Lanthanide and Actinide Chemistry and Spectroscopy - American

11

T e c h n i q u e s of M i c r o c h e m i s t r y a n d Some

Transcurium

Their

Applications

E l e m e n t s at B e r k e l e y a n d

Oak

to

Ridge

Downloaded by UNIV OF ARIZONA on April 26, 2017 | http://pubs.acs.org Publication Date: September 23, 1980 | doi: 10.1021/bk-1980-0131.ch011

J. R. PETERSON Department of Chemistry, University of Tennessee, Knoxville, T N 37916 and Transuranium Research Laboratory, Oak Ridge National Laboratory, Oak Ridge, TN 37830 Research on the transcurium elements r e q u i r e s s p e c i a l i z e d techniques. The inherent radioactivity of these elements often precludes otherwise r o u t i n e m a n i p u l a t i o n s , and the s m a l l amounts a v a i l a b l e r e q u i r e the development of n o v e l techniques to facilitate the study of their basic chemical and p h y s i c a l p r o p e r t i e s . Much of our present knowledge of the i n o r g a n i c and p h y s i c a l chemistry of the transuranium elements was first obtained from the a p p l i c a t i o n of microchemical techniques to submicrogram q u a n t i t i e s of m a t e r i a l . Indeed, the primary justification for the techniques of microchemistry is found in t h e i r a p p l i c a t i o n to the i n v e s t i g a t i o n of r a r e m a t e r i a l s . P r i o r to 1942 these a p p l i c a t i o n s were chiefly i n the fields of organic and biochemistry. With the p r o d u c t i o n of the first few micrograms of plutonium in June 1942, it became necessary to develop a broad a r r a y of microchemical methods s u i t e d to s u b m i l l i g r a m q u a n t i t i e s of m a t e r i a l . I t is not the purpose here to review all these techniques, but i n s t e a d to focus on those which c o u l d be or have been used f o r the study of some p r o p e r t i e s of Bk-249, Cf-249, and Es-253 on the microgram to milligram s c a l e . Excluded here are those techniques r e l a t i n g to t r a c e r - l e v e l work (below weighable q u a n t i t y of sample; measurement by r a d i o assay o n l y ) , f o r the concern here w i l l be w i t h the determination of b u l k p r o p e r t i e s of these elements. Tracer-scale studies u s u a l l y r e v e a l d i r e c t l y o n l y one property of the element under i n v e s t i g a t i o n , t h a t i s , i t s r e l a t i v e preference f o r one e n v i r o n ment over another, or more s i m p l y , i t s phase d i s t r i b u t i o n . Nevert h e l e s s , as each new transuranium element was discovered and was a v a i l a b l e o n l y i n t r a c e q u a n t i t i e s , a great d e a l of chemistry was learned by inference from t r a c e r - s c a l e s t u d i e s , i n c l u d i n g the i d e n t i t y of o x i d a t i o n s t a t e s , approximate v a l u e s of o x i d a t i o n or r e d u c t i o n p o t e n t i a l s , the composition and s t a b i l i t y of complex i o n s , and r e l a t i v e v o l a t i l i t i e s . In an e f f o r t to provide both some h i s t o r i c a l p e r s p e c t i v e of the development and some current usage of microchemical t e c h n i q u e s , as w e l l as to p r o v i d e some r e s u l t s of t h e i r r e s p e c t i v e 0-8412-0568-X/80/47-131-221$05.50/0 © 1980 American Chemical Society Edelstein; Lanthanide and Actinide Chemistry and Spectroscopy ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

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a p p l i c a t i o n s , the present d i s c u s s i o n w i l l be l i m i t e d to two main areas of r e s e a r c h . The f i r s t , s y n t h e s i s , i s the more important, s i n c e any program to study the bulk p r o p e r t i e s of the transcurium elements r e q u i r e s the s y n t h e s i s of the p a r t i c u l a r metal or compound of i n t e r e s t . Treated here as examples w i l l be the preparat i o n s of the m e t a l l i c s t a t e and s e v e r a l b i n a r y compounds l i k e oxides, h a l i d e s , chalcogenides, and p n i c t i d e s . The second area, i n v e s t i g a t i v e methods, w i l l d e a l p r i m a r i l y with a b s o r p t i o n spectrophotometry but w i t h some mention of the X-ray and e l e c t r o n d i f f r a c t i o n methods which have c o n t r i b u t e d much to the e l u c i d a t i o n of the s t r u c t u r a l p r o p e r t i e s of Bk, Cf, and Es.


