J. D. Fassett

Re-Os isotope systematics of Ni-Cu sulfide ores, Sudbury Igneous Complex, Ontario: evidence for a major crustal component

Sudbury Igneous Complex sublayer ores from the Levack West, Falconbridge and Strathcona mines were analyzed for their Re and Os concentrations and Os isotopic compositions. The Re-Os isotope systematics of three ores from the different mines give isochron ages of1 840 ± 60 Ma, 1770 ± 60 Ma and 1780 ± 110 Ma, suggesting that the Re-Os system became closed at the time of, or soon after the 1850 ± 1 Ma crystallization age of the complex. The Os isotopic compositions of different portions of the complex at the time of crystallization varied considerably, with initial187Os/186Os1850 ranging from 4.64 at Levack West to 7.55 at Strathcona. These heterogeneities require that the Os, and probably also the other platinum-group elements contained in the ores, were derived from at least two sources. In addition, the high initial187Os/186Os ratios indicate that the Os was derived predominantly from ancient crust. Previous studies have suggested that the complex either crystallized from a mixture of mantle-derived basaltic melt and ancient continental crust, or was derived exclusively from the fusion of ancient continental crust resulting from a meteorite impact. Results of modelling suggest that if a contemporaneous mantle-derived basaltic melt was involved in the origin of the SIC, it likely contributed < 50% of the Os to all three ores. The large percentage of ancient crust involved in the production of the ores is most consistent with an interpretation of substantial crustal fusion resulting from meteorite impact.

An improved method for the high-precision isotopic measurement of boron by thermal ionization mass spectrometry

An improved procedure for the determination of boron isotopic ratios, which is based on the measurement of the ion Cs2BO+2 has been investigated. Improved signal intensity and reproducibility is achieved by coating the filament substrate with graphite. Measurement of the 11B/10B ratio with a relative standard deviation of 0.006% has been demonstrated. The effect of various experimental factors on precision, including sample size, Cs:B ratio, and sample purity, have been evaluated. The boron isotopic compositions of samples of borax from the United States and Turkey are compared.

Protocol for isotope dilution using inductively coupled plasma-mass spectrometry (ICP-MS) for the determination of inorganic elements

The Comite Consultatif pour la Quantite de Matiere (CCQM) endeavours to identify and carry out key activities with the objective of facilitating world-wide comparability and traceability of chemical measurements. Towards this goal, the CCQM has identified comparisons to be carried out using candidate primary methods of chemical analysis. One such method is isotope dilution mass spectrometry. In the first comparison carried out by the CCQM (Study I), the concentrations of various inorganic elements were determined in water solutions using IDMS. The results did not meet the target level of 1% maximum relative deviation from the reference values of the unknowns. It was concluded that more guidance was necessary on the execution of the IDMS method and that a detailed protocol should be developed. Participants would use inductively coupled plasma (ICP) as the ionization source. Here we present the protocol developed for use by CCQM participants in the next comparison (Study III) on the determination of the concentration of lead in water using the IDMS method with an inductively coupled plasma-mass spectrometer.

Laser Resonance Ionization Mass Spectrometry

The analysis of inorganic atomic species is greatly facilitated by the coupling of lasers with mass spectrometers. A tunable dye laser, alone or in combination with a pump laser, ionizes atoms by resonant excitation processes; the ions are then analyzed in the mass spectrometer. The laser—mass spectrometer system promises to overcome traditional limits of sensitivity and selectivity and to have diverse applications in analytical chemistry.

The characterization of thermally-produced metastable excited-state atomic species using resonance ionization mass spectrometry

Abstract Resonance ionization mass spectrometry (RIMS) has been used to study atom plumes produced by thermal vaporization. Experimental results are presented for the elements Fe, Ni, Mo and Re. Ion intensity vs. laser wavelength spectra consistently demonstrate that low-level energy states are significantly populated in the interaction volume of the mass spectrometer. The experimental results are explained by assuming a Boltzmann distribution of states for atoms leaving the heated surface. Since collisional relaxation does not occur in the high-vacuum thermal atom source and the transitions from the excited state to ground state are not radiatively allowed, the Boltzmann distribution of states is maintained in the atom plume. Since many elements possess low-level energy states, both spectroscopic sensitivity and selectivity will be reduced. However, the greater number of intense lines per element allows an increased range of elements to be studied by RIMS in a given wavelength region and opens the possibility of multielement capabilities. The implications for more energetic atomization techniques such as ion sputtering or laser ablation are discussed.

Quantification of pulsed ion currents produced in resonance ionization mass spectrometry

Abstract An evaluation is made of a measurement system that quantifies the pulsed ion currents produced in resonance ionization mass spectrometry. An electron multiplier detector operated at intermediate gain has been combined with a preamplifier and a transient digitizer. The output of the transient digitizer is processed in real time so that no ionization information is lost. The linearity, pulse height distributions, and gain of the detector system have been examined. Operation of the detector in pulse counting and analog modes is demonstrated. Ratio measurements representative of these detection modes are presented for 185Re/187Re and 184Os/192Os.

Detection of Uranium from Cosmos-1402 in the Stratosphere

The nuclear reactor from the Soviet radar reconnaissance satellite, Cosmos-1402, reentered the earths atmosphere on 7 February 1983 and disintegrated over the South Atlantic Ocean. The reactor was powered by approximately 50 kilograms of uranium-235 (235U). In an effort to determine the fate of the reactor core, a series of aerosol samples were collected at altitudes between 27 and 36 kilometers in the Northern Hemisphere approximately 1.1 years later by high-altitude balloons. At an altitude of 36 kilometers a 53 � 20 percent excess in the 235U concentration was measured. The total excess of 235U in the stratosphere was calculated to be 44 � 15 kilograms.

Resonance ionization mass spectrometry of carbon

Resonance-ionization mass spectrometry (RIMS) for carbon has been demonstrated. A two-photon-resonant, three-photon ionization scheme provided large ionization signals from carbon atoms obtained by heating microgram samples of graphite. These results show that elemental carbon vapor can be detected at densities at least as low as 107 cm−3. The feasibility of efficient resonance ionization is a first step to the development of a RIMS-analysis capability for elemental and isotopic carbon.

Time-resolved magnetic dispersion for large isotope ratio measurements in resonance ionization mass spectrometry

Abstract The principle of time-resolved magnetic dispersion of ions can be used to improve the abundance sensitivity for elemental ratio measurement with laser ionization. A pulsed laser tuned to a discrete electronic transition of an element efficiently and selectively produces a pulsed ion beam. The pulsed ion beam is focused through a magnetic sector and, thus, mass filtering due to time-of-flight dispersion and magnetic dispersion is combined. The time-resolved magnetic dispersion is demonstrated using rhenium. The origin of scattered ions which cause loss of abundance sensitivity is displayed graphically in the magnetic field/time plane. Increased abundance sensitivity is demonstrated using tantalum.

Measurement of Low Abundance Isotopes By Laser Resonance Ionization Mass Spectrometry (Rims)

ABSTRACT The application of laser resonance ionization mass spectrometry (RIMS) to the measurement of low abundance isotopes was investigated. The long-lived radionuclide 129I was used to evaluate the present capabilities. Issues of sensitivity and selectivity were studied, as well as dynamic range limitations imposed by the low-duty-cycle pulsed ionization process.