An Easy Method for the Determination of Ra Isotopes and Actinide Alpha Emitters from the Same Water Sample

An Easy Me hod o he De e mina ion o Ra Iso opes and Ac inide Alpha Emi e s om he Same Wa e Sample* M. C. MORÓN, R. GARCÍA-TENORIO, E. GARCÍA-MONTAÑO M. GARCÍA-LEÓN and G. MADURGA Facul ad de Física, Uni e sidad de Se illa, Apdo. 1065, 41080 Se illa. Spain R�di_um _iso opes and ac inide a emi e n a e easil_y de e mined om he same wa e sample. The Ra ac on 1s ob amed by cop ec1p1 a on w1 h Ba. wh1le a Fe cop ecipi a ion is used o he ac inides Bo h ac 1�ns a e measu ed wi h a gas- low p opo ional coun e . Addi ionally he iso opic Ra comp�si ion 1s ob amed by measunng a! wo o h ee d1 c en llmes he a ac 1 i y om he Ra- ac ion. Thc me hod 1s apphed o am wa e and d inking wa e samples. l. In oduc ion Collec ion o he d y esidue upon e apo a ion, and subsequen eading o he low and high ampli ude pulses wi h a p opo ional coun e and a wo channel analyse , p o ide a as and low cos simul aneous es ima ion o he o al C1. and /j ac i i ies in wa e .º·2l This may be su icien o a quick gene al knowledge o he ac i i y le els in he aqueous en i onmen . Howe e he me hod has se ious limi a ions: (a) Fi s he indisc imina e collec ion o ali he solid ma e p esen in he wa e p oduces hick samples wi h weak and poo ly known C .-e iciency (because o he abso p ion) unless small olumes o wa e a e ea ed and consequen ly small absolu e ac i i y collec ed. In ei he case he e ec is a ela i ely high inaccu acy o he esul . (b) Mo eo e . as he po en ial dange assigned o di e en adionuclides is di e en and he me hod dis inguishes only x om /J-ac i i y, no di e en elemen s, he in o ma ion gained is o en insu icien . On bo h g ounds hese sho comings a e pa icu la ly impo an o C1. cmi c s bccause hei con amina ion haza d is dange ous o human beings e en a low concen a ion le els. In his pape an easy me hod o sepa a e x ac i i y om wa e samplcs is gi en. F om he same measu emen we can ob ain he x ac i i y associa ed wi h ac inides and he C1. ac i i y associa ed wi h Ra. Mo eo c , a ca e ul s udy o hc empo al e olu ion o he Ra ac ion ac i i y can gi e he iso opic con ibu ion, mos ly due o 226Ra and 224Ra. *Wo k pa ially suppo ed unde con ae! CAICYT No. 2849/83. Wi h his echnique o coun ing he o al C1. ac i i y, mo e de ailed in o ma ion is ob ained which includes: a ac i i y due o ac inides, which a e ela ed o U and Th p escn in hc sample, plus 226Ra and 224Ra ac i i ies sepa a ely. Hence, an inc ease in he quali y o he ob ained da a is eached and an easie handling o he da a is possible. A dcsc ip ion o hc adiochemical mc hod is gi en in Sec ion 2. The calib a ion o ou p opo ional de ec o o a-ac i i y is p esen ed in Sec ion 3. In Sec ion 4, we desc ibe he echnique used o e alua e he con ibu ion o each adium iso ope. So ne esul s on di e en wa e samples a e gi en in Sec ion 5, wi h a summa y and conclusions in Sec ion 6. 2. Radiochemical Me hod Essen ially he mc hod is one o cop ecipi a ion o adium wi h Ba and o he ac inides wi h Fe, ci he join ly [as desc ibed by Liebe man in Re .