Nobelium: Tracer Chemistry of the Divalent and Tri-Valent Ions

Lawrence Berkeley National Laboratory Lawrence Berkeley National Laboratory

Title NOBELIUM: TRACER CHEMISTRY OF THE DIVALENT AND TRI-VALENT IONS

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Authors Maly, Jaromir Sikkeland, Torbjorn Silva, Robert et al.

Publication Date 2008-04-18

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Lawrence Radiation Laboratory Berkeley, California

AEC Contract No. w-7405-eng-48

NOBELIUPIZ: TRACER CHETrIISTRY OF TH3 DIVmuT MID TRIVALENT IONS

Jaronir Maly, Torbjorn Sikkeland, Robert Silva, and Albert Ghiorso

February 1968 - - Submitted to SCIENCE

NOBELIUM: TRACER CHZMISTRY OF THE DIVALEXVT AND llRIVALEEIT IONS (1)

Jaromir Maly (2), Torbjorn Sikkeland, Robert Silva and Albert Ghiorso

Author - note: The authors are with the Nuclear Chemistry Division, Lawrence Radiation

Laboratory, University oi Califor~ia,Berkeley, Calif'arnia. -2 - uc1zr,-1~9g5

Abstract- In the absence of oxidizing or mducing agents the chr3nas3graphic and ~op~ecipitationbehavior of element 102 is similar to that of the alkill.ine earth elements. After oxidation with ceric ions, the behavior is that expected of a trivalent actinide. Our conclusion is that nobelium is the first actinid.? for which the +2 oxidation state is the? most stable species in aqueous 531iiii31. Results of the first attempts (3) and other m3re recent eff3rts (11.) t=, study the chemistry of element 1.02 sugges.Led the chemical behavior af n~beliurn to be that of a +3 actinide elenlent. On the other hand, new results indicated an increasing tendency toward formation of t2 states with increasing Z by the +2 heavy actinides (5) and this was confirmed by the discovery of the Md ion (6,7).

These results suggested that nobeXium might exhibit a fairly stable divalent state in addition to the expected thvalent state.

The recent discovery of 255~o,with an 'alpha half-life and decay energy of approximately 3 minutes and 8.1 MeV (8,9,10), has made.it pxis2ble to carry out tracer chemistry on element 102 (11). The short half-life and law yield of

255~oatoms per experiinent compelled us to modify and develop fast chemical procedures so that the total time necessary for separation, chemical study and preparation of a source suitable for alpha energy analysis would be less than

10 minutes. These procedures included chromatographic methods for the stGdy of - sin&-atom behavior and me-step coprecipitation reactions. As only a few 25'~o decays were observed per experiment, it was necessary to repeat each set af exgerlments 10-20 tlrnes in order to obtain statistically significant results.

Experimental Procedures and Results a, Production and Identif icatim

Th; 255~owas produced by i rradiating a 0.8 mg/cz -thick plutonium 16 target s'lpporte? by a 1-mil thick Be foil with 0 ions from the Berkeley SILK. 244 The isotopic composition 33 the target in atom percent was Pu - 71k.21, 2112~~ 2sopu - 25.32, 241~u - 0.094, - 0.312, 239~u- 0.064 and.238~11- 0.002. 2 The bean: currsnt was 2-1: parnps over an area of 9.2 cm . The n~beliwatam recoiling from the target were stopped in IIc gas ulld trbansfcrwd to u p1at;inum

catcher foil by gas jet as described elsewhere ( 9912). '!he maximum yield was

abtained at an oxygen-ion energy of approxinmtely 97 MeV as expected for the 244 15 PU( 0,5n)~~~~oreaction. The average number of muntable atoms at 50;b * geometry on the catcher foil at the beginning of the chemical operations was

determined, from 36 measurements, to be 6.020.5 a ct~/~am~of beam.

