Preparation, characterization, and decay of einsteinium(II) in the solid state

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Preparation, characterization, and decay of einsteinium(II) in the solid state

J. Peterson, D. Ensor, R. Fellows, R. Haire, J. Young

To cite this version:

J. Peterson, D. Ensor, R. Fellows, R. Haire, J. Young. Preparation, characterization, and decay of einsteinium(II) in the solid state. Journal de Physique Colloques, 1979, 40 (C4), pp.C4-111-C4-113.

�10.1051/jphyscol:1979435�. �jpa-00218831�

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JOURNAL DE PHYSIQUE Colloque C4, supplément au n" 4, Tome 40, avril 1979, page C4-111

Preparation, characterization, and decay of einsteinium(II) in the solid state (*)

J. R. P e t e r s o n , D . D . E n s o r , R. L . F e l l o w s (**), R. G. H a i r e ( t ) a n d J. P . Y o u n g (***) ( t ) Department of Chemistry, University of Tennessee, Knoxville, TN 37916 and Transuranium Research Laboratory, Oak Ridge National Laboratory, Oak Ridge, TN 37830, U.S.A.

(t) Transuranium Research Laboratory, Oak Ridge National Laboratory, Oak Ridge, TN 37830, U.S.A.

Résumé. — Pour la première fois, des échantillons de EsCl2, EsBr2 et Esl2 ont été préparés par réduction des trihalogénures d'einsteinium correspondants par de l'hydrogène à des températures élevées. Les trois dihalogénures ont été caractérisés principalement par leurs spectres d'absorption. Les produits de décrois- sance d'échantillons de EsX2 maintenus à la température ambiante et à la température de l'hélium liquide ont été suivis par spectrophotométrie. Dans tous les cas, l'identification positive des espèces petit-fils, CfX2, a été faite. Aucune preuve spectrale définitive de la présence possible du produit fils BkX2 n'a été obtenue.

Abstract. — Samples of EsCl2, EsBr2, and Esl2 have been prepared for the first time by reduction of the corresponding einsteinium trihalides with hydrogen gas at elevated temperatures. The three dihalides were characterized primarily by their absorption spectra. The products of the decay of EsX2 samples held at ambient and liquid helium temperatures have been monitored by spectrophotometry. In all cases positive identification of the granddaughter, CfX2, species has been made. No definite spectral evidence for the presence of the possible daughter products, BkX2, has been obtained.

1. Introduction. — T w o factors severely limit t h e s t u d y of einsteinium c h e m i s t r y in t h e solid s t a t e : (1) only several h u n d r e d m i c r o g r a m s of einsteinium b e c o m e available t w i c e a y e a r ; a n d (2) t h e intense radiation a s s o c i a t e d with t h e d e c a y of the p r e - d o m i n a n t isotope Es-253 (9.3 x 10s d i s / s • ixg ; 2.5 x 102 k J / m o l • s). B o t h factors r e q u i r e t h a t spe- cial microchemical t e c h n i q u e s b e u s e d in s u c h stu- d i e s , a n d t h e s e c o n d f a c t o r p r e c l u d e s t h e r o u t i n e u s e of X-ray p o w d e r diffraction for t h e analysis of bulk p h a s e einsteinium c o m p o u n d s .

A l t h o u g h t h e e x i s t e n c e of Es(II) h a s b e e n antici- p a t e d for s o m e time [1-3] a n d actually d e m o n s t r a t e d in two, tracer-level e x p e r i m e n t s [4, 5 ] , t h e p r e p a r a - tion of a b u l k p h a s e c o m p o u n d of Es(II) h a s b e e n a c h i e v e d only r e c e n t l y [6]. Since CfCl2 [7], CfBr2 [8], a n d Cfl2 [9] w e r e p r e p a r e d b y h y d r o g e n r e d u c t i o n of t h e c o r r e s p o n d i n g trihalides, w e e x p e c t e d t h a t t h e c o r r e s p o n d i n g Es(II) halides could b e p r e p a r e d in a n analogous w a y . W e r e p o r t h e r e t h e p r e p a r a t i o n of E s C l2, E s B r2, a n d E s l2, their c h a r a c - teristic a b s o r p t i o n s p e c t r a , a n d t h e r e s u l t s of m o n i - toring t h e p r o d u c t s f o r m e d b y t h e r a d i o a c t i v e d e c a y p r o c e s s

