Isotope separation by a q-switched continuous discharge CO2 laser

For ¹³C isotope separation it is more economic to use a q-swiched CO₂ laser than a TEA laser. It is shown that 40 mJ pulses are needed for full use of photons. With a laser of 20 mJ, isotope selective dissociation of ¹³CHClF₂ and ³²SF₆ is demonstrated in this work.     

Two-photon ionization of Li2: isotopic separation and determination of IP(Li2) and De(Li+2)

Complete isotope separation is achieved by two-photon ionization of Li₂ by a single mode Ar⁺ laser. With the use of two Ar⁺ lasers, the ionization potential of Li₂ is found to be 5.174 ± 0.013 eV, and the dissociation energy D_e(Li⁺₂) to be 1.274 ± 0.019 eV.     

Calciumisotopenseparation und Reaktionsenthalpie. Calciumisotopenseparation und Bestimmung der Reaktionsenthalpie beim Isotopenaustausch an einem stark sauren Kationenaustauscher

Calcium Isotope Separation and Reaction Enthalpy. Calcium Isotope Separation and Determination of Reaction Enthalpy in Ion Exchange Using a Strongly Acidic Cation Exchange Resin In the system of a strongly acidic cation exchanger/BaCl₂ solution the isotope separation between ⁴⁰Ca²⁺ and ⁴⁸Ca²⁺ is investigated using column experiments. ⁴⁸Ca²⁺ is enriched in the solution phase whereas ⁴⁰Ca²⁺ is enriched in the resin phase. A strong dependence of the isotope separation effect on the concentration of the BaCl₂ solution is found. The isotope separation increases with decreasing concentration. The isotope separation also depends on temperature: the isotope separation effect increases with decreasing temperature. A ΔH-value of —5.8 J/mol is determined for the calcium isotope exchange reaction.     

Thermal stability and IR-laser-driven selective photochemistry of a volatile uranyl compound at natural abundance

Molecular beam mass spectrometric measurements have been carried out to investigate the IR-laser chemistry of bis(1,1,1,5,5,5,-hexafluoropentane-2,4-dionato)dioxouranium(VI) tetrahydrofuran [UO₂[(CF₃CO)₂CH]₂] · THF. The compound has been characterized and shown to be stable in the gas phase up to 95°C. An isotope selectivity, factor for ²³⁸U species as high as three was obtained in on-line dissociations of this compound (with natural abundance of uranium isotopes) using the 10P(6) line of a TEA CO₂ laser IR-laser dissociation studies have also been carried out with the vapour in static or flowing condition in a cell. Negligible isotope selectivity is observed in the cell experiments.     

Separation of lithium isotope by azacrown tetramerrifield peptide resin

A study on the separation of lithium isotope was carried out with N₄O azacrown ion exchange resin. The lighter⁶Li isotope concentrated in the solution phase, while the heavier⁷Li isotope is enriched in the resin phase. Upon column chromatography (0.3 cm I.D.×15.5cm height) using 0.5M NH₄Cl as an eluent, single separation factor, α=1.00127 was obtained.     

Application of mercury isotopes and their production

Mercury isotopes are now broadly applied in various fields of science and technology. They are used in medicine, nuclear physics investigations, RF standards, nuclear gyroscopes, mercury analysing devices etc. One of the most promising applications is the use of weakly enriched (up to 3%) isotope¹⁹⁶Hg in fluorescent lamps for enhancing their light efficiency. Besides, the application of²⁰¹Hg and²⁰²Hg as the target material for the production at low-energy cyclotrons of one of the most consumed²⁰¹Tl isotope in medicine seems to be perspective. Various methods were proposed and examined for the separation of mercury isotopes. There are: electromagnetic, photochemical, centrifugal, laser, photoionizing method etc. But only two of them were effective for the mercury isotope separation: electromagnetic and photochemical ones. This paper presents a review of the experimental results on separation of various mercury isotopes by different methods.     

Separation of lithium isotopes with the N3O2 trimerrifield peptide resin

A study on the separation of lithium isotopes was carried out with 1,13-dioxa-4,7,10-triazacyclopentadecane-4,7,10-trimerrifield peptide resin [N₃O₂3M]. The resin having N₃O₂ as an anchor group has a capacity of 0.2 meq/g dry resin. Upon column chromatography [0.1 cm (I.D)×30 cm (height)] using 1.0M NH₄Cl solution as an eluent, a single separation factor of 1.00104 was obtained from the elution curve and isotope ratios based on theGlueckauf theory. The heavier isotope,⁷Li concentrated in the resin phase, while the lighter isotope,⁶Li enriched in the solution phase.     

