A mass spectrometric line for tritium analysis of water and noble gas measurements from different water amounts in the range of microlitres and millilitres

This paper describes the procedure followed for noble gas measurements for litres, millilitres and microlitres of water samples in our laboratory, including sample preparation, mass spectrometric measurement procedure, and the complete calibrations. The preparation line extracts dissolved gases from water samples of volumes of 0.2?μ l to 3?l and it separates them as noble and other chemically active gases. Our compact system handles the following measurements: (i) determination of tritium concentration of environmental water samples by the (3)He ingrowth method; (ii) noble gas measurements from surface water and groundwater; and (iii) noble gas measurements from fluid inclusions of solid geological archives (e.g. speleothems). As a result, the tritium measurements have a detection limit of 0.012 TU, and the expectation value (between 1 and 20 TU) is within 0.2 % of the real concentrations with a standard deviation of 2.4 %. The reproducibility of noble gas measurements for water samples of 20-40?ml allows us to determine solubility temperatures by an uncertainty better than 0.5?°C. Moreover, noble gas measurements for tiny water amounts (in the microlitre range) show that the results of the performed calibration measurements for most noble gas isotopes occur with a deviation of less than 2 %. Theoretically, these precisions for noble gas concentrations obtained from measurements of waters samples of a few microlitres allow us to determine noble gas temperatures by an uncertainty of less than 1?°C. Here, we present the first noble gas measurements of tiny amounts of artificial water samples prepared under laboratory conditions.     

Increasing the performance of tritium analysis by electrolytic enrichment†

Several improvements are described for the existing tritium enrichment system at the Isotope Hydrology Laboratory of the International Atomic Energy Agency for processing natural water samples. The improvements include a simple method for pretreatment of electrolytic cells to ensure a high tritium separation factor, an improved design of the exhaust system for explosive gases, and a vacuum distillation line for faster initial preparation of water samples for electrolytic enrichment and for tritium analysis. Achievements included the reduction of variation of individual enrichment parameters of all cells to less than 1% and an improvement of 50% of the stability of the background mean. It resulted in an improved detection limit of less than 0.4 TU (at 2s), important for application of tritium measurements in the future at low concentration levels, and resulted in measurement precisions of±0.2 TU and±0.15 TU for liquid scintillation counting and for gas proportional counting, respectively.     

Assessment of the origin and geothermal potential of the thermal waters by hydro-isotope geochemistry: Eskisehir province,Turkey

The thermal fluids vented over Eskisehir province have been investigated for their origin and to estimate the geothermal potential of the area. Thermal waters as well as bubbling and dissolved gases were collected and analysed for their chemical and isotopic features. Their isotopic composition varies in the range from ?11.5 to ?7.7?‰ for δ¹⁸O, ?84 and ?57?‰ for δ²H, and 0–7.2 TU for tritium. The gases (bubbling and dissolved) are mostly N₂-dominated with a significant amount of CO₂. The helium isotopic ratios are in the range of 0.2–0.66?R/Rac, indicate remarkable mantle-He contribution ranging between 2 and 10?% in the whole study area. Considering the estimated geothermal gradient about three times higher than the normal gradient, and the reservoir temperatures estimated to be between 50 and 100?°C using quartz and chalcedony geothermometers, a circulation model was built where possible mixing with shallow waters cool down the uprising geothermal fluids.     

Absolute validation of a diode laser hygrometer via intercomparison with the German national primary water vapor standard

Direct tunable diode laser absorption spectroscopy (dTDLAS) is a powerful diagnostic technique for absolute and accurate gas analysis with highest chemical specificity. Due to its first principles approach, dTDLAS is often claimed to be “calibration-free”, but this and the absolute accuracy has not been rigorously validated with respect to a high-accuracy reference. This work describes the first rigorous, side-by-side comparison of a dTDLAS hygrometer—called SEALDH—with a highly accurate, internationally validated, primary reference humidity generator (PHG), which also serves as the German national H₂O-standard. This PHG provides a humidified air stream with dew points between ?30 °C and +60 °C with an uncertainty of 0.035 K (2σ) (equivalent relative H₂O mixing ratio uncertainty: 0.4 %). Without any previous calibration, SEALDH was found to accurately reproduce the PHG reference values over the full range from 600 to 20,000 ppmv investigated in the 1-week lab study. Over this range, the SEALDH–PHG relative deviation was in average ?1.45 %, the worst case being ?2.5 % at 1,000 ppmv, the best ?0.2 % at 600 ppmv. As SEALDH’s relative uncertainty was metrologically determined to be 4.3 % (k = 2), these deviations are for all concentration steps in full compliance with the PHG reference. Systematic contributions to the relative deviation could be correlated with line shape deviations between the measured line profile and the fitted Voigt line shape. Using this information, SEALDHs absolute accuracy can be improved further to down to an average relative deviation to the PHG of +0.21 %.     

