The rotational spectrum,nuclear spin—spin coupling,nuclear quadrupole coupling,and molecular structure of KrHF

Rotational spectra have been assigned for the ⁸²Kr, ⁸³Kr, ⁸⁴Kr, and ⁸⁶Kr isotopic species of the KrHF and KrDF van der Waals molecules by using pulsed microwave Fourier transform spectroscopy in a Fabry—Perot cavity with a pulsed supersonic nozzle molecular source. The rotational, centrifugal distortion, nuclear spin—spin, and nuclear quadrupole coupling constants are used to determine the structure and obtain intramolecular potential binding information. The ⁸³Kr nuclear quadrupole coupling constants are 10.28 ± 0.08 MHz and 13.83 ± 0.13 MHz for KrHF and KrDF respectively. The electric field gradient at the krypton nucleus is calculated from the coupling constant and the known nuclear quadrupole moment and explained by Sternheimer shielding and formation of the van der Waals bond. There is a negligible charge transfer in the KrHF bond.     

83Kr nuclear magnetic moment in terms of that of 3He

High resolution NMR spectroscopy was applied to precisely determine the ⁸³Kr nuclear magnetic dipole moment on the basis of new results available for nuclear magnetic shielding in krypton and helium‐3 atoms. Small amounts of ³He as the solutes and ⁸³Kr as the buffer gas were observed in ³He and ⁸³Kr NMR spectra at the constant external field, B₀ = 11.7578 T. In each case, the resonance frequencies (ν^He and ν^Kr) were linearly dependent on the density of gaseous solvent. The extrapolation of experimental points to the zero density of gaseous krypton allowed for the evaluation of both resonance frequencies free from intermolecular interactions. By combining these measurements with the recommended ⁸³Kr chemical shielding value, the nuclear magnetic moment could be determined with much better precision than ever before, μ(⁸³Kr) = ?0.9707297(32)μ_N, with the improvement due to the greater accuracy of the spectral data. Copyright © 2014 John Wiley & Sons, Ltd.     

Quantitative and isotopic analysis of released and retained krypton and xenon fission gases from irradiated metallic fuels

We quantitatively measured the amounts and isotopic distributions of the released and retained fission gases (Kr and Xe) from two irradiated metallic fuels (U–10Zr and U–10Zr–5Ce) at approximately 2.9 at.% burnup, using a gas chromatography and a quadrupole mass spectrometer. The obtained Xe/Kr ratios indicate that the released and retained fission gases from the irradiated metallic fuels came primarily from the fission of ²³⁵U, instead of that of heavy isotopes such as ²³⁹Pu and ²⁴¹Pu. The calculated (⁸³Kr + ⁸⁴Kr)/⁸⁶Kr and (¹³¹Xe + ¹³²Xe)/¹³⁴Xe ratios suggest that no fuel rods became defective during the irradiation process.     

Microwave spectra and structures of KrAuF, KrAgF, and KrAgBr; 83Kr nuclear quadrupole coupling and the nature of noble gas-noble metal halide bonding

Microwave spectra of the complexes KrAuF and KrAgBr have been measured for the first time using a cavity pulsed jet Fourier transform microwave spectrometer. The samples were prepared by laser ablation of the metal from its solid and allowing the resulting plasma to react with an appropriate precursor (Kr, plus SF6 or Br2) contained in the backing gas of the jet (usually Ar). Rotational constants; geometries; centrifugal distortion constants; vibration frequencies; and 197Au, 79Br, and 81Br nuclear quadrupole coupling constants have all been evaluated. The complexes are unusually rigid and have short Kr-Au and Kr-Ag bonds. The 197Au nuclear quadrupole coupling constant differs radically from its value in an AuF monomer. In addition 83Kr hyperfine structure has been measured for KrAuF and the previously reported complex KrAgF. The geometry of the latter has been reevaluated. Large values for the 83Kr nuclear quadrupole coupling constants have been found for both complexes. Both the 197Au and 83Kr hyperfine constants indicate a large reorganization of the electron distribution on complex formation. A thorough assessment of the nature of the noble gas-noble metal bonding in these and related complexes (NgMX; Ng is a noble gas, M is a noble metal, and X is a halogen) has been carried out. The bond lengths are compared with sums of standard atomic and ionic radii. Ab initio calculations have produced dissociation energies along with Mulliken populations and other data on the electron distributions in the complexes. The origins of the rigidity, dissociation energies, and nuclear quadrupole coupling constants are considered. It is concluded that there is strong evidence for weak noble gas-noble metal chemical bonding in the complexes.     