The 255~owas identified by its alpha decay energy. The alpha spectrum

is known to be coxplex and there' is'good indication of more than one alpha

group spread over energies of 7.7 to 8.25 MeV. A composite decay curve of

this energy range was constructed from 36 measurements and gave a half -life of

3.620.5 minutes. Subportions of the rmin alpha spectrum gave half -liv?s in

general agreement with the corrposite val~~eso all alphas from yer( to 8.25 MeV

in energy vere assued to come from 255~o.

b. Electrodeposition

The first evidence of unexpected behavior for No was fo~mdduring

cathadic electmdeposi tion experimnts using standard procedures (13). In

these experiments the No atoms were washed from the catcher foil wrth a

saturated NH4C1 plating solution containing tracer quantities of the radio-

active elenrnts to be compared with the No. During plating the pH is very hi2h near the- cath~deand tracers are known to be deposited in approximately inverse proporcl3n to the solubility of their hydroxides, In Table 1 is

shgwn the pcrce~ltof tracers and nobelium that vere ylated (14). Also shmn

is the nu~5erof 255~oelpha decays observzd per number of decays -.xge;trd.

The latter was compi~tec!Por each experimnt Pr~mthe average nlmber af co~intabl-t. ak2.11 1.3 the famer rather than the latter elemnts. c . 'Chloride-- Volatility In these experlnients the volatility of nobelium chloride was cmpered to the valatility of tracer quaxtities of Pa, Am, Th, Pb ocd Iia by heating 0 thc platinum catcher foil to - 1039 C with a. Bunsen fl-art. alter conwrsioti ts the chlorides by evaporation to dryness with HC1. ?'he results in able 1 indicate that na'oelium does not exhibit an unusually volatile chloride as does

d, Catioc Exchange Column o Our atteinpt.~to elute No from 2 heatec? (83 c), &vex 50x12 ion exchztigs resir, col~unnui tk: amrzmium alpha-hydr~xyisobutyratein the predicted preeinsteiniux elution position (15) we E unsuccessful. The procedure was to first elu& the tracer +3 actinide ions with Z higher than A-n with 8 drops of dilute eluting solution (0.3?4,- pH 4.0) and then to elute Am and se-feral lawer

Z elements (~b,Sr, Ra, Ac and ~e)with 8 drops of concentrated eluting solution

(1.9~) pH 4.8). The results given in Table 2 .cleaily show that No was not eluted bef me Am.

An elution position for No relative to tracer quantities of Y, Sr, 3a

3 and R& B~Sjbtained for a heated (80 c), 0.2 cm diameter by 2 cm long ca+nn using the cancentrated eluting solution. The ca~positeresult for lj experixn5~ is presented in Fig. 1. The res~ltsshaw that under these c~nditiocsn~h?I.iu;:i docs n3t exhibit tine slightest resc:fiblence to the +3 actinides, f~rin slr:!',lar. tracer experir,!ents, Es, Cm, Am and P.c were el~tzdir! tile Y p~sitianxhich is Pb end Ce. The elution.of No near the SI* p~sitionstrengthened Qur growing suspicion that No was ex1ilbiti.ng a +2 valence.

Unsuccessful attempts were made to oxidize the suspected ~6~'to i\lot3 I. and elute it from the ion exchange column in the predicted +3 position, but when rapid oxidizing agents such as Ce+4 were present in sufficientlyl'dilute so cmcentrationdas not to effect the column operation, they were inmediately red~cedby the hot butyrate solution'. e. Fluoride Behavior

For the study of the c~precipitatbnbehavior of No fluoride, we used the residue adsorption technique (16,17). A drop of O.lM- HC1 containing the tracers ts which No was to be compared plus - 5pg each of the various charge- state carriers Ba, La and Zr was used to dissolve the No atom fr~mthe catcher foil. Two drops of 40$ HI? were added t~ convert to the fluorides and taken to dryness. The plate was then washed with H 0 several tinis and both 2 residue plate and Ii 0 washes were alpha energy analyzed. The results are 2 given in Table 2 and suggest that the solubility of No fluoride is more like