(5)] o successi ely. Figu e 1 ou lines he s eps ollowed: A 500 mL wa e sample, p ese cd wi h HNO,, is i s neu alized wi h NH40H, hen 20 mL o l M H2S04 a e added and he sample is hea ed a abou 50 C. Fi e mg Ba2" a e dissol ed in he sample while being s i ed. The Ba-Ra sulpha e o med p ecipi a es and is il e ed ou h ough a Millipo e memb ane. The p ecipi a e is d ied i s in a ho pla c and la e in a silicagel desicca o o p epa e i o coun ing. The emaining aqucous phase is boilcd o elimina e Rn and C02 ( hc la e can o hc wisc induce he o ma ion o complex compounds o U wi h ca bon a e and bica bona c ions ha a e e y soluble). The wa e is hcn b ough o oom empe a u e and hea ed again a abou 50 C o s a hc p occss o 500mLH20 Add 20 ml 1M S04 H2 Neu olize wilh NH40H + 5 mg Bo cc ie Heol 10 50ºC while s i ing o 30 min Fil e P ecipi a e Fill o!e D y 1A;-;;h� :Ou;: 1 (Ro 1 1 L _____ J Boil o 2 min and ollow il o sland o 3 h + 5 mg Fe co ie P ecipila!e wi!h NH 4 OH Hec o 50ºC while s i ing o 30 min Disca d he il o e ,----- ----1 D y ----... 1 Alpho Coun 1 1 ( Th, U, Np, Pu, Am,Cm 1 1 L ________ .J Fig. 1. Scheme o he p ocess. p ecipi a ion o ac inides. To achie e his, 5 mg o FeH a e dissol ed in he solu ion and NH40H is added d opwise un il he p ecipi a ion is p oduced. This p ecipi a e con ains he ac inides, :>: emi e s included, and is likewise il e ed and d ied, as be o c. The inal aqueous phase is disca ded. In p incipie ali he ac inides a e con ained in he second ac ion, bu in mos cases na u al :>: emi e s, i.e. U and Th, will domína e he :>: ac i i y o hc sample. Bo h ac ions, adium and ac inides, a e sepa  a ely coun ed wi h a con en ional gas low p opo  ional de ec o which has been desc ibed elsewhe c.()) 3. Calib a ion o he Coun ing Sys em The x e iciency o he de ec o is essen ially ene gy independen in he ypical egion o in e es (4--7 MeV), bu i a íes s ongly wi h he sample hickness as shown in Fig. 2. The calib a ion was made wi h a 500 mL wa e sample o which a known ac i i y o 239Pu was addcd. I was acidi ied wi h 20 mL o l M H2S04 and Ba2+ and Fe3 1 added. The esul ing speci ic ac i i y was (53.2 ± 1.2) dpm/mL. Se e a! aliquo s o his sample we e akcn, be wccn 10 and 115 mL, and comple ed, when necessa y, wi h dis illed wa e up o l 00 mL each. Thus we ob ained 20 ¡ T � 1 o:: 15 10 o I ! I !¡ 3 Thickness ( mg /cm2) 4 Fig. 2. Calib a ion cu e o hc coun ing sys cm by a s aigh line. p ecipi a es wi h di e en hicknesses by hc p o cedu e ou lined in he p e ious sec ion, only modi ied in ha bo h Ba and Fe we e join ly p ccipi a ed. The o al e iciency, R1, was ob ained as hc a io be wecn hc ne :x coun s and hc known ac i i y o he aliquo . RT is dependen on: geome y (which is he same o ali hc samples). sel abso p ion o alphas (which is nega i ely co cla ed wi h hc hick ness, as expec ed) and he adiochemical yicld o he p ocess desc ibed in Scc ion 2. The e o ba s ake in o accoun hc coun ing s a is ics and hc unce  ain y o he pipe ing. no hc luc ua ion o he chemical yield. I is clea ha hey unde es ima e he luc ua ion o eal alues o RT abou he smoo h analy ical calib a ion R(x) o Fig. 2. The la e has been aken. o con enience. wi hou any heo e ical p ejudice and in iew o he la gc ac ual luc ua ion. as