Isolation of Pu-isotopes from environmental samples using ion chromatography for accelerator mass spectrometry and alpha spectrometry

Else ie Edi o ial Sys em( m) o Analy ica Chimica Ac a Manusc ip D a Manusc ip Numbe : Ti le: Isola ion o Pu-iso opes om en i onmen al samples using ion ch oma og aphy o accele a o mass spec ome y and alpha spec ome y A icle Type: O iginal Pape Sec ion/Ca ego y: SEPARATION METHODS Keywo ds: Plu onium; AMS; alpha spec ome y; TEVA Co esponding Au ho : Physicis Elena Chamizo, Co esponding Au ho 's Ins i u ion: Cen o Nacional de Acele ado es Fi s Au ho : Elena Chamizo O de o Au ho s: Elena Chamizo; Ma ía del Ca men Jiménez-Ramos, PHD S uden ; Lukas Wacke , doc o ; Ignacio Vioque, Doc o ; Ana Calleja, PHD s uden ; Ra ael Ga cía-Teno io, p o esso ; Manuel Ga cía-León, p o esso Abs ac : A adiochemical me hod o he isola ion o plu onium iso opes om en i onmen al samples, based on he use o speci ic ch oma og aphy esins o ac inides (TEVA®, Eich om Indus ies), has been se up in ou labo a o y and op imised o hei pos e io de e mina ion by alpha spec ome y (AS) o accele a o mass spec ome y (AMS). The p oposed adiochemical me hod has eplaced in ou lab a well- es ablished one based on he use o a ela i ely un-speci ic anion-exchange esin (AG® 1X8, Bio ad), because i is clea ly less ime consuming, educes he amoun s and mola i ies o acid was es p oduced, and ep oducibly gi es high adiochemical yields. In o de o check he eliabili y o he p oposed adiochemical me hod o he de e mina ion o plu onium iso opes in di e en en i onmen al ma ixes, win aliquo s o a se o samples we e p epa ed wi h TEVA and wi h AG 1X8 esins and measu ed by AS. Some samples p epa ed wi h TEVA esins we e measu ed as well by AMS. As i is shown in he ex , he e is a com o able ag eemen be ween AS and AMS, which adequa ely alida es he me hod. Isola ion o Pu-iso opes om en i onmen al samples using ion ch oma og aphy o accele a o mass spec ome y and alpha spec ome y E. Chamizo a*, M.C. Jiménez-Ramos b, L. Wacke c, I. Vioque b, A. Calleja b, M. Ga cía-León a,b, R. Ga cía-Teno io b a Cen o Nacional de Acele ado es (CNA), A da. Thomas A. Edison , 41092, Se illa, Spain. b Applied Nuclea Physics G oup, Uni e si y o Se illa, P.O Box 1065, 41080, Se illa, Spain. c Ins i u e o Pa icle Physics, ETH Höngge be g, CH-8093 Zü ich, Swi ze land. * Co e Le e 1 Isola ion o Pu-iso opes om en i onmen al samples using ion ch oma og aphy o accele a o mass spec ome y and alpha spec ome y Abs ac A adiochemical me hod o he isola ion o plu onium iso opes om en i onmen al samples, based on he use o speci ic ch oma og aphy esins o ac inides (TEVA®, Eich om Indus ies), has been se up in ou labo a o y and op imised o hei pos e io de e mina ion by alpha spec ome y (AS) o accele a o mass spec ome y (AMS). The p oposed adiochemical me hod has eplaced in ou lab a well-es ablished one based on he use o a ela i ely un-speci ic anion-exchange esin (AG® 1X8, Bio ad), because i is clea ly less ime consuming, educes he amoun s and mola i ies o acid was es p oduced, and ep oducibly gi es high adiochemical yields. In o de o check he eliabili y o he p oposed adiochemical me hod o he de e mina ion o plu onium iso opes in di e en en i onmen al ma ixes, win aliquo s o a se o samples we e p epa ed wi h TEVA and wi h AG 1X8 esins and measu ed by AS. Some samples p epa ed wi h TEVA esins we e measu ed as well by AMS. As i is shown in he ex , he e is a com o able ag eemen be ween AS and AMS, which adequa ely alida es he me hod. 1.