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.