Pulmonary MRI contrast using Surface Quadrupolar Relaxation (SQUARE) of hyperpolarized Kr

Hyperpolarized ⁸³Kr has previously been demonstrated to enable MRI contrast that is sensitive to the chemical composition of the surface in a porous model system. Methodological advances have lead to a substantial increase in the ⁸³Kr hyperpolarization and the resulting signal intensity. Using the improved methodology for spin exchange optical pumping of isotopically enriched ⁸³Kr, internal anatomical details of ex vivo rodent lung were resolved with hyperpolarized ⁸³Kr MRI after krypton inhalation. Different ⁸³Kr relaxation times were found between the main bronchi and the parenchymal regions in ex vivo rat lungs. The T₁ weighted hyperpolarized ⁸³Kr MRI provided a first demonstration of surface quadrupolar relaxation (SQUARE) pulmonary MRI contrast.     

Detection of tobacco smoke deposition by hyperpolarized krypton-83 MRI

Despite the importance of the tobacco smoke particulate matter in the lungs to the etiology of pulmonary disease in cigarette smokers, little is currently known about the spatial distribution of particle deposition or the persistence of the resulting deposits in humans, and no satisfactory technique currently exists to directly observe tobacco smoke condensate in airways. In this proof-of-principle work, hyperpolarized (hp) 83Kr MRI and NMR spectroscopy are introduced as probes for tobacco smoke deposition in porous media. A reduction in the hp-83Kr longitudinal (T1) relaxation of up to 95% under near-ambient humidity, pressure and temperature conditions was observed when the krypton gas was brought into contact with surfaces that had been exposed to cigarette smoke. This smoke-induced acceleration of the 83Kr self-relaxation was observed for model glass surfaces that, in some experiments, were coated with bovine lung surfactant extract. However, a similar effect was not observed with hp-(129)Xe indicating that the 83Kr sensitivity to smoke deposition was not caused by paramagnetic species but rather by quadrupolar relaxation due to high adsorption affinity for the smoke deposits. The 83Kr T1 differences between smoke-treated and untreated surfaces were sufficient to produce a strong contrast in variable flip angle FLASH hp-83Kr MRI, suggesting that hp-83Kr may be a promising contrast agent for in vivo pulmonary MRI.     

Calibration of the isomer shift of83Kr

Radioactive⁸³Rb was implanted in 6 different cubic metals (Al, W, Au, Ir, Pt, Pb) and both internal conversion electron spectra and Mössbauer spectra of the daughter nucleus⁸³Kr were measured. A value (r ²)=+5.1(9)×10^–3 fm² (corresponding to R/R=+1.6(3)×10^–4) was derived for the change of the mean square charge radius during the 9.40 keV transition in⁸³Kr. The systematics of the isomer shifts of krypton and other sp-elements substitutionally dissolved in metals are discussed.     

Neutron production with mixture of deuterium and krypton in Sahand Filippov type plasma focus facility

This Letter reports the order of magnitude enhancement in neutron yield from Sahand plasma focus device with krypton seeded deuterium operation. The highest average neutron yield of 2.2×¹⁰⁹ neutrons per shot was achieved at 1.00 Torr deuterium with 3% krypton which is higher than the best average neutron yield of 3.18×¹⁰⁸ neutrons per shot for pure deuterium operation. Estimation of average neutron energy showed that the maximum and minimum average energies are 2.98±0.6 MeV at 16 kV in 0.25 Torr deuterium with 3% Kr and 2.07±0.2 MeV at 18 kV operation in 0.5 Torr deuterium with 3% Kr, respectively. The anisotropy of neutron emission from Sahand DPF showed that the neutrons are produced mainly by beam-target mechanisms.     

