Resonance Ionization Mass Spectrometry (RIMS) with Pulsed and CW-Lasers on Plutonium

The detection of long-lived plutonium isotopes in ultra-trace amounts by resonance ionization mass spectrometry (RIMS) is a well-established routine method. Detection limits of 10⁶ to 10⁷ atoms and precise measurements of the isotopic composition have been achieved. In this work multi-step resonance ionization of plutonium atoms has been performed with tunable lasers having very different output intensities and spectral properties. In order to compare different ways for the resonance ionization of plutonium broadband pulsed dye and titanium:sapphire lasers as well as narrow-band cw-diode and titanium:sapphire lasers have been applied for a number of efficient excitation schemes. It has been shown, that for identical excitation schemes the optical isotope selectivity can be improved by using cw-lasers (bandwidths < 10 MHz) instead of pulsed lasers (bandwidths > 2 GHz). Pulsed and cw-laser systems have been used simultaneously for resonance ionization enabling direct comparisons of pulsed and continuous ionization processes. So far, a three-step, three-color laser excitation scheme has been proven to be most practical in terms of efficiency, selectivity and laser wavelengths. Alternatively a newly discovered three-step, two-color excitation scheme which includes a strong two-photon transition from an excited state into a high-lying autoionizing state yields similar ionization efficiencies. This two-photon transition was characterized with respect to saturation behavior and line width.     

Laser resonance ionization for ultra-trace analysis on long-lived radioactive isotopes

Benefiting from the continuous laser developments, resonance ionization can be applied for a variety of experiments on radioactive isotopes, e.g. as a laser ion source for producing pure beams of short-lived isotopes at on-line facilities. In this paper the application of a compact set-up for resonance ionization mass spectrometry for ultra-trace analysis of the long-lived isotope Ca-41 is described. With this set-up a purely optical selectivity of 3×10⁹ and an overall detection efficiency of 1.2(4)×10⁻⁵ are demonstrated.     

Resonant Laser Excitation/Ionization and Mass Spectrometry in Isotope Geochemistry and Cosmochemistry

SCOPE OF REVIEW

This paper reviews the coupling of resonant laser ionization and laserexcited fluorescence with mass spectrometry to make difficult isotopic-ratio measurements. To keep this review focused and manageable in size, it covers only metal and noble-gas isotopic analyses that find applications in isotope geochemistry and cosmochemisty. Many research groups are applying lasers and mass spectrometry to atomic, molecular, and isotopic analyses that address problems in nuclear physics [1], materials science [2-4], biology [5,6], environmental science, and other areas of geochemistry and cosmochemistry [7,8]. Several previous reviews and monographs cover the basic principles and instrumentation of resonant laser processes and mass spectrometry in more breadth [9-12]. The latest Analytical Chemistry Fundamental Reviews [13] and the published proceedings of the biannual International Symposium on Resonance Ionization Spectroscopy and Its Applications provide updates of other recent work [8]. This review does not comprehensively encompass the use of lasers for analyte sampling by desoxption, ablation, sputtering, or melting. Several other specific reviews discuss laser sampling in elemental [14,15] and stable-isotope analyses [16,17]. This review does include applications in which pulsed ion sputtering and laser desoxption atomize analytes for ionization by resonance ionization mass spectrometry (RIMS). This review also does not include isotopic-analytical methcds that use solely optical spectroscopy. The continuing development of laser and plasma technology is leading to promising spectroscopic-only methods for stable-isotope analysis [18-21].     

Trace isotope detection enhanced by coherent elimination of power broadening

The selectivity and spectral resolution of traditional laser-based trace isotope analysis, i.e., resonance ionization mass spectrometry (RIMS), is limited by power broadening of the radiative transition. We use the fact that power broadening does not occur in coherently driven quantum systems when the probing and excitation processes are temporally separated to demonstrate significant improvement of trace element detection, even under conditions of strong signals. Specifically, we apply a coherent variant of RIMS to the detection of traces of molecular nitric oxide (NO) isobars. For large laser intensities, the detected isotope signal can be increased by almost 1 order of magnitude without any loss in spectral resolution.     

