Open University Uranium-Series Laboratory  
Earth and Environmental Sciences, The Open University, Milton Keynes, UK  

OUUSL laboratory

OUUSL maintains 2 U-series preparation laboratories with 5 laminar flow workstations and 4 laminar flow work benches. One prep lab is dedicated to high Th (silicate) samples, the other to low Th (authigenic and bone) samples. Chemical separation methods are primarily ion exchange chromatography.

OUUSL operates two mass spectrometers: a Finnigan MAT262-RPQ-II TIMS and a Nu Instruments MC-ICPMS, both are sector-field multi-collector instruments.
Both instruments are equipped with a deceleration lens to achieve the required abundance sensitivity for large isotope ratio measurements, and ion counting for ultimate detection limits.
The Finnigan MAT262-RPQ-II TIMS was recently refurbished by Spectromat with new solid-state power supplies, focussing system, magnet control system, parallel processor, fast interface and software, It is a high abundance sensitivity instrument, dedicated to U-series analysis
The Nu Instruments MC-ICPMS has various elctronic units replaced and a new set of 12 Faraday collectors and 3 discrete-dynbode Secondary Electrom Multipliers were installed.
The Nu Instruments MC-ICPMS, is used for most routine isotope ratio determinations. The normal mode of operation is that on Sunday evening the instrument is switched on and run on a wash cycle. Monday morning is used to tune all instrument variables and this culminates in a four magnet cycle analysis of CRM U112a (see figure below). This allows monitoring of many performance indicators including SEM yields, hydride formation, Abundance Sensitivity and RPQ performance. Then follows analysis of the ‘bracketing’ standard, -with isotope ratios and signal intensities similar to samples- and when the bracketing standard reproducibility is within expectation, samples are introduced. The instrument is then kept running (with overnight extended wash&standard cycles) for the rest of the week, or until the reproducibility of the bracketing standard gives cause for concern.
'tramline' diagram of CRM112a reproducibility
Reproducibility of ~1‰ for CRM112a uranium metal standard for 234U/238U with the Nu Instruments MC-ICPMS

The MAT262 TIMS is essential for high-precision sample measurements where high temporal resolutionis essential and sample availability is not an issue. TIMS is also used for the characterisation of standards that are used in the standard-sample-standard analysis strategy to correct for instrumental fractionation and drift in MC-ICPMS. This also ensures direct compatibility between the data from 3 instruments.

A UV laser ablation system with a 193 nm Excimer laser is used for the direct analysis of solids for trace element and isotope ratio determinations. A new Coherent: CompexPro F2/100 excimer was recently installed to replace the defunct TUI ExciStar M100V2 unit

The new high-resolution Ortec GEM FX γ-spectrometer is currently used only for analysis within the Pa analysis protocol but has the capability for other environmental analysis.

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© Peter van Calsteren
last updated: 23 December, 2011 10:52