用激光计数放射性氪原子

原子阱痕量分析是一种基于激光的新方法,能够对数微升氪气中丰度低至10^-14的⁸⁵Kr和⁸¹Kr原子进行计数测量．介绍了在合肥建成的痕量放射性氪同位素测量系统,包括ATTA装置、水中溶解气提取和氪气分离提纯的样品处理设备．利用该系统对国内多处大气中⁸⁵Kr浓度的测量结果为1.3～1.6 Bq/m³,与文献中北半球大气本底值相吻合．对华南和华北的几个浅层和深层地下水样品进行了⁸⁵Kr和⁸¹Kr测年,示范了该系统的应用．     

High-resolution diode-laser spectroscopy on a fast beam of metastable atoms for detecting very rare krypton isotopes

A fast krypton ion beam with an energy of 10 keV is transferred through a mass filter and neutralized in a Rb- (or Cs-) vapour charge exchange cell. The emerging beam of metastable Kr atoms of a selected Kr isotope is collinearly irradiated with a tunable cw GaAlAs diode laser at 811 nm. The spectrum of the 1s ₅–2p ₉ transition covers 10 GHz and consists of one line each for the five stable isotopes of Kr with even mass number and 15 hyperfine structure lines of⁸³Kr. The individual lines are recorded by detecting the fluorescence signal perpendicular to the beams. Photons are guided to the PM tube by diffuse reflection from a high reflectance thermoplastics light collector. Up to 20 photons per atom are emitted by cycling between the two states during the flight time of 1.2 µs through the detector. The observed absorption linewidth of 100 MHz is a combination of laser linewidth and energy uncertainty in the fast atomic beam. In order to achieve maximum isotope selectivity the beam energy has to be adjusted in such a way that the Doppler shifted lines of all isotopes form an optimum pattern for detecting the very rare isotopes⁸¹Kr and⁸⁵Kr in natural environmental samples.     

Hyperfine structure induced isotopic effects in krypton resonance ionization mass spectrometry

A time-of-flight mass spectrometer combined with a pulsed laser system has been used for determination of krypton isotope ratios of air samples containing 10⁶-10⁷ krypton atoms. A three-color, doubly resonant ionization scheme employing a 116.48 nm transition from the ground into the first 4s²4p⁵(²P°_1/2)5s J = 1 excitation level has been applied. The magnitude of a hyperfine splitting of this level has been estimated for ⁸¹Kr, ⁸³Kr and ⁸⁵Kr isotopes. Hyperfine structure induced isotopic effects have been investigated under different saturation conditions and found to be negligible when the first and the second transitions are strongly saturated.     

High-resolution mass spectrometric study of pure helium droplets,and droplets doped with krypton

Mass spectra of doped and undoped helium droplets are presented. The high resolution of the time-of-flight spectrometer (m/Δm ≅ 5000) makes it possible to fully resolve small helium cluster ions from impurities and to unambiguously identify abundance anomalies in the size distribution of He _n ⁺. The yield of He₄ ⁺ shows the well-known enhancement relative to other small cluster ions when the expansion changes from sub- to supercritical, provided the electron energy exceeds a value of 40 ± 1 eV, the threshold for formation of electronically excited ions. Upon doping with krypton, pure Kr _n ⁺ cluster ions containing up to 41 Kr atoms are observed. The spectra exhibit abundance anomalies at 13, 16, 19, 22 & 23, 26 and 29, in agreement with spectra obtained by ionization of bare krypton clusters that are formed in neat supersonic beams. Mixed clusters He _m Kr⁺ indicate closure of a solvation shell at m = 12.     

从环境样品中分离氩气和氪气用于放射性惰性气体探测

放射性惰性气体同位素⁸⁵Kr(半衰期为10.8年)、³⁹Ar(半衰期为269年)和⁸¹Kr(半衰期为22.9万年)是理想的环境示踪剂,基于激光技术的原子阱痕量分析方法(Atom trap trace analysis, ATTA)可以实现对空气、地下水等环境样品中这几种同位素的有效探测. 在进行ATTA测量之前,需要将样品中的氪气和氩气有效分离出来. 利用低温蒸馏、海绵钛化学吸附和气相色谱分离等技术,可以从1~10 L气体样品中分别提取出90%以上的氪气和98%以上的氩气,从而满足ATTA测量的样品要求. 通过对包括两个野外地下水样品等一系列样品进行分离实验,验证了气体分离装置的可靠性能.     

Atom trap trace analysis

A new method of ultrasensitive isotope trace analysis has been developed. This method, based on the technique of laser manipulation of neutral atoms, has been used to count individual ⁸⁵Kr and ⁸¹Kr atoms present in a natural krypton gas sample with isotopic abundances in the range of 10⁻¹¹ and 10⁻¹³, respectively. The method is free of contamination from other isotopes and elements, and can be applied to many different isotope tracers for a wide range of applications. This revised version was published online in August 2006 with corrections to the Cover Date.     