Isotope selective loading of an ion trap using resonance-enhanced two-photon ionization

We have demonstrated that resonance-enhanced two-photon ionization of atomic beams provides an effective tool for isotope selective loading of ions into a linear Paul trap. Using a tunable, narrow-bandwidth, continuous wave (cw) laser system for the ionization process, we have succeeded in producing Mg⁺ and Ca⁺ ions at rates controlled by the atomic beam flux, the laser intensity, and the laser frequency detuning from resonance. We have observed that with a proper choice of control parameters, it is rather easy to load a specific number of ions into a string. This observation has direct applications in quantum optics and quantum computation experiments. Furthermore, resonant photo-ionization loading facilitates the formation of large isotope-pure Coulomb crystals. Received: 21 December 1999 / Published online: 11 May 2000     

Novel method for the production of spin-aligned RI beams in projectile fragmentation reaction with the dispersion matching technique

For high precision and accuracy in isotopic ratio measurement of transuranic elements using laser ablation assisted resonance ionization mass spectrometry, a dynamic correction method based on correlation of ion signals with energy and timing of each laser pulse was proposed. The feasibility of this dynamic correction method was investigated through the use of a programmable electronics device for fast acquisition of the energy and timing of each laser pulse.     

Efficient three-step,two-color ionization of plutonium using a resonance enhanced 2-photon transition into an autoionizing state

Resonance ionization mass spectrometry (RIMS) has proven to be a powerful method for isotope selective ultra-trace analysis of long-lived radioisotopes. For plutonium detection limits of to atoms have been achieved for various types of samples. So far a three-step, three-color laser excitation scheme was applied for efficient ionization. In this work, a two-photon transition from an excited state into a high-lying autoionizing state, will be presented, yielding a similar overall efficiency as the three-step, three-color ionization scheme. In this way, only two tunable lasers are needed, while the advantages of a three-step, three-color excitation (high selectivity, good efficiency and low non-resonant background) are preserved. The two-photon transition has been characterized with respect to saturation behavior and line width. The three-step, two-color ionization is a possibility for an improved RIMS procedure.Received: 6 January 2004, Published online: 24 February 2004PACS: 82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI) - 32.80.Rm Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states) - 32.80.Dz Autoionization     

镥的激光共振电离同位素选择性研究

本文在速率方程基础上通过数值模拟方法 ,对镥的激光共振电离通道 :5d6s2 2 D3 /2 (5 73.6 5 5nm)→5d6s6 p4F3 /2 (6 4 2 .5 18nm)→ 6s6 p2 4P1/2 (6 4 3.5 4 8nm)→Autoionizationstate的激光诱导同位素选择性进行了研究。在实际实验条件下用这一方法计算得到的激光波长对激光诱导同位素选择性的关系与实验结果相符合。探讨了在偏振激光作用的情况下各种激光参数 (波长、带宽和激光强度 )对激光诱导同位素选择性的影响 ,并提出了在一定实验条件下激光共振电离质谱计较为准确地测定同位素比值的方法。这一理论方法 ,同样适用于研究其它元素的激光共振电离同位素选择性和选择激光同位素分离电离通道     

激光共振电离过程中铅同位素歧视效应研究

以速率方程为基础,通过数值模拟方法,对Pb的激光共振电离通道：“6s26p2 3P0—6s26p7s 3P0₁—电离”的激光诱导同位素歧视效应进行了研究,以探讨减小激光诱导歧视效应,准确测定Pb同位素比值的有效途径。通过考虑激光线型、原子吸收谱线线型、同位素位移及同位素超精细结构等因素的影响,对速率方程进行近似。在近似的速率方程基础上,以“1+1”激光共振电离过程为例,进而探讨激光峰值功率密度、带宽和中心波长对Pb的同位素歧视效应的影响。研究结果表明,利用最佳波长法,可基本消除同位素歧视效应的影响;提高激发光光强可使Pb同位素饱和电离,从而消除同位素歧视效应的影响;采用宽带激光激发,可减小同位素歧视效应的影响。     

