Fluorescent scanning thermal microscope based on a Blu-ray optical head to measure thermal diffusivity of radioactive samples.

Over the life of nuclear fuel, inhomogeneous structures develop, negatively impacting thermal properties. New fuels are under development but require more accurate knowledge of how the properties change to model performance and determine safe operational conditions. Measurement systems capable of microscopic thermal transport measurements and low cost are necessary to measure these properties and integrate into hot cells where electronics are likely to fail during fuel investigation. This project develops a cheaper, smaller, and easily replaceable Fluorescent Scanning Thermal Microscope (FSTM) using the blue laser and focusing circuitry from an Xbox HD-DVD player that incorporates novel fluorescent thermometry methods to determine thermal diffusivity. The FSTM requires minimal sample preparation, does not require access to both sides of the sample, and components can be easily swapped out if damaged, as is likely in irradiated hot cells. Using the optical head from the Xbox for sensing temperature changes, an infrared laser diode provides periodic heating to the sample, and the blue laser induces fluorescence in Rhodamine B deposited on the sample's surface. Thermal properties are fit to modulated temperature models based on the phase delay response at different modulated heating frequencies. With the FSTM method, the thermal diffusivity of a Nordic gold (euro) coin was found to be 21 ± 5 mm/s. This value is compared to laser flash and thermal conductivity microscope methods, which found the thermal diffusivity to be 30.4 ± 0.1 mm/s and 19 ± 3 mm/s. The system shows promise as a feasible property characterization technique with future refinement and testing in progress.