Synchrotron‐induced EDXRF determination of uranium and thorium in mixed uranium–thorium oxide pellets

Uranium and thorium in their mixed oxides were determined by synchrotron‐induced energy dispersive X‐ray fluorescence (EDXRF) spectrometry. Mixed oxide calibration mixtures containing uranium and thorium in different relative amounts and approximately fixed amount of yttrium were prepared in the form of pellets. The EDXRF spectra of the pellets were measured at the microfocus XRF (BL‐16) beam line of Indus‐2 synchrotron radiation facility (Raja Ramanna Centre of Advanced Technology, Indore, India). Characteristic X‐ray lines U Lα, Th Lα, and Y Kα were used as analyte lines. Calibration plot for the determination of uranium was prepared by plotting amount ratios of U and Y against the intensity ratios of U Lα and Y Kα. Similarly, a calibration plot for thorium analysis was also made. The amounts of uranium and thorium in the sample mixtures prepared in similar way as the calibration mixtures were determined using the aforementioned calibration plots. The precision values obtained for uranium and thorium determinations were found to be 0.3 and 0.2% (relative standard deviation, 1σ), respectively. The EDXRF results deviated from the expected values by 1% for uranium and 0.9% for thorium determinations. These analytical features are much superior compared with laboratory‐based analysis results. Copyright © 2012 John Wiley & Sons, Ltd.     

A comparative study on determination of uranium and thorium in their mixed oxides by EDXRF using tube and radioisotope X‐ray sources

Studies on the matrix effects of uranium and thorium on the determinations of each other in their mixed oxides using energy dispersive X‐ray fluorescence (EDXRF) spectrometry with tube and radioisotope excitations of U Lα and Th Lα are reported. An internal standard method for the determination of uranium and thorium in these mixed oxides is found suitable. Comparison of the analytical results of EDXRF determinations of uranium and thorium using tube and radioisotope excitation sources has been made. The analytical methodology involves preparation of mixed oxide calibration/sample mixtures of uranium and thorium oxides, mixing of internal standard yttrium in these mixtures, pelletizing the mixtures after thorough mixing and grinding using boric acid binder and measuring EDXRF spectra of the specimens thus prepared using Rh X‐ray tube as well as ¹⁰⁹Cd radioisotope source. The samples were analyzed for uranium and thorium on the basis of the calibration plots obtained by plotting the intensity ratios of the analyte and internal standard characteristic X‐ray lines and their corresponding amount ratios. An average precision of 1.2% (1 s RSD) was observed for the determination of U and Th and the results deviated from the corresponding expected values by 3% on average. Due to the refractory nature of thorium oxide, comparatively more grinding time was required for thorium determinations. Copyright © 2011 John Wiley & Sons, Ltd.     

Total reflection X-ray fluorescence and energy-dispersive X-ray fluorescence characterizations of nuclear materials

Nuclear energy is one of the clean options of electricity generation for the betterment of human life. India has an ambitious program for such electricity generation using different types of nuclear reactors. The safe and efficient generation of electricity from these reactors requires quality control of different nuclear materials, e.g. nuclear fuel, structural materials, coolant, moderators etc. These nuclear materials have to undergo strict quality control and should have different specified parameters for their use in nuclear reactors. The concentration of major and trace elements present in these materials should be within specified limits. For such chemical quality control of these materials, major and trace elemental analytical techniques are required. Since some of these materials are radioactive, the ideal chemical characterization techniques should have multielement analytical capability, should require very less sample (micrograms level) for analysis so that the radioactive waste generated, and radiation exposure to the detector and operator are minimum. Total reflection X-ray fluorescence (TXRF) and energy dispersive X-ray fluorescence (EDXRF) with improved features, e.g. application of filters, secondary target and instrumental geometry require very small amount of sample and thus can be suitably used for the characterization of nuclear materials mainly for the determination of elements at trace and major concentration levels. In Fuel Chemistry Division, TXRF analytical methods have been developed for trace element determinations in uranium and thorium oxides, chlorine determination in nuclear fuel and cladding materials, sulphur in uranium, uranium in sea water etc. Similarly, EDXRF analytical methods with radiation filters (to reduce background) and improved sample preapartion techniques, e.g. fusion bead and taking samples in the form of solution on filter papers have been used for developing analytical methods for the determination of U and Th in their mixed matrices, Cd in uranium etc. Some of these studies have been reported in this paper.     