BaFZ than LaF 3 Assuming that the nobelium was exhibiting a +2 valence under the above canditions, - attempts were made to oxidize the to which should form a less soluble fluoride. The procedure was the same as described above except the oxidant, ceric nitrate, was substituted for the Zr. As seen in Table 2, after oxidation uith Get" the distribution was in f amr of the Lol. phase. 3 The behavior of No fluoride after oxidation appears to be better ex2laine-i 57 the formtion 32 pIoF rather than i:3Fq. Under these dilute 3 N:,F~+mj-ght be expected to be as soluble as CcP 4 and ZrE' 4'

Reccnt wrk has shown that 90~can be separated from 90~rat room tenperatue by.elution from a SrSO4 column using 0.5N-24 H SO (18). In general it appears that the mare soluble sulfates are eluted before the less soluble ones. We used a similar col~unnfor the study of the behavior of nobelium sulfate. In each experiment the No; tracer activities to which Ko was to be compared, and - 5111; each of Zr and La were converted to the sulfate farm on the platinum catcher foil by evaporation to dryness with 1N- H2S04. The mess af Zr and La added was the saw as the mass of Ce+4 md used in later oxidatian experiments in order to duplicate the nlass effects on the col~m.

Th? Na and other elemnts were washed from the foil with H SO and 6~-24 transferred to the 0.2 cm dia. x 1 cm long SrSO4 column and the elution carried 3ut with 6~ H2S04. Tim and coimter linlltations made the elution m in fractions rather than dropwise necessary. The results are given in Table 2 and show No to be more strongly adsarbed on the column than Es and Am.

Similar experiments were carried out under oxidizing conditims using ~e+"and the results given in Tabla 2. In these expcrinnnls, the N'o Was eluted with-ES and before Am. This apparent change in salubility of nobelium sulfate is consistent with a change in valence state from t2 to -13.

Discussim

The results presented in this work indicate a very interesticg behavi~rby nobelium when conpared to otht-?r elemnts of the actinide fa1:31:. Urlcler the conditions of $our expcrinlents, nobelium exhibited thc following properties relative to the other heavy actinides in their -1-3state:

1) ' Its hydroxide or hydrous oxide has a high solubility.

2) Its fluoride has a high solubility. 3) Its sulfate has a low solubility. 4) Nobelium did not elute from a Dowex 50x12 ion exchange column

with anmonium (2-hydroxisobutyrate in the position predicted for -1-2 the +3 ion, In fact, yo was eluted near Sr and about the same

position as ~a+~under conditions where all other actinides were

eluted immediately. This behavior shows that previous claims

that No is eluted in the pre-Es position must be in error (3).

5) Though No chloride exhibits a low volatility, probably in the range of the +3 actinides, we do nat agree with the generalization

made in Rsf. 19 that the chemical behavior of nobelium is sinlilar

to +3 actinides.

6) In two types of experiments, fluoride coprecipitation and sulfate

column, there were strong indications that nobelium was oxidized t4 - by Ce to a forrr. where it behaved like a trivalent heavjr actinide

(~e'~- Ce'4 coogle .- -1.5 mlts).

W6 feel that the best interpretation of our results is that the dimlent ion is the most stable s_oecies for nobeli~unin aqueaus solution ar.d thus it exhibits a substantially different chemical behavior from the other actinides.

This w3uld appear to confirm the prediction made by Seaborg in 1949 (20) 3r' a .possible. stable +2 state for elemnt 102 due t:, the special stability af 14 the jf- electronic configuration. j\'ef e wuces and n'o.Lcs ,

1. l'he work discussed in this article was dme under tho o.uspicc:s 9.C thc

U. S. At3mi.c Energy Comruni~sion~

2. On leave of absence from the Institute of Nuclear Research, Prapie,

1 b CzechrJslovakia, 1967-1968.

