The determination of pure beta-emitters and their behaviour in a salt-marsh environment
The thesis describes the development of analytical procedures for the isolation and measurement of anthropogenic pure beta-emitting radioisotopes in low-level radioactive wastes and environmental samples. The research focussed on three key pure beta-emitting radioisotopes, namely 63Ni, 90Sr and 99Tc. Iron-55, which decays by electron capture, was also investigated. Source preparation and measurement techniques based on liquid scintillation counting were developed and optimised to permit the low-level measurement of all four radioisotopes. In particular, a technique was developed for increasing the amount of stable Fe that may be loaded into scintillant, reducing the limit of detection achievable for 55Fe measurement and increasing the sensitivity of analysis for 55Fe in Fe-rich materials such as sediments and steels. Chemistries for the isolation of the four radioisotopes were studied and optimised. Solvent extraction was chosen for the specificity offered by the technique. In most instances, improvements in separation efficiency were achieved by adsorbing the extractant onto an inert support producing an extraction chromatographic material. Key separation techniques were then combined to produce a sequential separation scheme that permitted a more rapid analysis of the four radioisotopes on a single sample. The sequential separation technique was then optimised for the analysis of 55Fe, 63Ni, 90Sr and 99Tc in both low-level wastes and environmental matrices (mainly sediments). Such separation schemes are crucial to the efficient analysis of samples in limited time spans and are vital when the amount of sample available is restricted. The optimised methods were used to investigate levels of anthropogenic pure beta-emitters in a saltmarsh sediment core collected from the Esk Estuary in Cumbria. Analysis of the four beta emitting radioisotopes was complemented by the analysis of major elements, trace elements and gamma emitting radioisotopes. This information was used to determine the behaviour of the beta emitters following deposition within the saltmarsh environment. Although all four beta emitters were detected in the core, only 90Sr and 99Tc were at sufficiently high levels to permit a more thorough investigation. The combination of geochemica! analysis and radiochemical analysis of this range of radioisotopes with widely varying chemistries has allowed a range of possible pre- and post-depositional processes to be investigated as well as providing data on the levels of previously unmeasured beta emitters in the saltmarsh environment. Such information is essential in assessing the long-term retention and potential re-release of these radioisotopes and their importance in radiological dose assessment. The information also has wider implications to the behaviour of inorganic pollutants in coastal waters.