he leas squa es linea exp ession R(x)= 18.75-2.486x ( 1) wi h Pea son co cla ion coe icien = -0.89. whe e R is gi en in '% and he hickness x in g,'cm2. To his calib a ion o mula we assign he expe i men al ela i e e o o 7% o x > 0.48 mgicm2 and 20% o x < 0.48 mg/cm2• This "e o " is accumu la ed quad a ically o he s a is ical e o s o he p oblem samples conside ed in Sec ion 5. A smalle se o 241Am samples o known ac i i y has con i med he alidi y o calib a ion ( 1) o his adionuclide. La gc olumcs (500 mL) will he ca ed o hc p oblem samplcs han hosc uscd o calib a ion (100 mL). To con i m he i ele ancc o hc olumc and o explo e an e en ual dcpendcnce on he adio nuclide, eigh la ge (0.5 L) samples wi h known ac i  i y o 239Pu o 241 Am we e p epa ed and coun ed. Thc a e age a io o hei e icicncy o ha p edic ed hy equa ion (1) is (100 ± 7)0 /c,. A simila cxpc icnce wi h 226Ra ac i i y ga c an a e age a io o ( 106 ± 7)';;, which is compa ible wi h equa ion ( 1) bu sugges s a ew 'Yo highe yield in hc Ra p ccipi a e. Con sequen ly. whcn applying calib a ion ( 1) u Ra samples we eno malize i wi h a ac o 1.06. 212Po 0.298 µ.s, i2128¡ 60.55min 20Bpb s oble ' '-'20BTI 3.053min 22sTh 1.9131y 224Ra 3.66d 220Rn 55.6s 216po 0.15 s 212pb 10.64 h '-'22BAc 6.13 h 232Th 1.4 X 1010 y '� � 21op0 138.38 d 206Pb s oble '-, 210Bi 5.013 d ' 214po 164 ¡LS 210Pb 22.3 Y ' 2148¡ 19.9 m 226Ro 1600 Y 222Rn 3.8235d 21Bp0 3.11min ¡ '-1 214Pb 1 26.� 207p� s oble ,, 223Ra 11.434d 219Rn 3.96s --"T,sPo 1.78ms 2� 2.14min ¡ '1 211pb 36.1 min 201TI 4.77min Fig. 3. Pa o h ee adioac i e se ies showing na u al adium iso opes wi h hei descendan s and hal -li es. Alpha decay goes downwa ds and be a decay goes up le . 4 223Ra 3 224 Ro -1 - o " " 2 226Ra 1�-�--�-�--�-�--�-� o 2 3 4 5 6 7 ldaysl Fig. 4. Time e olu ion o he o al ac i i y o '"Ra. ""Ra and 226Ra. wi h hei descendan s. s a ing wi h uni ac i i y o he pa en! a 1 = O. 4. Measu emen o he Iso opic Composi ion o he Ra F ac ion Fou Ra iso opes a e ound in Na u e, associa ed wi h hei ances o s and descendan s. Thei place in he adioac i e se ies is shown in Fig. 3. Th ee o hem a e Cl emi e s and (pa icula ly ''4Ra and 221Ra) ha e, among hei descendan s, o he e y sho li ed Cl emi e s. Immedia ely a e cop ecipi a ion wi h Ba, he sole ac i i y due o adium iso opes emains. O cou se, his will soon ecei e he con ibu ion o hei daugh e s. Figu e 4 shows he ime e olu ion o he o al ac i i y o each. 22.1Ra, 224Ra and 226Ra wi h hei descendan s, s a ing wi h uni ac i i y o he pa en a = O. mRa and 224Ra g ow in a ew seconds o abou h ee imes he o iginal ac i i y and a c wo o h ee days he whole amily will decay in secula equilib ium wi h he pa en 's pe iod ( 11.4 d and 3.66 d espec i ely). l is possible ha . since mRa is also collec ed in he p ecipi a e, i can egene a e 224Ra. The e is, howe e , a link, which has no been collec ed in he p ecipi a e (228Ac and 228Th, he second ha ing an almos 2 yea hal -li e). Thus 1 mon h (2 mon hs) a e he hypo he ical sepa a ion o sole 228Ra, he o al Cl ac i i y o i s desccndan s will each 12% (26%) o he ini ial /1 ac i i y o he pa en 228Ra. The ac i i y o he 226Ra amily is cha ac e ized mos ly by he hal -li e o he daugh e 4 3 1º ,• ·-· ,..