The melting behaviour of plutonium dioxide: A laser-heating study

In this work the melting behaviour of plutonium dioxide has been studied for the first time via laser heating. With this method, the short experiment duration combined with minimal contact between sample and containment minimized undesired side effects, such as sample reduction, vaporisation or reaction with the holder. The sample temperature was measured by fast pyrometry, and inflections in the recorded thermograms revealed the liquid-to-solid transition. This latter was also detected via a method based on the reflectance study of a low-power laser beam reflected by the sample surface. Multi-channel spectro-pyrometry was used to investigate, in parallel, the normal spectral emittance of the samples in the wavelength range between 550 and 920 nm at the investigated temperature. The present experimental melting temperature of (3017 ± 28) K is much higher than the values obtained in the past by traditional heating techniques. It is suggested that, in contrast to the present data, previous results were affected by extensive reaction of the plutonium dioxide samples with the containment and/or changes in the O/Pu ratio at high temperature.