溅射的同位素迷惑

影响多元材料溅射的机制是复杂的．在多元材料溅射中,同位素溅射是最简单的．虽然仅有质量效应在同位素溅射中起优势作用,但是在离子轰击溅射中,至今仍然是个“同位素迷惑”．争论的焦点有:（１）在零剂量时,同位素富集度是与出射角无关,还是与出射角有关？（２）同位素角效应是一次溅射效应,还是二次溅射效应？如何理解碰撞级联中的动量不对称性对同位素溅射的作用？文中综述了这些争论,并阐明了本小组的观点． Mechanisms affecting multicomponent material sputtering are complex. Isotope sputtering is the simplest in the multicomponent materials sputtering. Although only mass effect plays a dominant role in the isotope sputtering, there is still an isotope puzzle in suputtering by ion bombardment. The major arguments are as follows:(1) At the zero fluence, is the isotope enrichment ejection angle independent or ejection angle dependent? (2)Is the isotope angular effect the primary or the ...     

Ni原子倾斜轰击Pt(111)表面低能溅射现象的分子动力学模拟

采用嵌入原子方法的原子间相互作用势,通过分子动力学模拟详细研究了以不同角度入射的低能Ni原子与Pt (111)基体表面相互作用过程中的低能溅射行为.结果表明:随着入射角度从0°增加到80°,溅射产额Y_s和入射原子钉扎系数S的变化均可以根据入射角θ近似地分为以下三个区域:当θ ≤ 20°时,Y_s和S几乎保持不变,其值与垂直入射时接近,溅射原子的发射角分布和能量分布也与垂直入射时的情关键词：分子动力学模拟入射角低能溅射     

应用内标的APDC-Cu(Ⅱ)快速共沉淀分离富集和原子吸收光谱测定食盐中的铅

采用APDC(吡咯烷二硫代氨基甲酸铵)-Cu(Ⅱ)共沉淀体系,以Ni(Ⅱ)为内标,在pH 2.5的条件下快速共沉淀分离富集食盐中的铅,并用火焰原子吸收法(FAAS)测定。当试液为100 mL时方法的检测限为3.27×10-3 μg·mL-1,回收率为92%～101%,基本消除了基体干扰。该法快速、简便、重现性好。     

(e,2e)电子动量谱仪研制和若干原子分子的电子动量谱测量

研制成功了一台先进的多功能用途的（e,2e）电子动量谱仪．装置采用电子束和气体束交叉碰撞方式;使用微通道板一维位置灵敏电子探测器;成功地实现了多参数数据获取和离线分析技术．利用该谱仪分别测量了氦、氩原子和氢、甲烷分子的电离能谱和电子动量谱．该谱仪的能量分辨率为ΔE=1.8eV,动量分辨率为Δp～0.15au关键词：     

载能Ni原子斜入射Pt(111)表面的分子动力学模拟

采用嵌入原子方法的原子间相互作用势,利用分子动力学模拟,详细研究不同角度入射的载能Ni原子在Pt(111)基体表面的沉积过程.结果表明,随着入射角度θ从0°增加到80°,溅射产额、表面吸附原子产额、空位产额的变化情况均可按入射角度近似地分为θ≤20°,20° < θ < 60°和θ≥60°三个区域.当θ≤20°时,载能沉积对基体表面的影响与垂直入射时的情况类似,表面吸附原子的分布较为集中,入射原子容易达到基体表面第二层及以下,对基体内部晶格产生-定的影响;在20° < θ < 60°的范围内,入射原子的注入深度有所下降,对基体内部晶格的影响减小,表面吸附原子的分布较为均匀,有利于薄膜的均匀成核与层状生长;当θ≥60°时,所有入射原子均直接被基体表面反射,表面吸附原子产额、溅射产额、表面空位产额均接近0,载能沉积作用没有体现.     

宏观放电参数对快原子态氮(N+,Nf)的影响

采用氮直流辉光放电等离子体中快电子和重粒子(N₂⁺,N⁺,N_f)混合的蒙特卡罗方法,模拟研究了快原子态粒子(N⁺,N_f)的产生率及轰击阴极的能量分布随宏观放电参数(P,V)的变化规律.结果表明,存在一最佳放电条件,使阴极壁处粒子(N⁺,N_f)的粒子数密度大且能量高;当电压大于800V时,轰击阴极的活性粒子(N⁺,N_f),主要由N₂⁺-N₂离解过程产生,电压小于300V时,主要由e^--N₂离解过程产生,模拟结果与实验结果相符合.     

