光化学法锂同位素分离中化学反应速率常数测量

氢气与锂蒸气的化学反应速率常数是激光化学法锂同位素分离过程的一个重要参数。本文以可调谐半导体激光器为工具,通过监测锂原子蒸气对光的吸收测量原子蒸气密度的相对变化,建立了一种测量该速率常数的方法。在光化学锂同位素分离的典型条件下测得化学反应速率常数为9.0×10^-22 m³/s。该数值对于未来锂同位素分离装置中激光照射时间和氢气密度等参数的选择具有重要指导意义。     

核放消息

美国最近终于对“先进同位素分离”的发展方向做出选择[参看本刊3(3),161(1981)]。美国能源部已经决定支持劳伦斯利弗莫尔国家实验室(LLNL)对于原子蒸气激光分离(简称AYLIS)铀同位素的方法进行扩大实验,所用主要激光器是用铜蒸气泵浦的可调染料激光器。对于分子激光分离方法从     

基于光化学锂同位素分离条件的同位素比率测量

从光化学锂同位素分离实验研究的需求出发,基于其分离条件,提出了一种测量锂同位素比率的方法。该方法利用锂原子蒸气对探测光吸收峰的峰值来计算锂的同位素比率,避开了测量原子密度时所需的吸收信号频率定标与光强随频率变化积分中积分限的选择问题。该方法还根据锂同位素吸收谱的特殊性采用具有较强吸收效应的⁶Li的D₂线对应的吸收峰峰值,可在原子蒸气中⁶Li含量较低时提高对比率的测量精度。设计并搭建了实验装置,对该方法进行了测试。同一条件下所测得的同位素比率相对标准偏差小于1%,表明该方法对光化学分离方法中锂同位素比率相对变化是敏感的。这意味着该方法可作为以原子蒸气为分离介质的激光锂同位素分离研究的诊断手段。     

直接模拟蒙特卡罗法模拟二维平面蒸发亚稳态原子退激过程

在原子法激光同位素分离 (AVLIS)工程中 ,金属受电子束的加热而熔化 ,有一部分原子处于亚稳态能级 ,为了分析在蒸发过程中亚稳态原子退激对原子蒸气的速度、温度等物理特性的影响 ,采用直接模拟蒙特卡罗 (DSMC)法模拟钆原子蒸发过程 ,分析亚稳态原子退激过程对蒸气特性的影响。模拟结果表明 :亚稳态原子退激使得原子蒸气的速度增加 ,温度升高 ;克努森数Kn越小 ,原子间碰撞越频繁 ,亚稳态原子退激的影响越大     

一种测量弱吸收条件下锂同位素比率的新方法

在激光化学法锂同位素分离工作中,需对锂原子蒸汽密度进行实时监测。通过同位素比率的数值分析可提供分离实验中诸如激光功率、化学反应区温度、压强以及光化学反应时间等参数的优化依据。吸收光谱法可快速准确地测量非弱吸收条件下的锂同位素比率。对于低锂原子蒸汽密度的弱吸收条件,受示波器的分辨极限和存储时舍入误差的影响,不能得到准确有效的同位素比率数值。为了克服实验测量上存在的弱点,提出了一种基于差分电路采集信号的高分辨率高精度的研究方法,有效解决了弱吸收条件下的同位素比率测量问题。将该方法应用于天然锂进行了测试,得到的锂同位素比率为12.37±0.56。该方法对于采用吸收光谱法测量同位素比率具有通用性,也可在其他类似分离工作中应用。     

美国将在九十年代初建成激光浓缩铀实证性商业设施

[《欧渊核能》1988年5月号第47页报道]据美国能源部报告,在它的用原子蒸气激光分离同位素方法浓缩铀的研究和发展计划中,将原子蒸气激光分离过程的全规模实证性商业设施安排在90年代初建成。原子蒸气激光分离同位素技术,已于1987年在加利福尼亚的劳伦斯:利弗莫尔国家研究所进行的一系列1╱2规模浓缩试验中得到了证实。这些实验首次演示了为正确设计     

日本原子能研究所和原子激光分离工程研究协会达成有关浓缩铀的协议

【《日本原子》1987年7月号第23页报道】日本原子能研究所(JAERI)和激光原子分离工程研究协会(LASER-J)于1987年6月1日签订了“关于研究和发展原子蒸气激光分离铀同位素过程技术的基本合作协议”。 JAERI自1982年以来一直在从事有关原子蒸气激光分离过程的基础研究。为了促     

原子蒸气激光法比先进气体离心法浓缩铀更经济

【美国《核燃料》1984年10月第21期第2页报道】美国国会预算局认为,以原子蒸气激光分离铀同位素过程完全取代气体扩散技术的铀浓缩计划,看来可节省大量投资。对寻找新浓缩技术(原子蒸气激光分离     

美国验证用原子蒸气激光法生产武器级钚

【英国《核能》1989年2月刊第8页报道】美国加利福尼亚州劳伦斯利弗莫尔国家实验室(LLNL)的原子蒸气激光同位素分离(AULIS)计划的目的,是为民用动力堆浓缩铀。在最近的《能源和技术评论》报告(UCRL-52000)中,评论了该项计划。为执行该计划,安装了第二代铜蒸气激光器,     

