Worldwide measurements of radioxenon background near isotope production facilities, a nuclear power plant and at remote sites: the “EU/JA-II” Project

The Comprehensive Nuclear-Test-Ban Treaty (CTBT) specifies that radioxenon measurements should be performed at 40 or more stations worldwide within the International Monitoring System (IMS). Measuring radioxenon is one of the principle techniques to detect underground nuclear explosions. Specifically, presence and ratios of different radioxenon isotopes allows determining whether a detection event under consideration originated from a nuclear explosion or a civilian source. However, radioxenon monitoring on a global scale is a novel technology and the global civil background must be characterized sufficiently. This paper lays out a study, based on several unique measurement campaigns, of the worldwide concentrations and sources of verification relevant xenon isotopes. It complements the experience already gathered with radioxenon measurements within the CTBT IMS programme and focuses on locations in Belgium, Germany, Kuwait, Thailand and South Africa where very little information was available on ambient xenon levels or interesting sites offered opportunities to learn more about emissions from known sources. The findings corroborate the hypothesis that a few major radioxenon sources contribute in great part to the global radioxenon background. Additionally, the existence of independent sources of ^131mXe (the daughter of ¹³¹I) has been demonstrated, which has some potential to bias the isotopic signature of signals from nuclear explosions.     

Identification of unknown irradiated nuclear fuel through its fission product content

A procedure is demonstrated, through a simulation study, for the determination of the origin of unknown spent nuclear fuel, an important and challenging task in nuclear forensics. The procedure is an isotopic fingerprinting method relying on the fission product content of the unknown. The ‘unknown’ nuclear material is represented by the spent nuclear fuel of known origin in order to demonstrate the method and verify its predictive capabilities. The method is based on the comparison of the fission product compositions of the ‘unknown’ material and simulated known spent fuels from a range of commercial nuclear power stations using the multivariate statistical technique of factor analysis. Then, the provenance of the ‘unknown’ spent fuel is the commercial fuel with which it exhibits the highest similarity with respect to the fission product content.     

Optimization of a laser ablation-inductively coupled plasma “time of flight” mass spectrometry system for short transient signal acquisition

Simultaneous ion sampling and sequential detection offered by inductively coupled plasma ‘time of flight’ mass spectrometry (ICP-TOFMS) provides advantages for the analysis of short transient concentration-variable signals as produced in laser ablation. In order to investigate the capabilities of ICP-TOFMS in combination with an excimer laser ablation system, ablation studies on reference materials and geological samples were carried out. Various ICP-TOFMS parameters were optimized for laser-induced aerosols. Transverse rejection ion pulse was used to extend the dynamic range in concentration. A reduced volume ablation cell was designed and used in order to increase the sample density in the ICP. Results for 63 simultaneously measured isotopes (SRM 610 from NIST) lead to limits of detection in the 1–100 μg/g range for a 80 μm crater diameter (10 Hz, 1.2 mJ pulse energy). The reproducibility of signal ratios was determined to be better than 2% RSD for transient signals using 102 ms integration time. These optimized parameters were then used for the analysis of tin-rich fluid inclusions. Preliminary results of multielement analysis and isotopic ratio determinations on individual fluid inclusions (63 isotopes, 102 ms integration time) demonstrate the capabilities of ICP-TOFMS in combination with laser ablation. Received: 6 March 2000 / Revised: 11 May 2000 / Accepted: 14 May 2000     

Chemical standards for ion mobility spectrometry: a review

Ion mobility spectrometry (IMS), using stand-alone instrumentation and hyphenated with mass spectrometry (IM-MS), has recently undergone significant expansion in the numbers of users and applications, particularly in sectors outside its established user base; predominantly military and security applications. Although several IMS reference standards have been proposed, there are no currently universally recognised reference standards for the calibration and evaluation of mobility spectrometers. This review describes current practices and the literature on chemical standards for validating IMS systems in positive and negative ion modes. The key qualities and requirements an ‘ideal’ reference standard must possess are defined, together with the instrumental and environmental factors such as temperature, electric field, humidity and drift gas composition that may need to be considered. Important challenges that have yet to be resolved are also identified and proposals for future development presented.     