Green and efficient extraction strategy to lithium isotope separation with double ionic liquids as the medium and ionic associated agent

The paper reported a green and efficient extraction strategy to lithium isotope separation. A 4-methyl-10-hydroxybenzoquinoline (ROH), hydrophobic ionic liquid—1,3-di(isooctyl)imidazolium hexafluorophosphate ([D(i-C₈)IM][PF₆]), and hydrophilic ionic liquid—1-butyl-3-methylimidazolium chloride (ILCl) were used as the chelating agent, extraction medium and ionic associated agent. Lithium ion (Li⁺) first reacted with ROH in strong alkali solution to produce a lithium complex anion. It then associated with IL⁺ to form the Li(RO)₂IL complex, which was rapidly extracted into the organic phase. Factors for effect on the lithium isotope separation were examined. To obtain high extraction efficiency, a saturated ROH in the [D(i-C₈)IM][PF₆] (0.3 mol l^?1), mixed aqueous solution containing 0.3 mol l^?1 lithium chloride, 1.6 mol l^?1 sodium hydroxide and 0.8 mol l^?1 ILCl and 3:1 were selected as the organic phase, aqueous phase and phase ratio (o/a). Under optimized conditions, the single-stage extraction efficiency was found to be 52 %. The saturated lithium concentration in the organic phase was up to 0.15 mol l^?1. The free energy change (ΔG), enthalpy change (ΔH) and entropy change (ΔS) of the extraction process were ?0.097 J mol^?1, ?14.70 J mol K^?1 and ?48.17 J mol^?1 K^?1, indicating a exothermic process. The partition coefficients of lithium will enhance with decrease of the temperature. Thus, a 25 °C of operating temperature was employed for total lithium isotope separation process. Lithium in Li(RO)₂IL was stripped by the sodium chloride of 5 mol l^?1 with a phase ratio (o/a) of 4. The lithium isotope exchange reaction in the interface between organic phase and aqueous phase reached the equilibrium within 1 min. The single-stage isotope separation factor of ⁷Li–⁶Li was up to 1.023 ± 0.002, indicating that ⁷Li was concentrated in organic phase and ⁶Li was concentrated in aqueous phase. All chemical reagents used can be well recycled. The extraction strategy offers green nature, low product cost, high efficiency and good application prospect to lithium isotope separation.     

Dynamics of the dissociation of thes-tetrazine dication produced by one photon excitation of the neutral molecule

¹³C isotope separation by multiphoton dissociation of CHClF₂ was studied by a continuous-discharge CO₂ laserQ-switched at 8 kHz. This laser can easily emit two or more wavelengths with good spatial and temporal overlap. The best irradiation results were obtained by the line pair 9P16 + 9P28. After optimizing also the pressures of CHClF₂ and of buffer gases (He and Ar), the energy density and the gas speed, the process is now much less nonlinear than in previous experiments with a single wavelength. Differences to the TEA laser induced process were observed, and generally the pressure influence on yield and selectivity showed a variety of phenomena. They were interpreted in terms of collisional changes of spectra during the laser pulse.     

The Influence of Electric Parameters on the Dynamics of the Electrokinetic Decontamination of Soils

Elution chromatographic separation of lithium isotopes was carried out with aminobenzo-15-crown-5 bonded merrifield resin. This resin have a capacity of 0.24 meq/g dry resin. By column chromatography using 1.0M NH₄Cl solution as an eluent, a single separation factor 1.026 was obtained from the elution curve and isotope ratios according to the Glucckauf theory. The heavier isotope, ⁷Li was concentrated in the resin phase, while the lighter isotope, ⁶Li enriched in the solution phase.     

Simultaneous production of89Zr and90,91m92mNb in α-particle activated yttrium and their subsequent separation by TOA

A study on the separation of lithium isotopes was carried out with an ion exchange resin having 1,7,13-trioxa-4,10,16-triazacyclooctadecane (N₃O₃) as an anchor group. The lighter isotope,⁶Li concentrated in the resin phase, while the heavier isotope,⁷Li is enriched in the fluid phase. Upon column chromatography [0.6 cm (I. D.)×20 cm (height)] using 1.0M ammonium chloride solution as an eluent, single separation factor, , 1.068 (⁶Li/⁷Li)_resin/(⁶Li/⁷Li)_solution was obtained by theGlueckauf method from the elution curve and isotope ratios.     

