奇奇核90Nb的高自旋态研究

用能量为80MeV的19F束通过反应76Ge(19F,5n)90Nb布居了90Nb的高自旋态.通过在束γ测量分析90Nb退激γ射线的符合级联关系,发现了19条新的属于90Nb的γ跃迁,建立了90Nb的高自旋态能级纲图.通过经验壳模型计算指定了部分能级的组态,并结合实验DCO比值和与相邻N=49核素的系统比较,确认了新能级的自旋和宇称. The high spin states of~(90)Nb have been populated via reaction~(76)Ge(~(19)F, 5n)~(90)Nb at beam energy of 80 MeV. The de-exciting γ-rays have been measured with in-beam γ-ray spectroscopy method. After γ-γ coincidence analysis, 19 new γ transitions were identified and assigned to~(90)Nb. The new level scheme of~(90)Nb was established. Based on the semi-empirical shell model calculations, the configurations of the levels have been suggested. In addition, the spins and parities of the new levels ...     

稀土区奇奇核πh1／2×vi13／2带B（M1）／B（E2）比值增强特性

在稀土区奇奇核πh1／2×vi13／2转动带中，系统地观测到随转动频率或角动量增加，B(M1)／B(E2)曲线表现出所谓parabola-1ike形状，即在增加到某一转动频率或自旋后，B(M1)／B(E2)比值快速增强。基于推转模型和粒子转子模型关于奇奇核二准粒子转动带磁偶极约化跃迁几率的描述，对稀土区双奇核的这一行为进行了讨论。指出该现象的发生与vi13/2准中子转动顺排特性密切相关。B(M1)／B(E2)比值在接近第二带交叉(即BC准中子对顺排)的较高频率处的增强效果，可以理解为主要来源于带交叉引起的波函数中混合四准粒子成分的结果。通过对B(M1)/B(E2)比值的增强效果发生在较低频率处的分析，对稀土区奇奇核πh1／2×vi13／2带角动量耦合图像有了进一步认识。It is systematically observed that the B(M1)/B(E2) plots with the increasing of rotational frequency, behaves as a so called parabola like shape in the π h11/2 νi13/2 bands of rare earth doubly odd nuclei (i.e., the B(M1)/B(E2) ratios increase rapidly after a certain rotational frequency). Such a phenomenon is discussed based on the formula of magnetic dipole reduced transition probability deduced from the Cranking Shell Model and Particle Rotor Model respectively. It is pointed out that, the occurrence of this behavior is closely related to the alignment nature of the νi 13/2 quasineutron. The increasing of B(M1)/B(E2) occurring at large frequency approaching the second BC crossing can be understood as mainly resulted from the mixing of wave function with the 4 quasiparticle band caused by the band crossing. Insight into the angular momentum coupling scheme between the quasiparticles and collective core in the πh11/2 νi 13/2 structures of rare earth doubly odd nuclei is gained by analyzing the increasing behavior of B(M1)/B(E2) ratios occurring at low rotational frequency.     

Measurements of g-Factor of Rotational Band States in 82Sr

The g-factors of the positive parity rotational states up to spin I = 8^＋ for the ground state band in even-even nuclei S2Sr have been measured by a transient-magnetic-field ion implantation perturbed angular distribution method. The experimentally measured 9-factors increase with the increasing spin along the band and show that the g9/2 proton aligns only and the alignment starts from I =6^＋. The measured g-factors also indicate that the nuclei ^82Sr gain their spins by the quasi-proton alignment at higher spin.     

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.     

High-spin states in 128I

The high-spin states in ¹²⁸I have been studied by using in-beam γ-ray spectroscopy with the ¹²⁴Sn(⁷Li, 3n)¹²⁸I reaction at beam energies of 25, 28 and 42 MeV. A new level scheme including 20 new levels and 27 new γ-transitions for ¹²⁸I has been established preliminarily.     