C r i t e r i a f o r S e l e c t i o n of Microchemical

Techniques

Although space i s not a v a i l a b l e f o r a complete d i s c u s s i o n , the reader should be aware of the f o l l o w i n g f a c t o r s which i n fluence the choice of a p a r t i c u l a r technique f o r use i n t r a n s curium element r e s e a r c h : 1. A p p l i c a b i l i t y - the technique must be able to accomp l i s h the d e s i r e d goal on the s c a l e of o p e r a t i o n mandated by the a v a i l a b l e sample s i z e . One proves out any new technique by u s i n g i t on a s u b s t i t u t e sample (most o f t e n these are lanthanide m a t e r i a l s ) where c o n f i r m a t i o n of an a l r e a d y known property i s possible. 2. Safety of experimenter and equipment - here containment of the r a d i o a c t i v e sample i s the key f e a t u r e ; a l s o important i s the ease of manipulation i n order to minimize the chances of r a d i o a c t i v e contamination. 3. Maintenance of sample p u r i t y - f o l l o w i n g the d i f f i c u l t task to s y n t h e s i z e samples of h i g h p u r i t y , i t i s necessary to avoid t h e i r chemical contamination by the very a p p l i c a t i o n of some p a r t i c u l a r technique. Indeed, one of the most formidable problems encountered i n working w i t h very small samples i s that of maintaining a h i g h degree of sample p u r i t y through a s e r i e s of chemical and mechanical manipulations. Because of the great i n c r e a s e of the s u r f a c e - t o volume r a t i o [« (sample r a d i u s ) " ] on the m i c r o s c a l e , as compared to that on the macroscale, "chance" contamination i s much more probable w i t h small samples. A general g u i d e l i n e to use i n m i c r o s c a l e r e s e a r c h work i s to keep the a c t i n i d e sample i n a conc e n t r a t e d form and i n a small volume c o n t a i n e r . This l i m i t s the source of r a d i o a c t i v i t y and minimizes the e f f e c t s of chemical contamination of the sample by "chance" contact of the sample w i t h some impurity. 1

S i n g l e Ion-Exchange Resin Bead Technique One of the p i o n e e r i n g microchemical techniques developed i n the l a b o r a t o r y of the l a t e P r o f e s s o r B u r r i s B. Cunningham at the

Edelstein; Lanthanide and Actinide Chemistry and Spectroscopy ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

11.

Techniques

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(now) Lawrence Berkeley Laboratory was the s i n g l e ion-exchange r e s i n bead technique f o r the c o n c e n t r a t i o n and m a n i p u l a t i o n of p u r i f i e d a c t i n i d e i o n s . I n d i v i d u a l r e s i n beads a r e loaded t o s a t u r a t i o n by e q u i l i b r a t i o n w i t h a d i l u t e a c i d s o l u t i o n of the a c t i n i d e i o n . Excess a c t i n i d e and s u r f a c e contaminants a r e e a s i l y removed by washing the loaded bead i n water o r d i l u t e a c i d . The amount o f a c t i n i d e sorbed i s c o n t r o l l e d by the s i z e o f the r e s i n bead chosen; f o r example, 1 yg of a t y p i c a l t r i v a l e n t a c t i n i d e i o n i s sorbed by a Dowex 50 x 4 r e s i n bead whose a i r d r i e d (from H 0) diameter i s 0.15 mm. An a c t i n i d e - l o a d e d bead i s e a s i l y manipulated on a quartz f i b e r , represents an a c t i n i d e c o n c e n t r a t i o n of about 2 M, and, being s p h e r i c a l , has only a s i n g l e p o i n t of contact w i t h i t s c o n t a i n e r , thus m i n i m i z i n g s u r f a c e o r " c o n t a c t " chemical contamination. Examples o f the use of the s i n g l e bead technique f o r the p r e p a r a t i o n o f a c t i n i d e metal and compounds and f o r t h e study o f s p e c t r o s c o p i c and magnetic p r o p e r t i e s o f t r i v a l e n t a c t i n i d e ions a r e found i n t h e l i t e r a t u r e (1».2>3>4^5) . Here the p r e p a r a t i o n s o f b i n a r y compounds and the pure metals are discussed f i r s t . Then the development of microtechniques f o r o b t a i n i n g a b s o r p t i o n s p e c t r a i s t r a c e d from the use of s i n g l e beads o f ion-exchange r e s i n t o our present-day microscope spectrophotometer f a c i l i t y a t the Oak Ridge Transuranium Research Laboratory (TRL).


2

Compound P r e p a r a t i o n on the M i c r o s c a l e S t a r t i n g w i t h an a i r - d r i e d , a c t i n i d e - l o a d e d , s i n g l e r e s i n bead, an oxide i s produced by c a l c i n i n g the bead i n a i r o r oxygen at 1200 °C. A t the TRL the apparatus shown diagrammatically i n F i g u r e 1 i s used; the bead i s placed i n a P t c r u c i b l e which i s heated by r a d i a t i o n from an e n c i r c l i n g P t i n d u c t i o n s h i e l d . The r e s u l t i n g oxide sample might be t r a n s f e r r e d t o a s i l i c a c a p i l l a r y tube f o r attachment t o a general preparation/vacuum system ( F i g u r e 2) f o r subsequent chemical treatment. Alternatively, i t might be used d i r e c t l y f o r study by an a p p l i c a b l e p h y s i c a l property measurement technique, l i k e X-ray powder d i f f r a c t i o n , magnetic s u s c e p t i b i l i t y , s o l u t i o n c a l o r i m e t r y , e t c . The chemistry r e q u i r e d t o convert the oxide t o other b i n a r y compounds i s independent o f the s c a l e o f o p e r a t i o n . However, w i t h m i c r o s c a l e s y n t h e t i c methods a p p l i e d t o r a d i o a c t i v e m a t e r i a l s , s u c c e s s f u l p r e p a r a t i o n s are achieved more r e a d i l y by c a r r y i n g out the chemistry i n s i t u , t h a t i s , i n such a manner that e l i m i n a t e s , o r a t l e a s t minimizes, the n e c e s s i t y of having to "handle" the sample d u r i n g o r f o l l o w i n g i t s s y n t h e s i s . Thus, a c t i n i d e compounds are u s u a l l y prepared i n s i l i c a c a p i l l a r y tubes which can be flame sealed a t the c o n c l u s i o n o f a s y n t h e s i s to provide the d e s i r e d sample f o r study i n a s m a l l volume, quartz c o n t a i n e r . A s p e c i a l f e a t u r e o f the preparation/vacuum system i n the TRL i s the c a p a b i l i t y t o i n t e r r u p t a s y n t h e s i s , i s o l a t e (by means o f a stopcock) and remove the sample, examine i t i n



