Self-diffusion in plutonium metal
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W. SHORT,
JOHN
C. WALDEN,
We have d e t e r m i n e d s e l f - d i f f u s i o n coefficients for the epsilon, d e l t a p r i m e , delta, g a m m a , and beta p h a s e s of p o l y c r y s t a l l i n e p l u t o n i u m by the " t h i n f i l m " t r a c e r technique, and fine s e c t i o n i n g . Our e x p e r i m e n t s e n c o m p a s s e d a s a m p l e t e m p e r a t u r e r a n g e f r o m 393 to 886 K. The c o r r e s p o n d i n g diffusion t i m e s r a n g e d f r o m about 4 h to one y e a r . Although our r e s u l t s for the e p s i l o n phase c o r r o b o r a t e those of o t h e r s , our lattice diffus i v i t y v a l u e s for the d e l t a and g a m m a p h a s e s differ s i g n i f i c a n t l y f r o m p r e v i o u s l y r e p o r t e d v a l u e s . Our Do value for delta p l u t o n i u m is t w o - o r d e r s - o f - m a g n i t u d e higher than p r e v i o u s l y r e p o r t e d and our a c t i v a t i o n e n e r g y is about 30 pct h i g h e r . However, in c o n t r a s t to other s t u d i e s , our m e a s u r e m e n t s for the delta p l u t o n i u m phase c o v e r e d the e n t i r e t e m p e r a t u r e - s t a b i l i t y r a n g e . Diffusivity v a l u e s for the d e l t a - p r i m e phase have not p r e v i ously b e e n r e p o r t e d . Our diffusivity m e a s u r e m e n t s a r e r e a s o n a b l e , although our Do value and the a c t i v a t i o n e n e r g y d e r i v e d by l e a s t s q u a r e s a r e q u e s t i o n a b l y high. We have obt a i n e d new v a l u e s for lattice d i f f u s i v i t i e s for the g a m m a and b e t a p h a s e s . Values for the l a t t e r have not b e e n p r e v i o u s l y r e p o r t e d . We i n t e r p r e t r e l a t i v e l y high d i f f u s i v i t i e s r e p o r t e d e a r l i e r for the g a m m a phase as r e s u l t i n g f r o m s h o r t - c i r c u i t path effects. The u s u a l c o n c e n t r a t i o n v s p e n e t r a t i o n c u r v e s r e p o r t e d h e r e for g a m m a and beta p h a s e s a r e a n a l y z e d in t e r m s of d i s l o c a t i o n and other s h o r t - c i r c u i t paths. The f i n e r s e c t i o n i n g technique used in this study allowed us to s e p a r a t e the t r u e lattice d i f f u s i v i t i e s f r o m the s h o r t - c i r c u i t effects found in our g a m m a - and b e t a - p h a s e m e a s u r e m e n t s .
THE
self-diffusion coefficients of plutonium have previously been experimentally determined for the epsilon, delta and gamma phases. Divergent values were reported by Cornet I and Dupuy and Calais e for the epsilon phase. Tate and Cramer a published the only data for the delta phase, and their values for the activation energy and frequency factor appear to be much lower than either theory or correlation would indicate. The only values reported for the gamma phase are those of Tate and Edwards. 4 Consequently, the objectives of the present study were to resolve conflicting data, to verify or correct single source data, and to determine s
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