THEORY OF RECONSTRUCTIVE TRANSFORMATIONS IN ACTINIDE ELEMENTS - PACKING OF NONSPHERICAL ATOMS AND MACROSCOPIC SYMMETRIES

Atomistic and macroscopic mechanisms explaining the formation of the s tructures in crystals of eleven actinide elements are given, and shown to correspond to a small number of irreducible degrees of freedom of the parent bcc structure. The causes of the rich polymorphism and idio syncratic structures found in U, Np, and Pu are assigned to a close pa cking of ovaloid atoms. The incommensurate structure found in alpha-U is interpreted in this framework.