Isotopic Analyses of Barium in Meteorites and in Terrestrial

•'OO•,NALO• GEO•'IIYSlCALRESXAaCX VOL. ?4, NO. IS, JULY IS, 1969

Isotopic Analysesof Barium in Meteorites and in Terrestrial Samples

O. EUGSTER,F. TERA,AND G. J. WASSERBURG Charles Arms Laboratory o• the Division o• Geological Sciences Cali•Jrnia Institute o• Technology,Pasadena, California 91109

Isotopic compos•tien and concentration of barium in six stone meteorites and the silicate inclusionsof two iron meteorites and three terrestrial sampleswere measured by use of a 'double spike' isotopic dilution technique in order to correct for laboratory fractionation. Any differencesbetween the abundancesof the isotopesin meteoritic and terrestrial Ba were found to be less than 0.1% for all isotopes.The per cent abundancesof Ba found in our work for Ba '•s, Ba•, Ba•% Ba '•, Ba TM,Ba •', and Ba'•ø are 71.699, 11.232, 7.853, 6.592, 2.417, 0.1012, and 0.1058, respectively. Because of the higher precision, these abundancesshould replace the currently accepted values. These results show the variations in the Ba isotopesreported by S. Umemoto (1962) to be unsubstantiated.

INTRODUCTION Umemoto [1962] reported that the isotopic A comparison.of the isotopiccomposition of compositionof Ba in the Bruderheimchondrite and in the Pasamonte and Nuevo Laredo various elements in terrestrial samples,me- achondrites were distinct from terrestrial Ba teorites, and other materials of the solar system is of fundamental importance in determin- and showeda pattern of uniform fractionation relative to terrestrial Ba. The enrichments ob- ing the early history of the solar system and the mechanismsof nucleosynthesis.In ad- servedby him correspondto a 2% enrichment dition to effectsthat are a product of either in the ratio Ba•ø/Ba• compared with ter- long-lived natural activity or cosmic-rayinter- restrial materials. Previously, Krummenacher action with meteoritic material, isotopicabun- et al. [1962] found no anomaliesgreater than dancesmay be distinct from terrestrial material 3% for the isotopesBa •'-• in the Richardton chondrite. Since the established fractionation becauseof isotopicfractionation or incomplete isotopic homogenizationduring the formation patterns for Xe and the suggestedfractionation of the solar system. The only major variation of Ba reported by Umemoto were in the in isotopic abundancesobserved between ter- same direction, it was of great interest to con- restrial and meteoritic samples that is not firm or disprove the reality of this reported effect. The mechanisms for fractionation that causedby nuclear processesis found in the rare gasesneon [Pepin, 1967], krypton [Eugster et have been proposedfor Xe and Kr are far al., 1967], and xenon [Reynolds, 1960a]. The from satisfactory,and it was conceivablethat only apparent exceptionsto the constancyof someunknown mechanism might have also op- the isotopicabundances, with the exceptionof erated in fractionating the Ba isotopes.The the rare gases, are the elements lithium and magnitude of the fractionation proposedby barium. Investigationsof lithium by Gradsztajn Umemoto was significantly smaller than that et al. [1967] suggestthat there is a variation found for Xe, which is approximately4% per of the abundance of lithium in stone meteorites mass unit, whereasfor Ba Umemoto indicated of about 10%. These data have not yet been an effect of 0.25% per mass unit. It is well confirmedby work in other laboratories. known that isotopic fractionation may be in- duced during mass spectrometricanalysis, and great care must be taken to avoid the produc- x Contribution 1606 of the California Institute tion of this type of anomaly by laboratory of Technology. procedures.This is made quite evident by the work of Wetherill [1964] on molybdenum,who Copyright ¸ 1969 by the American GeophysicalUnion. demonstrated that the variations in molyb- 3897 3898 EUGSTER, TERA, AND WASSERBURG

TABLE 1. Isotopic Composition of the Double Spike Atom per cent abundances.