•" ---·-· -·····-·---·�--·-·-·-·-·-·-·__J 1�----�-----�----�- 0 10 20 30 1 (days) Fig. 5. Expe imen al alucs o hc ac i i y in di e cn imes compa ed wi h he heo e ical p edic ions o .411 = 97.4 cpm and 10 = 140 min. 222Rn (3.8 d) which is ollowcd by wo mo e 'l. emi e s wi h sho li es. Thus in a lcw wceks hc amily eaches ou imes he ini ial 'l. ac i i y: 380º1¡, in 15 days and 398. 7% in 30 days. Thc con ibu ion oi' he 21ºPo is s ongly dclaycd by hc in c posed Jong-li cd (22.3 y) /1 emi e 2w h. Fo a gi en iso opic composi ion o he adium p ecipi a e he expec cd ac i i y and numbe o coun s a a la e lime can be compu cd VÍlh he equa ions gi en in he Appendix. by adding he con ibu ions o he ou amilies ("4Ra is now an independen amily ini ially disconnec cd om 228Ra). Recip ocally i should be possiblc o deduce hc iso opic composi ion o he p ecipi a e om he ime e olu ion o he 'l. ac i i y. The e is, howe e , a p c ious ques ion o be e sol ed: Is he e a 1 = O? In he p ocess desc ibed in See ion 2, is he e an ins an when ali hc adium o be collec ed is al eady in he p ccipi a e wi hou any membc s o he adioae i e amily o he han Ra. ami a e his ins an nei he he de eloping daugh e s no any Ra is dissol ed') And. i so, whcn a c he addi ion o he Ba ca ie does ha hapcn'' We ha e looked o an expe imen al answe o his douhlc ques ion by p epa ing a s anda d wa e sample wi h a known amoun o '"'Ra, hen pe o ning a se ies o eadings o he ac i i y du ing a ew wceks and compa ing hcm wi h p edic ions o equa ion (A3) om he Appendix. (i) As a i s app oxima ion o he ini ial coun ing a e. R0, we ake i o he expe imen al coun ing a e ound in he las eading, 3 o 4 weeks a e he p epa a ion o he sample. This seems casonablc in iew o he conside a ions gi en abo e. (ii) Se e a! alues o he o igin o ime. 111 • a e hc addi ion o hc Ba ca ie . a e ied in he i . i.e. 1 - ,, is subs i u cd ins ead o I in equa ion (AJ). (iii) The quali y o he se e a] i s hus ob aincd is measu ed h ough hc qiJan i y i= ,il.'!, wi h l.2 = I (R l, - Rc,p),!(Re,p), 1-=l whc e N is he numbe o eadings. R'"'" he expe i men al alucs and R,h hc p cdic ions o cqua ion (A3). L depends on R0, which o hc mo nen is no changcd, and om 111• The bes il co esponds o mínimum alue o i. Fo N la ge enough a good hco y and good alucs o R0 and 10 imply L � 1. (i ) Fo he chosen aluc R11 • L is expec cd o depend quad a ically on 111 in he icini y o " i,,.,,,. Thus i akcs jus a c ials o ind he bes 10 o a gi en R0, i wc i he alues L (111) l'ound by a pa abola. ( ) Now o he alues o R11 a e in cs iga cd h ough s eps (ii)-(i ). Thus he i,..,,. (wi h cspec o 111)depends on he choscn alue R11• Again hc dc pendence ,,,,,,(R0) is expcc ed o be quad a ic nea hc mm1mum (wi h espcc o R0). and a ew ials su icc o ind hc bes alues R0, 10 which yield he eal mínimum o ,1. wi h espec o bo h o hem. This sequence has been ollowed wi h wo 500 mL wa e samples. each wi h an ini ial 226Ra added ac i i y o (531 ± 1 O) dpm. The numbe o eadings was /V = 29 in 32 days and N = 26 in 31 days espec i cly. The mínimum ,1. ob aincd was 1.86 wi h 10 = 140 min and R0 = 97.4 ± 0.3 cpm o he i s sample (sce Fig. 5) and ,1. = l.78 wi h 10 = 167 min and R0 = 98. 