An innovative portable detector for the live-monitoring of radionuclides in small terrestrial animals
Radionuclide measurements in wildlife are required to demonstrate that the environment is not significantly impacted by radioactivity. Determination of internal radionuclide activity concentrations often requires destructive sampling. Development of alternative (non-lethal) measurement methods is therefore desirable. This thesis presents the design, construction and testing of a new portable live-monitoring detector for measuring radionuclide activity concentrations in small terrestrial animals. The detector is unique in that it enables field-based measurement of both gamma and beta emitting radionuclides (caesium-137 and strontium-90 are tested in this work) in living small animals. Literature on detector characteristics and radionuclides in the environment informed a modelling approach that was used to optimise the detector design. The optimised design contains two caesium iodide scintillators and two plastic scintillators, which enable the measurement of 137Cs and 90Sr respectively; all four scintillators were shaped and positioned to maximise detection from the organism. Four photomultiplier tubes collect light from the scintillators and a single channel analyser provides signal processing. Surrounding the detection materials is a lead shield designed to give an optimal balance between portability and background reduction. The organism to be measured is put into a card restraint that is designed to humanely secure it during counting. The portable detector was tested in a laboratory using 137Cs and 90Sr sources to determine suitable operation and detection rates. The variation in detection rate caused by source movement within the restraint was determined to be minimal (standard deviation <5 % for 137Cs and <10% for 90Sr) provided the animal is placed in a restraint of similar size to its body. Field testing was then conducted on small rodent and bird species in the Chernobyl Exclusion Zone. Monitoring of internal activity concentrations for small rodents and birds showed a good correlation to results obtained using an alternative verified method (R2 > 0.9 for both 137Cs and 90Sr, N = 10 for each species). The field testing demonstrated the utility of this portable detector in a high radiation background environment for measuring radionuclide contamination within a range of different small animals. The results demonstrate the detector could be used for monitoring radionuclides in protected species and reduce the number of animals euthanised for the purposes of radioecological research. The design choices made provide a template for developing a broader range of detectors that could monitor different radionuclides, organism types and sizes.
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