Assessing the use of 3H–3He dating to determine the subsurface transit time of cave drip waters

³H–³He measurements constitute a well-established method for the determination of the residence time of young groundwater. However, this method has rarely been applied to karstified aquifers and in particular to drip water in caves, despite the importance of the information which may be obtained. Besides the determination of transfer times of climate signals from the atmosphere through the epikarst to speleothems as climate archives, ³H–³He together with Ne, Ar, Kr, Xe data may also help to give new insights into the local hydrogeology, e.g. the possible existence of a perched aquifer above a cave. In order to check the applicability of ³H–³He dating to cave drips, we collected drip water samples from three adjacent caves in northwestern Germany during several campaigns. The noble gas data were evaluated by inverse modelling to obtain recharge temperature and excess air, supporting the calculation of the tritiogenic ³He and hence the ³H–³He age. Although atmospheric noble gases were often found to be close to equilibrium with the cave atmosphere, several drip water samples yielded an elevated ³He/⁴He ratio, providing evidence for the accumulation of ³He from the decay of ³H. No significant contribution of radiogenic ⁴He was found, corresponding to the low residence times mostly in the range of one to three years. Despite complications during sampling, conditions of a perched aquifer could be confirmed by replicate samples at one drip site. Here, the excess air indicator ΔNe was about 10 %, comparable to typical values found in aquifers in mid-latitudes. The mean ³H–³He age of 2.1 years at this site presumably refers to the residence time in the perched aquifer and is lower than the entire transit time of 3.4 years estimated from the tritium data.     

On the conversion of tritium units to mass fractions for hydrologic applications

We develop a general equation for converting laboratory-reported tritium levels, expressed either as concentrations (tritium isotope number fractions) or mass-based specific activities, to mass fractions in aqueous systems. Assuming that all tritium is in the form of monotritiated water simplifies the derivation and is shown to be reasonable for most environmental settings encountered in practice. The general equation is nonlinear. For tritium concentrations c less than 4.5×10¹² tritium units (TU) – i.e. specific tritium activities<5.3×10¹¹ Bq kg^?1 – the mass fraction w of tritiated water is approximated to within 1 part per million by w ≈ c×2.22293×10^?18, i.e. the conversion is linear for all practical purposes. Terrestrial abundances serve as a proxy for non-tritium isotopes in the absence of sample-specific data. Variation in the relative abundances of non-tritium isotopes in the terrestrial hydrosphere produces a minimum range for the mantissa of the conversion factor of [2.22287; 2.22300].     

Role of water contamination within the GC column of a GasBench II peripheral on the reproducibility of 18O/16O ratios in water samples

The GasBench II peripheral along with MAT 253 combination provides a more sensitive platform for the determination of water isotope ratios. Here, we examined the role of adsorbed moisture within the gas chromatography (GC) column of the GasBench II on measurement uncertainties. The uncertainty in ¹⁸O/¹⁶O ratio measurements is determined by several factors, including the presence of water in the GC. The contamination of GC with water originating from samples as water vapour over a longer timeframe is a critical factor in determining the reproducibility of ¹⁸O/¹⁶O ratios in water samples. The shift in isotope ratios observed in the experiment under dry and wet conditions correlates strongly with the retention time of analyte CO₂, indicating the effect of accumulated moisture. Two possible methods to circumvent or minimise the effect of adsorbed water on isotope ratios are presented here. The proposed methodology includes either the regular baking of the GC column at a higher temperature (120 °C) after analysis of a batch of 32 sample entries or conducting the experiment at a low GC column temperature (22.5 °C). The effects of water contamination on long-term reproducibility of reference water, with and without baking protocol, have been described.     

