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31.
Wallenius M Morgenstern A Apostolidis C Mayer K 《Analytical and bioanalytical chemistry》2002,374(3):379-384
This paper describes the analytical methods (thermal ionization mass spectrometry, inductively coupled plasma mass spectrometry, and alpha spectrometry) that have been developed for determination of the age of uranium and discusses their advantages and limitations. With regard to potential application of the methods (e.g. Fissile Material Cut-off Treaty), the discussion focuses on highly enriched uranium, because this seems to be of highest strategic relevance.The different analytical methods were tested and validated by use of uranium reference materials of different (235)U isotope abundance and of known ages. The results show that thermal ionization mass spectrometry and alpha spectrometry are both very accurate and precise techniques for this application. Inductively coupled plasma mass spectrometry, on the other hand, although less precise, because of the different approach to the analytical problem, is still sufficiently accurate to be used as a rapid screening method. 相似文献
32.
The paper describes a methodology for a reference material preparation to be used for the determination of the production date (i.e. the time elapsed since the last chemical processing) of uranium materials based on the 230Th/234U radiochronometer. The reference material was prepared from highly enriched uranium by a complete separation of thorium decay products, thus zeroing the initial daughter nuclide concentration at known time. The complete elimination of thorium from the starting material was verified by gamma spectrometric measurements and by addition of a 232Th tracer to the material and its re-measurement in the final product after the separation. The validation of the methodology was carried out subsequently by comparing the ingrown daughter nuclide 230Th and the measured 230Th/234U ratio after recorded times following the last chemical separation with the calculated values obtained on the basis of their respective half-lives. The prepared reference material can be used as a quality control material for age determination of uranium in nuclear forensics and safeguards as well as for method validation. 相似文献
33.
Zsolt Varga Judit Krajkó Maxim Peńkin Márton Novák Zsuzsanna Eke Maria Wallenius Klaus Mayer 《Journal of Radioanalytical and Nuclear Chemistry》2017,312(3):639-654
The paper describes the applicability of different characteristics (signatures) in nuclear safeguards and forensics for assessment of uranium material provenance in terms of production process. The study follows a uranium ore concentrate production from an ore to a U3O8 product. It turned out that rare-earth elemental pattern, radiochronometry (age of ore body and material production date), sulphur and organic impurities are useful to find out the origin or history of the material, while certain trace-elements and isotopics of Pb or Sr were found to be inconclusive. The results will be important to understand the signatures in nuclear safeguards and forensics. 相似文献
34.
This paper examines a sequential multiple-criteria decision problem. The problem arises when a decision-maker is unable to consider all possible decision alternatives simultaneously. The decision-maker evaluates only a subset of all decision alternatives, from which he chooses the most preferred solution. Obviously, this solution is not necessarily ‘globally’ best. An interesting question is: how good is the most preferred solution and what are the chances of finding a better solution by considering additional alternatives? A unified approach to solving this problem based on probability theory is presented and illustrated with numerical examples. 相似文献
35.
Anion analysis in uranium ore concentrates by ion chromatography 总被引:2,自引:0,他引:2
In the present exploratory study, the applicability of anionic impurities for attributing nuclear material to a certain chemical
process or origin has been investigated. Anions (e.g., nitrate, sulphate, fluoride, chloride) originate from acids or salt
solutions that are used for processing of solutions containing uranium or plutonium. The study focuses on uranium ore concentrates
(“yellow cakes”) originating from different mines. Uranium is mined from different types of ore body and depending on the
type of rock, different chemical processes for leaching, dissolving and precipitating the uranium need to be applied. Consequently,
the anionic patterns observed in the products of these processes (the “ore concentrates”) are different. The concentrations
of different anionic species were measured by ion chromatography using conductivity detection. The results show clear differences
of anion concentrations and patterns between samples from different uranium mines. Besides this, differences between sampling
campaigns in a same mine were also observed indicating that the uranium ore is not homogeneous in a mine. These within-mine
variations, however, were smaller than the between-mine variations. 相似文献
36.
In a recent experiment performed at PSI, a peak in the time-of-flight distribution of pμ(1s) atoms could be identified with decay of ppμ* molecular ions situated below the 2s threshold, providing 900 eV of kinetic energy to the pμ atom. This finding may be interpreted in terms of the side path model which suggests that metastable muonic molecules may form with high probability in resonant collisions between muonic hydrogen in the 2s state and hydrogen molecules, e.g. $$p\mu (2s) + {\text{H}}_{\text{2}} \to [(pp\mu ^* )_{vJ}^{pq} - pee]_{vK} \to [(pp\mu ^* )_{v'J'}^{p'q'} - pe]^ + + e^ - .$$ The Coulombic decay of the Auger stabilised ppμ* molecular ion then leads to the formation of highly energetic pμ(1s) atoms. In the present paper calculations of resonant formation rates in pure hydrogen are presented and compared to the quenching rate of pμ(2s) atoms measured at low hydrogen density. 相似文献
37.
Hannele Wallenius 《European Journal of Operational Research》1982,10(3):221-228
In this paper the main approaches to optimizing macroeconomic policy problems are reviewed. These include the classical approaches of Tinbergen, Theil and Frisch as well as several mathematical programming methods, such as linear programming, goal programming, interactive multiple criteria optimization, and methods of optimal control. In addition, several applications are described. Finally, the usefullness and suitability of these approaches to solving macroeconomic policy problems in practice is discussed. 相似文献
38.
The side-path model previously suggested by us allows for muon transferfrom tritiumto deuterium via intermediate dtµ* resonances formed in tµ(2s)-D2 collisions. Taking this effect into account, the density dependence of the muon cycling rate in D-T mixtures at low temperatures is analysed. Compared with cascade models where only one-sided transfer is present, the predicted density dependence of c is in better agreement with measurements. 相似文献
39.
40.
Timo Tossavainen Hannele Suomalainen Tomi Mäkäläinen 《International Journal of Mathematical Education in Science & Technology》2017,48(4):520-532
We examine what kind of concept definitions of area a group of Finnish primary and lower secondary student teachers (N = 82) use, and how the quality of the definitions is associated with the participants’ success in seven exercises involving area. We are especially interested in how the understanding of the two-dimensionality of area appears in the participants’ responses. Only six student teachers were able to give a mathematically precise and correct definition of area. Altogether 26 participants defined it as ‘the size of a figure’ and 20 respondents required that a figure must be bounded. Further, 22 of them associated area with a formula or an example and eight respondents gave an incorrect or nonsensical definition. On average, student teachers master rather well the area formulae of a circle and a rectangle but already the relationship between the surface area of a cube and its volume is less commonly perceived. Most student teachers associate the area of an irregular domain with the method of exhaustion but clearly fewer of them acknowledge the difference between the area and an approximation of it. Surprisingly, there is only a weak Spearman correlation between the participants’ scores in the test exercises and the qualitatively ordered categories of concept definitions. 相似文献