The low-temperature heat capacity of (U_1-yAm_y)O _2−x for y = 0.08 and 0.20

The low-temperature heat capacity of (U _1-y,Am_y)O _2−x solid solution with y = 0.0811 and 0.2005 and x = 0.01–0.03 was determined from a minimum of 12.52 K up to 297.1 K and from 9.77 K up to 302.3 K, respectively, using hybrid adiabatic relaxation calorimtry. The low temperature heat capacity results of the investigated system revealed the absence of the magnetic transition specific for UO₂ in the temperature region of 30 K. Since there are no experimental data available for AmO₂ in this temperature region, the results obtained for the intermediate compositions are validated based on the experimental data of UO₂ end-member and the low-temperature heat capacity computation of AmO₂. In the measured temperature interval, excess heat capacity was observed for the two investigated intermediate compositions, which is concluded to be dominated by self-radiation effects at very low temperature.