EPR Spectrum of Kr2F

An intense EPR spectrum observed in UV-irradiated solid Kr/CF₃OF solutions at 10 K shows anisotropic hyperfine interactions of a single unpaired electron with one nuclear spin of $\text{1}\text{2}$ and (using isotopically enriched ⁸³Kr) two equivalent spins of $\text{9}\text{2}$. The spectrum is attributed to the linear radical KrFKr having a ²Σ_u ground state.     

Rotational spectra, structures, hyperfine constants, and the nature of the bonding of KrCuF and KrCuCl

Rotational spectra of KrCuF and KrCuCl have been measured in the frequency range 8-18 GHz, using a pulsed jet cavity Fourier transform microwave spectrometer. The molecules were prepared by ablating Cu metal with a pulsed Nd:YAG laser (1064 nm) and allowing the plasma to react with appropriate precursors (Kr plus SF(6) or Cl(2)) contained in the backing gas of the jet (Ar or Kr). Rotational constants, internuclear distances, vibration frequencies, and (83)Kr, Cu, and Cl nuclear quadrupole coupling constants have all been evaluated. The Kr-Cu bonds are short and the complexes are rigid. The (83)Kr coupling constant of KrCuF is large (128.8 MHz). The Cu nuclear quadrupole coupling constants differ radically from those of uncomplexed CuF and CuCl molecules. The results are supported by those of ab initio calculations, which have also yielded Mulliken populations, MOLDEN plots of valence molecular orbitals and Laplace concentrations, and electron localization functions. The results are consistent with those reported earlier for other noble gas-noble metal halide complexes. The results have been used to assess the nature of the bonding in the complexes and have produced good evidence for weak noble gas-noble metal chemical bonding.     

Exploring hyperpolarized 83Kr by remotely detected NMR relaxometry

For the first time, a hyperpolarized (hp) noble gas with a nuclear electric quadrupole moment is available for high-field nuclear-magnetic-resonance (NMR) spectroscopy and magnetic-resonance imaging. Hp (83)Kr (I=92) is generated by spin-exchange optical pumping and separated from the rubidium vapor used in the pumping process. Optical pumping occurs under the previously unstudied condition of high krypton gas densities. Signal enhancements of more than three orders of magnitude compared to the thermal equilibrium (83)Kr signal at 9.4 T magnetic-field strength are obtained. The spin-lattice relaxation of (83)Kr is caused primarily by quadrupolar couplings during the brief adsorption periods of the krypton atoms on the surrounding container walls and significantly limits the currently obtained spin polarization. Measurements in macroscopic glass containers and in desiccated canine lung tissue at field strengths between 0.05 and 3 T using remotely detected hp (83)Kr NMR spectroscopy reveal that the longitudinal relaxation dramatically accelerates as the magnetic-field strength decreases.     

Charge state distribution studies of pure and oxygen mixed krypton ECR plasma – signature of isotope anomaly and gas mixing effect