- In oduc ion Plu onium is an an h opogenic elemen ha has ound i s way in o he en i onmen since he beginning o he nuclea age in 1945. Among he di e en ac inides eleased due o nuclea ac i i ies, Pu dese es a special a en ion om he poin o iew o adioecology and oxicology. The main sou ce o Pu o he en i onmen we e he a mosphe ic nuclea weapons es s ca ied ou mainly in he 1950’s and he 1960’s, which in oduced 0.3 TBq o Pu in a global scale [1]. Addi ional amoun s o his elemen ha e been eleased a a local scale as a consequence o ci il nuclea eac o acciden s (as he Che nobyl acciden ), eleases om nuclea ep ocessing acili ies (as Sella ield, UK; La Hague, F ance; Mayak PA, Russia) and nuclea weapons acciden s (Paloma es, Spain; Thule, G eenland). * Manusc ip 2 Among he ou majo plu onium iso opes (241Pu, 238Pu, 239Pu and 240Pu), h ee a e alpha-emi e s: 238Pu (T1/2=87.7 y, Eα=5,499 MeV (72%)), 240Pu (T1/2=6564 y, Eα=5,168 (76%)) and 239Pu (T1/2=24110 y, Eα=5,157 (73,3%)). Con en ionally, hey a e de e mined in en i onmen al samples by alpha spec ome y (AS). Howe e , he wo mos abundan plu onium iso opes, 240Pu and 239Pu, canno be quan i ied independen ly in low-le el samples due o hei e y simila alpha-ene gy emissions (ΔE=11 keV). AS usually in o ms abou he joined ac i i y o 239Pu and 240Pu. In many cases, his is enough o a simple moni o ing o su eillance p og am. Ne e heless, he s udy o he a io o 240Pu and 239Pu o e s unambiguously in o ma ion abou he o igin o he plu onium. The 240Pu/239Pu a omic a io anges om 0.03 o 0.06 o weapon-g ade plu onium, and eaches a alue o 0.4 o eac o -g ade plu onium. This a io can be quan i ied by mass spec ome y echniques (MS): ei he he mal ionisa ion mass spec ome y (TIMS) [2], induc i ely coupled mass spec ome y (ICP-MS) [3], o accele a o mass spec ome y (AMS) [4]. Among hem, AMS o e s e y low de ec ion limi s (~1 µBq o bo h 239Pu and 240Pu), making i possible o s udy hese iso opes in any en i onmen al compa men . On he o he hand, limi ed in o ma ion on he Pu sou ce e m can be gained by measu ing he 238Pu/239+240Pu ac i i y a io by AS. We ou inely pe o m in ou labo a o y he de e mina ion o 238Pu and 239+240Pu in a wide a ie y o en i onmen al ma ixes by AS. Recen ly, we ha e gained as well expe ience in he ield o he de e mina ion o 239Pu and 240Pu by AMS [5]. In bo h cases, i is necessa y o apply a adiochemical p ocedu e o isola e he plu onium ac ion and adap i o op imum physicochemical condi ions o he inal measu emen : a) he elec o-deposi ion o plu onium on o s ainless s eel disks o i s de e mina ion by AS o b) he dispe sion o he plu onium in a me al/me al oxide ma ix o i s measu emen by AMS. In his pape , we desc ibe a adiochemical me hod, based on he