ALLOTROPIC TRANSITIONS OF NEPTUNIUM AND PLUTONIUM DETERMINED USING DIFFERENTIAL THERMAL-ANALYSIS

Temperatures and enthalpies of transition for Np and Pu have been determined using differential thermal analysis. The resuts for Np are α → β 282°C, 4.73 kJ mol; β → γ 583°C, 2.99 kj mol; and γ → l 644° C, 3.19 kJ mol. A comparison of the results obtained for Pu with those previously reported by others shows the accuracy of the technique. A value of 18.4 g cm3 for the density of γ-Np at 583 °C was calculated from the measured heat and the pressure variation of the transition [1]. Additional evidence for a fourth allotrope of Np is presented. © 1990.