1. Enriched Ba •37,measured 697 89.457 0.660 0.1290 0.0543 0.00119 0.00070 060 4-.070 4-.006 4-.0030 4-.0010 4-.00005 4-.00005 2. Enriched Ba TM,measured 867 1.646 1.789 4.080 84.572 0.0351 0.0115 150 4-.025 4-.018 4-.020 4-.200 4-.0004 4-.0003 3. Calculated compositionof 387 74.555 0.8515 0.7995 14.398 0.00695 0.00253 double spike based on com- 064 4-.058 4-.0059 4-.0040 4-.034 4-.00008 4-.00007 positionsof I and'2and on the amounts of Ba taken from the two salts *• 4. Measured compositionof 9.338 74.598 0.8500 0.7967 14.407 0.00690 0.00251 double spike, normalized to 4-. 004 4-. 0014 4-. 0014 4-. 00007 4-. 00006 Ba'37/Ba TM = 5.178 5. Typical compositionof a 39.403 44.020 4. 2322 3.5990 8.641 0.05260 0.05270 mixture of double spike plus 4-.010 4-.010 4-.0010 4-.0010 4-.010 4-. 00005 4-. 00005 sample, not corrected for fractionation (Nuevo Laredo)

Notes. For I and 2 the total errors are based on the errors for the uncertainty of the fractionation and on the statistical errors. The total error equals [•i (ai)2]•t•..For 3 the errors are based on the errors of I and 2. For 4 and 5 statistical errors are shown. * For the double spike the ratio of the total number of Ba atoms contributed by the enriched Ba xs• salt to the total number of Ba atoms contributed by the enriched Ba TMsalt was 4.8929 as calculated from the gravimetric data and from the atomic weights of the enriched Ba which was based on I and 2, respectively.

denumisotopic abundances reported by Murthy EXPERIMENTAL PROCEDURE [1962, 1963, 1964] were most likely due to in- Chemical treatment. A 0.2- to 5-gram sam- strumental fractionation. In this light, the iso- ple was mechanicallycleaned with a dental burr topic variations of Mo in terrestrial ore sam- to remove any surface contamination,washed ples reported by Crouch and Tuplin [1964] with acetone,dried in an oven, and, after grind- appear very doubtful. These authors seem to ing and splitting, weighedinto a 100-ml teflon be unaware of the other work in this field and beaker. The sample was dissolved in HC10, the instrumental problemsthat invariably exist. and HF, 5 ml of each acid per gram solid sam- Chakraburtty et al. [1964] reportedthat no en- ple, evaporated to dryness,and redissolvedin richment of Ag•ø• was found in seven iron me- 2.5 N HC1. An aliquot correspondingto about teorites, including Canyon Diablo for which an 0.2 gram of solid samplewas taken, evaporated anomalywas reportedby Murthy [1960], which to dryness, and then brought into solution in was most likely the effect of instrumental frac- 2 ml of 2 N HC1 which was loaded onto a cat- tionation. ion exchangecolumn (1 cm X 15 cm, packed It is known [Shields,1966] that isotopicfrac- with Dowex 50 X 8, 200-400 mesh). After most rionation effects can be minimized by very of the other elements were removed with 4 standard operational procedures during an- column volumes of 4 N HC1, the barium was alysis. It was deemed advisable, however, to collected in the following fraction of about 2 utilize a more reliable technique such as an in- column volumes of 4 N HC1. ternal isotopic standard of two isotopes.This Blank determinations showed that