Separation of lithium isotopes by N4S2 azacrown ion exchanger

The novel N₄S₂ azacrown ion exchange resin was prepared. The ion exchange capacity of N₄S₂ ion exchanger was 0.34 meq/g dry resin. A study on the separation of lithium isotopes was carried out with N₄S₂ azacrown ion exchange resin. The lighter isotope,⁶Li is concentrated in the resin phase, while the heavier isotope,⁷Li is enriched in the solution phase. With column chromatography [0.1 cm (I.D.)×32 cm (height)] using 2.0M NH₄Cl as an eluent, separation factor, a=1.034 was obtained.     

Anomalously large kinetic isotope effect

Activated diffusion of water between macromolecules in swollen cellulose is accompanied by anomalously high kinetic isotope effects of oxygen. The separation factor of heavy-oxygen water (H₂ ¹⁸O /H₂ ¹⁶O) is thousands of permilles instead of tens of permilles according to modern Absolute Rate Theory. This anomalous separation under usual conditions is disguised by the opposing process of very fast equalization to equilibrium through water-filled cellulose pores. This process is quicker by approximately 3 orders of magnitude than diffusion through the cellulose body. As a consequence, this opposition-directed equalization virtually eliminates the results of isotope separation. To reveal this anomaly it is necessary to suppress equalization, which was the primary problem for both discovery of this anomaly and its investigation. The method of investigating the anomalous separation in cellulose was developed with suppression of this negative influence. Discussion of the theoretical nature of the anomalous kinetic isotope effect is presented. This theoretical study would probably permit the discovery and use for isotope separation of the anomalously high isotope effect for other chemical elements, in particular, for those heavier than oxygen.      

Perspectives of laser-chemical isotope separation of a long-lived fission product: cesium-135

The cesium isotope ¹³⁵Cs has an extremely long half-life (τ_1/2 = 2.3 · 10⁶ y) and its high water solubility leads to the anxiety of exudation to ground water during geological disposal. Such a LLFP ¹³⁵Cs would be converted into ¹³⁶Cs (Its half-life is 13.16 d and it becomes stable ¹³⁶Ba) by neutron capture reaction. However intermingling ¹³³Cs of which the natural abundance is 100% disturbs this nuclear converting reaction because ¹³³Cs also absorbs neutrons and produces ¹³⁵Cs again. For separating ¹³⁵Cs from other cesium isotopes, laser-chemical isotope separation (LCIS) is believed to be suitable mainly due to the light absorption and emission stability. Isotope separation of alkali metal ⁸⁵Rb/⁸⁷Rb was successfully achieved, showed 23.9 of head separation factor by LCIS. The measured isotope shift of Cs D₂ line is within the reach of available semiconductor lasers having emission line width of less than 1 MHz, which shows that the selective excitation of ¹³⁵Cs may turn to be possible. It is known that cesium excited to the 6²P_3/2 state may forms cesium hydride while ground-state cesium does not. Therefore if the lifetime of 6²P_3/2 state is sufficiently longer than the inverse rate of the chemical reaction, ¹³⁵Cs can be extracted as cesium hydride. Applicability of the Doppler-free two-photon absorption method for selective excitation and further evaluation on Rydberg states and ionization should be investigated.     

Chemical separation of the unknown isotope 252Bk

Rapid chemical separation of berkelium is essential in order to measure the unknown isotope ²⁵²Bk. An anion exchange system of mineral acid and methanol was examined. An elution curve of Bk was obtained using ²⁵⁰Bk produced by the ²⁴⁸Cm+¹⁸O system and the ²⁵¹Bk activity could be measured in the preliminary experiments. The whole chemical separation was completed within 30 minutes.     

A modified lead–matrix separation procedure shown for lead isotope analysis in Trojan silver artefacts as an example

A modified Pb–matrix separation procedure using NH₄HCO₃ solution as eluent has been developed and validated for determination of Pb isotope amount ratios by thermal ionization mass spectrometry. The procedure is based on chromatographic separation using the Pb·Spec resin and an in-house-prepared NH₄HCO₃ solution serving as eluent. The advantages of this eluent are low Pb blanks (<40 pg?mL^?1) and the property that NH₄HCO₃ can be easily removed by use of a heating step (>60 °C). Pb recovery is >95 % for water samples. For archaeological silver samples, however, the Pb recovery is reduced to approximately 50 %, but causes no bias in the determination of Pb isotope amount ratios. The validated procedure was used to determine lead isotope amount ratios in Trojan silver artefacts with expanded uncertainties (k?=?2) <0.09 %.     

