Eu同位素浓缩的实验研究

极化原子束有许多重要的应用，如用来研究原子散射过程、制备极化核、检验宇称守恒性、研究表面特性以及应用于同位素的浓缩过程。本文主要描述通过磁偏转极化原子束的方法对Eu元素进行同位素浓缩实验，结合Eu原子特有的能级结构，分析了原子束的极化原理，描述了原子束极化和同位素浓缩的实验装置。用具有特定频率和偏振的激光对^153Eu进行选择性光抽运，分别得到正、负极化原子束，正、负极化原子束，正、负极化后的原子束穿过六极偏转磁铁后分别被聚焦和发散，最后用热丝探测器控制，得到了清晰的Eu原子的浓缩信号，当各参数为最佳状态时，仅用一台激光器对^153Eu进行抽运极化，其浓缩效率可达4％。     

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。     

原子无序起伏对反向极化稳定性的影响

考虑到缺陷、温度效应、掺杂等外界环境的影响,用方形随机分布和高斯随机分布模拟了格点原子的无序起伏,研究了在电场中高分子材料的双激子态反向极化的稳定性,发现当原子涨落不大于0.0148nm时,反向极化能够稳定存在.在格点扰动达到原子间距的14时,反向极化消失.进一步研究了简并参数te与反向极化的关系,同时讨论了在无序起伏较大时正向极化的起因. 关键词： 反向极化 双激子态 原子无序起伏     

厚原子蒸气介质中原子选择性光电离的理论研究

激光在厚原子蒸气介质中传播时会产生脉冲形变和延迟现象,这会直接影响原子多步光电离过程中的电离率和选择性.从原子蒸气激光同位素分离的实际出发,对厚原子蒸气介质中的原子光电离过程进行了研究,利用密度矩阵方法描述原子的光电离过程,利用Maxwell方程描述激光在厚介质中的传播,建立了介质中同时存在两种同位素的激光传播电离方程组,考察了原子蒸气参数和激光参数对厚介质中平均电离率和平均选择性的影响.研究结果表明:对于较厚的原子蒸气介质,激光功率的增加使平均电离率升高,平均选择性下降;对于相对较薄的介质,适当地降低激光功率可以同时提高平均电离率和平均选择性.存在一个正的激光延时使原子蒸气中目标同位素的平均电离率达到最大.尽量延长激光脉冲的宽度不仅可以同时提高目标同位素的平均电离率和平均选择性,还可以降低对激光脉冲之间相对延时的控制精度.     

Rb原子滤波器的实验研究

本文用热Rb原子进行了光学滤波的研究。将一束激光调谐到Rb原子D2线的F=1→F′=2共振吸收线上,使其泵浦Rb原子,实现原子布居极化(即将Rb原子制备到能级F=2上)。当一束信号光反向穿过该介质时,若信号光频率调谐到原子"吸收窗口"(D1线F=2→F′=2),该介质对信号光大量吸收,信号光透射率仅为0.14%;若信号光频率调谐到原子"透明窗口"(D1线F=1→F′=2),信号光透射率高于47.4%。这种极化的原子介质可以用来做光学滤波器。     

Eu原子束通过选态磁铁时的偏转特性

研究Eu原子束通过六极、二极磁铁选态系统时的偏转特性,主要考察如何合理选取选态系统参量以获得较高的选择性和较大的原子穿透立体角。本文结果,对磁偏转法浓缩非碱同位素等要求选态系统同时具备较高的选择性和较大的原子穿透立体角的实验有应用价值。 关键词：     

非单色激光场与同位素原子体系相互作用

本文研究了多模激光场与同位素原子体系相互作用动力学问题。采用混沌模型描述多模激光场，用Ｆｏｋｋｅｒ－Ｐｌａｎｃｋ方程方法，导出了有限带宽混沌场与同位素原子体系相互作用动力学方程。分析了激光线宽对同位素原子激发电离效率和选择性因子的影响。     

激光线宽和光强对同位素原子选择光电离的影响

本文研究了非单色(有限带宽)激光场与同位素原子体系相互作用的激发光电离过程. 采用混沌场随机模型描述激光场,用密度矩阵理论和Fokker-Planck方程方法首次给出了非单色激光场与多能级原子相互作用的激发动力学方程. 针对三能级同位素原子体系,讨论了激光线宽和激光光强对同位素原子电离概率和激光同位素分离过程中分离选择性的影响. 关键词： 激光同位素分离 激发动力学方程 激光线宽 Rabi频率     

激光分离同位素的动力学

本文针对激光分离同位素的主要历程建立了动力学模型,求得了两种典型情况下动力学方程组的解。在此基础上,导出了描述同位素浓缩过程特征量与各基元过程速率系数间函数关系的解析表达式。同时,借助于这些表达式,推论出使激光分离同位素获得高选择性的必要条件。最后研究了逆反应对同位素浓缩过程的影响。 关键词：     

弱场中光抽运极化Eu原子束的制备

自五十年代首次实现光抽运技术以来,人们用它已对多种原子进行了极化原子束制备的研究[1～5],但所有这些工作只是以相对简单的碱金属原子为对象,而对价电子数大于1的复杂原子的极化原子束的制备目前尚未见报道.描述了用一台连续波染料激光器对复杂原子Eu进行了弱场制备极化原子束的实验研究,得到了较满意的结果.     

