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Traceable measurement of medium and long-lived radionuclides for improved understanding of past, current and future climate change
by Dr. Ben Russell, Dr. Steven Bell, Dr. Hibaaq Mohamud, Dr. Emma Braysher, Mrs./Ms. Saskia Burke, Mrs./Ms. Svetlana Kolmogorova


Radionuclides with natural and cosmogenic origins are deposited in a range of environments including terrestrial sediments, snow and ice. These radionuclides can be used to improve the understanding of past climate, in turn helping with understanding current and projections of potential future climate changes. For example, 231Pa and 230Th occur naturally as part of the 235U and 238U decay chains. Analysis of the 231Pa/230Th isotopic ratio in sediment cores have been able to show historic changes that match the timing and magnitude of Atlantic and Meridional Overturning Circulation strength that improves understanding of abrupt past climate changes. Another example is assessment of changes in naturally occurring 14C in CO2 air samples as a result of increased contribution from fossil fuel combustion. To maximise the benefits of radionuclide metrology as a tool for climate change measurement, robust and reproducible procedures must be developed to expand the radionuclides measurable, supported by the provision of traceable standards for end-users, as well as precise and up-to-date recommended half-life values. This work presents results from a project involving several groups from the National Physical Laboratory, including Nuclear Metrology, Air Quality and Aerosol Metrology, and Emissions and Atmospheric Metrology. The strength of the project is combining expertise in stable and radioactive pollutant measurements to enhance measurement capabilities across a number of sectors including nuclear decommissioning, emergency preparedness, emission inventories and environmental regulation. The outcomes include provision of new standards, including 14C gas standards and isotopic ratio standards for source attribution, expanded measurement services, new international comparisons, and novel methods including a procedure for pre-concentration of atmospheric CO2. The expertise in areas such as gas counting and isotope ratio tandem plasma mass spectrometry (ICP-MS/MS) has expanded the number of radionuclides measurable, including a number of cosmogenic and naturally occurring radionuclides (3H, 210Pb, 32Si, 14C, 36Cl, 235U and 238U). The half-lives of these radionuclides ranges from approximately ten years to millions of years, enabling contributions to climate modelling over a range of timescales. This work will present the development of methods for determination of these radionuclides, including development of traceable standards and half-life measurement, utilising decay counting, gas counting and mass spectrometric capabilities. The results show how collaboration between different groups can expand the number of radionuclides measurable, and consequently the extent to which this can improve climate monitoring and enhance understanding of past, current and future climate change events.


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Topic : Theme 1: Biosphere Monitoring.
Reference : T1-D12

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