2. Experimental. — A c o m p l e t e s u m m a r y of t h e microscale p r e p a r a t i v e a n d s p e c t r o p h o t o m e t r i e t e c h n i q u e s e m p l o y e d in t h e p r e s e n t w o r k is available in [10] a n d t h e r e f e r e n c e s t h e r e i n . T h e r e a c t i o n s 2 EsX3 ( s ) + H2(g) - > 2 EsX2 ( s ) + 2 HX( e ) w e r e carried out b y repetitive t r e a t m e n t s for 15-20 m i n u t e s with H2 at t e m p e r a t u r e s in e x c e s s of 575 °C, 750 °C, a n d 800 ° C , r e s p e c t i v e l y , for t h e successively h e a v i e r h a l i d e s , w i t h intervening e v a c u a t i o n s t o r e m o v e H X . At a n y stage of t h e s y n t h e s i s w e could transfer [10]

t h e sample-capillary unit (closed with a s t o p c o c k ) t o a m i c r o s c o p e - s p e c t r o p h o t o m e t e r for analysis of t h e sample c o m p o s i t i o n . A d j u s t m e n t of t h e conditions of s u b s e q u e n t H2 t r e a t m e n t could t h e n b e m a d e , if n e c e s s a r y , t o e n s u r e essentially c o m p l e t e r e d u c t i o n t o E s X2.

F o r monitoring t h e sample c o m p o s i t i o n a s a function of t i m e , t h e s a m p l e capillary w a s flame sealed u n d e r r e d u c e d p r e s s u r e of H2 or A r . S a m p l e s t o b e s t o r e d in liquid H e w e r e further e n c a p s u l a t e d in a glass t u b e inside a c o p p e r t u b e b e f o r e immer- sion. T h e s e s a m p l e s w e r e r e m o v e d from t h e liquid H e prior t o spectral analysis. I n all c a s e s spectral data w e r e o b t a i n e d at a m b i e n t t e m p e r a t u r e w i t h o u t annealing t h e s a m p l e a n d t h e n again i m m e d i a t e l y following several m i n u t e s ' annealing at ~ 435 °C.

T h e latter t r e a t m e n t generally yields spectral d a t a of higher r e s o l u t i o n t h a n t h a t o b t a i n e d w i t h o u t a n n e a l - ing. H o w e v e r , t h e annealing p r o c e s s itself might effect a chemical c h a n g e in t h e s a m p l e .

3. Results and discussion. — S p e c t r a of E s C l2, E s B r2, a n d E s l2 a r e p r e s e n t e d in figure 1. A s p e c - (*) Research sponsored by the Division of Nuclear Sciences,

U.S. Department of Energy under contracts EY-76-S-05-4447 with the University of Tennessee (Knoxville) and W-7405-eng-26 with Union Carbide Corporation.

(**) Present address : Chemical Technology Division, ORNL.

(***) Analytical Chemistry Division, ORNL.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979435

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C4-112 J. R. PETERSON, D. D. ENSOR, R. L. FELLOWS, R. G. HAIRE AND J. P. YOUNG

WAVELENGTH (nm)

400 500 600 700 900 ti00

I I 1 I I 1 I

Fig. 1. - Absorption spectra of EsC12, EsBr,, Es12 and EsBr,.

trum of EsBr, [ l l ] is included for comparison. The dihalide absorption peak positions as well as the UV cutoffs shift to lower energy with the heavier halides. Some of the f-f absorption peaks of Es(I1) are similar to those of Cf(I1) [7,9], a fact which compli-

cates the interpretation of spectral data obtained from aged EsX, samples.

