FEL用于阈能反应分子法激光分离铀同位素研究

提出了自由电子激光（ＦＥＬ）的一种可能应用,指出静电电子加速器驱动的ＦＥＬ技术目前已有能力满足阈能反应分子法激光分离铀同位素的要求。阈能反应分子法由于只需一次激光激发,因此从原理上讲,它的一次分离系数很高,优于原子法与其他分子法,在高浓铀小规模（１０ｋｇ／ａ）生产中有其可行性。     

自由电子激光用于阈能反应分子法激光分离铀同位素的研究

提出了自由电子激光的一种可能应用。指出静电电子加速器驱动的FEL技术目前已有能力满足阈能反应分子法激光分离铀同位素的要求。阈能反应分子法由于只需一次激光激发,因此从原理上讲,它的一次分离系数很高,优于原子法与其他分子法,在高浓铀小规模(10kg级/年)生产中有其可行性。     

自由电子激光用于阈能反应分子法激光分离铀同位素的研究

 提出了自由电子激光的一种可能应用。指出静电电子加速器驱动的FEL技术目前已有能力满足阈能反应分子法激光分离铀同位素的要求。阈能反应分子法由于只需一次激光激发,因此从原理上讲,它的一次分离系数很高,优于原子法与其他分子法,在高浓铀小规模(10kg级/年)生产中有其可行性。     

分子束反应动态学及分子传能研究

本文扼要介绍了中国科学院大连化学物理研究所分子束反应动态学及分子传能课题组自１９７９年以来研究工作概况，井对 Ｂａ ＋ Ｃｌ２反应产生 ＢａＣｌ２＊的机理、Ｂａ＋Ｎ２Ｏ反应机理、Ｓｎ＋Ｎ２Ｏ反应机理、Ｃ＿２ｄ＿３态在 Ｎａ＋ ＣＣｌ４反应中生成机制和能量传递过程及碱土金属原子与卤代烷反应中反应产物的能量配置规律作了简要的说明．     

洞穴石笋中铀钍同位素测龄方法研究

为洞穴石笋拥有分布广泛、记录信息丰富、完整、测量精度高、取材简便等优势,是古气候研究和年代研究的热门材料之一。用石笋研究古气候涉及到的一个重要课题是石笋测龄,铀系不平衡测年是广泛应用于石笋测龄的一种重要方法,弄清石笋中铀钍同位素测龄流程对古气候研究有重要意义。本文试图研究铀钍同位素方法测龄的流程,以采自贵州省大方县仙人洞的一根石笋为对象,使用α谱仪和γ谱仪进行测龄,得到石笋取样位置沉积时间距今1130～1190年。     

原子法激光同位素分离光功率优化理论研究

利用速率方程方法研究了光学厚介质中原子多步电离过程的激光功率的配置问题.计算结果表明,在总激光功率一定的情况下,存在使原子电离几率为最大的激光功率分配方式.更重要的一个结果是,在保持激光照射原子数量不变的条件下,当总功率一定时,缩小激光束截面积,增加激光束在原子蒸汽中的传播距离可以大大提高原子的平均电离几率.     

原子蒸气激光法分离钆同位素的偏振选择性实验

对原子蒸气激光法分离钆同位素中的光电离选择性进行了实验研究.分析了在偏振选择定则基础上分离钆奇数同位素的基本原理;测量了电离路径中总角动量J=2→2→1→0变化时的光电离选择性;观察了光的偏振状态改变时光电离选择性的变化,通过控制光阑的大小观测到杂散光引起的光电离选择性降低;进行了外磁场对光电离选择性的影响实验,基本给出了磁场方向和大小对于光电离选择性的影响程度.在外磁场方向垂直于光束的偏振方向时,很微弱的磁场就能引起光电离选择性的降低,磁场大小在2×10-4T时就看到了明显的选择性变化.当外磁场的方向平行光束的偏振方向时,磁场对于选择性的影响就显得相对很小.     

碰撞能和同位素取代对H+BrF→HBr+F反应立体动力学影响的理论研究

基于拟合得到的London-Eyring-Polanyi-Sato势能面,运用准经典轨线方法对H+BrF→HBr+F反应的立体动力学性质进行了理论研究.计算了反映矢量相关的角分布和对光诱导的双分子反应实验敏感的四个极化微分散射截面.结果表明:随着碰撞能的增加,产物的转动极化变强,并且产物的后向散射占主导地位.通过比较D+BrF→DBr+F和H+BrF→HBr+F反应的产物极化,揭示了明显的同位素效应.     