Determination of uranium, thorium and plutonium isotopes by ICP-MS

Quantitative and isotopic measurement of actinide elements is required in many circumstances in the nuclear industry. For example, determination of very low levels of these alpha emitters in human urine samples is used to assess the internal committed dose for nuclear workers. Quantifying actinide isotopes in radioactive waste from nuclear processing and nuclear facility decommissioning provides important information for waste management. Accurate determination of the uranium isotopic ratios in reactor fuels provides fuel burnup information. Inductively coupled plasma mass spectrometry (ICP-MS) has been used for the determination of Th, U, and Pu in various samples including urine, nuclear waste, and nuclear fuel in our laboratory. In order to maximize the capability of the technique and ensure quality analyses, ICP-MS was used to analyze samples directly, or after pre-treatment to separate complicated matrices or to concentrate the analyte(s). High-efficiency sample introduction techniques were investigated. Spectral interferences to minor isotopes caused by peak tails and hydride ions of major actinide isotopes were studied in detail using solutions prepared with light and heavy waters. The quality of the isotopic ratio measurement was monitored using standard reference materials.     

Activation analysis of high-purity silicon

The triple comparator method is used for the analysis of impurities of high purity silicon by neutron activation. The ratios of the specific photopeak activities of the isotopes investigated to the specific photopeak activities of the gold, indium and cobalt comparators were determined. The triple comparator method avoids some tedious problems in the multi-element activation analysis and it is very well suited for the determination of ‘non-expected’ elements. Research associate of the N. F. W. O.     

Effect of humic acid,pH and ionic strength on the sorption of Eu(III) on red earth and its solid component

A highly sensitive separation procedure has been developed to investigate uranium and thorium activities and their isotopic ratios in environmental water samples in Tokushima, Japan. Uranium and thorium isotopes in environmental water samples were simultaneously isolated from interfering elements with extraction chromatography using an Eichrom UTEVA™ resin column. After the chemical separation, activities of U and Th isotopes coprecipitated with samarium fluoride (SmF₃) were measured by α-spectrometry. It has been confirmed that uranium isotopes are isolated successfully from thorium decay chains by analyzing a test aqueous solution as a simulation of an environmental water sample. The separation procedure has been first applicable to the determination of U and Th activities and their isotopic ratios in a drinking well water named “Kurashimizu” in Tokushima City, Japan. The specific activities of ²³⁸U and ²³²Th in “Kurashimizu” were deduced to be within the upper limits of <0.31 and <0.19 mBq/l, respectively.     

Do explanation formats in elementary chemistry depend on agent causality?

By setting out the grammar of event causality, as developed by Hume and Mackie, in contrast to the grammar of agent causality in the natural sciences, a kind of hybrid hierarchical format for chemical explanations is sketched. From this starting point the history of agentive concepts in chemistry is displayed as a progression from Newton’s ‘forces’, through the nineteenth century concepts of ‘affinity’ and ‘valency’ to recent theories of molecular binding in terms of the migration of electrons and protons as powerful particulars. The final stage of this development is the rewriting of chemical theory in terms of energy.     

Estimation of isotopic composition of plutonium from thermal reactors by neutron coincidence counting through isotopic correlation technique

Correlations have been established between %Eff ²⁴⁰Pu and various plutonium isotopes formed in thermal reactors. Based on these correlations, a method has been developed for the estimation of isotopic composition of plutonium obtained from thermal reactors. The method is simple, fast, non-destructive and finds application for the verification of plutonium isotopic composition in the finished products of known plutonium content. The method could be applied in the nuclear fuel fabrication to verify and confirm the fissile content (²³⁹Pu+²⁴¹Pu) specification. It has also been shown that in principle, similar correlations could be established for Pu obtained from different thermal reactor fuels with reactor specific fitting parameters.     

