Heat capacities of plutonium and neptunium

Abstract

The heat capacity of 242 Pu has been measured between 4 and 300 K. In addition, earlier work on the heat capacities of 237 Np and 239 Pu was extended to lower temperatures. For 242 Pu the conventional method of measurement was employed over most of the temperature range. In view of the high self heating of 239 Pu a different method was used which allowed extension to lower temperatures. 237 Np and 242 Pu were also investigated in this way. 242 Pu did not exhibit the heat capacity anomaly observed in all 239 Pu samples investigated earlier. Owing to the relatively small self heat of 242 Pu its electron heat capacity could be determined below 10 K. Where-­as the temperature coefficient of the linear heat capacity term, γ, was the same when determined at the lowest and highest temperatures in the case of 237 Np (13.7 mJ mol -1 K -2 ), the work on 242 Pu and 239 Pu is consi­stent with γ having approximately twice the value at low than at high temperatures. Electrical resistivity measurements on the 242 Pu sample are in good agreement with previous data for 239 Pu and confirm the high purity of the sample as shown by chemical analysis.