7 ± 0.3 cpm o he o he . The dcduced e iciencies o (18.3 ± 0.4) and (18.6 ± 0.4)% com pa ed wi h he calib a ion o equa ion ( 1) o he expe imen al hickncsses (0.56 and 0.52 mg/cm2) yielded he a e age e iciency o hc chemical p ocess o Ra as compa ed wi h Am and Pu which was quo ed in he p e ious Sec ion as (106 ± 7)%. The alues o ,1. nea he mínimum, and o he co esponding R0, a e no c y scnsi i c o changes o a cw cns o min in 10. So we will assume a 111 = 150 min a e hc addi ion o he Ba ca ie as he o igin o ime o equa ions (A 1) and (A3) o he Appendix. The alues ,1. a e close enough o I o gi e con idence o hc me hod. Bu hc p occdu e is oo long o a ou inc-likc de e mina ion o he iso opic composi ion o a adium sample. Howc e a much sho e numbe o measu emen s is su icien , especially i onc makes he ollowing easonable assump ions: (i) 221Ra, being a desccndan om hc ela i ely scan y 235U, is expec ed o be in negligible p opo ion compa ed o he o he Ra iso opes, unless he sample comes om places con amina ed by he nuclea indus y. Consequen ly, i s p escnce can be disca ded a a guess. (ii) 228Ra con ibu es almos no hing in hc i s wo mon hs. The c o e wo eadings should be cnough o a de e mina ion o he ini ial ac i i y o 224Ra and 226Ra: one in he i s o sccond day. when he 224Ra amily is ela i cly mo e ac i e, and hc o hc onc a c 2 o 3 weeks whcn almos! only he 226Ra amily is ac i e. Thus i e1 and e2 a e he o al ac i i ics ob ained om he numbe o coun s collcc ed in hc eadings s a ed a 1 and 12, F4(1) and F6( ) hc p edic ions o equa ion (A3) o uni ini ial ac i i y o 224Ra and 226Ra espec i ely, hen he co esponding expe imen al ini ial ac i i ies A4 and A6 a e ob ained om he sys em: e1 = A4Fil1) + A6F/11) (2) (iii) 224Ra and 228Ra can be in secula equilib ium i he sample has no unde gone chemical ac ions in hc p e ious ew yea s. This implics equal ac i i y al ime l0(A8 = A4• ollowing he no a ion o hc p e ious pa ag aph). A ncw mcasu emen madc so ne mon hs la e (say 11) may con i m he hypo hesis o secula equilib ium i he cading C, ul ills C = A ,FoU1) + A4Fs(1,) wi h ob ious no a ion as in he p e ious equa ions. Once he p esump ion o secula equilib ium (A4 = A8) has been con i med o a ype o en i on men al sou ce, i can be sys ema ically assumed in he u u e wi h only occasional con i ming es s. 5. Applica ion o he Me hod The me hod is cu en ly being applicd o di e cn en i onmen al wa e samples. We p esen so ne o he esul s he e. Table I Thc , ac i i y o ' ainwalc collec ed in h ec di e enl pe iods o ime (column 2) has heen measu cd by he di e en me hods desc ibed in his wo k. Columns 3 and 4 a e he ini ial ac i i ies o "'Ra and "'Ra ob ained h ough equa ion (2) om hc measu emenls o he Ba p ecipi a e. Column 5 gi es he ac i i y o ' hc ma c p ecipi a ed wi h Fe and is all ibu ed o ac inides. Columns 6 -9 gi c he o al > ac i i 1 measu ed a wo di e en imes om he join Fe+ Ba p ecipi a e. acco ding o hc me hod o Re '. (5). The compa ibili ) o hesc esul s wi h hose o column� 3 5 is explained in he cx . (Time is gi en in days in columns 7 Samplc RI R2 R.l and 9) Ac i i y (mBq, L) To al 'l. ac i ily Sampling da e 226Ra 2�..J.Ra Ac inides A, 1, A, Feb.