We report the charge state distributions of the pure, 25% and 50% oxygen mixed krypton plasma to shed more light on the understanding of the gas mixing and the isotope anomaly [A. G. Drentje, Rev. Sci. Instrum. 63 (1992) 2875 and Y Kawai, D Meyer, A Nadzeyka, U Wolters and K Wiesemann, Plasma Sources Sci. Technol. 10 (2001) 451] in the electron cyclotron resonance (ECR) plasmas. The krypton plasma was produced using a 10 GHz all‐permanent‐magnet ECR ion source. The intensities of the highly abundant four isotopes, viz. ⁸²Kr (~11.58%), ⁸³Kr (~11.49%), ⁸⁴Kr (~57%) and ⁸⁶Kr (17.3%) up to ~ +14 charge state have been measured by extracting the ions from the plasma and analysing them in the mass and the energy using a large acceptance analyzer‐cum‐switching dipole magnet. The influence of the oxygen gas mixing on the isotopic krypton ion intensities is clearly evidenced beyond +9 charge state. With and without oxygen mixing, the charge state distribution of the krypton ECR plasma shows the isotope anomaly with unusual trends. The anomaly in the intensities of the isotopes having quite closer natural abundance, viz. ⁸²Kr, ⁸⁶Kr and ⁸³Kr, ⁸⁶Kr is prominent, whereas the intensity ratio of ⁸⁶Kr to ⁸⁴Kr shows a weak signature of it. The isotope anomaly tends to disappear with increasing oxygen mixing in the plasma. The observed trends in the intensities of the krypton isotopes do not follow the prediction of linear Landau wave damping in the plasma. Copyright © 2016 John Wiley & Sons, Ltd.     

Krypton isotopic signature study of the primary coolant of CANDU nuclear power plant

To support interpretation of observed atmospheric krypton radioisotopes, a database of krypton radioisotope in the primary coolant of CANDU reactors has been established. This database is comprised of 40,000 records of high-quality ⁸⁹Kr, ⁸⁷Kr, ⁸⁸Kr and ^85mKr analyses. Records from the database were retrieved by a specifically designed data-mining module and subjected to further analysis. Results from the analysis were subsequently used to study isotopic ratios of observed krypton radioisotopes in the CANDU reactor primary coolant. These studies provided practical information on the characterization of CANDU reactor krypton radioisotope, which can potentially be used to discriminate between reactor effluent and fuel reprocessing for nuclear safeguard ⁸⁵Kr monitoring applications (Kalinowski et al., J Environ Radioact 73:203, 2004). The study also has some potential application to Fissile material cut-off treaty.     

Determination of low level85Kr and133Xe concentrations in the environment

This study was performed under the joint TRMC/INER program for the determination of low level⁸⁵Kr and¹³³Xe concentrations in the environmental air samples. Based on cryogenic adsorption of krypton and xenon on charcoal followed by chromatographic separation from other gases, the⁸⁵Kr and¹³³Xe recovered from 200 liters of atmospheric air can be determined by either on-line gas flow proportional counter or liquid scintillation counting. The recovery yields of krypton and xenon examined by using⁸⁵Kr and¹³³Xe tracers were nearly 100%. The minimum detectable activity of⁸⁵Kr and¹³³Xe by gas flow proportional counting is about 7.40 Bq. The method is satisfactory for environmental monitoring applications under abnormal conditions of nuclear facilities. However, for lower level environmental⁸⁵Kr and¹³³Xe measurements, the liquid scintillation counting method can be applied due to their extremely low detection limits (i.e. 0.107 Bq and 0.093 Bq for⁸⁵Kr and¹³³Xe, respectively). Using this method, the measurable limits of concentrations are 0.535 Bq/m³ and 0.466 Bq/m³ for⁸⁵Kr and¹³³Xe, respectively.     

Adsorption of <Superscript>85</Superscript>Kr radioactive inert gas into hardening mixtures

Changes in volumetric activity of ⁸⁵Kr radioactive inert gas take place in the atmosphere: it has increased by around 50% during the past 15 years. The main source of such gas is the operation of nuclear power plants and spent nuclear fuel reprocessing plants. ⁸⁵Kr as an inert gas spreads throughout the entire atmosphere and its ionizing radiation may result in changes of atmospheric electric phenomena. Therefore it is necessary to control ⁸⁵Kr emission into the atmosphere. However, there is no effective method for this as inert gases, under normal conditions, can hardly be adsorbed in different adsorbents and stored in special containers for a long period of time. This paper tries to show the possibility of keeping ⁸⁵Kr longer within the adsorbent by changing its aggregate state: gas is adsorbed into liquid adsorbent and desorption takes place from solid adsorbent. For this purpose, an epoxy resin is used which, after adding a special hardener at room temperature, turns into a solid material with density of around 1.2 × 10³ kg m⁻³. As a result of sample blending with substances which contribute to better solubility of ⁸⁵Kr, diffusion coefficient of this gas (i.e. desorption speed) changes within the adsorbent in the solid state.     