美国激光分离铀同位素计划正在向前推进

美国在过去多年所取得的进展基础上,正在进行一个要在1992年前完成的原子蒸气激光同位素分离(AVLIS)的全规模过程论证发展计划。该计划的完成可使 AVLIS 法到90年代中后期付诸实用。     

应用可调谐外腔半导体激光器测量锂同位素比率

采用中心波长固定的可调谐外腔半导体激光器作为光源,通过激光吸收光谱法对锂原子同位素比率进行测量。该方法利用PID温控器实现锂金属蒸发温度的控制和测量。采用激光斜入射的方式消除光路调试过程中产生的标准具效应。实验测量给出了6组不同腔体温度下⁶Li和⁷Li在671 nm附近的吸收光谱,通过对⁶LiD₁和⁷LiD₂吸收峰进行积分吸收计算,得到⁶Li/⁷Li同位素比率测量精度可达2.5%。     

Numerical Simulation for Metastable States' Deexcitation in Electron Beam Evaporation Process

A direct simulation Monte Carlo (DSMC) method was modified in order to analyze the evaporation process in atomic vapor laser isotope separation (AVLIS), whereby energy transfer between discrete energy levels of metastable states and continuous energy level of translation took place. The atomic excitation temperatures of gadolinium atom were calculated for the model in five low-lying states. Calculation results were compared with those of the experiments obtained by laser absorption spectroscopy. Two types of DSMC simulations which were different in inelastic collision procedures were carried out. It was concluded that the energy transfer was forbidden unless the total energy of the colliding atoms exceeded a threshold value. It was also found that the DSMC method is suitable for treating deexcitation of metastable states accompanied by rapid expansion in the AVLIS evaporation process.     

天光一号预放大器自动准直技术研究

天光一号高功率KrF准分子激光装置采用光学角多路实现了六束激光的主振荡功率放大，其光路复杂，人工调节繁琐，指向精度难以保证，且激光波长为248 nm，属于深紫外波段，无法采用常用的光束自动准直方法。为了保障六束激光聚焦叠加并稳定精准地照射到靶面上，需开展适合天光一号装置激光参数及光路特性的自动准直技术研究。本文以预放大器三束输入、输出光路为研究对象，探索适合天光一号装置的自动准直方法，建立了预放大器光路自动准直系统，实现了快速、高精度光束的调节，验证了自动准直方案的可行性，为天光一号KrF准分子激光装置实现全光路自动准直奠定了技术基础。     

Velocity Distributions in High Density Gadolinium Atomic Beam Produced with Axial Electron Beam Gun

The parallel and perpendicular velocity distributions of a gadolinium atomic beam produced with an axial electron beam gun have been measured by a Doppler-shift technique and a Doppler limited absorption spectroscopy, respectively. The atomic density of 10¹⁸~10¹⁹atoms/m³ at a laser irradiated zone was sufficient for the process, such as an atomic vapor laser isotope separation. The atomic beam velocity of 800 m/s was obtained by a free expansion near an evaporation surface. This velocity, however, was 100 m/s slower than that we had measured with a magnetic transverse electron beam gun in a previous experiment. The reasons for the slower velocity in this experiment than that in the previous one are discussed. In keeping with the deposition rate, the parallel translational temperature rapidly decreased to 200 K, while the perpendicular translational temperature gradually increased and approached to the parallel translational temperature. This result suggested that the collisional region where both translational temperatures are equal extended to the laser irradiated zone in high-rate evaporations.     

Studies of laser induced cesium and rubidium hydride formation in vapor cells and their application for isotope separation

We present the results of studies of alkali hydride formation in vapor cells under laser irradiation. Two mechanisms are studied: formation in the cell volume in the presence of hydrogen and formation on the laser irradiated cell window. The first mechanism is investigated in a room-temperature cesium vapor cell, while the second one in a heated natural rubidium cell. The studies are aimed at isotope separation by means of selective laser excitation of the vapor with subsequent hydride formation. In the first case we obtained the intensity dependence of the absorption and fluorescence and could evaluate, by comparing with calculations, the rate constant of the two-step reaction of CsH formation. In the second case a solid layer deposition was observed on the cell window and interpreted as rubidium hydride.     

金属原子二维平面蒸发动力学过程研究

从由Ｂｏｌｔｚｍｍａｎ方程来的ＢＧＫ方程发出,数值模拟长槽型坩埚二维平面蒸发动学过程,着重对分离器中加入精料收集板,贫料收集板和热离子收集板时蒸气原子的空间物理特征进行数值模拟和分析,并对收集板的吸收率和温度以及Ｋｎ变化时,蒸气原子的空间物理特性进行了分析。     

Time-Resolved Laser-Induced Fluorescence of UO2 2+ in Nitric Acid Solutions

A comparison between nitrogen and tripled Nd-YAG laser source for Time-Resolved Laser- Induced Fluorescence (TRLIF) of uranium in nitric acid solutions in the framework of on-line feasibility has been performed. Hence, for uranium on-line monitoring with fiber optics, nitrogen laser (337 nm), most usual source in TRLIF has several drawback; poor beam quality and non negligible nitric acid absorption at 337 nm. Tripled Nd-YAG laser (355 nm) despite lower uranium absorption coefficient has several advantages: no influence of nitric acid absorption, better beam quality, better fiber transmission and solid state technology. No significant difference for fluorescence spectra and lifetimes are observed for both lasers. Limit of detection for direct determination of uranium in nitric acid by TRLIF is in the μ/l (10^?8 M) range for both lasers.