀性的影响.寿命会随实验温度的升高不断增加,转化效率随温度的下降而减小.射频中心位置在小范围内变化时,核自旋单重态制备所受影响不明显;但当变化较大时,其转化效率与寿命明显减小.同时,核自旋单重态对J耦合的变化则比较敏感,当J值选择不精准时,转化效率及寿命都出现明显降低.     

Quantum Phase Transitions in Anisotropic Spin Ladders with Antiferromagnetic Rungs

We apply perturbation theory to study quantum phase transitions in anisotropic two-leg spin ladders with antiferromagnetic rungs in the strong interchain coupling limit. The energy gap is expanded up to the fourth order in the ratio of the intrachain to interchain couplings. The transition point is determined by examing the disappearance of the energy gap. Present results for the anisotropic ferromagnetic-leg spin ladder are consistent qualitatively with the nonlinear σ-model analysis and in good agreement with the numerical results by the diagonalization method.     

Anomalous Spin Textures in a 2D Topological Superconductor Induced by Point Impurities

Topological superconductors are foreseen as good candidates for the search of Majorana zero modes, where they appear as edge states and can be used for quantum computation. In this context, it becomes necessary to study the robustness and behavior of electron states in topological superconductors when a magnetic or non-magnetic impurity is present. The focus is on scattering resonances in the bands and on spin texture to know what the spin behavior of the electrons in the system will be. It is found that the scattering resonances appear outside the superconducting gap, thus providing evidence of topological robustness. Non-trivial and anisotropic spin textures related to the Dzyaloshinskii–Moriya interaction are also found. The spin textures show a Ruderman–Kittel–Kasuya–Yosida interaction governed by Friedel oscillations. It is believed that the results are useful for further studies which consider many-point-impurity scattering or a more structured impurity potential with a finite range.     

高能诱发核反应中粒子产生的相对信息熵

在本实验中，引用了一个新的特征量，相对信息熵Ｒ，研究了能量为１４．６，６０，２００ＡＧｅＶ的氧离子和２００ＡＧｅＶ的硫离子诱发核反应的产生粒子多重数分布．在目前的能区中，Ｒ近似地能量无关．Ｒ对快度窗口大小依赖的饱和性，揭示了中心区的熵集中产生．实验结果与Ｌｕｎｄ模型的ＦＲＩＴＩＯＦ模拟计算的预言一致．     

氘通量在钯中引发的异常核现象

以氚产生、氘通量在钯中引发的核嬗变和热流为例介绍凝聚态核科学(冷聚变)研究动态. Tritium production and the nuclear transmutation induced by deuterium flux inside Pd are described in order to illustrate the condensed matter nuclear science.