Cu(111)三维表面岛对表面原子扩散影响的分子动力学研究

采用嵌入原子方法的原子间相互作用势,利用分子动力学方法计算了同质外延生长中不同层数的三维Cu(111)表面岛上表面原子扩散激活能,分析了三维表面岛的层数对表面原子交换扩散和跳跃扩散势垒的影响. 研究结果表明,二维Enrilich-Schwoebel(ES)势垒小于三维ES势垒,且三维ES势垒不随表面岛层数的增加而显著变化. 对于侧向表面为(100)的表面岛,表面原子沿〈011〉方向上的扩散行为,随表面岛层数增加而逐渐变化;在表面岛层数达到3层时,扩散路径上的势垒变化趋于稳定,表面原子扩散以下坡扩散为主. 对于侧面取向为(111)的表面岛,当表面岛层数大于3层后,开始呈现上坡扩散的可能.关键词：表面原子扩散分子动力学模拟     

高分子固相柱用于微量Pb(Ⅱ)和Cd(Ⅱ)的富集分析

采用高分子聚合物固相萃取(SPE)柱,结合KI-MIBK萃取体系,对高Ca、Mg、Fe的水样及中草药等复杂基质样品中的Cd(Ⅱ),Pb(Ⅱ)进行同时富集实验并用火焰原子吸收光谱法(FAAS)分析。其与液-液萃取(LLE)相比,该法不仅提高了FAAS的灵敏度,其回收率、精密度,以及校准曲线的线性均有较大改善,且此法操作方便易行。     

流动注射在线分离富集-火焰原子吸收光谱法测定环境水样中Cr(Ⅲ)和Cr(Ⅵ)的形态

采用单阀阴离子和阳离子交换树脂微柱并联 ,两柱交替采样逆向洗脱流动注射在线分离富集环境水样中Cr(Ⅲ )和Cr(Ⅵ ) ,分别用 15 %HNO3和 8%NH4 NO3洗脱 ,火焰原子吸收光谱法直接检测。富集 1min时Cr(Ⅲ )和Cr(Ⅵ )的特征浓度分别为 :1 5 0 μg·L- 1 和 1 39μg·L- 1 ,Cr(Ⅲ )和Cr(Ⅵ )检出限 (3σ)分别为 1 0 3μg·L- 1 和 0 5 4 μg·L- 1 ;相对标准偏差 (10 μg·L- 1 )分别为 :3 4 1%和 1 80 % ,分析样品加标回收率在 93 5 %～ 10 7 5 %之间。     

不同能量的氦原子与同位素分子H2(D2,T2)碰撞分波截面的理论计算

用Tang-Toennies势模型和密耦近似方法计算了不同能量下惰性气体原子He与H2及其同位素D2,T2替代碰撞体系的振转激发碰撞截面.通过分析He-H2(D2,T2)各碰撞体系分波截面的差异,总结出在H2分子的对称同位素替代情形下He-H2(D2,T2)碰撞体系分波截面随量子数和体系约化质量变化的规律.结果表明,体系的约化质量及入射原子相对碰撞能量的变化均给体系的碰撞截面带来不同程度的影响.     

A preliminary quadrupole asymmetry study of a β=0.12 superconducting single spoke cavity

An Accelerator Driven System(ADS) has been launched in China for nuclear waste transmutation. For the application of high intensity proton beam acceleration, the quadrupole asymmetry effect needs to be carefully evaluated for cavities. Single spoke cavities are the main accelerating structures in the low energy front-end. The single spoke cavity has small transverse electromagnetic field asymmetry, which may lead to transverse RF defocusing asymmetry and beam envelope asymmetry. A superconducting single spoke resonator(PKU-2 Spoke) of β=0.12 and f =325 MHz with a racetrack-shaped inner conductor has been designed at Peking university. The study of its RF field quadrupole asymmetry and its effect on transverse momentum change has been performed. The quadrupole asymmetry study has also been performed on a β=0.12 and f =325 MHz ring-shaped single spoke cavity. Our results show that the quadrupole asymmetry is very small for both the racetrack-shaped and the ring-shaped single spoke cavity.     

Tendenzen in der Entwicklung kontinuierlicher Verfahren zur Trennung stabiler Isotope

Im Laufe des letzten Vierteljahrhunderts unterlag das Interesse an der theoretischen und technischen Problematik der natürlichen Isotope einer ständigen Entwicklung.     

同位素分布的标度参量对于两体碰撞的同位旋相关性和动量相关作用的依赖

利用同位旋相关的量子分子动力学模型, 对中能重离子反应产物中的同位素分布进行了研究, 重点分析了平均场中的动量相关作用和两体碰撞的同位旋相关性对于产物中同位素标度现象的影响. 结果表明: 这两个因素均明显减小了同位素标度参量α的值, 从而减弱了同位旋标度参量α对两个反应系统同位旋差的依赖性.     