-Ap . 1983 105 ± 8 25 ± 5 196 ± 19 361 ± 31 2 613 Ap . 1983 23 ± 2 12 ± 5 48 ± 7 128 ± 12 1 144 Ap .-May 1983 193 ± 14 28 ± 9 307 ± 24 923 ± 76 6 1049 Table 2. 226Ra and ac inide a-emi e ac i i ies measu ed in so ne d inking wa e samples (D) and lake wa e samples (L) (No signi ican 224Ra ac i i y was ound). Fo compa ison. o al � ac i i y is gi en. The !al e was de e mined ollowing he me hod o Re . (5) Ac i i y (mBq. l.) Sampling Sample da e :: >Ra Ac inides To al 1 (days) DI 2-16-84 1.7 0.6 14 4 19.0 2.9 4 D2 4-16-84 4.3 0.8 20 3 23.5 3.1 32 D3 7-13-84 1.7 0.6 16 3 7.9 2.5 22 LI 2-16-84 1.8 0.6 6 3 17.1 3.1 9 L2 4-16-84 0.3 0.5 9 3 13.5 3.9 16 L3 7-13-84 06 0.4 6 2 4 3 19 51 14 87 56 92 52 The ac i i ies ound in di e en ainwa e samples a e gi en in Table 1. They ha e been collec ed since Decembe 1982 al he Uni e si y o Se ille. The esul s show a conside able p csence o 22'Ra. qui e simila o hose om ac inides, and signi icanl 214Ra ac i i ies a e also ob ained. To al 'l. ac i i y was measu ed o one o se e al days a e chemical sepa a ion (A 1) and a e se e al mon hs (A2); he ime ha media ed be ween he p epa a ion and eading o he ae i i y is shown in eolumns 7 and 9 espee i ely. I is obse ed ha A2 is sys ema ieally highe han A 1• This is due o he 226Ra con en in he p epa ed sample. To compa e he measu emen s o he o al ac i i y (eolumns 6 and 8) wi h he sum o he pa ial measu emen s (columns 3. 4 and 5), one also has o includc hc con ibu ion o hc dcscenden s o Ra iso opes. which a y wi h ime. as cxplaincd in Sec ion 4. Thus a e 6 days he ac i i y o he 226Ra amily has inc eased by a ac o F6 (6) = 2.99, and ha o he 224Ra amily by a ac o Fi6) = 1.33. and a e 52 days by ac o s F�(52) = 4 and F4 (52) :,,: O. Thc e o c, i we look al he mosl ac i e sample R3, one has o compa e he o al ac i i y ound a e 6 days (923 ± 73) wi h 2.99 ( 193 ± 14) + 1.333 (28 ± 9) + (307 ± 24) = 921 ± 50 and he ac i i y ound a e 52 days ( 1049 ± 87), has lo be compa ed wi h 4(193± 14)+(307±24)= 1080±61. Simila ly, o he samples R I and R2 i is s aigh  o wa d o show ha he esul s o columns 6 and 8 a e compa ible wi h hose o columns 3-5 wi hin expe imen al luc ua ions. The ,'l. ac i i ies o so ne d inking wa e samples (named D) om Se ille a e gi en in Table 2. Ac inidc 'l. emi e concen a ions (column 4 o he Table) a e clea ly highe han hose o 226Ra (column 3). On he o he hand, signi ican! 224Ra ac i i y was no ound in his kind o samplc. In gene al, he spcci ic ac i  i ics a e e y low. wi h cla i c e o s anging om 15 o 35%. In hc las 2 columns o his Table hc o al 'l. ac i i y is gi en o cach samplc and hc ime a e sepa a ion when i was mcasu ed. In hc same Table. he esul s o a i icial lake wa e samples (named L in column 1) a e p esen ed. These ese oi s a e loca ed a ound Se ille and eed he wa e ea mcn plan s o he ci y. Nei he 224Ra no 226Ra a e signi ican ly p esen in hcsc wa e s. wi h he excep ion o sample L 1. The lc els o ac inidc ac i i ies a e c y low and he e a e no highly signi ican di e ences be wcen hese esul s and hose om d inking wa e samples. Again he da a o columns 5 and 6 can be shown o ag ec wi h he sum o he ac i i ies ound sepa a ely o Ra (column 3 plus desccndan s) and ac inidcs (column 4), al hough he la ge cla i e e o s make he check mo e ambig- c... e G � 1 � > <n ¡.e¡ C"-.JO "- l 'l o o°''°'° oo oc � ("� �.....: 6 1 1 -o . V(]'-. ; 1 1 1 ::¡:�¡u:!;'!; -OO'IC"'�.