Abstract
Nanograined nuclear materials are expected to have a better performance as spallation targets and nuclear fuels than conventional materials, but many basic properties of these materials are still unknown. The present work aims to contribute to their better understanding by studying the effect of grain size on the melting and solid–solid transitions of nanograined UC2−y. We laser-heated 4 nm–10 nm grain size samples with UC2−y as the main phase (but containing graphite and UO2 as impurities) under inert gas to temperatures above 3000 K, and their behavior was studied by thermal radiance spectroscopy. The UC2−y solidification point (2713(30) K) and α-UC2 to β-UC2 solid–solid transition temperature (2038(10) K) were observed to remain unchanged when compared to bulk crystalline materials with micrometer grain sizes. After melting, the composite grain size persisted at the nanoscale, from around 10 nm to 20 nm, pointing to an effective role of carbon in preventing the rapid diffusion of uranium and grain growth.
Highlights
The Isotope Separator On-Line (ISOL) technique allows the production of a wide variety of radioisotopes that can be used in many applications, such as nuclear physics, astrophysics, solid-state sciences, and medicine [1,2]
Results and Discussion certainty of ±1% was used for the values of temperature measured in this work
The higher-temperature thermal arrest was observed at 2713(30) K, which is slightly higher than the 2700 K reported for the β-UC2−y melting temperature by Benz et al [29] but lower than the 2737 K value more recently published [6]. These results indicate that the nanograined β-UC2−y material had a soser-heating cycles with different laser settings, that both temperature anomalies were independent of the laser pulse power and duration, within the experimental uncertainty
Summary
The Isotope Separator On-Line (ISOL) technique allows the production of a wide variety of radioisotopes that can be used in many applications, such as nuclear physics, astrophysics, solid-state sciences, and medicine [1,2]. In this method, a high-energy beam of atomic or subatomic particles hits a nuclear spallation target. The isotopes are formed by fragmentation, fission, and spallation nuclear reactions inside the target material They diffuse, effuse, vaporize, or sublimate; pass through an ionizer cavity; and are electrostatically accelerated and separated. High temperatures are usually needed to ensure the rapid diffusion, effusion, and vaporization or sublimation of isotopes [3]
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