Hydrogen-Bonding Assembly Meets Anion Coordination Chemistry: Framework Shaping and Polarity Tuning for Xenon/Krypton Separation

Hybrid hydrogen-bonded (H-bonded) frameworks built from charged components or metallotectons offer diverse guest-framework interactions for target-specific separations. We present here a study to systematically explore the coordination chemistry of monovalent halide anions, i.e., F⁻, Cl⁻, Br⁻, and I⁻, with the aim to develop hybrid H-bond synthons that enable the controllable construction of microporous H-bonded frameworks exhibiting fine-tunable surface polarity within the adaptive cavities for realistic xenon/krypton (Xe/Kr) separation. The spherical halide anions, especially Cl⁻, Br⁻, and I⁻, are found to readily participate in the charge-assisted H-bonding assembly with well-defined coordination behaviors, resulting in robust frameworks bearing open halide anions within the distinctive 1D pore channels. The activated frameworks show preferential binding towards Xe (IAST Xe/Kr selectivity ca. 10.5) because of the enhanced polarizability and the pore confinement effect. Specifically, dynamic column Xe/Kr separation with a record-high separation factor (SF=7.0) among H-bonded frameworks was achieved, facilitating an efficient Xe/Kr separation in dilute, CO₂-containing gas streams exactly mimicking the off-gas of spent nuclear fuel (SNF) reprocessing.     

Applications of gas chromatography and gamma spectrometry to fission gas measurements

A gas sampler with lead shield has been designed for transferring the grab gas sample taken from the sampling station of Taiwan nuclear power reactor. The methods involving gas chromatography and gamma spectrometry have been developed for the determination of fission gases. A gas chromatograph equipped with TCD was used for measurement of gas composition. Column requirements are identified and optimum operating conditions are discussed. A single analysis is completed within 25 minutes for all of the gas constitutents and 12 minutes for only Xe and Kr. The detection limit is 0.005 mm partial pressure for Kr and Xe and a precision of ±1% relative is achieved for all the sample constituents. Combined error determinations for the method denote an attainable accuracy of less than ±2% for constituents at a sample pressure above 10 mm. Mixing and dispensing of the radioactive gases were carried out in a special gas mixing line. In experiment, calibration factors for measurement of¹³³Xe and⁸⁵Kr in ampules are determined in an isotope calibrator and by Ge(Li) gamma ray spectrometry. The relative precisions of 0.14% and 0.5% are readily achieved for⁸⁵Kr and¹³³Xe, respectively. The calibration uncertainty in⁸⁵Kr measurement is 0.4%.     

Theoretical description of nuclear quadrupole coupling in light diatomic molecules

A practical procedure for calculation of nuclear quadrupole coupling constants for light diatomic molecules is discussed. The procedure is based on a molecular wave function that explicitly describes nuclear motion. The approach is capable of yielding quadrupole coupling constants for excited rovibrational levels of diatomic molecules in their ground and excited electronic states. An application of the procedure to the X¹Σ⁺_g and B¹Σ⁺_u states of HD and D₂ is presented.     

Nuclear quadrupole resonance of 14N in imidazole and related compounds

Using the technique of nuclear double resonance with spin mixing by level crossing, the nuclear quadrupole resonance of ¹⁴N has been measured in L-histidine, D-L-histidine, L-histidine hydrochloride monohydrate, sodium urocanate and urocanic acid at 77 K. The nuclear quadrupole resonance of both ¹⁴N and ²D has been measured in deuterated imidazole at 77 K. The previously measured spectra for normal imidazole have been positively assigned with the electric field gradient parameters for the tri-coordinated nitrogen site given by e²qQ/h = 1424 kHz and η = 0.980, and for the di-coordinated nitrogen site by e²qQ/h = 3267 kHz and η = 0.129.     