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Figure 1.

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Schematic of resin-head calcination apparatus



Figure 2.

5

DRYING T U B E

ABSOLUTE P R E S S U R E GAGE

Schematic of preparation-vacuum system used for synthesizing transcurium element compounds

2

jillll P 0



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s i t u v i a a b s o r p t i o n spectrophotometry and/or X-ray d i f f r a c t i o n , and then r e t u r n i t to the preparation/vacuum system should a d d i t i o n a l chemistry be r e q u i r e d . In Table I are summarized some g e n e r a l l y u s e f u l chemical r e a c t i o n s f o r the p r e p a r a t i o n of transplutonium element metal and some compounds. For s i m p l i c i t y , and because of v a r i a b l e o x i d a t i o n s t a t e s , the equations are not n e c e s s a r i l y balanced. The o x a l a t e p r e c i p i t a t i o n and subsequent c a l c i n a t i o n to the oxide i s reserved f o r multimicrogram and greater q u a n t i t i e s of a c t i n i d e s and f o r Es-253, whose i n t e n s e r a d i a t i o n precludes the use of the r e s i n bead technique. The p r e p a r a t i o n of f l u o r i d e compounds i s not c a r r i e d out i n quartz but i n Monel ( 6 ) . D e t a i l s of the cond i t i o n s of temperature, pressure, e t c . to e f f e c t these chemical r e a c t i o n s are a v a i l a b l e i n the l i t e r a t u r e (1,3,6-11). Metal P r e p a r a t i o n on the M i c r o s c a l e Two methods f o r producing transcurium element metal are l i s t e d i n Table I. In both routes the a c t i n i d e compound, which might have been prepared u s i n g the s i n g l e bead technique, and reductant metal are placed i n a metal c r u c i b l e ( u s u a l l y Ta), which i s heated to promote the r e d u c t i o n r e a c t i o n . The method of c h o i c e depends upon the q u a n t i t y of a c t i n i d e a v a i l a b l e and the p h y s i c a l form of the product metal r e q u i r e d . For b u l k product metal w i t h only a l i m i t e d amount of m a t e r i a l (yg q u a n t i t i e s ) , the f l u o r i d e r e d u c t i o n method i s b e t t e r . The e s s e n t i a l d i f f e r e n c e i n the two s y n t h e t i c routes i s that i n the f l u o r i d e r e d u c t i o n , the product metal remains i n s i d e the c r u c i b l e system (byproducts, excess reductant, and v o l a t i l e i m p u r i t i e s l e a v e ) , whereas i n the oxide r e d u c t i o n , the product metal leaves the heated c r u c i b l e (along w i t h any v o l a t i l e i m p u r i t i e s ) and d e p o s i t s on a c o o l e r s u r f a c e , completely separated from the byproduct oxide, nonv o l a t i l e i m p u r i t i e s , and excess reductant. Unless at l e a s t s e v e r a l hundred micrograms of metal are being produced, the metal product obtained by oxide r e d u c t i o n i s i n the form of a thin f o i l . Advantage has been taken of t h i s form of metal product f o r s t r u c t u r a l s t u d i e s by e l e c t r o n d i f f r a c t i o n (12). The apparatus used f o r the production of metal on the few microgram s c a l e v i a f l u o r i d e r e d u c t i o n has been improved cons i d e r a b l y between i t s use f o r the f i r s t p r e p a r a t i o n of Bk metal (2) and the more recent p r e p a r a t i o n s of Bk metal on the h a l f m i l l i g r a m s c a l e (13,14) and Cf metal on the A n ( C 0 ) 2

2

4

3

+

An oxide

Halides An oxide + HX -> AnX An + HX -> AnX AnX

3

3

+ H

+ HI -> A n l

3

AnX

3

+ H

2

+ AnX

2

+ H0 2

(An + X

2

2

-> AnX ) 3

+ HX

o

2

2

AnF^

Oxyhalides An oxide ( A n X j + HX/H 0 3 2 Semimetallies An metal + H

(X = F,Cl,Br)

+ HX

An oxide (AnF ) + F 3

3

r

gas

> AnOX

-> An hydride

An metal + VA element •> An p n i c t i d e An metal + VIA element -* An chalcogenide


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p r o p e r t i e s of these small samples (18). A l s o the s o l u t i o n m i c r o c a l o r i m e t e r (19) a t Oak Ridge has s u f f i c i e n t s e n s i t i v i t y to measure the heats o f r e a c t i o n o f these metal samples with aqueous a c i d . The p r e c i s i o n o f the r e s u l t s o f the c a l o r i m e t r i c and magnetic s u s c e p t i b i l i t y measurements i s s e v e r e l y l i m i t e d on the m i c r o s c a l e by the p r e c i s i o n to which the samples can be weighed. Both i n v e s t i g a t i v e devices were s p e c i f i c a l l y designed f o r the c a p a b i l i t y of o b t a i n i n g data from samples o f transcurium elements and compounds.


