同位素分子势能函数的核运动及同位素效应

一般的分子势能函数均未考虑核运动效应,仅是Born-Oppenheimer近似下电子的本征能量函数,因此,具有相同电子数和不同质量数的同位素分子势能函数不可区分.基于核运动效应,用核的振动、转动和平动能修正Born-Oppenheimer近似下的电子能量,可求得同位素分子的离解能和力常数,并以此确定三体项的参数.利用同位素效应,可推导同位素两体项势能函数的各参数,由此可获得同位素分子的多体项展式解析势能函数.以HTO((X)1A1)为例,用核运动效应和同位素效应获得了其多体项展式解析势能函数,其等值势能图正确反映了((X)1A1)的平衡构型和离解能、H和T的同位素效应,以及H OT-HTO和T OH-HTO的反应特征.     

LiX(X=H,D,T)与水的反应机理和动力学研究

采用Gaussian03软件包中的量子化学从头计算法,在6-311G(d)水平上,用量子化学MP2方法研究了LiX(X=H,D,T)与水的反应,计算了反应体系最低势能面上各驻点的构型参数、振动频率和能量,全面研究了反应机理;利用经典过渡态理论,考虑量子化矫正,计算了反应的速率常数。计算结果显示,LiH(LiD、LiT)与水的反应受温度影响很大,温度越低反应速率常数越小。     

ThO分子基态X~1∑~ 和激发态H~3△的量子力学计算

用全相对论量子力学理论计算得到Th的27个能级和电子状态,用原子分子反应静力学原理推导出ThO的一系列的可能电子状态并证明了基态X~1Σ~ 和激发态H~3Δ的离解极限,在考虑相对论有效原子实势(RECP)近似下,用G94W程序的CISD方法计算得到了ThO分子基态X~1Σ~ 和激发态H~3Δ的Murrell-Sorbie解析势能函数及其对应的平衡几何与光谱参数,结果与实验数据符合得比较好。热力学函数的计算结果也与实验符合得较好。这表明RECP近似用于锕系元素化合物的量子力学计算是一种可行方法。     

氢-水同位素交换反应热力学理论研究

本文采用量子化学从头计算法对氢同位素分子及相应的氢同位素水分子进行了几何结构优化和振动频率计算,得到了6种氢-水同位素交换体系的热力学函数和气相反应平衡常数。研究结果表明:平衡常数的理论计算值与实验结果吻合,在0.1 MPa和283.2~373.2K的反应条件下,HD-H2O体系平衡常数的计算值与实验值间相对偏差小于6%。     

~6LiD在HFETR中作为14MeV中子源的研究

在高通量工程试验堆(HFETR)内6LiD转换器中的14 MeV中子通量计算分析模型中,考虑转换器对辐照孔道中子通量的扰动和氚在6LiD中的泄漏,建立热中子转换为14 MeV中子的有效产额计算模型。计算结果表明,6LiD最佳厚度为0.85 mm,转换器中的一个热中子转换为14 MeV中子的有效产额为3.18×10-4。     

氢-苯乙烯体系中氢-氚同位素交换反应的热力学研究

采用6-311G全电子基函数和B3p86方法对聚苯乙烯-二乙烯基苯(polystyrene-divinylbenzene,SDB)单体之一的苯乙烯分子结构进行优化计算.根据热力学原理,计算得到SDB官能团分子氢氚取代反应在不同温度下的标准生成自由能函变、反应平衡常数及氚气和氢气的反应平衡压力比.结果表明,温度的升高不利于氢氚取代反应T2(g) SDB(H2)(s)→H2(g) SDB(T2)(s)正向进行,这与Pt/SDB疏水催化剂在氢-水同位素交换的催化反应实验过程中的氢氚取代研究结论一致.     

铀与O_2相互作用的从头计算研究

用量子化学从头计算(ab initio)方法, 计算了 U—O 体系气态分子的优化几何构型、总能量、振动频率和成键情况,并构筑了该体系有关相互作用的势能面。计算的铀氧化物优化构型和振动频率同现有的实验数据符合较好。布居数分析结果表明在形成铀氧化物时,主要是 U5f电子参加了与氧成键,但在 UO 和 UO3中,U6d 轨道电子成键的成分相对于 UO2有所增大。同时,由于铀的 7s 和 6d及 5f 轨道能量很接近,形成 ds 杂化轨道并参与成键。各氧化物的第一电离能同文献数据符合较好。势能面分析结果表明铀氧化产物取决于铀原子与 O2相互作用的方式。     