A cyclic neutron activation system using an isotopic neutron source for the measurement of short-lived isotopes

The design and construction of an activation analysis system using an isotopic neutron source which allows the measurement of prompt and delay gamma-rays, in conventional activation and cyclic activation modes, is briefly described with emphasis laid on its flexibility, transportability and low cost. Photon spectra obtained from the irrdiation of large samples under prompt, delay and cyclic conditions using both NaI(Tl) and Ge(Li) detectors are presented and described with respect to ‘in-vivo’ neutron activation analysis and the measurement of N, O, Na, P, Cl and Cd. It is pointed out that, despite the attractive possiblity of measuring Se in liver, ‘in-vivo’, by cyclic activation analysis, the system may potentially prove a very useful tool for industrial and other non-medical applications.     

Explanation and theory formation in quantum chemistry

In this paper I expand Eric Scerri’s notion of Popper’s naturalised approach to reduction in chemistry and investigate what its consequences might be. I will argue that Popper’s naturalised approach to reduction has a number of interesting consequences when applied to the reduction of chemistry to physics. One of them is that it prompts us to look at a ‘bootstrap’ approach to quantum chemistry, which is based on specific quantum theoretical theorems and practical considerations that turn quantum ‘theory’ into quantum ‘chemistry’ proper. This approach allows us to investigate some of the principles that drive theory formation in quantum chemistry. These ‘enabling theorems’ place certain limits on the explanatory latitude enjoyed by quantum chemists, and form a first step into establishing the relationship between chemistry and physics in more detail.     

Mass-independent isotopic fractionation of tin in chemical exchange reaction using a crown ether

Tin isotopes were fractionated by the liquid-liquid extraction technique with a crown ether, dicyclohexano-18-crown-6. The isotopic ratios of ^mSn/¹²⁰Sn (m: 116, 117, 118, 119, 122 and 124) were measured by multi-collector inductively coupled plasma spectrometry (MC-ICP-MS) on a Nu Plasma 500 with a precision better than 0.05 permil amu⁻¹ on each isotopic ratio. Odd atomic mass isotopes (¹¹⁷Sn and ¹¹⁹Sn) showed depletions compared to the even atomic mass isotopes (¹¹⁶Sn, ¹¹⁸Sn, ¹²²Sn and ¹²⁴Sn). We show that this odd-even staggering property originates from the nuclear field shift effect. The contribution of the nuclear field shift effect to the observed isotope enrichment factor was estimated to be ∼35%.     

Scoring Functions – the First 100 Years

The use of simple linear mathematical models to estimate chemical properties is not a new idea. Albert Einstein used very simple ‘gravity-like' forces to explain the capillarity of different liquids in 1900–1901. Today such models are used in more complicated situations, and a great many have been developed to analyse interactions between proteins and their ligands. This is not surprising, since proteins are too complicated to model accurately without lengthy numerical analysis, and simple models often do at least as good a job in predicting binding constants as much more computationally expensive methods. One hundred years after Einstein’s ‘miraculous year’ in which he transformed physics, it is instructive to recall some of his even earlier work. As approximations, ‘scoring functions’ are excellent, but it is dangerous to read too much into them. A few cautionary tales are presented for the beginner to the field of ligand affinity prediction by linear models.     

41Ca ultratrace determination with isotopic selectivity > 1012 by diode-laser-based RIMS

⁴¹Ca ultratrace determination by diode-laser-based resonance ionization mass spectrometry with extremely high isotopic selectivity is presented. Application to environmental dosimetry of nuclear reactor components, to cosmochemical investigations of production cross sections, and biomedical isotope-tracer studies of human calcium kinetics are discussed. Future investigations are possible use in ⁴¹Ca-radiodating. Depending on the application, ⁴¹Ca isotopic abundances in the range of 10^–9 to 10^–15 relative to the dominant stable isotope ⁴⁰Ca must be determined. Either double- or triple-resonance optical excitation with narrow-band extended cavity diode lasers and subsequent non-resonant photoionization of calcium in a collimated atomic beam were used. The resulting photoions are detected with a quadrupole mass spectrometer optimized for background reduction and neighboring mass suppression. Applying the full triple-resonance scheme provides a selectivity of ∼ 5 × 10¹² in the suppression of neighboring isotopes and > 10⁸ for isobars, together with an overall detection efficiency of ∼ 5 × 10^–5. Measurements on a variety of sample types are discussed; the accuracy and reproducibility of the resulting ⁴¹Ca/⁴⁰Ca isotope ratios was better than 5%. Received: 4 January 2001 / Revised: 19 February 2001 / Accepted: 27 February 2001     