Circularly polarized X-rays probing nuclear magnetic moments and magnetism of solids

It is demonstrated how circularly polarized x-rays can be used in nuclear and solid state physics. Detection of the radiation pattern of circularly polarized x-rays emitted in highly converted decays of oriented radio isotopes allows the determination of nuclear magnetic moments. Studying the absorption profiles of energy-tunable intense circularly polarized x-rays emitted from high-energy electron storage rings provides a powerful method to determine spin structure of electronic states, local magnetic moments and magnetic short range order in ferromagnetic materials.     

Die Erzeugung von negativen polarisierten Deuteriumionen aus metastabilen Deuteriumatomen im 2S 1/2-Zustand

An experimental method to produce polarized negative hydrogen ions is discussed and compared with other methods. The method makes use of the different lifetimes of the metastable 2S 1/2 state and the 2P 1/2 state of the hydrogen atom. Polarized ion beams are obtained by using a selective quenching process followed by selective ionisation. Experimental results are given for the intensity and polarization of the polarized negative ion beam of deuterons. These results were obtained as a function of the quenching-field, the magnetic field in the argon-cell and the density of argon and cesium. The yield of negative ions can be expressed by the cross sections for the different charge exchange reactions in argon. The measured tensorpolarisationP ₃₃ can be interpreted as a function of the cross sections, the argon-density and the magnetic field along the beam axis. Beams of 50 nA intensity were produced with a polarization ofP ³³=?0.250±0.006. The main advantage of this method is a low beam emittance, values of 0.7 cm rad eV^1/2 were achieved. The production of a polarized positive deuteron beam seems to be possible.     

Anlage zur Kernpolarisation mittels polarisierter Neutronen

An experimental set-up to be used for nuclear polarisation by means of the absorption of thermal polarized neutrons is described. The set-up consists essentially of a double spectrometer arrangement for polarized neutrons in connection with an arrangement for the detection of the nuclear polarisation by means of the anisotropic β-decay. The described method is especially useful for short-living isotopes which cannot be polarized by other methods.     

Production of polarized molecules of hydrogen isotopes

The possibility of producing polarized molecules of hydrogen isotopes by their spin separation in the inhomogeneous field of superconducting magnets has been demonstrated. This method proposed in our previous works has been implemented with a source of polarized atoms developed at the Budker Institute for Nuclear Physics. The measured flux of polarized molecules is compared with the simulation results. The possibility of developing a more intense source of polarized molecules is discussed.     

Dynamic nuclear polarization and nuclear orientation in an antiferromagnet

Dynamic nuclear polarization is a well established technique which has been used to produce polarized targets for experiments in nuclear physics. This paper suggests experiments of a similar type but involving the nuclear magnetic resonance of two isotopes, one stable and the other radioactive. The substance is an antiferromagnet, dysprosium phosphate, at temperatures below the Néel point, where line widths are comparatively small. The effect may be detected through changes in the rate of gamma ray emission observed by a nuclear orientation experiment.     

Action d'un champ magnetique sur le taux de polarisation de la raie interdite 2655,6 Å (61S0-63P0) du mercure

The forbidden radiation 2655.6 Å (6¹S₀-6³P₀) emitted by the odd isotopes of mercury is polarized in a magnetic field, even if the atoms are isotropically excited. The degree of polarization has been calculated for the case of ¹⁹⁹Hg. The experimental results agree with the theoretical predictions.     

Advantages of Mössbauer polarimetric methods in material studies

Mössbauer spectroscopic methods combined with the use of circularly polarized radiation offer element selective, unambiguous measurements of the orientation of hyperfine magnetic field at the nucleus. The paper presents applications of the method in investigations of antiferromagnets and distribution of magnetization inside iron-based nanoparticles. Selected examples showing development of Mössbauer conversion electron polarimetric methods are also reported.     

Concept of an Optical Magnetometer Based on the Spectroscopy of Alkali Vapors Confined in Nanometric-Thick Cells

In this article, we present the concept of an optical scalar magnetometer based on the spectroscopy of hot alkali vapors confined in nanometric-thick cells. We present an appropriate theoretical model to describe the interaction of linearly and circularly polarized light with atomic alkali vapors confined in extremely thin cells where a longitudinal magnetic field is applied. This model can be used to perform consecutive fittings of experimental spectra recorded by derivative selective reflection method, in order to measure the value of magnetic field. We illustrate the model with various calculated spectra for natural Rb vapor, while equivalent results hold for other alkalis (Na, K, Cs). We analyze the feasibility of the concept for different cases depending on light polarization and cell thickness, and discuss possible limitations of the technique.     

零闭锁激光陀螺磁敏感特性研究

与腔内运行线偏振光的抖动陀螺相比,腔内运行圆偏振光的零闭锁激光陀螺对磁场更为敏感.为了减小零闭锁激光陀螺的磁敏感性,理论分析了其磁敏感特性.当左、右旋陀螺的比例因子修正相等时,陀螺零偏不随磁场的变化而变化,同时陀螺比例因子线性度也将得到改善.试验测试了零闭锁激光陀螺的磁敏感性,结果表明陀螺存在磁不敏感点.试验结果与理论分析吻合.与传统的被动磁屏蔽方法相比,通过主动控制使得零闭锁激光陀螺工作在磁不敏感点的方法对于降低该陀螺的磁灵敏度和提高准确度具有实用价值.