铀与O_2相互作用的从头计算研究

用量子化学从头计算(ab initio)方法,计算了U—O体系气态分子的优化几何构型、总能量、振动频率和成键情况,并构筑了该体系有关相互作用的势能面。计算的铀氧化物优化构型和振动频率同现有的实验数据符合较好。布居数分析结果表明在形成铀氧化物时,主要是U5f电子参加了与氧成键,但在UO和UO_3中,U6d轨道电子成键的成分相对于UO_2有所增大。同时,由于铀的7s和6d及5f轨道能量很接近,形成ds杂化轨道并参与成键。各氧化物的第一电离能同文献数据符合较好。势能面分析结果表明铀氧化产物取决于铀原子与O_2相互作用的方式。     

235UF6和238UF6同位素分子共振能量转移研究

本文利用长程力碰撞理论计算了²³⁵UF₆和²³⁸UF₆同位素分子间ν₃振动能量的近共振碰撞转移过程,得到了不同温度下共振函数随能量差变化的曲线,发现共振函数的宽度随温度的升高而增大。计算了不同温度下共振转移几率和共振转移速率,发现它们随温度的升高而减小。可见,²³⁵UF₆和²³⁸UF₆同位素分子的平动会降低其共振转移几率和共振转移速率,这为激光光化学法分离铀同位素提供了理论依据。     

铀的双原子分子化合物的势能函数和热力学性质

应用原子分子反应静力学基本原理和相对论有效原子实的量子力学ab initio计算方法。系统地研究了铀的双原子分子化合物UX（X=0、H、C、N)的平衡结构和离解能,确定了其正确的电子状态和合理的离解极限,拟合出双原子分子的Murrell-Sorbie势能曲线,在此基础上导出光谱数据和力常数,并采用量子力学方法计算了其热力学函数值。     

HFETR 6LiD中子转换器芯体厚度优化研究

介绍了通过在裂变堆中布置⁶LiD转换器将热中子转换为14MeV中子的原理,给出了⁶LiD转换器结构和材料的选取原则,建立了芯体厚度优化的目标函数。分别计算分析了在水和氦气两种冷却剂情况下,转换器结构、辐照样品数量对⁶LiD芯体厚度优化值的影响,给出⁶LiD芯体厚度对堆芯性能的影响。结果表明,布置于HFETR辐照孔道中的⁶LiD转换器芯体厚度优化设计值为0.7mm。     

LiD与H2O反应机理及动力学

在6-311G（d）水平下,采用微扰理论的MP2方法,研究了LiD与H2O的反应。结果表明,反应存在两个通道：LiD+H2O→LiOH+HD（R1）;LiD+H2O→LiOD+H2（R2）。298K下,两通道的势垒高度分别为9.31和195.08kJ/mol,反应速率常数分别为1.88×1010和3.74×10－26（mol•dm－3）－1•s－1。     

高温高压下LiD热力学性质的密度泛函理论研究

采用MS中CASTEP模块中的密度泛函理论方法,计算晶体的能量随体积变化的关系（E-V曲线）,运用准谐振子Debye模型研究了压力0~100GPa、温度0~2000K下的晶体LiD的热力学性质,包括热膨胀系数α随温度和压强的变化关系、体弹模量B₀随温度的变化、热容C_v与温度和压强的关系。预测了LiD晶体在高温、高压下的热力学性质。     

利用蒙特卡罗方法计算6LiD中子源的产额与能谱分布

利用^6LiD中子源转换靶室将反应堆热中子转换成聚变谱中子，可用来进行聚变中子辐照环境下的材料性能研究。应用蒙特卡罗方法模拟聚变谱中子的产生过程，从理论上验证了这种中子源的可行性。初步计算表明：1个热中子作用在^6LiD源室外表面将在源室内腔中产生0．1314个快中子；所产生的快中子具有很好的聚变谱特点，能量集中在13．5～15．5MeV之间。     

Measurement of the Efficiency of a 6LiD Thermal-to-14 MeV Neutron Converter in the Experimental Channel of an IVV-2M Reactor