Betterment in EDXRF analytical results for compositional characterization of mixed uranium thorium oxide samples with bead specimens compared with pressed pellet specimens

A comparative study on the energy dispersive X‐ray fluorescence analytical results of uranium determinations, in uranium and uranium–thorium mixed oxides, using specimens in the form of fused beads and pressed pellets, has been made. It was observed that in case of fusion bead specimens, the intensity of the analyte lines was approximately 1.6 times of that observed in pellet specimens under identical instrumental conditions. In case of uranium oxide samples, the analytical results with bead specimens were slightly better compared with the pellet specimens. However, in case of the uranium–thorium oxide mixtures, the average precision obtained with bead specimen was significantly better (1%, 1 s) in comparison with that achieved using pellet specimens (7%, 1 s). This difference may be due to the hardness of thorium oxide compared with uranium oxide, which affects the homogeneity of the pellet specimens prepared. In fusion bead method of sample preparation, even highly refractory material like ThO₂ forms uniform glass beads. Addition of internal standard further improves the analytical results, with reduction in the percent deviation of energy dispersive X‐ray fluorescence results from the expected values to 3% from 7% compared with that obtained using without internal standard. The fusion bead method of sample preparation will be very useful for characterization of sintered (U,Th)O₂ pellets, which are highly refractory and difficult to dissolve. Copyright © 2016 John Wiley & Sons, Ltd.     

Evaluation of radiation level and radon exhalation rate of rock samples from Mahd Ad Dahab mine in Saudi Arabia

Mahd Ad Dahab mine is the largest and oldest gold mine in the middle East, situated in the western region of Al-Madina Al-Munawara in Saudi Arabia. By using a high-resolution gamma-ray spectroscopy system, various radionuclides in about 20 rock samples, collected from four different locations of the Mahd Ad Dahab mine, have been identified quantitatively based on their characteristic spectral peaks. The activity concentrations of the natural radionuclides uranium (²³⁸U), thorium (²³²Th), and potassium (⁴⁰K) as well as some radiological parameters were measured in the rock samples. The activity concentration of uranium was found to vary from 7.94 to 38.52 Bq/kg, thorium from 3.14 to 17.79 Bq/kg and potassium activity from 93.51 to 175.83 Bq/kg. The radon emanation coefficient of the rock samples was estimated. It ranged between 0.48 and 0.55. Moreover, the radium equivalent activity in the samples ranged between 19.3 and 77.49 Bq/kg, which is lower than the allowed maximum value for worker safety. The external and internal hazard indices and gamma-radiation hazard index were found not to exceed the permissible limits.     

Determination of thorium and uranium contents in soil samples using SSNTD’s passive method

Thorium-to-uranium ratios have been determined in different soil samples using CR-39 and LR-115-II solid-state nuclear track detectors (SSNTDs). A calibration method based on determination of SSNTD registration sensitivity ratio for α-particles of thorium and uranium series has been developed. Thorium and uranium contents of the standard soil samples have been determined and compared with its known values. There is a good agreement between the results of this method and the values of standard samples. The method is simple, inexpensive, non-destructive and has a wide range of applications in environment, building materials and petroleum fields.     

江西相山铀矿区与非铀矿区稻谷中天然放射性核素含量对比研究

文章对比分析研究了江西相山铀矿区和非铀矿区稻谷中天然放射性核素U和Th的含量特征。样品分别采自江西省相山铀矿区及远离铀矿区的抚州市郊丘陵水稻种植区。结果表明相山铀矿区稻谷中天然放射性核素U的含量显著高于非铀矿区的稻谷,铀矿区内稻谷中放射性核素U含量平均值是非铀矿区的5.30倍;但铀矿区内稻谷中放射性核素Th的含量却较非铀矿区稻谷含量低,仅为其Th含量的50%。另外,相山铀矿区内稻谷中放射性核素U和Th之间存在较为显著的线性关系,稻谷中放射性核素Th的含量随U含量的增加而升高。铀矿区内稻谷中放射性核素U含量显著高于非铀矿区的原因还有待于进一步深入研究,然而加强该领域的研究对于保证我国区域稻谷质量和食品安全是非常重要和有意义的。     

