U：CaF2晶体的分凝特性与光谱性质

应用TGT法生长了直径为75mm的U：CaF2晶体，宏观上透明完整.应用公式K0=Cs/Cl计算了U在CaF2晶体中的分凝系数等于0.53.应用溶质分布一般公式Cs=K0C0(1-g)K0-1，计算U的浓度分布与测量值，数值符合说明晶体生长过程接近平衡状态.分析不同条件下生长的U: CaF2晶体的晶胞参数和吸收光谱，结果表明生长气氛决定U的价态及电荷补偿机理：无PbF2存在的条件下，U为+4价，晶体呈绿色；PbF2的加入起到氟化去氧作用，U倾向于以离子半径最接近于Ca2+的U3+存在，晶体呈红色.从晶体生长开始到结束的部位，U3+:CaF2晶体吸收光谱的峰位不变，峰强呈现与U浓度相同的增加趋势.U3+:CaF2晶体外层厚约5mm处呈黄色，含有U3+和U2+的混合价态离子，其原理是石墨坩埚的还原作用通过单质铅，使部分的U3+进一步还原成了U2+. 关键词： 铀 氟化钙晶体 分凝系数 晶胞参数     

吡啶—2,6—二羧酸体系导数荧光法同时测定铀,钐,铕,铽,镝

本研究了吡啶－２，６－二羧酸（ＤＰＡ）体系导数荧光法同时测定铀，钐，铕，铽，镝的最佳条件。在ｐＨ５．５，４．８×１０＾－＾５ｍｏｌ／ＬＤＰＡ，激发波长２７２ｎｍ的条件下，可分别在５１８，６３９，６２１，５３９和６６ｎｍ处测定铀，钐，铕，铽和镝，检测限分别达到７，０．４，０．００４，０．０２６和０．２５ｎｇ／ｍＬ。应用本法测定了混合成试液中上术五种离子含量，回收率为９２．３－１０８．１％。     

A theoretical study of the structure and bonding of UOX4 (X = F, Cl, Br, I) molecules: the importance of inverse trans influence.

During nitroxide-mediated polymerization (NMP) in the presence of a nitroxide R2(R1)NO*, the reversible formation of N-alkoxyamines [P-ON(R1)R2] reduces significantly the concentration of polymer radicals (P*) and their involvement in termination reactions. The control of the livingness and polydispersity of the resulting polymer depends strongly on the magnitude of the bond dissociation energy (BDE) of the C-ON(R1)R2 bond. In this study, theoretical BDEs of a large series of model N-alkoxyamines are calculated with the PM3 method. In order to provide a predictive tool, correlations between the calculated BDEs and the cleavage temperature (T(c)), and the dissociation rate constant (k(d)), of the N-alkoxyamines are established. The homolytic cleavage of the N-OC bond is also investigated at the B3P86/6-311++G(d,p)//B3LYP/6-31G(d), level. Furthermore, a natural bond orbital analysis is carried out for some N-alkoxyamines with a O-C-ON(R1)R2 fragment, and the strengthening of their C-ON(R1)R2 bond is interpreted in terms of stabilizing anomeric interactions.     

Crystal Structure, Infrared Spectrum and Isotope Effect of Uranium-Crown Ether Complexes

According to the experiment results of X-ray diffraction and IR, the reduced partition function ratio (RPFR) and the contribution of various related vibration modes of uranium-crown ether complex (DCH18C6·H_3O)_2UO_2Cl_4 were theoreticallv calculated in detail. The equilibrium constant K_(eq) (that is, the single stage isotopic separation factor α) of exchange reaction for uranium isotopic chemical exchange system UO_2~(2+)(H_2O)_5—(DCH18C6.H_3O)_2UO_2Cl_4 is estimated to be 1.000746 at 12℃ and 1.000672 at 29℃, respectively, which are quite close to the experimental values 1.0010±0.0002 arid 1.0012±0.0004. Theoretical analysis shows that in the course of forming the complex of uranium with crown ether, the coordinated water of uranium is stripped, which performs a key action on the remarkable isotope effect for this system.     