IR multiphoton absorption and isotopically selective dissociation of CHCIF2 in a herriott multipass cell

The small absorption is a major problem in isotopically selective IR multiphoton dissociation. Usually the radiation diverges before it is fully absorbed. To solve this problem, we have demonstrated the application of a refocusing (Herriott) multipass cell. It can generally help in laser isotope separation to use the photons more efficiently. Employing such a cell and a Q-switched CO₂ laser at high repetition rate, the dissociation yield of CHCIF₂ was 23 times higher than in a single pass. The number of passes used (up to 60) was more than is conventionally possible in such small cells. The increased number was permitted by making use of spherical aberration. With 18 passes, we also measured the multiphoton absorption for various wavelengths and pressures, in part separately for¹²CHCIF₂ and¹³CHCIF₂, and also for two-wavelength irradiation. Appropriate change of pressure or wavelength increased the absorption. But the corresponding increase of the dissociation was larger in every case. To explain this and other observations, we invoke the molecular distribution over the energy levels.     

Negative thermal ionization mass spectrometry of selenium part 3.* Selenium trace determination in food samples

Summary Selenium traces are analysed in different animal tissue samples with isotope dilution mass spectrometry using the formation of negative Se^– thermal ions (NTI-IDMS) for isotope ratio measurements. An enriched⁸²Se spike is applied for the isotope dilution technique. After decomposition of the food samples with a HNO₃/HCIO₄ mixture selenium is separated by the formation of SeH₂ using a hydride generation system which is normally applied for atomic absorption spectrometry. Selenium hydride is absorbed in a cone. HNO₃ solution, from which sample mass spectrometric determinations are carried out. The recovery of selenium for the total sample treatment has been determined with a⁷⁵Se tracer to be about 62%. The precision of the IDMS method in the concentration range of 0.1–10 g/g lies between 1.8% and 4.1 %. The IDMS results agree well with the certified values of the analysed standard reference materials. A comparison of these results with those achieved by an isotope dilution method, using the formation of piazselenol and gas-chromatographic separation (GC-IDMS), and by hydride generation atomic absorption spectrometry (HGAAS) is given. Whereas the NTI-IDMS and GC-IDMS results are in very good agreement, HGAAS can be affected by interferences.

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Negative Thermionen-Massenspektrometrie von Selen Teil 3. Selenspurenbestimmung in Lebensmittelproben

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Part 2: see [131

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Dedicated to Prof. Dr. G. Tölg on the occasion of his 60th birthday     

Precise and accurate compound-specific carbon and nitrogen isotope analysis of RDX by GC-IRMS

A new analytical method is presented for the compound-specific carbon and nitrogen isotope ratio analysis of a thermo-labile nitramine explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by gas chromatograph coupled to an isotope ratio mass spectrometer (GC-IRMS). Two main approaches were used to minimise thermal decomposition of the compound during gas chromatographic separation: programmed temperature vaporisation (PTV) as an injection technique and a high-temperature ramp rate during the GC run. δ¹⁵N and δ¹³C values of RDX measured by GC-IRMS and elemental analyser (EA)-IRMS were in good agreement within a standard deviation of 0.3‰ and 0.4‰ for nitrogen and carbon, respectively. Application of the method for the isotope analysis of RDX during alkaline hydrolysis at 50°C revealed isotope fractionation factors ε _carbon?=??7.8‰ and ε _nitrogen?=??5.3‰.     

Laser ablation isotope ratio mass spectrometry for enhanced sensitivity and spatial resolution in stable isotope analysis

Stable isotope analysis permits the tracking of physical, chemical, and biological reactions and source materials at a wide variety of spatial scales. We present a laser ablation isotope ratio mass spectrometry (LA‐IRMS) method that enables δ¹³C measurement of solid samples at 50 µm spatial resolution. The method does not require sample pre‐treatment to physically separate spatial zones. We use laser ablation of solid samples followed by quantitative combustion of the ablated particulates to convert sample carbon into CO₂. Cryofocusing of the resulting CO₂ coupled with modulation in the carrier flow rate permits coherent peak introduction into an isotope ratio mass spectrometer, with only 65 ng carbon required per measurement. We conclusively demonstrate that the measured CO₂ is produced by combustion of laser‐ablated aerosols from the sample surface. We measured δ¹³C for a series of solid compounds using laser ablation and traditional solid sample analysis techniques. Both techniques produced consistent isotopic results but the laser ablation method required over two orders of magnitude less sample. We demonstrated that LA‐IRMS sensitivity coupled with its 50 µm spatial resolution could be used to measure δ¹³C values along a length of hair, making multiple sample measurements over distances corresponding to a single day's growth. This method will be highly valuable in cases where the δ¹³C analysis of small samples over prescribed spatial distances is required. Suitable applications include forensic analysis of hair samples, investigations of tightly woven microbial systems, and cases of surface analysis where there is a sharp delineation between different components of a sample. Copyright © 2011 John Wiley & Sons, Ltd.