The Effect Of Lattice Disorder On The Low-Temperature Heat Capacity Of (U1-Ythy)O-2 And Pu-238-Doped Uo2

The low-temperature heat capacity of (U1-yThy)O-2 and Pu-238-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 Pu-238-doped UO2 around 25 K. The magnetic behaviour of UO2 exposed to the high alpha dose from the Pu-238 isotope was studied over time and it was found that 1.6% Pu-238 affects the magnetic transition substantially, even after short period of time after annealing. In both systems the antiferromagnetic transition changes intensity, shape and Neel temperature with increasing Th-content and radiation dose, respectively, related to the increasing disorder on the crystal lattice resulting from substitution and defect creation.