In this paper we introduce a new mathematical model, which can be used to investigate the response of a long-period fibre grating to changes in ambient refractive indices of values both greater and less than that of the cladding. A numerical method to calculate the HE core and cladding modes is presented. The results show that even when the ambient refractive index is higher than that of the cladding, the coupling (resonance) wavelengths experience a measurable shift (a few nm). The result obtained suggests that LPGs coated with a material of higher refractive index than the cladding may be used as index sensors.

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The gas-phase synthesis of uranyl fluoride (UO 2 F 2 ) particles via the hydrolysis of uranium hexafluoride (UF 6 ) has been investigated in a purposely designed laboratory-scale aerosol reactor. An in situ particle sampling technique was developed for collecting particle samples from a chemically aggressive and safety critical environment. The effects of two key process variablessnamely, UF 6 concentration and the molar ratio of steam to UF 6 son the particulate product properties were investigated. Image analysis of environmental scanning electron microscopy (ESEM) images of sampled particulates indicated an increase in the mean single particle size with residence time. The number and size of agglomerates also increased as a function of residence time, suggesting the presence of both surface reaction and coagulation growth mechanisms. A notable transition of the UO 2 F 2 particles from a spherical morphology to a platelet morphology was observed when the UF 6 concentration and the steam:UF 6 ratio reached values of 1.3 × 10 -3 mol/L and 10, respectively.

AlN thin film ultrasonic transducers are being developed for non-destructive testing (NDT) applications in detection and monitoring in a high temperature environment. The ultrasonic transducers were fabricated by RF sputter deposition of c-axis oriented AlN films on aluminum alloy and carbon steel substrates. High temperature performance and durability of the transducers were investigated using pulse-echo experiments at elevated temperatures, and the transducer failure mode was characterized. Results showed that the sputtered AlN films maintained a stable crystalline structure and orientation at elevated temperatures up to 600 °C. The high temperature performance of the ultrasonic transducers, however, was limited by the deterioration of substrate properties. The high temperature limit for the films on aluminum alloy was found to be the melting temperature of the substrate. The AlN films deposited on the carbon steel substrate operated up to 500 °C, but if the temperature was increased further, rapid surface oxidation of the carbon steel caused the transducer to fail.