Equation of State of Uranium and Plutonium

Abstract

The objective of this work is to define the parameters of the three-term equation of state for uranium and plutonium, appropriate for conditions in which these materials are subjected to strong shock compressions, as in cylindrical and spherical implosions. The three-term equation of state takes into account the three components of the pressure that resist to compression in the solid: the elastic or "cold" pressure (coulombian repulsion between atoms), the thermal pressure due to vibratory motion of atoms in the lattice of the solid and the thermal pressure of electrons thermally excited. The equation of state defined here permits also to take into account the variation of the specific heat with the transition of the solid to the liquid or gaseous state due to continued growth of temperature in strong shock compressions. In the definition of uranium equation of state, experimental data on the uranium compression, available in the open scientific literature, are used. In the plutonium case, this element was considered initially in the alpha-phase or stabilized in the delta-phase. In the last case, an abrupt and instantaneous transition to the alpha-phase was considered when the delta-phase plutonium is submitted to strong compressions.