Absorption Spectrophotometry on the M i c r o s c a l e Techniques f o r o b t a i n i n g a b s o r p t i o n s p e c t r a from small samples o f transcurium element species have advanced c o n s i d e r a b l y over the l a s t twenty years. In a f i r s t attempt to observe the s o l u t i o n a b s o r p t i o n spectrum o f Bk(III) i n a " r i s k f r e e " manner, Cunningham and colleagues (5) i n the l a t e 1950s attached a c a p i l l a r y a b s o r p t i o n c e l l (y 7 yL) to the lower end o f the i o n exchange column used i n the f i n a l p u r i f i c a t i o n step, so that the p u r i f i e d B k ( I I I ) s o l u t i o n passed through the c e l l on i t s way to i t s f i n a l c o n t a i n e r . A bench spectrometer served as the l i g h t analyzer i n the v i s i b l e wavelength r e g i o n of the spectrum. A l though no B k ( I I I ) a b s o r p t i o n bands were detected, these workers were able to s e t an upper l i m i t on the molar e x t i n c t i o n coeff i c i e n t ^ 20) o f any Bk(III) a b s o r p t i o n band i n t h i s wavelength r e g i o n from p r e l i m i n a r y experiments w i t h Am(III) and Nd(III) using the same c e l l . U t i l i z i n g the c a p a b i l i t y o f a s i n g l e ion-exchange r e s i n bead t o concentrate the sorbed a c t i n i d e i o n and to provide good o p t i c a l transparency i n the v i s i b l e and near i n f r a r e d wavelength r e g i o n s , Cunningham and Wallmann attempted to o b t a i n the absorpt i o n s p e c t r a o f Bk(III) and C f ( I I I ) . T h e i r apparatus (Figure 3) was t e s t e d using Am(III) and they observed the 503 nm Am(III) a b s o r p t i o n band (e ^ 350) through a hand spectroscope with only 1 ng o f Am(III) sorbed i n the bead. L a t e r improvements o f t h i s same b a s i c technique i n c l u d e d b e t t e r masking of s t r a y l i g h t (Figure 4 ) , p r o v i s i o n s f o r i n c r e a s i n g the e f f e c t i v e pathlength by s t a c k i n g s e v e r a l a c t i n i d e - l o a d e d beads, i n c l u s i o n of a quartz " l i g h t p i p e " to gather more e f f e c t i v e l y the transmitted l i g h t , and automated r e c o r d i n g o f the spectrum v i a f i l m techniques. With t h i s multibead-stack apparatus Green and Cunningham (4) recorded the C f ( I I I ) a b s o r p t i o n spectrum and demonstrated, using P r ( I I I ) , that the "bead" spectrum was very s i m i l a r to an absorpt i o n spectrum obtained i n a c i d s o l u t i o n . The next development took p l a c e during the course of the Ph.D. research of the author a t Berkeley. With a t o t a l o f only 2 yg of Bk-249 w i t h which to work, the f i r s t s p e c t r o s c o p i c measurements were made using the s i n g l e bead technique, but i n an apparatus (Figure 5) designed f o r use with a Cary Model 14 Recording Spectrophotometer. The Bk-loaded bead was placed i n the


Techniques


PETERSON

of

Microchemistry

ION

EXCHANGE

C OVER

BEAD

SLIP

PLATINUM

DISK

SLIDE Microchemical Journal Symposium Series

Figure 3.

Schematic of first single-bead microabsorption cell (1)

Cation-exchange resin bead

.002-in.-thick Pt disk

0

Coverslips Lucite support Figure 4.

Schematic of improved, single-bead microabsorption cell


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To Cary detector

Zeiss Achromat UV-Kond 0.8 condenser

Quartz light pipe.