Photoacoustic spectrometer for accurate,continuous measurements of atmospheric carbon dioxide concentration

We have developed a portable photoacoustic spectrometer that offers routine, precise and accurate measurements of the molar concentration of atmospheric carbon. The temperature-controlled spectrometer continuously samples dried atmospheric air and employs an intensity-modulated distributed feedback laser and fiber amplifier operating near 1.57 µm. For measurements of carbon dioxide in air, we demonstrate a measurement precision (60-s averaging time) of 0.15 µmol mol^?1 and achieve a standard uncertainty of 0.8 µmol mol^?1 by calibrating the analyzer response in terms of certified gas mixtures. We also investigate how water vapor affects the photoacoustic signal by promoting collisional relaxation of the carbon dioxide.     

Linking chloride mass balance infiltration rates with chlorofluorocarbon and SF6 groundwater dating in semi-arid settings: potential and limitations

In the framework of the investigation of enrichment processes of nitrate in groundwater of the Kalahari of Botswana near Serowe, recharge processes were investigated. The thick unsaturated zone extending to up to 100 m of mostly unconsolidated sediments and very low recharge rates pose a serious challenge to study solute transport related to infiltration and recharge processes, as this extends past the conventional depths of soil scientific investigations and is difficult to describe using evidence from the groundwater due to the limitations imposed by available tracers. To determine the link between nitrate in the vadose zone and in the uppermost groundwater, sediment from the vadose zone was sampled up to a depth of 15–20 m (in one case also to 65 m) on several sites with natural vegetation in the research area. Among other parameters, sediment and water were analysed to determine chloride and nitrate concentration depth profiles. Using the chloride mass balance method, an estimation of groundwater infiltration rates produced values of 0.2–4 mm a^?1. The uncertainty of these values is, however, high. Because of the extreme thickness of the vadose zone, the travel time in the unsaturated zone might reach extreme values of up to 500 years and more. For investigations using groundwater, we applied the chlorofluorocarbons CFC-113, CFC-12, sulphur hexafluoride (SF₆) and tritium to identify potential recharge, and found indications for some advective transport of the CFCs and SF₆, which we accounted for as constituting potential active localised recharge. In our contribution, we show the potential and limitations of the applied methods to determine groundwater recharge and coupled solute transport in semi-arid settings, and compare travel time ranges derived from soil science and groundwater investigations.     

惰性气体黏度的剩余熵标度模型

黏度是能源、动力、化工等系统设计分析中常用的重要物性参数.本文探讨了5种惰性气体(He、Ne、Ar、Kr、Xe)气相和超临界黏度的计算,以实际气体与同温度稀薄气体的黏度之比作为无量纲对比黏度,发现5种惰性气体的无量纲对比黏度与剩余熵之间满足同一单值函数关系,据此建立了惰性气体的气相和超临界黏度模型,其中稀薄气体黏度关联...     

Segregation of vapor and gas in a sonoluminescing bubble

Computer simulations of bubble oscillations in water are performed for various noble gases taking into account the segregation of water vapor and noble gas inside a collapsing bubble, which was predicted by Storey and Szeri [J. Fluid Mech. 396 (1999) 203]. It is clarified that the number of water vapor molecules dissociated inside a collapsing bubble is larger for heavier noble gases because of the lower thermal conductivity and the segregation of vapor and noble gas. It is also clarified that the temperature inside a helium bubble at the collapse increases considerably by the mixture segregation because a lesser amount of vapor is trapped inside a collapsing bubble. It is also clarified that multibubble sonoluminescence (MBSL) from heavier noble gases is brighter because of the lower ionization potential which results in the higher electron density and stronger plasma emissions.     