The results of measurements of the efficiency of a ⁶LiD thermal-to-fast neutron converter for neutrons from DT and ⁶LiT fusion reactions with energy 14 MeV in the experimental channel of an IVV-2M reactor are presented. The first experimental estimates of the conversion coefficients for the corresponding fusion reactions are obtained: K ^D 2.11·10^–4 and K ^Li 1.36·10^–4. The value found in this work for the total conversion coefficient 3.47·10^–4 is approximately 1.7 times greater than the previously measured value and about 20% greater than the maximum computed estimate for a ⁶LiD converter.An experimental apparatus with a ⁶LiD converter in an IVV-2M channel is an accessible, comparatively inexpensive, and unique (for now) source of 14 MeV neutrons that can provide continuous and approximately uniform irradiation of Ø4 × 20 cm samples by neutrons from DT and ⁶LiT fusion 2.7·10¹⁰ sec^–1·cm^–2 for a comparatively long time (500 h).     

Preliminary spectrum shifter design for intermediate energy nuclear data benchmark experiments with DT neutrons

Integral benchmark experiments with DT neutrons are not always sufficient for nuclear data benchmarking in the MeV region, below 10 MeV. A neutron spectrum shifter, which will be placed between a sample and a DT neutron source, is effective to moderate DT neutrons incident to the sample. In order to estimate effects of the spectrum shifter, the ratio of the contribution of 14 MeV neutrons in the leakage neutron and gamma-ray spectra was calculated with MCNP-4C for an experimental configuration at FNS of JAEA, Japan. The calculations were carried out for a Li₂TiO₃ sample with a Be, D₂O, or ⁷LiD spectrum shifter. It was found out that the Be shifter was superior to others and the Be shifter was effective to decrease the contribution of 14 MeV neutrons especially for secondary gamma-ray spectrum measurements.     

Decomposition pressures in the (α + β) fields of the Li-LiH,Li-LiD,and Li-LiT systems

Decomposition (“plateau”) pressures of H₂, D₂, and T₂ over Li-LiH, Li-LiD, and Li-LiT alloys were determined between 600 and 850°C, for pressures ranging from 3 to 460 Torr, and for alloy compositions falling within the (α + β) miscibility gaps. The measurements were carried out separately for each hydrogen isotope using the same lithium sample and experimental procedures. For each system the ln P vs. 1/T data form a pair of linear segments, the intersection of which represents the monotectic temperature (694°C for Li-LiH, 690°C for Li-LiD, and 688°C for Li-LiT). For a given temperature plateau pressures were in the order P_T2 >P_D2 >P_H2. The $\text{D}\text{H}$ and $\text{T}\text{H}$ isotope effects in pressures varied from 1.48 and 1.74 at 600°C to 1.34 and 1.45 at 850°C. The results were used to calculate the standard free energies of formation of solid LiH, LiD, and LiT. The tritium gas used in this study had significant amounts of hydrogen and deuterium. A method for correcting the plateau pressures of this mixture to those of pure tritium is presented.     

The preparation of palladium for cold fusion experiments

Techniques have been established to prepare palladium specimens for cold fusion experiments using an ultra-high-vacuum, allmetal, high-temperature furnace to melt palladium metal in high purity alumina molds having a test tube shape. To date 6-mm and 15-mm cylinders have been fabricated, the latter being used to fabricate a sphere 12.5-mm in diameter. Techniques and facilities used for palladium-hydrogen isotope pressure-volume-temperature measurements^1–4 have been used to anneal these palladium specimens after machining and, in some cases, to charge these specimens with deuterium to PdD_0.63 stoichiometry prior to their use in electrochemical cells. The modeling of palladium-hydrogen isotope pressure-composition-temperature curves is described wherein existing data^5,6 is used to derive models that accurately describe the existing data and that extrapolate to high compositions. Experiments for reacting⁶LiD with Pd rods at 700°C to 800°C, in an attempt to precharge⁶Li into the Pd rods, are being prepared.Operated for the U.S. Department of Energy by Martin Marietta Energy Systems, Inc. Under Contract no. DE-AC05-84OR21400.     

Criteria for neutron fusion

The reaction ⁶Li(n, α) T is studied as a possible mechanism for driving a fuel pellet of ⁶LiD to fusion temperatures through bombardment with low energy neutrons. The criterion Jt 10²³ for fusion by this scheme is derived where J is incident neutron current (cm⁻² · s⁻¹) and t is time (s). The possibility of fusion through implosion is also examined. Ablation pressure exerted by products of the Li(n, α) T reaction is found to be independent of the cross section of this reaction. The index of refraction of neutrons in the neV to eV range indicates total absorption on a sample of ⁶Li.