PF/CNTs-Cu复合材料的制备及其载流摩擦磨损机理研究

以酚醛树脂(PF)、碳纳米管(CNTs)和泡沫铜(Cu)为原料,在反应釜内经无压浸渗和加压固化技术,制得一种新型PF/CNTs-Cu复合材料.在CSM摩擦磨损仪上,对不同CNTs含量的PF/CNTs-Cu复合材料进行了载流摩擦磨损测试.结果表明:未经CNTs改性的PF/Cu复合材料,摩擦系数和磨损率均最大,摩擦表面存在大量的犁沟痕迹,表现为典型的磨粒磨损.经CNTs改性后的PF/CNTs-Cu复合材料,载流摩擦磨损性能获得较大程度的改善.当CNTs质量分数在0.25%~1.0%范围内时,随着CNTs含量的增加,摩擦系数和磨损率逐渐减小,并在质量分数为1.0%时达到最小值.摩擦磨损机制则由最初的磨粒磨损逐渐转变为黏着磨损.当CNTs达到1.5%时,由于CNTs的团聚作用,导致复合材料的摩擦磨损性能急剧下降,摩擦磨损机制转变为磨粒磨损和黏着磨损共同作用形式.     

Exchange effect and magneto-plasmon mode dispersion in an anisotropic two-dimensional electronic system

The exchange effect and the magneto-plasmon mode dispersion are studied theoretically for an anisotropic twodimensional electronic system in the presence of a uniform perpendicular magnetic field.Employing an effective lowenergy model with anisotropic effective masses,which is relevant for a monolayer of phosphorus,the exchange effect due to the electron-electron interaction is treated within the self-consistent Hartree-Fock approximation.The magnetoplasmon mode dispersion is obtained by solving a Bethe-Salpeter equation for the electron density-density correlation function within the ladder diagram approximation.It is found that the exchange effect is reduced in the anisotropic system in comparison with the isotropic one.The magneto-plasmon mode dispersion shows a clear dependence on the direction of the wave vector.     

基于瞬发伽马谱学的元素重建算法

质子治疗中的瞬发伽马射线是质子和靶标之间核反应的产物,瞬发伽马射线的特征能量和强度可以用来确定靶中元素的种类和数量,在之前的实验中已经证明,无论反应截面多么复杂,一旦确定了被照射元素和入射质子的能量,元素浓度与伽马射线光子数之间就存在一定的线性关系。然而,这种线性关系很难应用于医学成像,而且氢的非线性行为迄今尚未研究。本文将这种线性关系推广到包括氢等非线性情况的混合元素材料,并提出了一种通用的数学形式,即基于瞬发伽马谱学的重建算法 (PGSRA)。PGSRA的基本假设是样品材料的PGS与元素的每摩尔伽马射线有某种关系。对于碳和氧,这种关系是线性的,而对于氢,这种关系是非线性的。由于2.23 MeV的伽马线来源于中子吸收辐射,我们仔细研究了氢非线性行为。利用蒙特卡罗模拟验证了碳、氧和氢的不同组合,如PMMA、戊二醇和乙醇二醇的线性和非线性关系。在这项工作中开发的PGSRA可能是PGS和医学成像之间的第一座桥梁。     

基于白光中子源的197Au中子辐射俘获截面测量及共振参数分析

中子辐射俘获反应在反应堆运行、核装置设计及核天体物理研究中起重要的作用. 4πBaF₂探测装置有着高时间分辨能力、低中子灵敏度、高探测效率等优点,适合开展中子辐射俘获反应截面数据的测量.中国原子能科学研究院核数据重点实验室建立了伽马全吸收装置(Gamma total absorption facility, GTAF),该装置用28块六棱BaF₂晶体和12块五棱BaF₂晶体构成了外径25 cm,内径10 cm的球壳,覆盖了95.2%的立体角.利用GTAF在中国散裂中子源Back-n束线上,测量了197Au(n, γ)的反应截面数据.测量数据通过能量筛选、PSD方法、晶体多重性筛选进行了初步本底扣除,随后结合对^natC及空样品的测量数据对本底进行了分析及扣除,获得了197Au俘获反应的产额,利用SAMMY程序拟合得到了¹⁹⁷Au在1—100 e V的共振能量、中子共振宽度和伽马共振宽度参数.实验测量结果与ENDF/B-VIII.0数据库符合良好,其共振参数存在一定差异,分析原因可...