Measurements of radon concentration levels in thermal waters in the region of Konya,Turkey

²²²Rn (radon) is one of the most important sources of natural radiation to which people are exposed. It is an alpha-emitting noble gas and it can be found in various concentrations in soil, air and in different kinds of water. In this study, we present the results of radon concentration measurements in thermal waters taken from the sources in the region of Konya located in the central part of Turkey. The radon activity concentrations in 10 thermal water samples were measured by using the AlphaGUARD PQ 2000PRO radon gas analyser in spring and summer of the year 2012. We found that radon activity concentrations range from 0.60±0.11 to 70.34±3.55 kBq m^?3 and from 0.67±0.03 to 36.53±4.68 kBq m^?3 in spring and summer, respectively. We also calculated effective doses per treatment in the spas for the spring and summer seasons. It was found that the minimum and maximum effective doses per treatment are in the range of 0.09–10.13 nSv in spring and in the range of 0.1–5.26 nSv in summer.     

Magnetically-coupled piston pump for high-purity gas applications

Experiments based on noble elements such as gaseous or liquid argon or xenon utilize the ionization and scintillation properties of the target materials to detect radiation-induced recoils. A requirement for high light and charge yields is to reduce electronegative impurities well below the ppb (parts per billion, 1 ppb \(=1\times 10^{-9}\) mol/mol) level. To achieve this, the target material is continuously circulated in the gas phase through a purifier and returned to the detector. Additionally, the low backgrounds necessary dictate low-Rn-emanation rates from all components that contact the gas. Since commercial pumps often introduce electronegative impurities from lubricants on internal components or through small air leaks, and are not designed to meet the radiopurity requirements, custom-built pumps are an advantageous alternative. A new pump has been developed in Muenster in cooperation with the nEXO group at Stanford University and the nEXO/XENON group at Rensselaer Polytechnic Institute based on a magnetically-coupled piston in a hermetically sealed low-Rn-emanating vessel. This pump delivers high performance for noble gases, reaching more than 210 standard liters per minute (slpm) with argon and more than 170 slpm with xenon while maintaining a compression of up to 1.9 bar, demonstrating its capability for noble gas detectors and other applications requiring high standards of gas purity.     

Isotope-analytical results of a study of gas generation in L/ILW

The paper presents the results of a long-term measurement series using hermetic containers to make more precise quantitative estimation of the generation rates and radioactivity of the gas in a drum of low and intermediate level radioactive waste (L/ILW) packages. Development of special preparation lines and isotope-analytical measurements of the headspace gas samples were performed in the ATOMKI. Stable isotope measurements were executed from the CO₂ and CH₄ fractions by stable isotope ratio mass spectrometer. Noble gas (He) measurements were done by noble gas mass spectrometer. The tritium content of the vapour, H₂ and CH₄ fractions was measured in H₂O chemical form by a low background liquid scintillation counter. The ¹⁴C content of the CO₂ and CH₄ fractions of the headspace gas samples was measured by a low background gas proportional counter system.     

The formation of molecular hydrogen through photolysis of water vapor in the presence of oxygen

1. A light source was constructed for the investigation of the photolysis of water vapor. A xenon discharge arc of a pressure of about 50 mm in a thin wall quartz tubing was used. 2. Molecular hydrogen formed from water vapor in the presence of other gases was measured by employing tritium as a tracer. A vacuum system was constructed, allowing the separation of water vapor from hydrogen to better than 10^?8 parts, and the counting of tritiated hydrogen in a Geiger counter. All measurements were carried out in a semi-quantitative way and it was found that the light source and the technique of measuring small amounts of free hydrogen by employing a tritium tracer can be used effectively for further studies of the reactions involving hydrogen and water. 3. Self-decomposition of tritiated water vapor with and without addition of oxygen was measured and was found to be negligible under the particular conditions of the experiments over periods of several months. 4. The photochemically induced exchange of tritium between tritiated water vapor and molecular hydrogen was studied. The quantum yield of this exchange was found to be under the conditions of the experiments of the order of one and probably slightly larger than one. 5. It was possible to demonstrate the formation of free hydrogen from the photolysis of water vapor in the presence of oxygen and to measure these amounts as a function of oxygen pressure. The steady state concentrations of H₂ formed from water vapor by irradiation in the presence of oxygen under the influence of UV light were found to be smaller than expected. 6. Photochemical oxidation of H₂ by O₂ under the particular conditions of the experiments and at pressures of about one millimeter was found to have a quantum yield of the order of magnitude of one.     