the barium technique,often called the double spiking tech- contamination introduced by the complete nique, was recently used by Wetherill [1964] chemical processingwas less than 5 X 10-g in his study on molybdenum.To distinguishbe- gram. This blank contribution to the sample tween laboratory effectscaused either by chem- was always less than 2%, which is negligible istry or massspectrometry, an isotopicinternal insofar as the isotopicratios are concerned.The standard or double spike was added to the sam- Ba concentrationswere, however,corrected for ples beforethe chemicalseparation. this small blank. ISOTOPIC ANALYSES OF BARIUM 3899 Mass spectrometry. The sampleof approxi- positionwas as shownin Table 1 for a typical mately 10-6 gram barium was depositedas the compositionof a mixture of doublespike plus chlorideand analyzedby meansof the single- sample.The Ba•/Ba •85ratios were always be.: filament (Ta) surface ionization technique.A tween 11 and 14. These ratios have been cor- single-focusing,30.48-cm radius, 60 ø sectortype, rected for the massspectrometer fractionation, programmablemagnetic field massspectrometer which was basedon the ratio Ba•/Ba •85.For all with digital output and with on-linedata proc- four samples this ratio was between 1.17 and essing[Wasserburg ei al., 1968,1969] wasused 1.18. Figure I showsthe variation of the ratio for most analyses.Some of the unspikedsam- Ba•37/Ba• as a function of the Ba•7 ion cur- ples were analyzedwith the same mass spec- rent normalized to the value of this ratio ob- trometer by usinga recorderfor analogoutput. tained at about 0.4 volt. Below 12 volts the The mass spectrometricdata were taken in input resistor can be consideredto be linear sets of ten completesweeps of the spectrum. within 0.1%. In a few casesin which data were Becauseof the programmablemagnetic field de- taken at intensities over 12 volts, corrections vice and the on-line data processing,one set of were applied for the nonlinearity. data for all isotopesincluding zeros on eachside Because of the wide range (up to 103) in of every peak couldbe taken within about 10 ion currents of the different isotopes,it was minutes. Systematicchanges in the isotopic necessaryto eliminate errors causedby the in- ratiosduring this time wereless than 2 parts in complete dischargeof the high input resistor 104 for all ratios. We therefore assume the frac- and the amplifier system. Time intervals be- tionation during each set to be constant.One tween data acquisition were established by analysisof a doublespiked sample consisted of making a time study of normal potassium,so six to ten sets taken at different intensities that any errors due to these sourceswere less rangingin most casesfrom about 0.5 to 12 than I part in 104 for all isotopes.This effect volts for Ba• with a 10•-ohm input res;stor. was also minimized by a scanningsequence in The linearity of this resistorwas examined care- which a high-abundanceisotope did not im- fully up to 42 volts.Four differentsamples were mediately precedea rare isotopein the detector. used for this examination. Their isotopic corn- In the chosenscanning sequence Ba TM usually