Method for the determination of thorium and uranium in urine by ICP-MS

ICP-MS (inductively coupled plasma mass spectrometry) is shown as a very sensitive method for quantitative determination of Th and U concentration and excretion analysis in urine without any sample pretreatment. The current standard method for incorporation monitoring applies alpha-spectrometry, a very tedious and time consuming technique. ICP-MS offers an attractive alternative for monitoring of thorium and uranium body burdens in occupationally exposed subjects and also larger groups of the general population. A limit of determination of 0.5 ng/L in aqueous solutions and 1 ng/L in urine samples for both elements was achieved, with a precision of about ± 10% in the concentration range of appr. 10 ng/L. Due to the lack of a suitable reference material, the accuracy of the method was tested by comparing some of the results with those obtained by -spectrometry, especially for U. There was a sufficient agreement on both results.     

Ultra-trace analysis of U,Th, Ca and selected heavy metals in high purity refractory metals with isotope dilution mass spectrometry

A method for the determination of trace impurities (U, Th, Ca, Fe, Cr, Ni, Cu, and Cd) in the refractory metals molybdenum and tungsten with isotope dilution mass Spectrometry (IDMS) has been developed. This method enables determinations of uranium and thorium down to the lowest pg/g level with high precision and accuracy. Selective chromatographic, extractive and electrolytic methods for the trace-matrix separation were combined with positive thermal ionization mass spectrometry. Different samples of high purity (4N) and of ultra high purity (UHP) materials for advanced technologies were analysed. The detection limits reached are (in ng/g): U 0.006, Th 0.008, Ca 10, Fe 19, Cr 0.5, Ni 0.6, Cu 2.7, and Cd 0.12. A comparison of results with other sensitive analytical methods (ICP-MS, GDMS, SIMS) makes obvious the urgent necessity of a reliable calibration method like IDMS because the analytical results obtained by the other methods often spread over a wide range.     

一个新的铀（Ⅵ）三元协萃体系

研究了由４，４＇－癸二酰－双－（１－苯基－３－甲基－５－吡唑啉酮）（ＤＢＰＭＰ，简作Ｈ２Ａ），氧化三辛基膦（ＴＯＰＯ），吡啶（Ｐｙ）组成的三元体系从硝酸溶液中对铀的协同萃取，斜率法确定萃合物组成为ＵＯ２Ａ．ＴＯＰＯ．Ｐｙ，制取了固体协萃配合物，并用元素分析、ＩＲ及ＨＮＭＲ等进行了表征。     

Investigations for Modification of Polyacrylamide-Bentonite by Phytic Acid and its Usability in Fe3+, Zn2+ and UO2 2+ Adsorption

Composite of polyacrylamide-bentonite (PAA-B) was prepared by direct polymerisation of PAA in a suspension of bentonite (B). Adsorption and thermodynamic features of phytic acid (Phy) adsorption onto B, PAA and PAA-B, and those of Fe³⁺, Zn²⁺, UO₂ ²⁺ adsorption onto PAA-B and its modification by Phy (PAA-B-Phy) have been investigated. The reusability, storagability, ion selectivity and recoverability of sorbed ions with 1 M HCl have also been considered.The chemical and physical structure of adsorbents has been characterised by means of FT-IR and XRD. All adsorption isotherms for Phy and the ions were L-type of the Giles classification except, the one which is S type for adsorption of Phy onto PAA. The maximum adsorption capacities for the ions adsorbed were in order of UO₂ ²⁺ > Fe³⁺ > Zn²⁺ for PAA-B and Zn²⁺ > Fe³⁺ > UO₂ ²⁺ for PAA-B-Phy. Langmuir equilibrium constants for the adsorption of ions onto PAA-B-Phy were significantly higher than those found for PAA-B; the magnitude of increase for UO₂ ²⁺ was about 100. The thermodynamic parameters indicated that adsorption reactions are spontaneous in terms of adsorption free enthalpy.The chemical structure of PAA-B-Phy was not changed at the end of the studies of reusability and storagability. The composite was selective for UO₂ ²⁺ of the ions of interest.The composite of PAA-B and its modification by Phy have been used for the first time in this investigation. It is proposed that the composites can be practically used in the investigations and applications of adsorption.