Lawrence Berkeley National Laboratory Lawrence Berkeley National Laboratory Title NOBELIUM: TRACER CHEMISTRY OF THE DIVALENT AND TRI-VALENT IONS Permalink https://escholarship.org/uc/item/9bv6z274 Authors Maly, Jaromir Sikkeland, Torbjorn Silva, Robert et al. Publication Date 2008-04-18 eScholarship.org Powered by the California Digital Library University of California TWO-WEEK LOAN COPY t lr,' ." ' "" i".&,$l~~ -""a"&*,, ! This is a Library Circulating Copy > I which may be borrowed for two weeks. , i-. o~~:*~~ For ar personal retention copy, call Tech. Info. Diuisisn, Ext. 5545 Subaitted to Science 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.