Natural Transmutation of Actinides via the Fission Reaction in the Closed Thorium–Uranium–Plutonium Fuel Cycle

It is shown for a closed thorium–uranium–plutonium fuel cycle that, upon processing of one metric ton of irradiated fuel after each four-year campaign, the radioactive wastes contain ~54 kg of fission products, ~0.8 kg of thorium, ~0.10 kg of uranium isotopes, ~0.005 kg of plutonium isotopes, ~0.002 kg of neptunium, and “trace” amounts of americium and curium isotopes. This qualitatively simplifies the handling of high-level wastes in nuclear power engineering.     

Determination of the REE content,geological age,and absorbed alpha dose of allanite mineral from Palawan,Philippines

Allanite is a common accessory mineral in igneous rocks that contains significant amounts of rare-earth elements (REEs), thorium (Th), and uranium (U). The presence of Th and U in the allanite exposes it to radiation resulting in radiation damage in its crystal structure and further leads to metamictization. Hence, allanite can be used as a natural analogue to assess the long-term radiation effects in materials for high-level nuclear waste disposal. It provides information on the effect of α-decay on the crystal structure including the stability and integrity of the material. In this study, the absorbed α-dose of allanite from Ombo, Palawan, Philippines, was estimated from the Th and U content and geological age of the mineral using X-ray fluorescence and gamma-ray spectrometry. The amount of Th and REE was measured to be around 1.37 and ~30.4 wt.%, respectively. Radiometric dating using gamma-ray spectrometry estimated the age of the allanite mineral to be around 24–35 million years. Having obtained the amount of radioactivity and the time of exposure, the corresponding absorbed α-dose was estimated to be at 2.84 × 10¹⁴ α-decays/mg. Results suggest that the allanite mineral studied has not accumulated significant radiation damage to cause amorphization and still exhibit a crystalline structure. This study may provide data on the properties of allanite or silicate matrices as part of the ongoing studies on silicate minerals as natural analogues.     

On the role of fusion neutron source with thorium blanket in forming the nuclide composition of the nuclear fuel cycle of the Russian Federation

The possible role of available thorium resources of the Russian Federation in utilization of thorium in the closed (U–Pu)-fuel cycle of nuclear power is considered. The efficiency of application of fusion neutron sources with thorium blanket for economical use of available thorium resources is demonstrated. The objective of this study is the search for a solution of such major tasks of nuclear power as reduction of the amount of front-end operations in the nuclear fuel cycle and enhancement of its protection against uncontrolled proliferation of fissile materials with the smallest possible alterations in the fuel cycle. The earlier results are analyzed, new information on the amount of thorium resources of the Russian Federation is used, and additional estimates are made. The following basic results obtained on the basis of the assumption of involving fusion reactors with Th-blanket in future nuclear power for generation of the light uranium fraction ^232+233+234U and ²³¹Pa are formulated. (1) The fuel cycle would shift from fissile ²³⁵U to ²³³U, which is more attractive for thermal power reactors. (2) The light uranium fraction is the most “protected” in the uranium fuel component, and being mixed with regenerated uranium, it would become reduced-enrichment uranium fuel, which would relieve the problem of nonproliferation of the fissile material. (3) The addition of ²³¹Pa into the fuel would stabilize its neutron-multiplying properties, thus making it possible to implement a long fuel residence time and, as a consequence, increase the export potential of the whole nuclear power technology. (4) The available thorium resource in the vicinity of Krasnoufimsk is sufficient for operation of the large-scale nuclear power industry of the Russian Federation with an electric power of 70 GW for more than one quarter of a century. The general conclusion is that involvement of a small number of fusion reactors with Th-blanket in the future nuclear power industry of the Russian Federation would to a large extent solve its problems and increase its export potential.     

