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Studies of einsteinium metal
R. Haire, R. Baybarz
To cite this version:
R. Haire, R. Baybarz. Studies of einsteinium metal. Journal de Physique Colloques, 1979, 40 (C4),
pp.C4-101-C4-102. �10.1051/jphyscol:1979431�. �jpa-00218827�
JOURNAL DE PHYSIQUE Colloque C4, supplément au n° 4, Tome 40, avril 1979, page C4-101
Studies of einsteinium metal (*)
R. G. H a i r e a n d R. D . B a y b a r z ( t )
Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, U.S.A.
Résumé. — Nous avons préparé des films minces d'einsteinium métallique par réduction de Es203 par du lanthane, puis par distillation de Peinsteinium métallique et condensation sur une grille de microscope électronique sur laquelle on a préalablement effectué un dépôt de carbone. Les dépôts de métal ont été analysés par diffraction d'électrons. Les résultats montrent que l'einsteinium déposé à partir de la vapeur est divalent et présente la phase cf c (a0 = 5,75(1) Â) très semblable à la phase dilatée du californium métallique [1, 2 , 3 ] .
Abstract. — Thin films of einsteinium metal were prepared by reducing Es203 with lanthanum, distilling the einsteinium metal, and condensing it on carbon substrates supported by electron microscopy grids. The metal deposits were then analysed by electron diffraction. The results show that vapour-deposited einsteinium metal is divalent and exhibits a fee phase (a0 = 5.75(1) A) very similar to that reported for the expanded form of californium metal [1, 2, 3].
1. Introduction. — T h e scarcity of einsteinium i s o t o p e s a n d t h e high specific radioactivity of t h e m o s t available i s o t o p e (253Es, 5.6 x 1010 a . m i n "1
(xg_1) r e q u i r e t h a t m i c r o t e c h n i q u e s b e u s e d for p r e - paring a n d studying t h e metallic s t a t e of einsteinium.
F u r t h e r , since einsteinium is available only t w i c e a y e a r , it is n e c e s s a r y t o c a r r y out t h e s e studies o v e r a long period of t i m e .
T h e u s e of e l e c t r o n diffraction for studying eins- teinium metal minimizes s o m e of t h e e x p e r i m e n t a l difficulties e n c o u n t e r e d w h e n X - r a y diffraction is u s e d for analysis. T h e larger sample sizes and longer film e x p o s u r e s r e q u i r e d for X-ray analysis a r e not c o m p a t i b l e with t h e rapid d e g r a d a t i o n of t h e m e t a l ' s crystallinity a n d t h e s e v e r e blacking of t h e film in p o w d e r c a m e r a s from t h e s a m p l e ' s radioactivity.
2. Experimental. — T h e einsteinium in this w o r k w a s o b t a i n e d t h r o u g h t h e T r a n s u r a n i u m E l e m e n t s P r o g r a m of t h e U . S . D e p a r t m e n t of E n e r g y . B o t h p u r e 253Es a n d 253Es-254Es m i x t u r e s ( < 1 % 254Es) f r o m several different purification r u n s w e r e u s e d in making t h e metal s a m p l e s . Final purifications of t h e einsteinium w e r e d o n e b y i o n - e x c h a n g e tech- niques [4]. Single p i e c e s ( ~ 20 u.g) of E s203 w e r e p r e p a r e d b y microprecipitation of einsteinium oxala- t e followed b y calcination of t h e latter a t 1 000 °C in air [5].
T h e einsteinium metal s a m p l e s w e r e p r e p a r e d b y r e d u c i n g E s203 with l a n t h a n u m metal a t ~ 1 050 °C in a t a n t a l u m effusion crucible a n d allowing t h e einsteinium v a p o u r t o c o n d e n s e o n a 3-mm O . D . ,
e l e c t r o n m i c r o s c o p y grid w h i c h w a s c o v e r e d w i t h a c a r b o n film. T h e t e c h n i q u e s a n d conditions for einsteinium w e r e similar t o t h o s e previously u s e d for p r e p a r i n g a n d analysing californium metal [1].
3. Results and discussion. — T h e d a t a r e p o r t e d h e r e w e r e o b t a i n e d f r o m e l e v e n E s203- l a n t h a n u m p r e p a r a t i o n s ; a p p r o x i m a t e l y t h r e e s u c c e s s i v e distil- lations a n d d e p o s i t s w e r e obtained f r o m e a c h p r e p a - r a t i o n . S i n c e 10-200 ng of einsteinium w e r e desired on a m i c r o s c o p y grid, e x p e r i m e n t a l conditions w e r e c h o s e n s o t h a t t h e major p o r t i o n of t h e volatilized metal c o n d e n s e d in t h e t a n t a l u m c h i m n e y b e l o w t h e grid. I t w a s e x p e c t e d t h a t this material w o u l d s e r v e as a getter for a n y residual impurities b e f o r e t h e metal s t a r t e d t o d e p o s i t o n t h e grids. T h e a m o u n t of metal d e p o s i t e d on t h e grids w a s a function of t h e a m o u n t of E s203 in t h e crucible, t h e diffusion time a n d t h e t e m p e r a t u r e of b o t h t h e crucible a n d t h e c h i m n e y . A r o u g h e s t i m a t e of t h e q u a n t i t y of einstei- n i u m that h a d collected o n a grid could b e m a d e b y o b s e r v i n g t h e grid in t h e helium a t m o s p h e r e of t h e glove-box in t h e d a r k , and noting t h e illumination that r e s u l t e d from t h e interaction of t h e einstei- n i u m ' s radiation with t h e helium.
