Automated separation and measurement of radioxenon for the Comprehensive Test Ban Treaty

A fully automatic radioxenon sampler/analyzer (ARSA) has been developed and demonstrated for the collection and quantitative measurement of the four xenon radionuclides,^131mXe(11.9 d),^133mXe(2.2 d),¹³³Xe(5.2 d), and¹³⁵Xe(9.1 hr), in the atmosphere. These radionuclides are important signatures in monitoring for compliance to a Comprehensive Test Ban Treaty (CTBT). Activity ratios of these radionuclides permit source attribution. Xenon, continuously and automatically separated from the atmosphere, is automatically analyzed by electron-photon coincidence spectrometry providing a lower limit of detection of about 100 μBq/m³. The demonstrated detection limit is about 100 times better than achievable with reported laboratory-based procedures for the short-time collection intervals of interest.     

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.     

Determination of 131mXe and 133mXe in the presence of 133gXe via combined beta-spectroscopy and delayed coincidence

The International Monitoring System for the Comprehensive Nuclear-Test-Ban Treaty will include measurements of Xe fission products. Pacific Northwest National Laboratory has developed an automated system for separating Xe from air which detects Xe fission products using a beta-gamma counting system for ^131mXe, ^133mXe, ^133gXe, and ^135gXe. Betas and conversion electrons are detected in a plastic scintillation cell containing the Xe sample. Gamma and X-rays are detected in a NaI(Tl) scintillation detector which surrounds the plastic scintillator sample cell. Two-dimensional pulse-height spectra of gamma-energy versus beta-energy are obtained. The plastic scintillator spectrum in coincidence with the 31-keV X-rays from ^131mXe. ^133mXe, and ^133gXe is a complex mixture of conversion electrons and betas. A new technique to simultaneously measure the delayed coincidence (T _1/2 = 6.27 ns) between beta-particles from ^133gXe and conversion electrons depopulating the 81-keV state in 133 Cs is being developed. This technique allows separation of the ^133gXe beta spectrum from the conversion electrons due to ^131mXe and ^133mXe and uniquely quantifies all three nuclides.     

Measurement of heterogeneous reaction rates: three strategies for controlling mass transport and their application to indium-mediated allylations

We describe three new strategies for determining heterogeneous reaction rates using photomicroscopy to measure the rate of retreat of metal surfaces: (i) spheres in a stirred solution, (ii) microscopic powder in an unstirred solution, and (iii) spheres on a rotating shaft. The strategies are applied to indium-mediated allylation (IMA), which is a powerful tool for synthetic chemists because of its stereoselectivity, broad applicability, and high yields. The rate-limiting step of IMA, reaction of allyl halides at indium metal surfaces, is shown to be fast, with a minimum value of the heterogeneous rate constant of 1 × 10(-2) cm/s, an order of magnitude faster than the previously determined minimum value. The strategies described here can be applied to any reaction in which the surface is retreating or advancing, thereby broadening the applicability of photomicroscopy to measuring heterogeneous reaction kinetics.     

Influence of solvents and novel extraction methods on bioactive compounds and antioxidant capacity of <Emphasis Type="Italic">Phyllanthus amarus</Emphasis>

Phyllanthus amarus (P. amarus) is a herbal plant used in the treatment of various diseases such as hepatitis, diabetes, and cancer. Efficiency of its bioactive compounds extraction and therefore the biological activity of the extracts are significantly influenced by both solvent character and extraction method. This study is aimed at the determination of the influence of six various solvents (water, acetonitrile, ethanol, methanol, ethyl acetate, and dichloromethane) and nine different extraction methods (conventional, ultrasound-assisted, microwave-assisted, and six novel methods) on the extraction efficiency and antioxidant capacity of P. amarus. The results indicated that water extracted the maximal amount of phenolics from P. amarus and had the highest antioxidant capacity, while microwave-assisted extraction provided the highest yields of phenolics and saponins, and the highest antioxidant capacity with the lowest energy consumption when compared to the other extraction methods. These findings implied that water and microwave-assisted extraction are recommended as the most effective solvent and method for the extraction of bioactive compounds from P. amarus for potential application in the pharmaceutical and nutraceutical industries.     

Highly Resolved Pure-Shift Spectra on a Compact NMR Spectrometer

Benchtop NMR spectrometers experience a great success for a wide range of applications. However, their performance is highly limited by peak overlaps. Emerging “pure-shift NMR” (PS NMR) methods have been intensively used at high field to enhance the resolution by homodecoupling strategies. Here, different PS methods have been implemented on a compact NMR spectrometer operating at 43 MHz. Among the PS methods, the recent PSYCHE scheme appears more sensitive than Zangger-Sterk (ZS) experiments and offers a substantial resolution improvement as compared to 1D ¹H. On the other hand, despite their slightly lower sensitivity, ZS methods are more efficient to reduce broad signals and are more immune to strong couplings. Finally, the classical J-resolved pulse sequence is more efficient to reduce larger signals for bigger-sized molecules. The three approaches appear relevant for benchtop NMR and their combination forms an efficient toolbox to analyze a great diversity of samples.     

Magneto-elastic effects in single-crystal USb0.8Te0.2

A high resolution X-ray diffraction study has been performed on a single crystal of USb_0.8Te_0.2. At room temperature this material has the cubic FCC (NaCl) structure. On cooling through the Néel point of 205 K USb_0.8Te_0.2 is known to enter a triple-q antiferromagnetic phase. Below T_C 175 K USb_0.8Te0.2 is a ferromagnet with net magnetisation along the 1 1 1 body diagonal. Four-circle X-ray scattering data from high-symmetry {h O h} and {h h h} reflections are presented as a function of temperature. We confirm that this magnetisation directly leads to a magneto-elastic distortion of the crystal lattice with a rhombohedral extension along the 1 1 1 body diagonals. At 130 K, this distortion is found to correspond to a rhombohedral bond angle of = 89.856° ± 0.004° consistent with previous results. In this single-crystal study we also present evidence for additional associated effects which we attribute to inter-grain stresses and sample mosaic structure.     

Synthesis and utilisation of 2,7′-diindolylmethanes and a 2-(2-indolyl)pyrrolylmethane as macrocyclic precursors

Treatment of 3-(4-chlorophenyl)-7-hydroxymethyl-4,6-dimethoxyindole with 3-(4-chlorophenyl)-4,6-dimethoxyindole results in the generation of two geometrically isomeric diindolylmethanes in addition to a novel triindolyl oligomer, which has been structurally characterised. The 2,7′-diindolylmethanes were found to be unstable under Vilsmeier formylation conditions, thus hampering macrocyle precursor construction. In an alternate approach, the 3-(4-chlorophenyl)-4,6-dimethoxyindole-7-carbaldehyde was converted into the indolyl-pyrrolyl macrocycle precursor 5-(3-(4-chlorophenyl)-4,6-dimethoxyindole-2-ylmethyl)-4-ethyl-3-methylpyrrole-2,7-dicarbaldehyde, which was used to generate an unsymmetrical pentaaza macrocycle.     

Parallel radioisotope collection and analysis in response to the Fukushima release

In order to co-recycle neptunium, uranium and plutonium using the PUREX process, numerical simulations were used to investigate the behaviors of neptunium in the first solvent extraction cycle. Counter-current extraction experiments using a miniature mixer-settler were performed to verify the simulation. Calculated results based on experiments show that the concentrations of nitric and nitrous acid, saturation of uranium, flow ratio and residence time have important effects on the pathway of neptunium, and accumulation of neptunium may appear with the presence of uranium and plutonium.