Mineral zircon: A novel thermoluminescence geochronometer

Mineral zircon contains trace amounts (typically 10-1000 v ppm) of the f -emitters uranium and thorium, which irradiate this mineral internally. This outstanding feature of zircon turns out to be extremely useful when this mineral is applied as a thermoluminescence (TL) dating medium, because the build-up of the age-dependent luminescence is dominated by the presence of well-defined internal radioactive sources and the contributions to the dose from external radiation sources are two orders of magnitude smaller. The results presented in this paper have led us to the conclusion that for zircon dating it is necessary to carefully select the best and homogeneous zircon grains of the highest optical quality. For successful dating experiments on very young and historically well-defined coastal dune sands, selection of the most stable luminescence component by means of narrow band interference filters is needed. Our results suggest that ultimately optical zircon dating will allow us to determine the age of extremely young samples ( e.g. 12 months!).     

Calibrated U-TH glasses for neutron dosimetry and determination of uranium and thorium concentration by the fission track method

We have prepared a series of standard uranium glasses. A primary standard containing 41 ppm of added U had its concentration and isotope ratio verified by mass spectrometry and by fission track techniques. Secondary standards were compared to the primary standard using the fission track technique. These glasses are useful for measuring both Th and U in solids. The U concentration in an unknown is determined by comparing the fission track density induced by thermal neutron irradiation with the corresponding density in the standard. Th is measured by a cyclotron irradiation using the same U standards. The glasses are also useful for neutron dosimetry. Investigators may obtain small samples of most of these standards from R. H. Brill of the Corning Museum of Glass. Although most of the glasses were fabricated from depleted uranium, one standard containing natural uranium is available. A standard Th glass with concentration of 41 ppm was also made.     

Chemical Determination of Uranium in Natural Waters with DBM by the Adsorption of U(VI) on Fe(OH)3

The feasibility of determining uranium in natural waters for uranium exploration using dibenzoil methane (DBM) by the adsorption of U(VI) on ferric hydroxide, was investigated. The yields of coprecipitation were determined by a Scintrex UA-3 laser fluorimetric uranium analyser using standard uranium solutions. After dissolving the coprecipitate, uranium was selectively separated by carbonate precipitation and determined with DBM. Fe(OH)₃ - DBM method was controlled using both standard solutions and uranium analyser measurements of some natural water samples taken from Northern Ege Region where detailed radiometric investigation has been going on. The advantage of this method     

Determination of cobalt marker in cow ruminal fluid by EDXRF and SRTXRF

This article describes a comparison of conventional energy‐dispersive X‐ray fluorescence (EDXRF) and synchrotron radiation total‐reflection X‐ray fluorescence (SRTXRF) for Co determination in ruminal fluid from Holstein cow. This element is used as marker for animal nutrition studies. For EDXRF, 200 µl of the sample were dried on 6.35 µm Mylar film at 60 °C. The excitation was carried out using an X‐ray tube with Mo target and Zr filter operated at 30 kV/20 mA. For SRTXRF, 10 µl of the sample were pipetted on a Lucite carrier and dried at 60 °C. In both the techniques, Ga was used as internal standard and the acquisition time was 200 s. The trueness of both techniques was evaluated through the standard addition method, the recoveries obtained by SRTXRF and EDXRF were 76 and 99%, and the limits of detection, 13 and 240 µg l^?1, respectively. Copyright © 2011 John Wiley & Sons, Ltd.     

内标法在土壤重金属镍元素X荧光分析中的应用研究

利用能量色散型XRF重金属实验平台,在实验室自然大气环境下获取土壤的X射线荧光,通过X射线荧光光谱法定量分析了国家标准土壤样品中元素Ni的含量。实验研究了土壤中Ni元素的X荧光特征分析谱线,采用加入内标法测定了Ni元素定标曲线,并依据实验结果分析了内标元素选取方法。实验结果表明,对土壤样品进行内标法分析时,可选取基体中适宜元素作为内标元素;使用Pb的Lα线,Cu和Fe的Kα线作内标线时相对标准偏差(RSD)分别为6.24%,5.24%和5.22%,说明选择合适基体主量元素的特征谱线作为内标线,可有效提高测量结果的准确性。     

The discoveries of uranium 237 and symmetric fission - from the archival papers of Nishina and Kimura

Shortly before the Second World War time, Nishina reported on a series of prominent nuclear physical and radiochemical studies in collaboration with Kimura. They artificially produced (231)Th, a member of the natural actinium series of nuclides, by bombarding thorium with fast neutrons. This resulted in the discovery of (237)U, a new isotope of uranium, by bombarding uranium with fast neutrons, and confirmed that (237)U disintegrates into element 93 with a mass number of 237. They also identified the isotopes of several middle-weighted elements produced by the symmetric fission of uranium. In this review article, the highlights of their work are briefly summarized along with some explanatory commentaries.     