A b o u t one-third of t h e grids h a d einsteinium d e p o - sits t h a t initially yielded g o o d e l e c t r o n diffraction p a t t e r n s . T h e remaining s a m p l e s either c o n t a i n e d a n insufficient a m o u n t of einsteinium or h a d a m o r p h o u s - l i k e d e p o s i t s . D e p o s i t s w h i c h w e r e ini- tially crystalline, d e c r e a s e d in crystallinity w i t h time (several h o u r s ) d e p e n d i n g on t h e a m o u n t of einstei- n i u m p r e s e n t . T h e b e s t diffraction p a t t e r n s w e r e o b t a i n e d f r o m t h e h e a v i e r d e p o s i t s , b u t t h e crystalli- nity of t h e s e d e g r a d e d rapidly a n d data t a k e n f r o m t h e s e s a m p l e s w e r e p r o b a b l y affected b y t h e self- irradiation of einsteinium.
(*) Research sponsored by the Office of Basic Energy Scien- ces, U.S. Department of Energy, under contract (W-7405-eng-26) with the Union Carbide Corp.
(+) Deceased.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979431
C4-102 R. G . HAIRE A N D R. D. BAYBARZ
The initially crystalline deposits were indexed on the basis of a fcc structure with a , = 5.75(1)h;
(average of ten samples). The variation in parameter reflects the radiation damage not only t o the einstei- nium deposits but probably also to the internal standard (gold) used to calibrate the wavelength of the electron beam. A line list from one of the samples is given in table I, where a least-squares refinement yielded a lattice parameter of
a , = 5.746(5)
A.
Table I. - Electron diffraction data for einsteinium metal.
hkl
-
111 200 220 3 11 222 400 33 1 420 422 511 440 53 1 620 533
obs.
- 3.317 2.858 2.033 1.736 1.661 1.439 1.318 1.295 1.178 1.110 1.012 0.969 0.909 0.875
calc.
-
3.315 2.871 2.030 1.731 1.658 1.436 1.317 1.284 1.172 1.105 1.015 0.971 0.908 0.876
Intensity - 10
6 8 8 4 2 4 2 2 4 2 4 2 2
When the initial metal deposits were heated in the electron microscope, it was possible to observe the particles coagulate t o form puddles. This process was believed to be due to melting of the metal, and the temperature at this point was taken t o be the melting point of einsteinium metal (860 2 50 "C). As a consequence of the greater reactivity of the molten metal, the carbon substrates had a very limited lifetime under these conditions. No evidence for carbide formation was noted ; it was assumed that the reaction to form carbides was responsible for breakage of the carbon substrate, which then pre- vented further diffraction analysis. In some instan- ces, diffraction patterns attributed to einsteinium oxides [6] were observed after extended heating of the deposits, but oxide formation in the einsteinium samples was less prevalent than found in similar work with rare earth metals.
The fcc form of einsteinium metal is very similar to the divalent form of californium metal prepared either by vapour deposit or by high-temperature trifluoride reduction [ I , 21. Due to the scarcity of einsteinium and its high specific activity, studies of its metallic state will be limited, and another metallic valence state of einsteinium, if it exists, may not be observed. Further, it is necessary to understand fully the californium metal system t o extrapolate its behaviour to aid in interpreting the einsteinium sys- tem. At this point in time, the experimental data for einsteinium metal is consistent with that reported for californium metal, and also with theory, which pre- dicts the increased stability of the divalent state in going across the actinide series [7].
References
[I] HAIRE, R. G. and BAYBARZ, R. D., J. Inorg. Nucl. Chem. 36 [4] BAYBARZ, R . D., KNAUER, J. B. and ORR, P. B., USAEC
(1974) 1295. Rept., ORNL-4672 (1973).
[2] NOE, M. and PETERSON, J. R., Transplutonium Elements, [5] YOUNG, J. P., HAIRE, R. G . , FELLOWS, R. L. and PETERSON, 1975, Miiller and Linder Ed. (North-Holland Pub. Co., J. R . , J. Radioanal. Chem. 43 (1978) 477.
Amsterdam) 1976. [6] HAIRE, R. G . , J. Inorg. Nucl. Chem. 35 (1973) 489.
[3] HAIRE, R. G . and ASPREY, L. B . , Inorg. Nucl. Chem. Lett. 12 [7] NUGENT, L. J . , BURNETT, J. L. and M o ~ s s , L. R., J. Chem.
(1976) 73. Themzodynamics 5 (1973) 665.