一类有机体系的分子内光致电子转移反应重组能的理论研究

对一类以双酚Ａ为连接链，９，１０－二甲氧基蒽为电子给体，带不同取代基的苯为电子受体的给体－受体体系的光致电子转移反应的重组能进行了理论计算研究，获得与实验值接近的结果，说明所用的理论计算方法具有可行性。     

超高碰撞能23.84 kJ/mol下反应F+D2→DF+D的交叉分子束研究

本文搭建了一套新的实验设备,首次将氢原子里德堡态标记的飞行时间谱技术与激光爆破束源技术相结合,进行超高碰撞能下化学反应的动力学研究. 初步进行了F+D₂→DF+D在超高碰撞能23.84 kJ/mol下的实验研究. 在研究中应用了两种类型束源：一类是通过激光爆破过程产生的高能F原子束源,另一类是通过液氮冷却脉冲阀而产生的D₂束源. 实验中探测了反应产物振动态分辨的微分散射截面. 结果显示,大部分反应产物DF主要呈现侧向和后向散射分布,而产物DF(v''=4)则主要分布在前向. 对前向散射产物DF(v''=4)的动力学来源进行了讨论.     

ELECTRODYNAMICS OF A QUASI-(1+1)DIMENSIONAL ELECTRON GAS

A hydrodynamic model. is used to study the electrodynamics of a quasi-(1+1)-dimensional electron gas arranged in a periodic array and neutralized by rigid inert positive background The theory is applied to discuss a new model of quasi-(1+1)-dimensional electron gas with a complex unit cell and an analytical expression of the dispersion relation for this system is derived. The results are the same as. those der-ived caith the semi-classical theory dealing with collective excitations.     

A study of the Li(p,n)Be reaction by the neutron threshold technique

The reaction ⁶Li(p,n)⁶Be has been studied by slow-neutron detection, with particular attention to the ⁶Be ground state threshold. The detector response was calculated by a Monte Carlo technique and verified with a measurement of the ⁷Li(,n)¹⁰B threshold. An analysis of the shape of the ⁶Be threshold indicated that both s- and p-wave neutrons contribute significantly to the reaction. The results depend on what mode of decay is assumed for the ground state of ⁶Be. If a two-stage process is assumed, with either an alpha particle and an unbound diproton or ⁵Li and a proton as intermediate state, the width is found to be 95±28 keV and the Q-value obtained for the ⁶Li(p,n)⁶Be reaction is −5074±13 keV. It was not possible to detertmine which process is predominant. No higher thresholds in the slow neutron yield up to 4 MeV of excitation in ⁶Be were observed. The data above the ground state threshold are consistent with a broad excited state of ⁶Be or with the occurrence of other neutron-producing reactions.     

DWIA in the momentum space for (γ, π0) reaction near threshold

The differential and total cross-sections of neutral pion photoproduction off⁴He,¹²C and⁴⁰Ca nuclei are calculated in the framework of the DWIA in the momentum space. It is shown that the inclusion of pion wave distortion gives a less than 25% increase of the total cross sections. A good agreement with experimental data is achieved by using the full elementary amplitude that includes the pion-momentum nonlinear terms and the terms depending on nucleon momenta.     

电子束引起的残余含氧气体在镍(001)面上的吸附

当一束具有一定能量和强度的电子束轰击超高真空系统中残余的水汽、一氧化碳和二氧化碳时,将导致这些气体分子通过如下反应:H₂O→O_ad+H₂,CO₂→O_ad+CO,CO→O_ad+C_ad分解并共吸于镍表面。碳和氧的原子各自占据镍(001)面部份四重吸附位置,形成结构为p(2×2)或c(2×2)的许多独立的吸附畴,电子束轰击促进畴的成核、长大、连结和有序化。当氧和碳的原子占据了镍(001)面约一半的四重吸附位后,上述吸附反应将与导致氧和碳的脱附反应:C^*+O_ad→CO,O^*+C_ad→CO平衡,氧化镍与碳化镍开始成核。由于残余含氧气体中氧的含量超过碳,氧化镍成核占优势,使碳的吸附被排斥,已吸附的碳被排挤,形成电子束斑内氧高碳低、束斑外碳高氧低的“互补”分布。电子束轰击过程中碳的俄歇峰形的变化反映着碳原子与基底原子的不同结合状态。电子束的解离效应在吸附的初始阶段起重要作用,而其热效应对氧化镍的长大起重要作用。 关键词：     