Quartz cover slip

I Quartz capillary t u b i n g . ^ ^ ^ (silvered on outside)

1

|

v—

Aquadag coating over epoxy

Quartz

cover slip

Zeiss ultrafluor UV objective

Cary

Figure 5.

light beam

Schematic of single-bead microabsorption cell for use in Cary spectrophotometer



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c e l l and secured by the quartz l i g h t pipe making o p t i c a l contact w i t h the bead. The d i f f i c u l t y w i t h t h i s apparatus was i t s i n a b i l i t y t o transmit more than a percent o r two of the Cary l i g h t beam. Despite poor s p e c t r a l r e s o l u t i o n , repeated wavelength scans confirmed the o b s e r v a t i o n of about s i x a b s o r p t i o n peaks. Another d i s t i n c t disadvantage i n t h i s p a r t i c u l a r case was that the bead was l e s s transparent i n the near u l t r a v i o l e t wavelength r e g i o n , where B k C l I I ) seemed t o have s i g n i f i c a n t a b s o r p t i o n . These l i m i t a t i o n s on the s i n g l e bead a b s o r p t i o n c e l l f o r t h e study o f the s p e c t r a l p r o p e r t i e s o f berkelium s t i m u l a t e d the development o f a new experimental technique - one which had the c a p a b i l i t y o f higher r e s o l u t i o n and a l s o allowed i n v e s t i g a t i o n i n t o the u l t r a v i o l e t wavelength r e g i o n . The chosen method centered around t h e suspension of a drop o f B k ( I I I ) s o l u t i o n between two tapered quartz rods. Prototype c e l l s loaded w i t h drops o f Nd(III) s o l u t i o n were found t o y i e l d s i g n i f i c a n t l y improved s p e c t r a . The f i r s t "suspended drop" o r " l i g h t - p i p e " c e l l c o n s t r u c t e d f o r berkelium work i s shown s c h e m a t i c a l l y i n F i g u r e 6. A 1-mm diameter quartz rod was drawn down i n a flame to about 100 um i n diameter and mounted i n a brass d i s k . This "entrance l i g h t p i p e " was a l i g n e d w i t h and spaced about 200 um from the "catcher l i g h t p i p e " , a short (y 1 mm) s e c t i o n o f quartz rod about 100 urn i n diameter. The B k ( I I I ) s o l u t i o n was t r a n s f e r r e d t o the l i g h t - p i p e c e l l as a 50-60 nL drop suspended on the end o f a m i c r o p i p e t t e . The c e l l a l s o i n c l u d e d water-soaked paper t o m a i n t a i n a wet atmosphere i n an e f f o r t t o prevent v a p o r i z a t i o n o f the d r o p l e t t o the p o i n t where s o l i d formation would r e s t r i c t l i g h t t r a n s m i s s i o n through the c e l l system. The l i g h t source and a n a l y z e r was again the Cary spectrophotometer. The B k ( I I I ) spectrum obtained w i t h t h i s l i g h t - p i p e c e l l was s i m i l a r t o t h a t obtained from the bead c e l l but provided new evidence f o r B k ( I I I ) a b s o r p t i o n i n the near u l t r a v i o l e t wavel e n g t h r e g i o n . U n f o r t u n a t e l y , however, only a s m a l l percentage of the Cary l i g h t beam was t r a n s m i t t e d through the c e l l system. Improvement o f the c e l l o p t i c s was the prime m o t i v a t i o n f o r f u r t h e r developmental work on the l i g h t - p i p e c e l l design, but other c o n s i d e r a t i o n s were drop s t a b i l i t y , c o n t r o l o f drop s i z e , and ease of h a n d l i n g . The c e l l o p t i c s were e v e n t u a l l y improved to the p o i n t where ^ 30% o f the Cary l i g h t beam condensed by t h e o b j e c t i v e l e n s was t r a n s m i t t e d through the c e l l . These improvements were r e a l i z e d by shortening the l e n g t h o f the entrance l i g h t p i p e , by c o a t i n g the entrance l i g h t pipe w i t h s i l v e r o r aluminum, by p o l i s h i n g the ends o f the l i g h t p i p e s , and by i n c l u d i n g a n e a r l y s p h e r i c a l bulge i n the entrance l i g h t pipe t o c a t c h more o f the i n c i d e n t l i g h t and t o reverse the d i r e c t i o n o f back-reflected l i g h t . The s i z e o f the drop o f s o l u t i o n i n the c e l l , which determined the c o n c e n t r a t i o n o f the absorbing s p e c i e s , was cont r o l l e d by the h e a t i n g e f f e c t o f t h e i n f r a r e d source lamp o f the spectrophotometer and by the a d d i t i o n o f d i l u t e , h i g h p u r i t y a c i d



