Abstract
The low-temperature heat capacity of (U1−yThy)O2 and 238Pu-doped UO2 samples were determined using hybrid adiabatic relaxation calorimetry. Results of the investigated systems revealed the presence of the magnetic transition specific for UO2 in all three intermediate compositions of the uranium-thorium dioxide (y = 0.05, 0.09 and 0.12) and in the 238Pu-doped UO2 around 25 K. The magnetic behaviour of UO2 exposed to the high alpha dose from the 238Pu isotope was studied over time and it was found that 1.6% 238Pu affects the magnetic transition substantially, even after short period of time after annealing. In both systems the antiferromagnetic transition changes intensity, shape and Néel temperature with increasing Th-content and radiation dose, respectively, related to the increasing disorder on the crystal lattice resulting from substitution and defect creation.
Highlights
Jean-Christophe Griveau[1], The low-temperature heat capacity of (U1−yThy)O2 and 238Pu-doped UO2 samples were determined using hybrid adiabatic relaxation calorimetry
All tetravalent actinide ions can be hosted in the AnO2 dioxide close-packed fluorite structure and complete solid solution series exists between all end members
The heat capacity of (U1−y,Thy)O2 solid solution with y = 0.05, 0.09 and 0.12 is shown in Fig. 1 together with the heat capacity of UO23 and ThO24,5. λ-type anomalies are observed around 27.2 K, 25.1 K and 21.8 K, respectively for the intermediate compositions Th5, Th9 and Th12 with a maximum CP (J · K−1 · mol−1) of 33.3, 23.3 and 20.5, respectively
Summary
Jean-Christophe Griveau[1], The low-temperature heat capacity of (U1−yThy)O2 and 238Pu-doped UO2 samples were determined using hybrid adiabatic relaxation calorimetry. The magnetic behaviour of UO2 exposed to the high alpha dose from the 238Pu isotope was studied over time and it was found that. In both systems the antiferromagnetic transition changes intensity, shape and Néel temperature with increasing Th-content and radiation dose, respectively, related to the increasing disorder on the crystal lattice resulting from substitution and defect creation. The regular substitution of one or more atoms in the crystal lattice of solid solution phases can affect their thermodynamic properties significantly. O21 showed that there is a substantial composition effect and the excess heat capacity was explained by the strain resulting from the substitution of isovalent ions of significantly different size on the cation sublattice, 96 pm for
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