use o he ex ac ion ch oma og aphy esin TEVA (Eich om Indus ies), o he isola ion o he plu onium om di e en en i onmen al ma ixes. The ollowing poin s ha e been s udied: eco e y yields, alpha-peak esolu ion in AS, and he magni ude o he U, Th and Dy decon amina ion ac o s as po en ial in e e ences o AMS o AS. The necessa y alida ion was pe o med by applying he TEVA me hod and he con en ional one, based on he AG 1-X8 esin (Bio ad), o di e en samples, and compa ing he ob ained esul s by AS. Also some independen aliquo s we e p epa ed wi h he 3 TEVA me hod and measu ed by AMS. Tha way, he alidi y o he ecen ly adap ed TEVA me hod o bo h AS and AMS has been checked. A desc ip ion o he TEVA me hod is gi en in Sec ion 2, i s main cha ac e is ics and ad an ages a e highligh ed in Sec ion 3 and, inally, he esul s ob ained in he alida ions exe cises a e shown and discussed in Sec ion 4. 2.- Expe imen al 2.1.- S anda ds, esins, equipmen s and samples The samples ha e o be spiked wi h a known amoun o 242Pu bo h o AS and o AMS measu emen s. This spike is necessa y in bo h echniques o he de e mina ion o plu onium concen a ions by he iso ope-dilu ion me hod: 239+240Pu ac i i y in AS, o 239Pu and 240Pu ac i i ies in AMS. In AS, his spike can be used as well o es ima e he chemical eco e y yields o he p ocedu e. The s anda d solu ion o 242Pu was supplied by NPL, England, and was dilu ed o ob ain s ock solu ions wi h a concen a ion o 20.9 mBq/ml (144 pg/ml) in a 2M HNO3 ma ix. The ex ac ion ch oma og aphy esin used was TEVA (Eich om Indus ies), which has been p o ed o be a good op ion o he sepa a ion o e a alen ac inides (Pu4+, Np4+ and Th4+) in 2-4 M ni ic acid om Am3+ and U6+ [6]. Ready- o-use mini-columns (diame e : 7 mm; leng h: 8 cm) packed wi h 2 ml o esin (100-150 µm mesh) we e used o hese analyses. The AS sys em used o he measu emen s was an alpha spec ome e Alpha Analys (Canbe a) wi h eigh independen chambe s ha can wo k in pa allel. Each chambe was equipped wi h a 450 mm2 passi a ed implan ed plana silicon de ec o (PIPS, 18 keV o nominal esolu ion). The measu emen s we e pe o med by placing he samples a a dis ance o 1.5 mm om he de ec o . In hese condi ions a coun ing e iciency o 34% was achie ed [7]. . The AMS measu emen s we e pe o med wi h he ETHZ/PSI compac AMS sys em Tandy adap ed o he measu emen o ac inides. B ie ly, he plu onium was ex ac ed om he Cs+ spu e ing ion- sou ce as PuO-, s ipped o Pu3+ wi h an A s ippe gas a a e minal ol age o 330 kV, and coun ed wi h a gas ionisa ion de ec o wi h 1.3 MeV o ene gy. This de ec o ea u es wi h a 3x3 mm2 4 silicon ni ide en ance window, which is 40 nm hick o op imal sepa a ion o he plu onium ions om he 2+ molecula agmen s wi h he same M/q a io [4]. The ICP-MS de e mina ions, ca ied ou o s udy he magni ude o he U, Th and Dy decon amina ion ac o s, we e done wi h an Agilen -7500C mass spec ome e . The analysed samples we e he ollowings: a) a i icially aced wa e , b) ashes o wood, c) supe icial soils collec ed in Paloma es (Spain) and d) supe icial soils wi h allou plu onium. Some o hese samples we e used ei he in he decon amina ion ac o s s udy o in he alida ion exe cises. 