Isotope shifts and hyperfine structure in the transitions of gadolinium

High-resolution resonance ionization mass spectrometry has been used to measure isotope shifts and hyperfine structure in all (J = 2-6) and the transitions of gadolinium (Gd I). Gadolinium atoms in an atomic beam were excited with a tunable single-frequency laser in the wavelength range of 422-429 nm. Resonant excitation was followed by photoionization with the 363.8 nm line of an argon ion laser and resulting ions were mass separated and detected with a quadrupole mass spectrometer. Isotope shifts for all stable gadolinium isotopes in these transitions have been measured for the first time. Additionally, the hyperfine structure constants of the upper states have been derived for the isotopes ^{155, 157} Gd and are compared with previous work. Using prior experimental values for the mean nuclear charge radii, derived from the combination of muonic atoms and electron scattering data, field shift and specific mass shift coefficients for the investigated transitions have been determined and nuclear charge parameters for the minor isotopes ^{152, 154} Gd have been calculated. Received 18 November 1999     

NMR, EPR, and mass spectroscopy estimates of the antiradical activity of water with modified isotope composition

The dynamics of the change in the deuterium content in plasma of laboratory animal blood is studied by nuclear magnetic resonance spectroscope using water with modified isotope composition. The change in deuterium content in lyophilized animal tissues is determined by mass spectrometry. The content of paramagnetic centers in a dose and in pathology is determined on an electron paramagnetic resonance spectrometer.     

Structural Investigation of Biomacromolecules Using Ultrahigh-Resolution Mass Spectrometry and Isotope Exchange

We present a new analysis methodology for arbitrary complex molecular systems using ultrahigh-resolution mass spectrometry and isotope exchange. The kinetics of the hydrogen–deuterium exchange reaction is described for large biomacromolecules. The possible applications of the proposed methodology for the analysis of linear oligosaccharides, proteins, and molecular ensemble of humic acids are discussed.     

Counting individual 41Ca atoms with a magneto-optical trap

Atom trap trace analysis, a novel method based upon laser trapping and cooling, is used to count individual atoms of 41Ca present in biomedical samples with isotopic abundance levels between 10(-8) and 10(-10). The method is calibrated against resonance ionization mass spectrometry, demonstrating good agreement between the two methods. The present system has a counting efficiency of 2x10(-7). Within 1 h of observation time, its 3-sigma detection limit on the isotopic abundance of 41Ca reaches 4.5x10(-10).     

Isotope shifts and hyperfine structure in calcium 4snp and 4snf F Rydberg states

Isotope shifts and hyperfine structure have been measured in 4snp ¹ P₁ and Rydberg states for all stable calcium isotopes and the radioisotope ⁴¹Ca using high-resolution laser spectroscopy. Triple-resonance excitation via Rydberg state was followed by photoionization with a CO₂ laser and mass selective ion detection. Isotope shifts for the even-mass isotopes have been analyzed to derive specific mass shift and field shift factors. The apparent isotope shifts for ⁴¹Ca and ⁴³Ca exhibit anomalous values that are n-dependent. This is interpreted in terms of hyperfine-induced fine-structure mixing, which becomes very pronounced when singlet-triplet fine-structure splitting is comparable to the hyperfine interaction energy. Measurements of fine-structure splittings for the predominant isotope ⁴⁰Ca have been used as input parameters for theoretical calculation of the perturbed hyperfine structure. Results obtained by diagonalizing the second-order hyperfine interaction matrices agree very well with experimentally observed spectra. These measurements allow the evaluation of highly selective and sensitive methods for the detection of the rare ⁴¹Ca isotope. Received 17 December 1999 and Received in final form 29 March 2000     

Cobalt coated substrate for matrix-free analysis of small molecules by laser desorption/ionization mass spectrometry

Small molecule analysis is one of the most challenging issues in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. We have developed a cobalt coated substrate as a target for matrix-free analysis of small molecules in laser desorption/ionization mass spectrometry. Cobalt coating of 60-70 nm thickness has been characterized by scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, and laser induced breakdown spectroscopy. This target facilitates hundreds of samples to be spotted and analyzed without mixing any matrices, in a very short time. This can save a lot of time and money and can be a very practical approach for the analysis of small molecules by laser desorption/ionization mass spectrometry.     