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s o l u t i o n . This a d d i t i o n was accomplished by a pump, which cons i s t e d of a c l o s e d r e s e r v o i r system operated by s o l u t i o n expans i o n induced by Pt w i r e r e s i s t a n c e h e a t i n g . A photomicrograph of the pump n o z z l e , p o s i t i o n e d between the two l i g h t p i p e s , i s shown i n F i g u r e 7. An improved c e l l design allowed g r e a t e r ease i n the l o a d i n g , drop o b s e r v a t i o n , and o p t i c a l alignment procedures. A photograph of t h i s c e l l w i t h i t s s l i d i n g cover i s shown i n F i g u r e 8. With the r e c e i p t of an a d d i t i o n a l 28 yg of Bk-249 at Berkeley, t h i s c e l l system was used w i t h d r o p l e t s c o n t a i n i n g ^ 4 yg of B k ( I I I ) . Considering the u s u a l o p e r a t i n g volume of s o l u t i o n across the l i g h t - p i p e gap, the emerald green d r o p l e t represented a B k ( I I I ) c o n c e n t r a t i o n of about 4 M. A t y p i c a l B k ( I I I ) s o l u t i o n absorpt i o n spectrum recorded over the wavelength range 320 to 680 nm i s shown i n F i g u r e 9. The h i g h background a b s o r p t i o n i n the lower wavelength r e g i o n i s probably caused by the presence of H 0 and/or C l , generated r a d i o l y t i c a l l y from the aqueous HC1 s o l u t i o n . L a t e r experiments w i t h Es-253 i n an e s s e n t i a l l y i d e n t i c a l m i c r o a b s o r p t i o n c e l l have been reported i n the l i t e r a t u r e (20,21). The microscope spectrophotometer system i n r o u t i n e use at the TRL i s d e s c r i b e d i n reference ( 7 ) , so no d e t a i l s of the apparatus and i t s use are given here. Instead a b r i e f d e s c r i p t i o n of the reason f o r developing and c o n t i n u a l l y r e f i n i n g the microscope spectrophotometer f a c i l i t y w i l l be presented. Hist o r i c a l l y the way to c h a r a c t e r i z e a s o l i d - s t a t e sample of a transplutonium element has been by standard X-ray powder d i f f r a c t i o n a n a l y s i s . When a systematic study of element 99, e i n s t e i n i um, was undertaken, i t was found that o b t a i n i n g u s e f u l d i f f r a c t i o n data from E s - c o n t a i n i n g m a t e r i a l s was a very d i f f i c u l t , i f not an i m p o s s i b l e , task (22). The i n t e n s e l y r a d i o a c t i v e Es-253 not only caused r a p i d b l a c k e n i n g of the f i l m used to record the d i f f r a c t i o n p a t t e r n , but more i m p o r t a n t l y , i t degraded the c r y s t a l l i n i t y of the sample. In c o n t r a s t to the n e c e s s i t y of having r e p e t i t i v e l o n g range order f o r o b t a i n i n g an X-ray powder d i f f r a c t i o n p a t t e r n , an a b s o r p t i o n spectrum r e s u l t s from the summation of a l l the l o c a l a c t i n i d e i o n environments i n the a n a l y z i n g l i g h t path through the sample. A b s o r p t i o n spectrophotometric a n a l y s i s i s a l s o f a s t e r and has g r e a t e r s e n s i t i v i t y f o r the d e t e c t i o n of minor components than does X-ray a n a l y s i s . Because of t h i s s e n s i t i v i t y , s p e c t r a l s t u d i e s of Es compounds can be, and have been, undertaken to i n v e s t i g a t e progeny growth i n Es compounds. This r e s e a r c h a l s o r e q u i r e s the knowledge of the a b s o r p t i o n s p e c t r a of Bk and Cf compounds i n t h e i r r e s p e c t i v e pure s t a t e s , because of the g e n e t i c r e l a t i o n s h i p 2

2

253, Es 99

a = 20.5

d

249. ,Bk 97

= 314 d

249 Cf. 98 (


2


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Figure 6.

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Schematic of first light-pipe microabsorption cell for berkelium solution

Figure 7. Light-pipe area of microabsorption cell showing position of pump nozzle


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Figure 9. Absorption spectrum of berkelium(lll)

