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Detection of radiological hazards in the solution phase using conventional means is considerably more
difficult than in the gas phase. A new approach is required to provide a reliable, specific and low cost
method of protecting sensitive national assets, such as water supplies, from a terrorist dirty bomb attack.
Fibre optic sensors provide the required speed of response, the optical platforms are mature and of
relatively low cost with proven reliability in the field. This paper describes the combination of a low cost
sensor platform and smart sensor molecule (Isoamethyrin) for the selective determination of uranyl and
other actinide species in water at sub ppm levels. Isoamethyrin is a synthetic porphyrin which has been
demonstrated to show high selectivity for uranyl ions with an associated colour change on complexation.
Fibre optic sensors are created by revealing an evanescent wave in a section of the fibre and covalently
bonding the isoamethyrin to the fibre surface in this region. Colour changes occurring as a result of
interaction between isoamethyrin and uranyl ions are monitored over 3 wavelength ranges covering the
red, green and blue regions of the visible spectrum. Sensors created in this manner were found to be fast
responding (<5s), sensitive (detection threshold <500ppb), specific (response restricted to certain
actinides and lanthanides) and low cost.
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