Probing the internal environment of PVP networks generated by irradiation with different sources

Poly(N-vinyl-2-pyrrolidone) (PVP) hydrogels have been synthesised from the aqueous solutions of the same linear polymer by two different radiation sources: electron beams and UV rays. The present investigation couples conventional hydrogel characterisation techniques with the study of the partition equilibria, fluorescence behaviour and release of two different molecular probes, 1-anilino-8-naphthalene sulphonate (ANS) and Thioflavin T (ThT). The two probes have comparable molecular weight and different structural and optical properties. The ‘chemical’ networks produced upon irradiation in different experimental conditions presented quite distinctive mechanical spectra, yielded to different porous solids upon freeze-drying and showed specific rehydration ratios when ‘equilibrated’ in water. More interestingly, they offered ‘hydrophobic pockets’ to host the ANS molecules in a way that the probe is completely occluded from water, making it fluoresce. Conversely, the generated PVP networks did not show any specific affinity towards the hydrophilic ThT that was only barely untaken.     

Evaluation of a new generation quadrupole-based ICP-MS for uranium isotopic measurements in environmental samples

We compare the analytical performance of a modern quadrupole-based ICP-MS (“X-Series”, Thermo-Electron, Winsford, UK) with a single-collector double-focusing sector-field ICP-MS (“Axiom”, VG Elemental, Winsford, UK) for uranium isotopic measurements in environmental samples. We focus on the precision and accuracy obtained with both instruments for the ²³⁵U/²³⁸U isotopic ratios and on the abundance sensitivity that is a key parameter for low ²³⁶U/²³⁸U isotopic ratios measurements. We observe that isotopic measurements are more precise accurate with the “X-Series” than with the “Axiom”. Besides, we demonstrate that the “Axiom’s” higher abundance sensitivity limits its capability to measure ²³⁶U/²³⁸U ratio below a few ppm.     

Neutron activation analysis by combined capture and decay gamma-spectrum method

The usual method of the neutron activation analysis is performed by the measurement of the characteristic nuclear radiations of the produced radioactive isotope by neutron irradiation. An advance in this field has recently been proposed in which the prompt capture γ-rays are observed in addition to the nuclear radiation of the produced nucleus. The characteristic energy spectra of these two kinds of γ-radiations are the main basis for the combined activation analysis method. The experimental setup consists of a γ-radiation pulse height energy spectrum system which is synchronized with a pulsing neutron generator of ‘D—T’ or ‘D—D’ reaction. The present results indicate that a qualitative and semi-quantitative determination of a number of elements is feasible, with an overall error of 10–15%.     

Thermoanalytical investigation of cavity filling natrolite group minerals in basalts

Cavity filling natrolites in basalts from several localities of Balaton Highland were investigated by different methods. The measurements of different thermal parameters (corrected decomposition temperature and activation energy) were first applied for natrolite. Energy dispersive spectroscopy (EDS) was used for the observation of chemical composition. Few of the minerals are regular, ordered natrolite, the majority proved to be so called ‘tetranatrolite’. According to our observations both natrolite and ‘tetranatrolite’ may appear in the same locality and chemical inhomogenity can be demonstrated within a single natrolite needle.     

A probabilistic approach to heroin signatures

The probability density functions of amount ratios of compounds (total codeine/total morphine, 6-monoacetylemorphine/total morphine, papaverine/total morphine, and noscapine/total morphine) from the analysis of seized heroin, originating from known world regions (South East Asia, South West Asia, South America, Mexico) allows calculation of likelihood ratios for ‘unknown’ samples. Application of Bayes Theorem with a suitable prior probability, for example the frequency of a particular region in the database, leads to the probability that a particular profile comes from a given target region. Data from 2549 seizures of heroin at Australia’s border illustrates the method, and results are compared with simple HS1 ratio approaches for assigning geographical origin. The method can be implemented in a spreadsheet and gives more refined intelligence of the origins of seized drugs than simple ranges.