2.2.- P oposed TEVA adiochemical me hod Sample p e- ea men ( 20 h) A known amoun o 242Pu (1 ml o he 20.9 mBq/ml solu ion o AS, and 20 μl o he same solu ion o AMS) was added o each sample (wa e , soils, wood) as a spike, oge he wi h some ml o dilu ed HCl o i s homogenisa ion. The solid samples we e d ied a 70ºC o 2 hou s. A e wa ds, hey we e ashed in a mu le u nace o emo e he o ganic ma e in wo sequen ial s eps: i s ly a 150ºC du ing 2 hou s, and inally a 550ºC du ing 6 hou s. The wa e sample was di ec ly e apo a ed o d yness. Once cooled, he esidues we e placed in a e lon beake and 20 ml o 8M HNO3 and 2 ml o H202 we e added. A e hea ing a 90ºC o 1 hou , 1 ml o concen a ed HF was added in o de o enhance he quan i a i e ex ac ion o he e ac o y plu onium ha may be p esen , pa icula ly in he analysed soils om Paloma es. The mix u e was hen hea ed o 5 hou s, adding 8M HNO3 o keep he olume a 20 ml. The supe na an was he eby isola ed by cen i uga ion (4000 pm, 10 minu es). The solid esidue was disca ded. The supe na an was hen e apo a ed o d yness and he esul ing esidue was dissol ed wi h 1 ml 8M HNO3 and 10 ml o dis illed wa e , gi ing a 0.7M HNO3 solu ion. The plu onium was hen subjec ed o a edox cycle: educ ion o Pu3+ wi h Fe2+, adding 0.1 g o FeSO4, and oxida ion o Pu4+, adding 8 ml o 8M HNO3 and 0.2 g o NaNO2. A hese condi ions, he plu onium o ms a 5 nega i ely cha ged ni a e complex, Pu(NO3)62-, which is e ained in he column. The ob ained solu ion (abou 19 ml in a 3 M HNO3 medium) was inally condi ioned o a 0.5M Al(NO3)3 medium by adding 3 g o Al(NO3)3-9H20, o complex he oxala es ha educe he e en ion o he plu onium in he column [6]. The sample was hen loaded in o he ex ac ion ch oma og aphy esin TEVA. Sepa a ion by TEVA esins (4 h) A e he condi ioning o he comme cially p e-packed 2 ml TEVA esin wi h 10 ml o 3M HNO3, he sample solu ion was loaded on o he column. A hese condi ions, he Pu is s ick o he esin, and mos o he U and ma ix elemen s a e elu ed (see pos e io discussion). The esin was hen washed successi ely wi h h ee di e en acid solu ions: i s ly wi h 10 ml o 3M HNO3, secondly wi h 40ml o 2M HNO3 o assu e he emo al emaining aces o U and, inally, wi h 15 ml o 6M HCl o elu e he Th. In a las s ep he Pu was elu ed wi h 20 ml 0.5 M HCl. The Pu ac ion was hen eady o he p epa a ion o he Pu sou ce in he o m equi ed o each echnique. P epa a ion o he Pu sou ce The inal plu onium ac ion has o be adap ed o an op imum physicochemical medium o each echnique. In he case o AS, he plu onium in ou labo a o y is con en ionally deposi ed on o a s ainless-s eel disk, ollowing a well-es ablished elec odeposi ion me hod [8]. Fo AMS he plu onium, as plu onium oxide, needs o be dispe sed in a me allic ma ix o i s measu emen in a Cs+ spu e ing ion-sou ce. To p epa e he AMS a ge , 0.5 mg o Fe3+ (as Fe(NO3)3) was added o he inal plu onium ac ion om he TEVA esin (20 ml o 0.5 M HCl) as a ca ie . This solu ion was e apo a ed o d yness (5 h). The esidue was baked a 800ºC in a mu le u nace o 3 hou s o con e he plu onium and i on o oxides (Pu3O8, Fe2O3). Finally, 2 mg o pu e aluminium powde we e mixed wi h he oxides and p essed in o a 1 mm diame e aluminium ca hode. Tha way, he sample was eady o be measu ed by AMS [4, 9]. A comple e low-diag am o he analy ical TEVA p ocedu e p oposed in his pape o Pu de e mina ion in en i onmen al samples is shown in Fig. 1. 