Transition probabilities in Kr II and Kr III spectra

On the basis of the relative line intensity ratio (RLIR) method, transition probability values of the spontaneous emission (Einsteins A values) of 14 transitions in the singly (Kr II) and 7 transitions in doubly (Kr III) ionized krypton spectra have been obtained relatively to the reference A values related to the 435.548 nm Kr II and 324.569 nm Kr III, the most intensive transitions in the Kr II and Kr III spectra. Our Kr III transition probability values are the first data obtained experimentally using the RLIR method. A linear, low-pressure, pulsed arc operated in krypton discharge was used as an optically thin plasma source at a 17 000 K electron temperature and 1.65 x 10²³ m^-3 electron density. Our experimental relative A values are compared with previous experimental and theoretical data.Received: 16 June 2003, Published online: 16 September 2003PACS: 52.70.Kz Optical (ultraviolet, visible, infrared) measurements - 32.70.Cs Oscillator strengths, lifetimes, transition moments - 32.70.Fw Absolute and relative intensities     

A new laser concept for isotopically selective analysis of noble gases

A new laser approach for the isotopically selective analysis of noble gases is presented. This approach uses noble gas atoms prepared in the 1s ⁵ metastable state. Hyperfine levels in the 1s ⁵ and 2p ⁹ states form two-level systems in Ne, Ar, Kr, and Xe which can be excited by a commercially available single-frequency laser system. Absorption of photons from such a laser, and the resulting momentum transfer, can be used to selectively deflect the desired isotope from a supersonic atomic beam into a detection area. Light from the same laser can then be used to selectively count atoms of the desired isotope using the photon-burst technique. Thus, enrichment and selective detection are accomplished with a single laser in a single pass through the apparatus.The problem of analyzing for⁸⁵Kr in a sample of noble gases extracted from the air is examined in detail. This is a stringent test of the selectivity of this approach because⁸⁵Kr has the same nuclear spin, and thus similar hyperfine splittings, as naturally occurring⁸³Kr. Calculations indicate that isotopic selectivity of the new approach is easily adequate to resolve⁸⁵Kr in a 10¹⁰ excess of⁸³Kr.     

Aufbau einer anordnung zur probennahme und messung von krypton-85 in luft und messergebnisse

A method for sampling and measurement of krypton 85 in the atmosphere was developed based on the technique described by Stockburger et al. [1, 2]. The air is pumped through charcoal cooled with liquid nitrogen. Krypton is obtained from the air sample by fractionated desorption followed by gaschromatographic separation with simultaneous determination of the krypton volume. The ⁸⁵Kr activity is measured in a proportional counter. The calibration was carried out with an accuracy of ±5.2% (significance level 95%).

The ⁸⁵Kr activity concentration of a sample collected from 30 April to 3 May 1986 (Chernobyl accident) in Neuherberg near Munich was more than twice of the mean value of 1 Bq/m³ air.

Subsequently a continuous 14-day sampling along the north-south direction at three locations in Bavaria was carried out. From 1986 to 1991 a mean linear increase of the atmospheric ⁸⁵Kr activity concentration of 0.037 ± 0.010 Bq/m³ per year (significance level 95%) was determined.     

An open-access, very-low-field MRI system for posture-dependent 3He human lung imaging

We describe the design and operation of an open-access, very-low-field, magnetic resonance imaging (MRI) system for in vivo hyperpolarized ³He imaging of the human lungs. This system permits the study of lung function in both horizontal and upright postures, a capability with important implications in pulmonary physiology and clinical medicine, including asthma and obesity. The imager uses a bi-planar B₀ coil design that produces an optimized 65 G (6.5 mT) magnetic field for ³He MRI at 210 kHz. Three sets of bi-planar coils produce the x, y, and z magnetic field gradients while providing a 79-cm inter-coil gap for the imaging subject. We use solenoidal Q-spoiled RF coils for operation at low frequencies, and are able to exploit insignificant sample loading to allow for pre-tuning/matching schemes and for accurate pre-calibration of flip angles. We obtain sufficient SNR to acquire 2D ³He images with up to 2.8 mm resolution, and present initial 2D and 3D ³He images of human lungs in both supine and upright orientations. ¹H MRI can also be performed for diagnostic and calibration reasons.     