The reversibility of the

reactions has been demonstrated. We determined through repetitive cycles of chemical syn- thesis/spectral analysis that high temperature (at or above the melting point of EsX,) is required for complete reduction. Low-temperature reduction may lead only to mixed-valence compounds [12].

An interesting feature of our research has been the study of the chemical species that result from the radioactive decay of EsX, compounds. Is BkX,, unknown in bulk phase, produced through the alpha decay of EsX,? Or more generally, are chemical oxidation states maintained through alpha and beta decay processes ? Samples of the three einsteinium dihalides (and one each of (Es, Yb)Cl, and Es(I1) in LaCl,) sealed in Hz and stored at ambient temperature have been under study for various lengths of time.

A sample of EsCl,, sealed in Ar and stored at ambient temperature, is under study as a companion sample to the above to test the influence of the sample's atmosphere. A sample of EsBr, sealed in H z was stored for 200 days in liquid He to minimize sample self-annealing.

Common to all the aged EsX, samples analysed s o far is the presence of the corresponding granddaughter CfX, species and the absence of new absorption peaks which might be attributed to BkX, species. One might speculate that since the parent and granddaughter species have been identified as dihalides, the intermediate, daughter species should also be a dihalide.

In two, aged samples of EsBr,, limited (

<

5 %) oxidation to the (111) state occurred, producing CfBr, in the sample stored at ambient temperature but producing CfOBr in the sample stored in liquid He.

This result, which suggests the occurrence of different chemistry at the different temperatures, awaits confirmation. Continued study of the effects of time, storage temperature, and sample atmosphere on the chemical consequences of the radioactive decay of EsX, is planned or presently underway.

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[2] NUGENT, L. J., BAYBARZ, R. D., BURNETT, J . L. and RYAN, J. L., J. Phys. Chem. 77 (1973) 1528 and the references therein.

[3] DAVID, F., SAMHOUN, K . , GUILLAUMONT, R. and EDELSTEIN, N., J. Inorg. Nucl. Chem. 40 (1978) 69 and the references therein.

[4] EDELSTEIN, N . , CONWAY, J. G . , FUJITA, D . , KOLBE, W. and MCLAUGHLIN, R., J. Chem. Phys. 52 (1970) 6425.

[5] MIKHEEV, N. B . , SPITSYN, V. I., KAMENSKAYA, A. N . , RO-

SENKEVITCH, N . A . , RUMER, I. A. and AUERMAN, L. N . , Inorg. Nucl. Chem. Lett. 8 (1972) 869.

[6] FELLOWS, R. L., PETERSON, J. R., YOUNG, J. P. and HAIRE, R. G . , The Rare Earths in Modem Science and Techno

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logy, McCarthy, G . J. and Rhyne, J. J. Editors (Plenum Press, New York) 1978, p. 493.

[7] PETERSON, J. R . , FELLOWS, R. L., YOUNG, J. P. and HAIRE, R. G . , Radiochem. Radioanal. Lett. 31 (1977) 277.

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PREPARATION, CHARACTERIZATION, AND DECAY OF EINSTEINIUM(I1) C4-113

[8] PETERSON, J. R. and BAYBARZ, R. D., Inorg. Nucl. Chem. [ l l ] FELLOWS, R. L., PETERSON, J. R., NOE, M., YOUNG, J. P.

Lett. 8 (1972) 423. and HAIRE, R. G., Inorg. NucI. Chem. Lett.

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^~ ^f ^, ^E[12] HAIRE, ^~ R. G . , YOUNG, J. P., PETERSON, J. R. and FELLOWS, J. P., J. Inorg. Nucl. Chem. 40 (1978) 811. R. L., The Rare Earths in Modem Science and Techno-

logy, McCarthy, G . J . and Rhyne, J. J. Editors (Plenum [lo] YOUNG, J. P., HAIRE, R. G., FELLOWS, R. L. and PETERSON, Press, New York) 1978, p. 501, and the references

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