3. P. R. Fields, A. M. Friedman, J. Mils>ed, II. Atterling, W. Forsling; 0 L. W. liolm, 3. ~str&, Phys. Rev. -107, 1460 (1957) and Arkiv for

Phys. -15, 225 (1959). . 4. Ju. T. Chuburkov, R. Caletka, M. R. Shalaevsky, I. Zvara, Preprint

JINR ~6-3076, Dubna, 1966,

5. J. Maly, Lzlwrence Radiation Laboratory Report UCKTJ-17524,Nay 1967.

6. J. Maly and B. B. Cunningham, Lawrence Radiation Laboratory Hepsrt

7. E. I(. Hulet, R. W. Lougheed, J. D. Brady, R. E. Stone, M. S. Coops,

science, -158, 486 (1967).

o.r( V. A. Druin, G. N. Alkapjev, A. G. Ikrnier, Yu. V. Lgban~v, B. V. Fefilov,

C. N. Flenv, L. P. Cheluokov, ~tomnaja Energia 22, 127 (1967).

9. A. Shiorso, T. Sikkeland, M. J. Nurmia, Phys. Rev. Letters -18, 11, 401 (1967).

10. G. N. Flerov, S, M. Polikanov, V. L. Micheev, V. J. Iljuschenko,

V. F. -Kuschinruk, M. V. Miller, A. M. Sukhov, V. A. Schegolev, Yzdern. Fisika -5, 1186 (1967). 11. Preiir.inar-y report of the present work was given by on? of us (A.G. ) a':

October 17-20, 1967. 1 A. Ghiorso and T. ~iklreland, Physics Today 3, 25 (1-96~().

13 C. H. Choppin, Experimental Nuclear ChemIs try, Prentj ce ilall, Ynglcwood

Cliffs, N. J. (1961).

14. In this, and subsequent experiments, the probable error in the tracer b percentages is < 10%.

15. G. T. Seaborg, The Transuranium Elements, Yale University Press, New Has32

( 19581 * 16. 11. h'. Kirby, J. Inorg. Nucl. Chem., -25, 483 (1965). 17. H. W. Kirby, J. Inorg. Nucl. Chem., -27, 1700 (1965). 18. B. Hamogw:hi, N. On~wa, T. Watanabe, R. Kuroda, Nature, -211, 1295 (1965). 19. G. Ti. Flerov, ?reprint ~7-3444, JINR, Dubna, 1967.

20. G. T. Seeborg, J. J. Katz, W. M. Mannfng, The Transuranium Elemnts, Part IV,

, Netilnal Nuclear Energy Series, 1.148, Paper 21.1, McGraw-Hill, Nez Y3rk (1949) .

21. We thank Professor 8. B. Cunningham for many suggestions, Mr. T. Bmman

for help in preparation of the Pu target, and the HILAC crew. One of us

(J.M. ) expresses his gratitude to IAEA, Vienna, for. a research grant. Percent in Fraction 211pb ~bscrved/~x~?cted Expcrimnt 53~s 243~m 31~a 227~h 22 3~a 2%Na Counts 2f' 112 Tsble 2. Results of Elution fnm Cation ~xcha~i~eColumn with ammonium ~~-h~droxisobul~ra.te(A),

Fluoridc Coprecipitation with Lo and Ba Carrier (B), and Elution from SrSO4 column with 611-- H2S04 (c). Exper-iment Oxidizing Percent in Fraction 0bservcd/33xpected .

-Fraction Conditions 253~s 243Am 223~a 133~a 255~0 Counts of 110

0.3. 43 6

Pig. 1 Elutfon of nobelium from a heated (80"~)~Cowex 50x1-r, ceti~n exchanie column with 1.)).MJ - pH 4.8 armmiurn a-hydroryisob~i~jratc . I I I I I 1 I 20 40 80 00 100 I20 140 Drop number

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