-* oo --oo l.n�'-ncici oc <n --<n ... -1 ' OC MLlJ- 0 OC::=; .....:� o 1 1 <n ... o, -1 Ml ) '<:j'" � OC: M * OOC:NN i .Ni.ne -:� -:c 1 <n oc e -e 1 i ... oc <'1 N *e* e o o 1 e V '° o -- Ne -MNC-C V'lOOa. .-OONO 1 I, 1 1 �- '<: N ci.....: 6 1 z .§ e}¡ uous in hese cases, han o he ain samples o Table l. 6. Summa y and Conclusions Mos en i onmen al labo a o ies de o e a la ge pa o hei wo k o he de e mina ion o a ac i i y in wa e . As a i s s age he measu emen o o al a ac i i y is cu en ly used. Since hese esul s a e di icul o in e p e , o he me hods a e needed ha could b oaden and quali y he in o ma ion ob ained. In his wo k a me hod is gi en o he sepa a e measu emen o Ra and ac inide a emi e s om he same en i onmen al wa e sample. Ra is i s eco  e ed by cop ecipi a ion wí h Ba, and la e he ac i nides wi h Fe. In addi ion, a s udy o he empo al e olu ion o Ra ac i i y gi es he iso opic com posi ion o he ex ac ed Ra, i.e. 226Ra and 224Ra concen a ions. The de ails o his s udy ha e been ca e ully de e mined. Wi h his easy p ocedu e mo e and be e in o ma ion han simple, g oss a de e mina ion, is ex ac ed om each wa e sample. Mo eo e , in so ne cases, his me hod can easily compe e wi h o he s o g ea e sophis ica ion. Re e ences l. Ga cía-León M. and Ga cía-Mon año E. In P oc. 3 d /ni. Symp. lhe Socie1y ó Radiological P oleclion: Adz,ances in Theo y and P aclice, 6--11 June 1982, ln e ness, Sco land. Vol. 2, p. 637. 2. Ga cía-León M., Galla do M., Ga cía-Mon año E. and Madu ga G. An. Fís. 880, 1 (1984). (In Spanish.) 3. Ga cía-León M., Ga cía Mon año E. and Madu ga G. ln . J. Appl. Radial. !sol. 35, 195 (1984). 4. Seg é E. Nuclei and Pa licles (Benjamín, New Yo k, 1964). 5. Radiochemisl y P ocedu es Manual (Ed. Liebe man R.) (Eas e n En i onmen al Radia ion Facili y, Mon  gome y, U.S.A., 1984). APPENDIX The o al o: ac i i y o ígina ed by a whole amily a a ime 1 a e he isola ion o he pa en! Ra iso ope, is deduced om Ba eman's equa ions (see o example Re . 4) and can be exp essed as (Al) i= o whe e A0 is he ini ial ac i i y o he pa en! (/J o nsRa, o: o he o he s) and he coe icien s b¡ can be w i en ).¡ l k b, =-:-- L k D' ).,!(A, -A,) (A2) ).Ok=I ¡=0 He e n is he numbe o adioac i e descendan s conside ed (2º7TI and 'º8Tl need no be compu ed, as no o: emissíon ollows, and 212Po because o í s ex emely sho li e is "embodied" ín 212Bi as í he la e had 100% alphas), k ís he ac íon o o: emíssion by he k h descendan ( , = O o J emi e s, k = l o o: emi e s). By he symbol we mean a p oduc whe e he ac o j = i is excluded wi h he complemen a y con en ion o n= i. /=O The alues o n, b, and i.; a e abula ed in Table 3 o he chaíns o igina ed by each Ra iso ope. The numbe o coun s de ec ed in he in e al om I o + /',./ ís R = R0 i ��exp(-).;1)[1-exp(-Á,M)] (A3) 1--=-0 A, whe e R0 = F,A0 ande is he e iciency o he coun íng sys em.