4.002

4DO0

0.998

0.996

0.994 _ q:[ Ba5' Ba35]/[Ba3Ba35]at,,,O.4 Volt 0.992

I I I I ! I ,/ o.5 2 5 20 50 VOLTSBa 157 IONCURRENT Ba 137(10 -IAMPS) Fig. l. Voltagedependence q of the 10S-ohmresistor used as • functionof ion current. The B•=7/B•• r•tios are correctedfor changesin fraction•tion.Each point representsthe mean of • set of ten r•tios. Errors shown are the mean deviations. 3900 EUGSTER, TERA, AND WASSERBURG followed Ba•". This sequencerepresented the spike and analyzed. The fractionation was de- greatest differencebetween a high- and low- terminedfor this analysisby the doublespike intensity isotope.The ratio Ba•/Ba •8' was al- techniqueas describedbelow. The isotopiccom- ways about 68. The isotopeBa •" was measured positionof the doublespike was as given in twice successively,integrating both times at Table 1 (measuredcomposition) and lhe con- least 12 seconds(including the zero lines). So centration of Bas' in the double spike was we were able to detect any possibleerrors due 0.6257 X 10-9 mol/g solution as determined to incompletedischarge of the input system. from gravimetry and from the measurediso- topic compositionof Ba in the separatenitrates DOUBLE SPIKE (Table 1). The isotopiccomposition of normal Highly enriched and precisely weighed Ba was as reportedin this work. The concen- Ba•'(N08),. and Ba•'(N08),. obtainedfrom Oak tration of Ba • in the normal Ba standard cal- Ridge were used to prepare standard solutions culated by two independentisotopic dilution of BaTM and Ba• in 2.5 N HC1. The isotopic experimentswere 2.819 and 2.822 X 10-9 mol/g composition of these two solutions were de- solution, respectively.The differencesbetween termined and are given in Table 1. The data as thesevalues and the gravimetricallydetermined tabulated are uncorrectedfor massspectrometer concentration of the normal Ba standard are fractionation. The relative abundance of Ba •' well within the errorsfor the gravimetryand in the enriched Ba • and that of Ba •' in the the stochiometryof the salts, the gravimetry enriched BaTM were each less than 2%. The of the aliquotstaken and the analyticalerrors. atom fraction of the principal isotope (Ba •' The doublespike was addedto the sample and Ba•, respectively)in the two solutionsis beforethe chemicalseparation in sucha way considered to be accurate to within 0.3 and that over 85% of Ba•' and Ba•, respectively, 0.1%, respectively.The absolute stochiometric originatedfrom the doublespike, whereas over compositionof the salts used was not demon- 85% of the other isotopesoriginated from the strated; however, cation impurities were esti- sample.A typical compositionof a mixture of mated to be below 0.1% basedon ORNL spec- the double spike plus sample is included in troscopicanalyses. Table 1. Any subsequentfractionation, either By assumingthe saltsto be stochiometricand in the chemicalseparation or in the massspec- using the measured isotopic abundances,a trometrie analysesis therefore corrected for in doublespike was prepared by mixingaliquots this procedure.The proportionsof doublespike of the two solutionsto give a calculatedratio and sample were kept constant in most cases Ba•/Ba •' = 5.178. The measured isotopic to within 10% to minimize error propagation. compositionof the double spike correctedfor In addition,the samemass spectrometric meas- discriminationusing Ba•¾Ba TM -- 5.178is given urements permitted a determination of the Ba in Table 1 and is compatible with the results concentrationin the sample since the use of givenfor the compositionsof the separatespikes a, doublespike is essentiallyan isotopedilution within the errorsgiven.. with two spikeisotopes. A normal Ba standard (BaCO• spec. pure, The mixture of sample barium and double Johnson,Mathey, and Co.) with a gravimetri- spike was analyzedon the massspectrometer, cally determinedconcentration of 2.816 X 10-9 and the differencein the fractionationfactor per tool Ba•/g solutionwas mixed with the double massunit was determinedfrom the equation