New stage of search for 2K(2ν) capture of 78Kr

A technique to search for 2K capture of ⁷⁸Kr with a large low-background proportional counter filled with a sample of krypton enriched in ⁷⁸Kr up to 99.8% at a pressure of 4.51 atm is described in this paper. The results of first measurements are presented. An analysis of data collected for 159 h yielded a new limit to the half-life of ⁷⁸Kr with regard to 2K capture (T _1/2 ≥ 1.5 × 10²¹ yr (90% C.L.)). The sensitivity of the facility to the process for one year of measurement was evaluated to be S = 1.0 × 10²² yr (90% C.L.). The text was submitted by the authors in English.     

Search for superconducting effect on the decay of99m Tc

An experimental investigation of the influence of superconductivity on the decay rate of^99m Tc, _T, has been performed by means of a differential method. The^99m Tc samples containing⁹⁹Tc as a carrier were prepared by electrodeposition on a copper plated tungsten wire. For production of metallic technetium the samples were reduced in pure hydrogen gas at 800~1000°C. X-ray analysis of the samples showed they were surely metallic with anhcp structure. The lattice constants observed area=2.741 Å andc=4.398 Å. The transition temperature was found to be 7.5±0.2K. Comparison of two sources, normal (room temperature) and superconducting (4.2 K), did not show an appreciable effect of superconductivity on the decay rate of^99m Tc exceeding the limit of uncertainty of our experiment:/ _T=(1.1±2.7) × 10^–4.     

Charge-transfer reactions in clusters excited with synchrotron radiation

Charge-transfer reactions are observed in a photoluminescence study of NF₃\rm NF_3-doped free krypton clusters. They show up in emissions from Kr⁺F^-\rm Kr^{+}F^{-}free excimers ejected from the clusters, and from excited Kr₂⁺F^-\rm Kr_2^{+}F^{-}and Kr₂⁺(NF₃)_m^-{\rm Kr}_2^{+}({\rm NF}_3)_m^{-} (m 3(m\geq 1) solvated in the clusters. The results show that reaction dynamics in clusters differs considerably from that in the gas and solid phases.     

Spectroscopic study of a glow discharge in krypton

The concentrations of excited atoms at the 4p⁵5s and 4p⁵5p levels of Kr I are determined by the reabsorption and emission methods. The absolute values off for ten Kr I lines in the infrared region of the spectrum are determined from the known value off ₈₈₁₂ and from measured relative values of the oscillator strengths. Processes leading to the formation and decay of excited states of krypton atoms are discussed.In conclusion, the authors wish to thank Professor A. N. Tekuchev for valuable comments, and also Yu. P. Grigorov, T. F. Dubtsov, L. V. Zaitsev, and V. S. Korchunov for assisting with the experiments.     

Gd complexes of diethylenetriaminepentaacetic acid conjugates of low-molecular-weight chitosan oligosaccharide as a new liver-specific MRI contrast agent

This study was to describe the synthesis of complexes of gadolinium diethylenetriaminepentaacetic acid conjugates of low-molecular-weight chitosan oligosaccharide Gd-DTPA-CSn (n = 6, 8, 11) as a new class of contrast agent as well as its magnetic property in a pilot magnetic resonance imaging. The efficacy of the contrast agent was assessed by measuring the longitudinal relaxivity (r₁), FLASH imaging in phantoms in vitro and signal intensity in vivo of the rat abdominal axial imaging. The r₁ of Gd-DTPA-CS₁₁ was up to 11.65 mM^− 1·s^− 1, which was 3 times higher than that of the analogous MRI contrast agent Gd-DTPA in commercial use. In vivo MR images of rat obtained with Gd-DTPA-CS₁₁ showed strong signal enhancement in liver and the vessels of the liver parenchyma during the extended period of time. The present study suggests that the new synthesized gadolinium complexes can be used as a new class of practical liver-specific MRI contrast agent because of its superior performance compared with Gd-DTPA.     

Extended analysis of the Kr V spectrum

The spectrum of four-times-ionized krypton (Kr V) has been observed in the 230–4900 Å wavelength range, resulting in 91 new classified lines. We were able to identify 21 new energy levels belonging to the 4s²4p5d, 4s²4p5s, 4s²4p6s, 4s²4p5p and 4s4p²4d configurations. Relativistic Hartree–Fock calculations were used to predict energy levels and transitions.