in aqueous HCl solution



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With such s p e c t r a l data i d e n t i f i c a t i o n o f the progeny s p e c i e s i n an Es compound can be made by assignment o f the peaks i n i t s a b s o r p t i o n spectrum. The change i n percentage composition o f an i n i t i a l l y pure Es compound as a f u n c t i o n o f time i s shown i n Figure 10. F o l l o w i n g an i n i t i a l i n t e r e s t i n j u s t c h a r a c t e r i z i n g t r i v a l e n t (23) and d i v a l e n t (24,25) Es i n the s o l i d s t a t e , the more recent emphasis has been d i r e c t e d toward e l u c i d a t i o n o f t h e chemical consequences o f r a d i o a c t i v e decay v i a s t u d i e s of some h a l i d e compounds o f Es (and Bk) over l o n g time p e r i o d s . Although b u l k B k ( I I ) i s unknown i n the s o l i d s t a t e , does nature produce i t v i a the alpha decay o f E s ( I I ) compounds? The decay o f t h e Es d i h a l i d e s has been monitored s p e c t r o p h o t o m e t r i c a l l y , and t h e granddaughter C f ( I I ) products have been i d e n t i f i e d on the b a s i s of the knowledge o f C f ( I I ) s p e c t r a obtained from d i r e c t s y n t h e s i s of Cf d i h a l i d e s (26,27,28,29). No a b s o r p t i o n peaks a t t r i b u t a b l e to B k ( I I ) have been observed. Can C f ( I I ) r e s u l t from the decay of E s ( I I ) without going through B k ( I I ) ? Are the c h a r a c t e r i s t i c a b s o r p t i o n peaks o f B k ( I I ) o u t s i d e the u s e f u l wavelength range (300-1100 nm) o f the microscope spectrophotometer, o r are they masked by the a b s o r p t i o n peaks o f E s ( I I ) and/or C f ( I I ) ? Current Attempts t o S y n t h e s i z e and C h a r a c t e r i z e B k ( I I ) At the present time t h i s problem i s being a t t a c k e d by a t tempting t o s y n t h e s i z e b u l k B k ( I I ) d i r e c t l y (30). Because the microchemical techniques employed combine most o f the ones discussed here, a b r i e f d e s c r i p t i o n o f the experimental approach w i l l be presented. Although H i s a s u f f i c i e n t l y s t r o n g reductant to reduce the Cf and Es t r i h a l i d e s to the corresponding d i h a l i d e s , i t w i l l not reduce B k B r to B k B r . Therefore Bk metal was chosen to be the reducing agent f o r the r e a c t i o n Bk + 2BkBr -> 3BkBr . The B k B r was prepared i n a quartz c a p i l l a r y by t r e a t ment o f B k F w i t h anhydrous HBr. The Bk metal was prepared by L i metal r e d u c t i o n o f BkF*». I n an i n e r t atmosphere enclosure a p i e c e o f Bk metal was placed i n t o the c a p i l l a r y c o n t a i n i n g the sample o f B k B r , which was subsequently evacuated and flame sealed to an o v e r a l l l e n g t h s u i t a b l e f o r mounting i n an X-ray powder camera. F o l l o w i n g p o s i t i o n i n g o f the p i e c e o f Bk metal on top o f the sample o f B k B r (performed by v i b r a t i n g the s e a l e d c a p i l l a r y ) , the bromide was melted and quenched. A b s o r p t i o n s p e c t r a l a n a l y s i s confirmed the presence o f Cf ( I I ) , the beta decay daughter o f Bk, and X-ray d i f f r a c t i o n a n a l y s i s produced a poor powder p a t t e r n d i f f e r e n t from those known f o r Bk metal and B k B r . D e t a i l e d a n a l y s i s o f these data i s c u r r e n t l y i n progress. There are both advantages and disadvantages of these complementary a n a l y s i s methods. One advantage i s the p o s s i b l e conf i r m a t i o n of the X-ray r e s u l t s by the r e s u l t s o f the s p e c t r a l a n a l y s i s and v i c e v e r s a , l e n d i n g support f o r the c o n c l u s i o n s drawn on the b a s i s o f the r e s u l t s o f e i t h e r a n a l y s i s alone. A disadvantage i s t h a t f o r o b t a i n i n g h i g h - q u a l i t y powder d i f f r a c t i o n 2

3

2

3

2

3

3

3

3

3



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ELAPSED TIME , days

Figure 10. Ingrowth of berkelium-249 and calif ornium-249 from initially pure einsteinium-253 as a function of time


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data the sample should be m i c r o c r y s t a l l i n e i n n a t u r e , whereas f o r o b t a i n i n g h i g h - q u a l i t y a b s o r p t i o n s p e c t r a l data the sample should be m a c r o c r y s t a l l i n e i n nature ( t h i s i s u s u a l l y achieved by m e l t i n g the sample). A d d i t i o n a l experiments to synthesize and c h a r a c t e r i z e B k ( I I ) i n b u l k w i l l be c a r r i e d out by r e d u c t i o n of a Bk t r i h a l i d e w i t h Bk metal and a n a l y s i s of the products by X - r a y powder d i f f r a c t i o n and a b s o r p t i o n spectrophotometry.


Acknowledgments A number of c o l l e a g u e s , graduate s t u d e n t s , and p o s t d o c t o r a l research a s s o c i a t e s have c o n t r i b u t e d much toward the development and a p p l i c a t i o n of microchemical techniques to research w i t h the transplutonium elements. The author g r a t e f u l l y acknowledges t h e i r a s s i s t a n c e and p a t i e n c e . I n view of space o n l y t h e i r names are l i s t e d h e r e . At the B e r k e l e y l a b o r a t o r y (LBL): B u r r i s Cunningham, Jim Wallmann, Tom Parsons, J e r e Green, Dennis F u j i t a , and Judy Copeland. At the Oak Ridge l a b o r a t o r y (TRL): Rus Baybarz, Dick H a i r e , George Werner, Jack Young, P a u l Huray, Jim Fahey, Jim Stevenson, Bob F e l l o w s , Maxy No£, Mickey R a s c h e l l a , D a n i e l Damien, and Stanley Nave. This research was sponsored by the D i v i s i o n of Nuclear S c i e n c e s , U . S . Department of Energy under c o n t r a c t s DE-AS0576ER04447 w i t h the U n i v e r s i t y o f Tennessee ( K n o x v i l l e ) and W-7405-eng-26 w i t h the Union Carbide C o r p o r a t i o n . Literature 1. 2. 3. 4. 5. 6. 7. 8.