137•• (137,•• •(138•• 1-•/.•,•,.= \l-•/mix[1 -- 3(a" a')]-[- [1 -- 4(a" (381i

x [1-- ISOTOPIC ANALYSES OF BARIUM 3901 where a' is definedby example of the calculationfor the case of the ratio Ba'•ø/Ba•'. The ratios for the mixture of = 1 q- 3a' the double spike plus sample (subscriptmix) •--•/.••./ originate from the same particular analysisas and a" by for equation1.

130••' (130•• [1 q- S(a" -- a')]

.')]-

(2) 137hz/ (137• where (130/138),,mp•ois defined by

Here a' and a" are the fractionation factors (130•"' /(130• "uø = 1-- 8a' per massunit for the spikeanalysis and for the The second term in equation 2 was for all mixture of double spike plus sample, respec- sample ratios of Table • approximately 10% tively. The superscript M always represents of the first term measuredvalues on the massspectrometer and the superscriptstrue represent the absolute ratios. The ratios indicated by the subscript \138/,•mr•o130'•"'•'• 1.1 (130]\•--•/.i• • ] spike are the ratios in the pure doublespike; thoseindicated by the subscriptsample are the Theratio (130/138)sample•' is the isotopicratio of Ba•*ø/Ba•'8 in the sampleas if it had •der- ratios in the sample; those indicatedby the gone the samefractionation per massunit a' as subscriptmix are the ratios in the mixture of the pure doublespike. The other isotopicratios doublespike plus sample. • the sample as tabula•d (Table 4) are aH The spiking was done so that the second calculatedsimilarly. term in equation 1 was always less than 2% Beturning to a considerationof the error of the first term; i.e. propagationfor this procedurefrom the calibration of the nomal Ba salt with the doublesp•e, 137'•'• (137,•• it follows that the possiblegravimetric errors in the doublespike solutionare only constrained The differencea" -- a' was calculateddirectly by (•/8) -- (4•/8) < fractional error in the or by an iterative procedureby using the ex- Ba • calibration •2 X 10-•. perimental resultsfor each run and the inde- Here pendently measured spike composition run (Table 1). The error in a" -- a• contributed by an uncertainty in the absoluteabundances of 1% per mass unit would be less than 1% and of a" -- a'. The values of a/' -- a' were always lessthan 2 parts in 10". The knowledge of the difference a" -- a' [C,•]-.. allows the calculation of isotopic ratios in the where [C •] is the concentrationof BaTM in the sample as if they had the same fractionation doublespike. The superscriptass represents the a' as that for the analysisof the pure double assumedconcentration based on the gravimetry spike as given in Table 1. Equation 2 is an of the salts. 3902 EUGSTER, TERA, AND WASSERBURG Because of the lack of knowledge of the there were no Ba•* added, we would obtain absolute stochiometry of the salts composing false fractionorion difference the double spike, it is not possibleto draw any proximately strong conclusionsabout the absolutefractiono- rion a' from these data. a* --a •-- a • •- 3 X 10-4-- a • (3) To demonstratethe sensitivity of the double and would thus attribute an inherent fractiona- spike technique,the ratio (137/134)•sp,•eof the tion of 3 parts in 104 per mass unit to the doublespike was changed,adding to the original sample.Inspection of theseequations shows that amount of Ba•7 in the double spike 9 parts in this is equivalent to measuring a sample that 104 of pure fissionproduced Ba •7. This enriched was chemically fractionated by this amount. double spike was mixed with an aliquot of the This correspondsto a sample fractionation for Forest City sample (Table 4) and analyzed. Ba•ø/Ba• of The ratio of (137/134)•sp,•e.in the slightly enriched double spike would thus be a factor of (1 + 0.0009) greaterthan in the originaldouble = (1 q- 8 X 3 X 10-4) spike, all other ratios being essentially un- fractionated changed.Returning to equation 1, which deter- . (130h•' (4) mines the massspectrometer discrimination, we \138/•m.• have unf ract ionat ed Table 2 shows the results for the enrichment 137•• (137•• experiment compared with the results for an •-•/..ke*-(1 -+- 9 X 10-4) aliquot of the samesample whose double spike has not been enriched. The measured differences (137•• are in good agreement with the differences -- [1-- 3(a"-- O•')]\-•/mix+ R calculatedaccording to equations3 and 4. This experiment showsthat a true fractiono- where R is unchangedfrom the original double rion of 3 parts in 104 per mass unit can clearly spike. To the necessaryaccuracy be detectedby the describedtechnique. 1-•/•,•-- [1-- 3(•"-]- 3 X 10-• -- RESULTS AND DISCUSSION Isotopic ratios of barium. The resultsfor the analysesof three unspiked meteoritesare shown (137•• + -- 9 X in Table 3. Sincethese analyseswere carried out when the automatic digitized data acquisition Here a" and a' are again the true instru- system was still in an early stage of comple- mental fractionorion factors. If we were to cal- tion, someof the data had to be taken by the culate the discrimination difference in the ex- usual analog techniqueby measuringthe peak periment with the enriched double spike as if heightson a strip chart.

TABLE 2. Resultsfor Two Runs of the Forest City ChondriteDouble Spikedwith BsTM snd Bs The doublespike of run B hsd sn sdditionMenrichment of 9 psrts in 10• of pure fissionproduced BalaO/Ba138X 104 Bs's•/Bsm X 104 Ba,la•'/Ba, la8X 104 Ba,laø/Ba, TMX 104

A Forest City 1095.4 4- .3 919.5 4- .4 14.12 4- .02 14.76 4- .02 B Forest City 1096.0 4- .9 920.6 4- .8 14.14 4- .03 14.81 4- .05 (spike enriched) Fractional differences between run A •nd B (p•rts in 10a) 5.5 12 14 34 Fractional differences c•lcu- l•ted •ccording to (3) and (4) (p•rts in 104) 6.0 9 18 24 ISOTOPIC ANALYSES OF BARIUM 3903