Preparation of arsenic‐containing white rice grains as calibration standards for X‐ray fluorescence analysis of total arsenic in cereals

A preparation method of arsenic‐containing white rice grains as calibration standards was developed for the X‐ray fluorescence (XRF) analysis of arsenic in rice grains. Calibration standards were prepared by adding 10 g of white rice grains (from Japan) to 100 ml methanol‐containing dimethylarsinic acid corresponding to 2–100 µg arsenic. The mixture was heated, dried at 150 °C, cooled to room temperature, and then stored in a silica gel desiccator. A total of 5.0 g of each calibration standard was packed into a polyethylene cup (32 mm internal diameter and 23 mm height) covered with a 6‐µm‐thick polypropylene film and then analyzed by wavelength‐dispersive XRF spectrometry. The calibration curve for arsenic obtained from the white rice grains containing arsenic showed good linearity over a concentration range of 0.21–5.00 mg kg^?1 arsenic. The limit of detection of arsenic was 0.080 mg kg^?1. To check the reliability of the XRF method, the concentrations of arsenic in six samples of grain cereals and two samples of flour were compared with those obtained by atomic absorption spectrometry after acid decomposition. The values obtained by both analytical methods showed good agreement. Copyright © 2016 John Wiley & Sons, Ltd.     

Hybrid fusion–fission reactor with a thorium blanket: Its potential in the fuel cycle of nuclear reactors

Discussions are currently going on as to whether it is suitable to employ thorium in the nuclear fuel cycle. This work demonstrates that the ²³¹Pa–²³²U–²³³U–Th composition to be produced in the thorium blanket of a hybrid thermonuclear reactor (HTR) as a fuel for light-water reactors opens up the possibility of achieving high, up to 30% of heavy metals (HM), or even ultrahigh fuel burnup. This is because the above fuel composition is able to stabilize its neutron-multiplying properties in the process of high fuel burnup. In addition, it allows the nuclear fuel cycle (NFC) to be better protected against unauthorized proliferation of fissile materials owing to an unprecedentedly large fraction of ²³²U (several percent!) in the uranium bred from the Th blanket, which will substantially hamper the use of fissile materials in a closed NFC for purposes other than power production.     

偏磷酸钛基体中四价铀离子的荧光

本文用蒸发溶液法制备了Th(PO3)4、U(PO3)4及掺杂了U4+的Th(PO3)4:U4+单晶,确定了β-U(PO3)4属于正交晶系Cmca-D2h18点群,α-U(PO3)4和Th(PO3)4都为三斜晶系P1或P1点群,给出了它们的晶格参数.测量了U(PO3)4吸收谱,和Th(PO3)4基体中U4+的激发和荧光谱.在近紫外光激发下,Th(PO3)4:U4+产生一组荧光,对应于U4+离子的6d-5f电子跃迁.270和298nm的荧光寿命约10ns,对应于电偶极跃迁.在波长为553nm绿光激发下,Th(PO3)4:U4+中四价铀的电子产生上转换效应,释放出358和533nm窄带荧光、它们属于U4+的5f-5f电子跃迁,分别对应于3P2-3H4和1I5-3H4。给出了相应的荧光和上转换效应的跃迁能级图.     

Preliminary results of calculations for heavy-water nuclear-power-plant reactors employing <Superscript>235</Superscript>U, <Superscript>233</Superscript>U,and <Superscript>232</Superscript>Th as a fuel and meeting requirements of a nonproliferation of nuclear weapons

A physical design is developed for a gas-cooled heavy-water nuclear reactor intended for a project of a nuclear power plant. As a fuel, the reactor would employ thorium with a small admixture of enriched uranium that contains not more than 20% of ²³⁵U. It operates in the open-cycle mode involving ²³³U production from thorium and its subsequent burnup. The reactor meets the conditions of a nonproliferation of nuclear weapons: the content of fissionable isotopes in uranium at all stages of the process, including the final one, is below the threshold for constructing an atomic bomb, the amount of product plutonium being extremely small.