激光抽运极化原子束磁偏转铀浓缩方案

将激光抽运选择性极化原子束磁偏转方案用于铀同位素浓缩,考察了铀原子基态各子能级的磁偏转特性,提出了选择性光轴运极化的实验方案,讨论了可能得到的浓缩结果。     

计及溅射损失的平行板静电场法离子引出和收集

采用粒子模拟-Monte Carlo碰撞(particle in cell_Monte Carlo collision)方法研究了 原子蒸气激光同位素分离工程中一维平行板静电场法离子引出和收集过程,记录引出离子的 能量分布和角度分布,计算离子在收集板上造成的溅射损失.模拟结果表明,增加引出电压 可以缩短引出时间,降低碰撞损失,但是增加了溅射损失,使得收集率降低;增加电子温度 可以缩短引出时间,提高收集率;增加初始等离子体密度将使引出时间增加,收集率降低;而目标同位素丰度较高的情况下,离子引出过程的碰撞损失关键词：原子蒸气激光同位素分离离子引出溅射     

Single spin asymmetry in πp Drell–Yan process

We study the single spin asymmetries for the πp^↑→μ⁺μ⁻X$\pi p^{\uparrow }\to {\mu }^{+}{\mu }^{-}X$ process. We consider the asymmetries contributed by the coupling of the Boer–Mulders function with the transversity distribution and the pretzelosity distribution, characterized by the sin(?+?S)$\sin (?+{?}_S)$ and sin(3?−?S)$\sin (3?-{?}_S)$ azimuthal angular dependence, respectively. We estimate the magnitude of these asymmetries at COMPASS by using proper weighting functions. We find that the sin(?+?S)$\sin (?+{?}_S)$ asymmetry is of the size of a few percent and can be measured through the experiment. The sin(3?−?S)$\sin (3?-{?}_S)$ asymmetry is smaller than the sin(?+?S)$\sin (?+{?}_S)$ asymmetry. After a cut on qT$q_T$, we succeed in enhancing the asymmetry.     

非对称核物质中同位旋对称势的动量和密度依赖性

在Brueckner-Hartree-Fock理论框架内, 研究了同位旋非对称核物质中质子和中子单粒子势的动量相关性及其随同位旋非对称度的变化, 在此基础上计算了同位旋对称势, 并讨论了三体核力的影响. 结果表明同位旋对称势对于同位旋非对称度的依赖性很弱, 但对于动量和密度均有较强的依赖性. 当密度固定时, 同位旋对称势随动量增加而减小. 尽管三体核力对于质子和中子单粒子势的动量相关性有较大影响, 但对同位旋对称势的影响很小. 还与目前重离子碰撞输运理论模型中所使用的各种参数化的唯象对称势进行了比较.     

A novel methodological approach for δ18O analysis of sugars using gas chromatography-pyrolysis-isotope ratio mass spectrometry

Although the instrumental coupling of gas chromatography-pyrolysis-isotope ratio mass spectrometry (GC-Py-IRMS) for compound-specific δ¹⁸O analysis has been commercially available for more than a decade, this method has been hardly applied so far. Here we present the first GC-Py-IRMS δ¹⁸O results for trimethylsilyl-derivatives of plant sap-relevant sugars and a polyalcohol (glucose, fructose, sucrose, raffinose and pinitol). Particularly, we focus on sucrose, which is assimilated in leaves and which is the most important transport sugar in plants and hence of utmost relevance in plant physiology and paleoclimate studies. Replication measurements of sucrose standards and concentration series indicate that the GC-Py-IRMS δ¹⁸O measurements are not stable over time and that they are amount (area) dependent. We, therefore, suggest running sample batch replication measurements in alternation with standard concentration series of reference material. This allows for carrying out (i) a drift correction, (ii) a calibration against reference material and (iii) an amount (area) correction. Tests with ¹⁸O-enriched water do not provide any evidence for oxygen isotope exchange reactions affecting sucrose and raffinose. We present the first application of GC-Py-IRMS δ¹⁸O analysis for sucrose from needle extract (soluble carbohydrate) samples. The obtained δ¹⁸O_{sucrose/ Vienna Standard Mean Ocean Water (VSMOW)} values are more positive and vary in a wider range (32.1–40.1 ‰) than the δ¹⁸O_{bulk/ VSMOW} values (24.6–27.2 ‰). Furthermore, they are shown to depend on the climate parameters maximum day temperature, relative air humidity and cloud cover. These findings suggest that δ¹⁸O_sucrose of the investigated needles very sensitively reflects the climatically controlled evaporative ¹⁸O enrichment of leaf water and thus highlights the great potential of GC-Py-IRMS δ¹⁸O_sucrose analysis for plant physiology and paleoclimate studies.     

对冲击摆及几种类似结构的力学分析

本文对冲击摆及几种类似的结构进行了力学分析,深化了动量、角动量等教学内容．     

Separation of Deuterium Isotope by Chemical Exchange between Hydrogen and Water Vapour

The separation factor of deuterium (α) for the exchange reaction between hydrogen and water vapour at 100 °C has been measured and was found to be equals to 2.52 and 2.50, depending on the used experimental technique.

An empirical equation relating the variation of the separation factor with temperature for such isotopic exchange reaction has been deduced. The values of α were calculated from 0–800 °C and indicated close agreement with those calculated from spectroscopic data.

Comparison of the deduced empirical equation with the general equation relating the separation factor with temperature for such reaction, allowed the calculation of the zero point energy, as well as the free energy as a function of temperature.