•o •'•

o o

o o o o o 3904 EUGSTER, TERA, AND WASSERBURG

TABLE 4. Isotopic Ratios of Barium in the InvestigatedSamples after Correction for Fractionation by Means of a Double Spike of BaTM and Ba•a7 These data are taken with an integrating digital voltmeter. Ba•6/BaTM X 104 Ba•5/Ba•sX 104 Ba•a•'/Ba•sX 104 Ba•ø/Ba•s X 10* Terrestrial Samples Reagent Ba 1094.5 q- . 8 * * 14.76 q- . 1 1095.3 q- .7 919.6 q- .7 * 14.75 q- .04 Terrestrial standard W-1 1095.2 q- .7 919.1 q- .5 * 14.75 q- .04 Average and mean deviation 1095.0 q- .3 919.4 q- .3 14.75 q- .003 Chondrites Bruderheim a 1095.0 q- .3 919.3 q- .3 * 14.76 q- .02 b 1095.3 q- .9 919.4 q- .9 * 14.74 q- .04 Leedey 1096.7 q- 1.5 919.2 q- 1.4 * 14.74 q- .05 Forest City 1095.4 q- .3 919.5 q- .4 14.12 q- .02 14.76 q- .02 Abee 1094.5 q- .8 919.1 q- 1.4 14.11 q- .05 14.75 q- .04 A chondrites Pasamonte 1095.6 q- 1.0 919.5 q- 1.3 * 14.74 q- .05 Nuevo Laredo 1095.1 q- .4 919.4 q- .6 14.12 q- .02 14.77 q- .02 Silicate Inclusionsof Iron Meteorites E1 Taco 1095.8 q- .6 919.7 q- .6 14.14 q- .09 14.77 q- .09 Weekeroo Station 1095.6 q- 1.2 919.4 q- 1.0 14.13 q- .02 14.79 q- .03 Average for all meteorites and mean deviation 1095.4 q- .4 919.4 q- .1 14.12 q- .01 14.76 q- .01

* No data taken.

For the individual analyses tabulated, the three terrestrial and nine meteoritic samples mean deviations of 10 ratios are shown. The after correction for the mass spectrometer data taken with a strip chart recorder have fractionation and of the contribution of mean deviationsup to four times greater than Ba•ø' •3•' •' •' • • by the doublespike using for the data taken in the digital mode. Fur- equations1 and 2. All data in Table 4 are taken thermore,all valuesobtained in the analogmode with a single-focusingmass spectrometer with a have an additional error of about 0.05% due to programmablemagnetic field and a digital volt- the uncertainty in the correction for the re- meter for ion beam integration [Wasserburg corder nonlineartry. Because each analysis is et al., 1968, 1969]. normalized to Ba•/Ba • -- 0.09194 (the aver- The errors in Table 4 were evaluatedby cal- age for nine doublespiked samples corrected for culating new ratios fractionation, see Table 4), the scatter for the .otherratios is enlarged. (Ba-/Ba•s)•' The total spreadof the isotopicratios for all usingvalues for the ratios in equations1 and 2 six terrestrial and meteoritic samplesin Table 3 differing by one mean deviation from their is less than 0.2% for the isotopesBa •3•-• and average measuredvalues and in the direction to about 0.8% for the lessabundant isotopes Ba TM give the maximum spread in the two calculated and Ba•'. The averages for the terrestrial Ba ratios agreewell with thosefor the meteoriticBa; the differencesare 0.2% or less and they are well (Ba•/Ba•as•,• •ampl•' e within the experimental errors. Thus, we can conclude,so far, that there are no anomalies Figure 2 showsthe values of 3• plotted causedby nuclear processesin these meteorites versusmass numbers (m) obtained for the data at any particular massposition. givenin Table 4. Table 4 shows the isotopic ratios of Ba in Here 3• is definedby

