Advancement Towards Collinear Resonance Ionisation Spectroscopy Enhanced ICP-MS for 90Sr Detection

Abstract

The UK nuclear waste inventory is expected to reach a total volume of 4.56 × 106 m3 by 2100. Of this waste, 1.56 × 105 m3 is expected to be cross-boundary waste between low level waste and very low level waste. The characterisation and quantification of radionuclides below the parts-per-trillion (ppt) level (ultra-trace) within this category is estimated to save £1,000 per cubic metre in disposal costs. This equates to an estimated saving of £150M up to 2100. ICP-MS is an ideal technique for introducing an environmental sample into an analytical instrument. However, for isotopes of interest which have isobars that dominate the spectral signal (such as 90Zr with 90Sr), ICP-MS may be combined with higher-selectivity techniques to extending the instrument’s mass resolving power. This work advances the combination of Inductively Coupled Plasma Mass Spectrometry (ICP-MS) with collinear Resonance Ionisation Spectroscopy (CRIS) by (1) establishing a method for strontium analyte retention and 90Zr isobaric suppression through an ICP-MS/MS for ion beam entry into CRIS and (2) the development of a novel PCB linear Paul ion trap for cooling and bunching an ion beam within the CRIS beamline. An Agilent 8900 ICP-MS/MS instrument was optimised for 90Zr suppression whilst retaining strontium. A maximum suppression of 10-5 was achieved via varying oxygen flow rate into the collision/reaction cell. This was then used for environmental sample analysis. Chromatographic separation and cold plasma techniques were also investigated for further isobar suppression. A concentration gradient method was implemented to improve the isotope ratio measurements of 87Sr/86Sr by an order of magnitude, thereby highlighting this method for ICP-MS-CRIS application. An argon ion bunch width of < 2.4 μs was achieved by a PCB trap with a 3D printed chassis. This device forms the basis for a general purpose ion trap which will be implemented in ICP-MS-CRIS instruments for industry and academia, along with the CRIS beamline at ISOLDE, CERN.

Date of Award	1 Aug 2025
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Kieran Flanagan (Supervisor) & Giles Edwards (Supervisor)