A density functional study of molecular oxygen adsorption and reaction barrier on Pu (100) surface

Oxygen molecule adsorptions on a Pu(100) surface have been studied in detail, using the generalized gradient approximation to density functional theory. Dissociative adsorption with a layer by layer alternate spin arrangement of the plutonium layer is found to be energetically more favorable compared to molecular adsorption. Hor2 approach on a bridge site without spin polarization was found to the highest chemisorbed site with an energy of 8.787 eV among all the cases studied. The second highest chemisorption energy of 8.236 eV, is the spin-polarized Hor2 or Ver approach at center site. Inclusion of spin polarization affects the chemisorption processes significantly, non-spin-polarized chemisorption energies being typically higher than the spin-polarized energies. We also find that the 5f electrons to be more localized in spin-polarized cases compared to the non-spin-polarized counterparts. The ionic part of O-Pu bonding plays a significant role, while the Pu 5f-O 2p hybridization was found to be rather week. Also, adsorptions of oxygen push the top of 5f band deeper away from the Fermi level, indicating further bonding by the 5f orbitals might be less probable. Except for the interstitial sites, the work functions increase due to adsorptions of oxygen.     

Scanning kinetic spectroscopy (SKS): A new method for investigation of surface reaction processes

Multiple reaction pathways are available to a polyatomic molecule interacting with a solid surface. Delineation of exact temperature regions in which the various pathways are either active or inactive is accomplished using a new method, Scanning Kinetic Spectroscopy (SKS). SKS uses a calibrated and collimated beam of reactant molecules incident upon a clean single crystal surface in UHV. A multiplexed quadrupole mass spectrometer (QMS) is enclosed inside a differentially pumped random flux shield, in line of sight to the crystal surface. The crystal temperature is programmed with a linear ramp (dT/dt = 2K/s.) and reactant consumption, product evolution, and desorption of stable surface species are simultaneously measured in one experiment. SKS data are presented here which characterize the reactions of methanol with the single crystal surfaces Ni(111), Cu(111), and Cu(111) plus preadsorbed oxygen. Application of the SKS method as an efficient probe of surface reaction pathways is illustrated by the contrasting chemistry of these surfaces. The methanol plus Ni(111) system is examined in detail in order to relate the observed SKS features to specific molecular reaction pathways on the Ni(111) surface.     

Deuteron breakup in the 2H(e,e' p) reaction at low momentum transfer and close to threshold

Deuteron breakup has been studied in a 2H(e,e' p) coincidence experiment at low momentum transfer and for energies close to threshold. The longitudinal-plus-transverse ( L+T) and longitudinal-transverse ( LT) interference cross sections are deduced. Nonrelativistic calculations based on the Bonn potential and including leading order relativistic contributions, meson exchange currents, and isobar configurations describe the ( L+T) data well. Surprisingly, large deviations of 30% to 45% are observed for the LT contribution.     

KCl中FH(CN)-的吸收、发射光谱及e-v能量转换机理研究

以扩展离子处理方法(SLC)从理论上研究了KCl中F_H(CN)^-缺陷中心的基态和激发态的特性,理论计算值与F_H(CN)^-在KCl中的吸收、发射光谱的实验值符合得很好。计算了(CN)^-分子在KCl中的本征振动频率,解释了F_H(CN)^-的振动荧光光谱及相应的Raman谱,指出Raman振动谱中峰的劈裂应该来源于(CN)^-分子在KCl中的 关键词：     

静电场作用下α-碘酸锂单晶中子衍射的增强(Ⅱ)

在以前工作的基础上,继续作了以下的实验:(1)在低温条件下测定了α-碘酸锂单晶在静电场中的衍射情况,观察到在～180K以下出现“冻结”现象,即加上电场并不能使衍射增强,撤去原在室温所加的电场后衍射强度也并不减弱;(2)用狭束中子探测了加静电场后晶体的不同部位,观察到衍射增强是体效应而不是表面层效应;(3)测定了低频交变电场对晶体中子衍射强度的影响,衍射束增强的程度随频率的下降而加大,频率在1500Hz时衍射束的增强已不明显。