m 1•8 a Jmeteorite , . (•138,,, • [Ba"'/B,as, m --138 [Ba /Ba' 1,,,..,.,,,:. ,o,,•.,.r .ampi.. x 10,• ISOTOPIC ANALYSES OF BARIUM 3905 •, is the fractional differencein parts per alies [Murthy, 1960, 1962, 1963; Umemoto, thousandof the isotopicabundance relative to 1962; $hima and Honda, 1963]. a terrestrial standard. We would clearly see an effect of 0.2% in the The total spread of the corrected isotopic average Ba•8ø or Ba•8• abundance. For chon- ratios for all isotopesof the twelve terrestrial drites this correspondsto a measurable differ- and meteoritic samples is in most cases less ence of 3 x 10•ø atoms per gram. This is than 0.2%. The averages for the meteorites equivalent to the number of excess atoms of agree with those for the three terrestrial sam- Xe TMwhich is typically found [Reynolds,1960b] pleswithin much lessthan 0.1% for all isotopes and attributed to I • decay. and the agreementbetween the spiked and the Our data excludethe productionof Ba•ø and normalizedunspiked samples as well within the BaTM by a radioactiveprecursor with an abun- small experimentalerrors. By using the lower dancecomparable to that of I TM,which enriched extremeof the terrestrialaverage and the upper the meteoritic Ba relative to the terrestrial extreme of the meteoritic average for the ratio Furthermore, upper limits can be placed on Ba•8ø/BaTM, an upper limit for the fractionation differencesin integrated high-energy proton of the meteoritesversus the terrestrial samples fluxes for uniform irradiation conditions in the can be estimatedas being lessthan 2 parts in early history of the solar system.If an average 10' per massunit. target concentrationof 5 ppm at about mass It is evidentthat thesedata showthe previous 140 and an effective spallation crosssection of results of Umemoto [1962] to be spurious.The 10 mb are assumed,a high-energyproton flux effectshe reported are most probably the result of about 5 x 10•9 protons/cm"is required to of instrumentalfractionation, which appears to enrichBa •ø or Ba• in chondritesby 0.2%. This be characteristic of the so-called La Jolla anom- is one order of magnitudehigher than the upper

Bruderheima (4) O Pasamonte(:5) [] ForestCity (4) <:• Bruderheimb (4) (•) Leedey(4) A Abee (4) • Bruderheim(::5) Leedey(:5) A EI Taco (4) + Pasamonte (4) Nuevo Laredo(4) V Weekeroo(4) X

AVERAGE FRACTIONATION OF UMEMOTO AX

v+ +

-2

d54 '!:55 456 '1:57 '158 mass m

Fig. 2. B•rium •"xssvalues for the investigated meteorites. The numbers (3) and (4) •fter the meteorite names refer to the correspondingt•ble in this work.

The fractionation line to be expected from the work of Umemoto [1962] is showa for comparison. 3906 EUGSTER, TERA, AND WASSERBURG '• TABLE 5. Concentration of Barium in the Investigated Samples Metallic iron was magneticallyremoved from the Leedeyand Abee samples,but not from all other samples.

Ba Concentration, ppm

Sample Class This Work LiteratureValues

Bruderheim L chondrite 3.37 3.4/ Leedey L chondrite 3.85 3.76" ForestCity It chondrite 3.37 3.65% 4. I a, 9e Abee Enstatite chondrite 2.41 2.41" Pasamonte Eucrite 28.2 28.6", 26 c Nuevo Laredo Eucrite 39.3 39.4", 40%46 a E1 Taco Ni-poor ataxite 2.37 Weekeroo Station Octahedrite 8.70 Terrestrial standard W-1 158 158 b

Tera, Burnett, and Wasserburg,to be published. Schnetzleret al. [1967]. Duke and Silver [1967]. Hamaguchi ½tal. [1957]. Pinson et al. [1953]. Wyttenbach and Dulakas (private communication,1965).

limit of 3 X 10•8 particles/cm• for •500-Mev figuresis lessthan 1%. The differencesbetween particles calculated by Burnett et al. [1966] these values and the results obtained by other based on isotopicanalyses of potassiumin ter- authors are most probably due to inhomo- restrial and meteoritic samples.The latter ex- geneitiesof the meteorites. periment is of coursemuch more sensitivefor Isotopiccomposition o/ natural barium. The the determinationof an upper limit for the flux values in Table 6 given for this work represent of an early irradiation of the solar system. the averagesfor both meteoritesand terrestrial Barium concentrations. The concentration of samples,since no differencesin the isotopiccom- Ba found in the meteorites and in the diabase positionhave beenfound. The ratiosBa•/Ba • standard W-1 is given in Table 5. A small and Ba•/Ba • representthe averagesof the six laboratory blank contribution of less than 2% unspikedsamples (Table 3), whereasthe other was corrected. The analytical error in these ratios representthe averagesfor the data tabu-

TABLE 6. Isotopic Compositionof Barium The errorsof this work equal 3• .... = 3[• /Xx?/n(n - 1)]• calculatedfrom the mean valuesfor each mass spectrometeranalysis as given in Tables 3 and 4. Nier believeshis ratios to be correctwithin 2% exceptthe onesfor Ba•aø and Ba•a•, which may be in error by 4%. The errorsgiven by us for the valuesof Umemoto have been recalculatedby us from his data to correspondto 3• .... for six analyses.