Mass Spectrometric Determination of Transuranium Elements

Abstract

Mass spectrometric techniques are playing a predominant role for the determination of transuranium elements in bulk samples as well as in microparticles. Their applications to liquid and solid samples for the determination of the isotopic composition as well as for the concentration measurements are discussed. The new developments for the characterization of microparticles stemming from different release scenarios of radioactivity are considered. Inductively coupled plasma mass spectrometry and its hyphenation with other techniques for resolving isobaric interferences are presented. The application of glow discharge and laser ablation directly to solid samples is highlighted. Finally, the exploitation of secondary ion mass spectrometry, accelerator mass spectrometry, resonance ionization mass spectrometry, and thermal ionization mass spectrometry for the determination of the isotopic composition of uranium and plutonium in microparticles is illustrated.     

Ionization Scheme Development at the ISOLDE RILIS

The resonance ionization laser ion source (RILIS) of the ISOLDE on-line isotope separation facility is based on the method of laser step-wise resonance ionization of atoms in a hot metal cavity. The atomic selectivity of the RILIS complements the mass selection process of the ISOLDE separator magnets to provide beams of a chosen isotope with greatly reduced isobaric contamination. Using a system of dye lasers pumped by copper vapour lasers, ion beams of 24 elements have been generated at ISOLDE with ionization efficiencies in the range of 0.5–15%. As part of the ongoing RILIS development off-line resonance ionization spectroscopy studies carried out in 2003 and 2004 have determined the optimal three-step ionization schemes for scandium, antimony, dysprosium and yttrium.     

The ISOLDE RILIS pump laser upgrade and the LARIS Laboratory

On account of its high efficiency, speed and unmatched selectivity, the Resonance Ionization Laser Ion Source (RILIS) is the preferred method for ionizing the nuclear reaction products at the ISOLDE on-line isotope separator facility. By exploiting the unique electronic energy level ‘fingerprint’ of a chosen element, the RILIS process of laser step-wise resonance ionization enables an ion beam of high chemical purity to be sent through the mass selective separator magnet. The isobaric purity of a beam of a chosen isotope is therefore greatly increased. The RILIS, comprising of up to three frequency tunable pulsed dye lasers has been upgraded with the installation of a Nd:YAG pump laser as a replacement for the old Copper Vapor Laser (CVL) system. A summary of the current Nd:YAG pumped RILIS performance is given. To accompany the RILIS pump laser upgrade, a new ionization scheme for manganese has been developed at the newly constructed LAser Resonance Ionization Spectroscopy (LARIS) laboratory and successfully applied for on-line RILIS operation. An overview of the LARIS facility is given along with details of the ionization scheme development work for manganese.     

A NEW EXPERIMENTAL METHOD IN THE STUDY OF IONIC RYDBERG STATES BY RESONANCE IONIZATION MASS SPECTROSCOPY

We report a new method for detecting highly excited ions. With a strong constant electric field ionization following the extracting of ions by a pulsed electric field in a time-of-flight mass spectrometer, the direct multi-photon ionization background can be eliminated in laser multi-step resonance ionization mass spectroscopy of ionic Rydberg states. A high detection efficiency call be obtained for law members of ionic Rydberg states by use of this method. We have applied the method in the study of the spectroscopy of ionic Rydberg states ia ytterbium.     

激光熔蚀-电感耦合等离子体质谱法测定底泥沉积物中的总汞

采用激光熔蚀-电感耦合等离子体质谱法(LA-ICP-MS)测定了底泥沉积物中的总汞,沉积物样品经高压压坯后直接进行激光熔蚀测定,并对内标选定、样品粒度以及汞的形态等影响因素进行了研究,以2个底泥标准样和1个土壤标准样的测定结果来绘制标准曲线,并用于实际样品的测定,方法简便实用,测定结果与同位素稀释冷蒸气发生ICP-MS法十分吻合,方法检出限为0.02 mg·kg-1,测定速度可达每小时10样。