A new81Rb−81mKr generator from enriched82Kr gas for medical use

Present work describes the construction and results of a new⁸¹Rb production target system using highly enriched⁸²Kr (99.95%) gas target material. The method yields a carrier-free product of highest activity and highest possible purity. It allows complete recovery of the expensive target material by freezing and avoids tedious chemical separation procedures. The remote-controlled target system has been constructed and functions extremely well.⁸¹Rb is used for the preparation of a new type of⁸¹Rb–^81mKr generator with a capacity of approximately 60 mCi for use in nuclear medical diagnostic (lung ventillation studies and angioscintigraphy).     

An improved apparatus for the determination of krypton-85 and xenon-133 in an emergency situation

A simple and portable apparatus was developed for measurements of⁸⁵Kr and¹³³Xe that would be released into the atmosphere in an emergency situation of nuclear facilities. The method is based on cryogenic adsorption of these gases on charcoal followed by chromatographic separation from other gases. The⁸⁵Kr and¹³³Xe recovered from atmospheric air are determined separately by liquid scintillation counting. It takes about 1 hour for the stepwise determination of⁸⁵Kr and¹³³Xe. The atmospheric concentration of 3·10^–3 Ci per m³ air (1.1·10² Bq/m³ air) is measurable for both nuclides with 20% counting error.     

The microwave spectrum of chloroacetyl chloride

The microwave spectrum, rotational constants and centrifugal distortion parameters for CH₂³⁵ClCO³⁵Cl are reported. The nuclear quadrupole coupling constants of the two non-equivalent Cl atoms were determined from partially resolved quadrupole splittings. The molecule is planar in the conformation studied here and both Cl atoms occupy the trans position as shown from their substitution coordinates.     

N nuclear quadrupole resonance of picolinic,nicotinic, isonicotinic and dinicotinic acids

The ¹⁴N nuclear quadrupole resonance (NQR) quadrupole coupling tensors of picolinic, nicotinic, isonicotinic and dinicotinic acids have been determined. Two different ¹⁴N quadrupole coupling constants 1007 kHz and 4159 kHz have been observed for picolinic acid demonstrating the presence of both protonated and non-protonated nitrogen atoms in this system in the solid. Only one set of non-protonated ¹⁴N NQR lines has been observed in other pyridinecarboxylic acids demonstrating the absence of the protonated zwitter ion forms observed in picolinic acid. The non-protonated ¹⁴N quadrupole coupling constant is the highest for the non-protonated nitrogen in picolinic acid and decreases to 3774 kHz in nicotinic acid and 3570 kHz in isonicotinic acid. It is the lowest in dinicotinic acid where the corresponding ¹⁴N quadrupole coupling constant is 2794 kHz. The observed anomalous decrease in the ¹⁴N quadrupole coupling constant of dinicotinic acid with decreasing temperature is tentatively explained as reflecting the increase in the residence time of the N–H?O bonded proton in the potential well close to the nitrogen.     

Substituent Effect on the Stability and 14N NQR Parameters of Linkage Isomers of Nitriles in a Rhodium Half‐Sandwich Metallacycle: A Theoretical Study

In this work, using the MPW1PW91 method, the substituent effect on the stability and on the ¹⁴N NQR parameters of linkage isomers of nitriles in a rhodium half‐sandwich metallacycle is illustrated. After determination of the corresponding isomerization transition state (TS), the substituent effect on the barrier energy and on the activation thermodynamic parameters (ΔG^‡ and ΔH^‡) of isomerization is explored. The electric field gradient tensor, nuclear quadrupole coupling constant, asymmetry parameter, and nuclear quadrupole resonance frequencies of the studied isomers are calculated. Also, linear correlations between these parameters and Hammett constant of the substituent are explored.