Elastic Properties of Pu Alloys using Resonant Ultrasound Spectroscopy

Determining the elastic properties of Pu alloys and their changes as a function of temperature and time is a powerful tool to study thermodynamic and dynamic changes. Temperature dependence informs the nature of the free energy of the different phases, as elastic moduli are fundamental thermodynamic susceptibilities and connect directly to thermodynamics, electronic structure, and mechanic properties. Changes occurring as a result of self-irradiation change the elastic moduli and affect thermodynamic phase transitions. In turn, these changes are translated to changes in the hardness and brittleness of the compound. Similarly, sound attenuation provides information about dynamic processes such as dissipation associated with defect movement, annealing or re-crystallization. Thus, measurements of elastic moduli and sound attenuation help determine the origin of the phenomena found in ²³⁹Pu and its Ga alloys.<br/>By measuring the mechanical resonance frequencies of a sample, the Resonant Ultrasound Spectroscopy (RUS) technique can extract with extreme precision and accuracy the elastic moduli without corrections. Using RUS we perform time- and temperature-dependent measurements of the mechanical resonance frequencies of polycrystalline Pu with different Ga concentrations. From these measurements, elastic moduli and the sound attenuation can be extracted. I will show the changes in elastic moduli and sound attenuation with time for samples with different ages and Ga concentrations.