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Cunningham, B . B . Microchem. J. Symp. S e r . , 1961, 1, 69. P e t e r s o n , J. R . ; Fahey, J. A.; Baybarz, R. D. J. I n o r g . N u c l . Chem., 1971, 33, 3345. P e t e r s o n , J. R . ; Cunningham, B . B . I n o r g . N u c l . Chem. Letters, 1967, 3, 327. Green, J. L.; Cunningham, B . B . I n o r g . N u c l . Chem. L e t t e r s , 1966, 2, 365. Cunningham, B . B . J. Chem. Ed., 1959, 36, 32. Stevenson, J. N.; P e t e r s o n , J. R. J. I n o r g . N u c l . Chem., 1973, 35, 3481. Young, J. P.; H a i r e , R. G.; F e l l o w s , R. L.; Peterson, J. R. J. R a d i o a n a l . Chem., 1978, 43, 479. Noé, M.; P e t e r s o n , J. R. "Transplutonium Elements 1975"; M ü l l e r , W. and L i n d n e r , R . , E d s . ; N o r t h - H o l l a n d P u b l i s h i n g C o . , Amsterdam, 1976; p . 69. Damien, D. A.; H a i r e , R. G.; P e t e r s o n , J. R. J. de Physique, 1979, 40, C4-95. P e t e r s o n , J. R. J. I n o r g . N u c l . Chem., 1972, 34, 1603. K e l l e r , C. "The Chemistry of the Transuranium Elements"; V e r l a g Chemie, Weinheim, Germany, 1971.


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H a i r e , R. G . ; Baybarz, R. D. J. I n o r g . N u c l . Chem., 1974, 36, 1295. Stevenson, J. N.; P e t e r s o n , J. R. Microchem. J., 1975, 20, 213. Fuger, J.; P e t e r s o n , J. R.; Stevenson, J. N.; Noé, M.; H a i r e , R. G. J. I n o r g . N u c l . Chem., 1975, 37, 1725. H a i r e , R. G.; Asprey, L . B . I n o r g . N u c l . Chem. L e t t e r s , 1976, 12, 73. H a i r e , R. G . ; Baybarz, R. D. J. de Physique, 1979, 40, C4-101. Burns, J. H.; P e t e r s o n , J. R. "Rare Earths and A c t i n i d e s 1977"; Corner, W. D. and Tanner, B . K., E d s . ; Institute of P h y s i c s , London, 1978; p . 52. Nave, S. E.; Huray, P . G. J. de Physique, 1979, 40, C4-114. R a s c h e l l a , D. L. " S o l u t i o n M i c r o c a l o r i m e t e r for Measuring Heats of S o l u t i o n of R a d i o a c t i v e Elements and Compounds"; Ph.D. D i s s e r t a t i o n , The U n i v e r s i t y of Tennessee, K n o x v i l l e , December 1978; U . S . Department of Energy Document No. ORO4447-081, 1978. Cunningham, B . B.; P e t e r s o n , J. R . ; Baybarz, R. D . ; Parsons, T. C. I n o r g . N u c l . Chem. L e t t e r s , 1967, 3, 519. F u j i t a , D. K.; Cunningham, B . B.; Parsons, T. C . ; P e t e r s o n , J. R. I n o r g . N u c l . Chem. L e t t e r s , 1969, 5, 245. H a i r e , R. G . ; P e t e r s o n , J. R. "Advances in X-Ray A n a l y s i s " , Volume 22; McCarthy, G. J.; B a r r e t t , C. S . ; Leyden, D. E.; Newkirk, J. B . and Ruud, C. O., E d s . ; Plenum P u b l i s h i n g C o r p . , New Y o r k , 1979; p . 101. F e l l o w s , R. L.; P e t e r s o n , J. R.; Noé, M.; Young,J.P.; H a i r e , R. G. I n o r g . N u c l . Chem. Letters, 1979, 1 1 , 737. F e l l o w s , R. L.; P e t e r s o n , J. R.; Young, J. P.; H a i r e , R. G. "The Rare Earths in Modern Science and Technology"; McCarthy, G. J. and Rhyne, J. J., E d s . ; Plenum P u b l i s h i n g C o r p . , New Y o r k , 1978; p . 493. P e t e r s o n , J. R . ; Ensor, D. D . ; F e l l o w s , R. L.; H a i r e , R. G.; Young, J. P. J. de Physique, 1979, 40, C4-111. Young, J. P.; Vander Sluis, K. L.; Werner, G. K.; P e t e r s o n , R . ; Noé, M . J. I n o r g . N u c l . Chem., 1975, 37, 2497. Young, J. P.; H a i r e , R. G.; F e l l o w s , R. L.; Noé, M.; P e t e r s o n , J. R. "Transplutonium Elements 1975"; Müller, W. and L i n d n e r , R . , E d s . ; N o r t h - H o l l a n d P u b l i s h i n g C o . , Amsterdam, 1976; p . 227. P e t e r s o n , J. R . ; F e l l o w s , R. L.; Young, J. P.; H a i r e , R. G. Radiochem. R a d i o a n a l . L e t t e r s , 1977, 31, 277. W i l d , J. F.; H u l e t , E . K.; Lougheed, R. W.; Hayes, W. N.; P e t e r s o n , J. R . ; F e l l o w s , R. L.; Young, J. P. J. I n o r g . N u c l . Chem., 1978, 40, 811. P e t e r s o n , J. R . ; Ensor, D. D . ; H a i r e , R. G . ; Young, J. P. U n i v e r s i t y of Tennessee and Oak Ridge N a t i o n a l L a b o r a t o r y , unpublished results, 1979.

13. 14. 15. 16.


17.

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23. 24.

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28. 29.

30.

RECEIVED December 26, 1979.


Lanthanide and Actinide Chemistry and Spectroscopy - American

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