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 cm 3 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.