Ba•/Ba,•S Ba•/Ba•S Ba•/Ba•S Ba•4/Ba•S Ba•/Ba•S Ba•0/Ba•S X 104 X 104 X 104 X 104 X 104 X 104

This work 1566.54-0.5 1095.34-0.5 919.44-0.2 337.1 4-0.3 14.12 4-0.02 14.76 4-0.02 Nier [1938] 1580 1090 920 337 13.6 14.1 Umemoto [1962] 1547.94-3.0 1086.84-2.7 908.04-2.4 331.974-1.0 13.7124-0.05 14.2154-0.06 Values of Umemoto normalized to Ba•/Ba• = o. 09194 1554.4 1095.9 919.4 337.5 14.06 14.69 ISOTOPIC ANALYSES OF BARIUM 3907

TABLE 7. Percentage Abundances of the Isotopes of Barium

Mean of Atomic Weight of Ba Ba• Ba•7 Ba•6 Ba• Ba•4 Ba•2 C •'- -- 12 Scale

Atomic weight C •'- •- 12 scale [Matranch et al. 1965] 137.9050 136.9055 135.9043 134.9056 133.9046 131.9051 129.9062 Atom per cent abundance, this work 71.699 11.232 7.853 6.592 2.417 0.1012 0.1058 137.327 Statistical error 4-.007 4-.004 -•.004 q-.002 -•.003 q-.0002 q-.0002 Atom per cent abundance (Nuclear data tables U.S. 71.66 11.32 7.81 6.59 2.42 0.097 0.101 Atomic Energy Commission, compiled by G. H. Fuller, 1959. Data from Nier [1938]) 4-1.4 4- .2 4- .16 4- .13 4- .05 4- .004 4- .004

lated in Table 4. The error for the ratios Acknowledgments. We wish to thank D. S. Ba•O,•8,, •5, •/Ba• introducedby the correction Burnett for valuable discussionsand suggestions of the contribution of the double spike is less and D. A. Papanastassiou for his support in the mass spectrometry. We are indebted to our col- than 0.1%. leagues who supplied meteorite samples used in The given errors do not include the uncer- this work: Pasamonte, Leedey, Forest City, and tainty of the gravimetrically determined value Weekeroo Station were obtained from the of Ba•/Ba •' on which the correction of the Nininger Meteorite Collection at the Arizona State University through the aid of C'. W. Moore. laboratory fractionation is based. These data E1 Taco was obtained from YI. Hintenberger, represent our best estimates of the absolute M.P.I., Mainz, Germany. Bruderheim was given ratios, although it should be clear that the to us by L. T. Silver from a sample provided to purpose of this work was to search for isotopic him by R. E. Folinsbee. Nuevo Laredo was given variations and not to establish absolute ratios, to us by L. T. Silver. Abee was provided by J. A. V. Douglas, Geological Survey of Canada. which require better gravimetric procedures This work was supported by the National than used here. The data in Table 6 are all Science Foundation (grants GP 9114 and GP self-consistentto within the precisiongiven with 7976). a fixed fractionation per mass unit. REFERENCES In Table 6 the isotopiccomposition obtained in this work is compared with the terrestrial Burnett, D. S., I-I. $. Lippolt, and G. $. Wasser- burg, The relative isotopic abundance of K 'ø in composition given by Nier [1938] and by terrestrial and meteoritic samples, J. •eolrhys. Umemoto [1962]. If we normalize Umemoto's Res., 71, 1249, 1966. (See also; Correction, J. values to Ba•5/Ba• -- 0.09194 and extend the •eophys. 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