6 2.3. - Con en ional me hod This adiochemical p ocedu e is ully desc ibed in [7]. B ie ly, i consis s o he ollowing s eps: S ep 1.- The samples a e ashed (in o de o emo e he o ganic ma e ) and hen we -oxidised o pu Pu-iso opes and o he elemen s in dissolu ion. S ep 2.- A e il a ion, he dissol ed sample is passed h ough an AG® 1-X8 anion exchange esin, om whe e a e se e al elu ions (in o de o emo e in e e ing elemen s), he Pu-iso opes a e s ipped in a e y pu i ied solu ion. S ep 3.- The Pu-iso opes a e inally elec odeposi ed on o s ainless-s eel planche s. The Pu sou ces so ob ained a e hen eady o measu emen . 3.- Resul s and Discussion U, Th and Dy decon amina ion ac o s In o de o check he eliabili y o he TEVA me hod o bo h AS and AMS, he quali y o he plu onium ac ion om he TEVA esin has been s udied. In bo h cases, he achie emen o a pu i ied plu onium ac ion is impo an : in AMS, he PuO- cu en ex ac ed in he spu e ing ion sou ce imp o es wi h he concen a ion o Pu in he a ge ; in AS, he esolu ion o he ene gy spec a is closely ela ed o he hickness o he elec odeposi s. Mo eo e , special a en ion mus be paid o he decon amina ion ac o s achie ed o some ace elemen s ha may be po en ial plu onium in e e ences in AS (228Th and 241Am) o AMS (238U and 160Dy). As long as alpha spec ome y is conce ned, i is impo an o emo e aces o 241Am (T1/2=432.2 y, Eα=5.486 MeV (85%)) and 228Th (T1/2=1.91 y, Eα=5.420 MeV (73%)) in he inal plu onium ac ion, as hei main alpha-emissions in e e e wi h he ones o 238Pu (T1/2=87.7 y, Eα=5.499 MeV (72%)) in he ene gy spec a. In he case o he compac AMS sys em Tandy, 238U may each he de ec o e en when he machine is uned o 239Pu, due o s aggling on he esidual gas in he acuum sys em o due o ins umen al 1 Table 1 Sample AG 1X8 TEVA Soil-1 115 68 Soil-2 60 36 Soil-3 70 44 Wa e 50 35 Table 2 Sample Pu eco e y yield (%) TEVA me hod Pu eco e y yield (%) AG 1-X8 me hod Wa e 76 61 Soil-1 74 54 Soil-2 62 55 Soil-3 68 51 Ashes 60 39 Table 3 AS Sample 239+240Pu (Bq/kg) TEVA me hod 239+240Pu (Bq/kg) AG 1X8 me hod Wa e 35.0 ± 2.2 Bq/m336.0 ± 2.1 Bq/m3 Ashes 0.08 ± 0.01 Bq/kg 0.08 ± 0.01 Bq/kg Soil-1 (Paloma es) 49.4 ± 1.0 Bq/kg 46.5 ± 2.3 Bq/kg Soil-2 (Fallou ) 2.40 ± 0.15 Bq/kg 2.37 ± 0.09 Bq/kg Soil-3 (Fallou ) 1.48 ± 0.08 Bq/kg 1.44 ± 0.07 Bq/kg Table 1-4 2 Table 4 AS AMS Sample 239+240Pu (Bq/kg) TEVA me hod 239+240Pu (Bq/kg) AG 1X8 me hod 239+240Pu (Bq/kg) TEVA me hod Soil-2 (Fallou ) 2.40 ± 0.15 2.37 ± 0.09 2.65 ± 0.14 Soil-3 (Fallou ) 1.48 ± 0.08 1.44 ± 0.07 1.53 ± 0.09 Soil-4 (Fallou ) 1.55 ± 0.06 1.50 ± 0.05 Soil-5 (Paloma es) 0.06 ± 0.01 0.049 ± 0.005 Figu e 1 Click he e o download high esolu ion image Figu e 2 Click he e o download high esolu ion image Figu e 3 Click he e o download high esolu ion image Figu e 4 Click he e o download high esolu ion image