The thermal conductivity of three polyatomic gases and air at 27.5°C and pressures up to 36 MPa

The paper reports accurate measurements of the thermal conductivity of ethane, ethylene, nitrous oxide, air and argon-free air as a function of density at a temperature of 27.5°C. In the case of ethane the experimental data extend over the pressure range 0.6–3.4 MPa, for ethylene over the range 0.6–5 MPa and for nitrous oxide over the range 0.6–4.5 MPa. The measurements on the two samples of air cover the range 0.8–36 MPa. All the measurements have been carried out in a transient hot-wire instrument and have an estimated uncertainty of ±0.2%.For air the few experimental data that exist deviate by up to 5% from the present results which are to be preferred owing to their higher accuracy. In the case of the pure gases the experimental data are combined with accurate viscosities and employed to estimate collision numbers for rotational relaxation in the gases.     

High-energy femtosecond laser pulse compression in single- and multi-ionization regime of rare gases: experiment versus theory

We report experimental and numerical results on the post-compression of 40 fs duration pulses down to 10 fs at high energy level (multi-mJ). The spectral broadening is achieved through the self-phase modulation resulting from optical-field-ionization of different noble gases (He, Ne, Ar) by the 40-fs laser pulse propagating in a low-pressure gas-filled hollow capillary. We discuss the influence of the multi-ionization dynamics, through the gas dependence, on the laser energy carried by the capillary, as well as on the duration and temporal shape of the post-compressed pulses. In all the different experimental conditions investigated in this article (pressures and gases used), the experimental data is in good agreement with the numerical results from a three-dimension propagation code. Through this study, we demonstrate the robustness of the proposed post-compression technique with regard to multi-ionization, indicating that it can be used on a large intensity range by judiciously choosing the gas.     

Ultra trace determination of fluorobenzoic acids in reservoir and ground water using isotope dilution gas chromatography mass spectrometry

The accurate ultra-trace analysis of six fluorobenzoic acids (FBAs) via isotope dilution gas chromatography mass spectrometry through their deuterated analogues is described. North Sea reservoir and ground water samples were spiked with six deuterated FBAs (dFBAs), enriched using solid-phase extraction (SPE) and analysed using GC/MS after derivatisation with BF ₃· MeOH. All FBAs were enriched and determined simultaneously. SPE allowed a 250-fold enrichment of the acids if 100 mL of sample volume was used. The method enables the determination of FBAs down to the range of 8–37 ng L ^?1 with recoveries between 66 % and 85 %. It uses low amounts of chemicals and is adaptable to larger and smaller sample volumes.     

Fluorescence spectroscopy of anisole at elevated temperatures and pressures

Laser-induced fluorescence of anisole as tracer of isooctane at an excitation wavelength of 266 nm was investigated for conditions relevant to rapid compression machine studies and for more general application of internal combustion engines regarding temperature, pressure, and ambient gas composition. An optically accessible high pressure and high temperature chamber was operated by using different ambient gases (Ar, N₂, CO₂, air, and gas mixtures). Fluorescence experiments were investigated at a large range of pressure and temperature (0.2–4 MPa and 473–823 K). Anisole fluorescence quantum yield decreases strongly with temperature for every considered ambient gas, due to efficient radiative mechanisms of intersystem crossing. Concerning the pressure effect, the fluorescence signal decreases with increasing pressure, because increasing the collisional rate leads to more important non-radiative collisional relaxation. The quenching effect is strongly efficient in oxygen, with a fluorescence evolution described by Stern–Volmer relation. The dependence of anisole fluorescence versus thermodynamic parameters suggests the use of this tracer for temperature imaging in specific conditions detailed in this paper. The calibration procedure for temperature measurements is established for the single-excitation wavelength and two-color detection technique.     

Optical spectra of water sonoluminescence

The sonolumiescence spectra of water saturated with noble gases were studied in a 220–500 nm interval. Total light power of sonoluminescence and the rate of hydrogen peroxide formation were measured. The number of photons emitted by OH^*-radicals was compared with the yield of OH-radicals. The intensity of the shortwave part of the spectra and the OH^*/OH ratio increased while the atomic weight of the gas increased.