Radiop o ec ion - Collogues, olume 37, CI (2002) Cl-1015
Applica ion o a liquid scin illa ion coun e o he measu emen
o acing adioac i i y in expe imen s on suspended ma e up ake
in aqua ic en i onmen s
R. El-M abe , G. Manjon1, J.M. Ab il2 and R. Ga cia-Teno io1
Depa amen o de Física A ómica, Molecula y
Nuclea ,
Facul ad de Física,
Uni e si y o Se ille, Apdo. 41060 Se illa, Spain
1 Depa amen o de Física 2, Uni e si y o Se ille, ETSA,
A da. Reina Me cedes s/n, 41012 Se illa, Spain
2 Depa amen o de Física Aplicada 1, Uni e si y o Se ille, EUITA,
Ca e e a de U e a km 1, 41013 Se illa, Spain
Abs ac , The expe imen s on he s udy o he kine ic ans e coe icien s o conse a i e and non-conse a i e
adionuclides, in aqua ic en i onmen s, need o de e mine adionuclide ac i i y in la ge numbe o samples.
Di e en adioac i i y measu emen echniques can be selec ed o analyses, bu he liquid scin illa ion echnique is
p e e ed due o i s easy sample ea men and i s low ime consump ion. Samples a e ini ially aced wi h a known
ac i i y o a selec ed adionuclide (239Pu, MIAm o "Tc). The ans e ence o adionuclides, om he wa e o he
suspended ma e , is s udied h ough he de e mina ion o he esidual ac i i y in aliquo s o wa e sample, which
a e successi ely collec ed wi h ime. In his wo k, we p esen he expe imen al p ocedu es used o he 239Pu, 241Am
and "Tc ac i i y measu emen by liquid scin illa ion coun ing, using a Wallac Quan ulus
1220
spec ome e .
Resul s o he applica ion o his echnique o aced wa e samples a e also shown in his s udy.
1.
INTRODUCTION
The so p ion and elease kine ics o 239Pu, 241 Am and "Tc by eshwa e suspended pa icles we e
in es iga ed o be e iden i y he biogeochemical p ocesses in ol ed and o unde es and he beha iou o
hese
elemen s in aqua ic en i onmen s. Time se ies da a can be ob ained om labo a o y s udies and can
be
analysed o s udy he ans e ence o adionuclides ac i i y om he wa e o he suspended ma e .
T acing expe imen s we e pe o med du ing a la ge ime using na u al aqueous suspensions om h ee
aqua ic sys ems (Ge gal ese oi , he Guadalqui i i e and he es ua y o he Tin o i e ). Scien i ic
li e a u e lis s many examples o expe imen al s udies on up ake kine ics o dissol ed adionuclides by
suspended loads [1, 2]. In his wo k we ca y ou a se ies o acing expe imen s wi h 239Pu, 241Am and
"Tc by using en i onmen al samples o un il e ed wa e s om h ee aqua ic sys ems in he Sou h o
Spain. The expe imen al p ocedu e ensu es he p ese a ion o en i onmen al condi ions. As he
expe imen al me hod equi es he de e mina ion o Pu, Am and Tc ac i i ies in a la ge numbe o
samples, i is impo an o selec a measu emen echnique wi h low ime consump ion. Recen ly, liquid
scin illa ion coun ing has been applied o Pu, Am and Tc-iso opes. In wo ks epo ed by [3],
239+240pu
we e
simul aneously measu ed using a liquid scin illa ion coun e PERALS™ and wo ex ac i e scin illa o s.
Liquid scin illa ion echnique is p e e ed because he edious sample ea men equi ed, e.g. o alpha
spec ome y, is no necessa y. The poo esolu ion o his echnique (abou 300 keV) will be no ele an
in ou
measu emen s because a single alpha emi e , adio ace , will be p esen in ou samples.
This
echnique allows us o in es iga e newe and in e es ing aspec s o he kine ic o he elec oly ic
eac ions o Pu, Am and Tc in esh wa e ecosys ems.
I MATERIAL AND METHODS
21
Sampling
Wa e samples we e collec ed om h ee di e en aqua ic scena ios om he Sou h o Spain. The
i s s a ion was loca ed he Ge gal ese oi (NW om Se ille). The second sample was collec ed in he
Guadalqui i i e , nea he own o Se ille. Wa e s we e da k g ey colou ed by he e luen s om
ac o ies and u ban sewage in he su oundings. Finally a hi d sample was collec ed in he Tin o es ua y,
dose
o he
A lan ic Ocean, du ing he low ide.
A icle published by EDP Sciences and a ailable a h p://www. adiop o ec ion.o g o
h p://dx.doi.o g/10.1051/ adiop o/2002118
Cl-1016 RADIOPROTECTION - COLLOQUES
A each sample si e, we illed ou 25
1
plas ic bo les. Tempe a u e, pH and elec ical conduc i i y
we e measu ed jus a e collec ion. Samples we e hen ca ied o ou labo a o y and s o ed in da k
du ing
ew hou s. The acing expe imen s gene ally begun a he ollowing mo ning. We used a nephelome e o
measu e he suspended ma e con en . To con e NTU in o mg/1 we weigh ed he d y ma e ob ained
a e il e ing 50
1
o wa e by using a 0.45 um NUCLEOPORE il e . This calib a ion was epea ed
o
each new en i onmen . In Table 1 we show he empe a u e, pH, he elec ical conduc i i y, and he
suspended ma e con en o collec ed samples, co esponding wi h na u al condi ions p e ailing du ing
he sampling.
Table 1. Tempe a u e, pH, elec ical conduc i i y and suspended ma e con en in wa e samples measu ed jus a e
collec ion. Da a can be conside ed as en i onmen al condi ions.
En i onmen Tempe a u e PH Conduc i i y Suspended ma e
(°C) (mS) (mg/1)
Ge gal ese oi 27.1 8.35 0.46 7.37
Guadalqui i i e 20.4 7.84 1.37 12.6
T in o es ua y 19.4 7.86 66.25 7.62
He ea e he solid ac ion will be conside ed ha o med by suspended pa icles wi h a diame e la ge
han
0.45
um. The dissol ed (mo e p ope ly he il e ed) ac ion is o med by he wa e , dissol ed elemen s and pa icles
wi h smalle sizes. This is a p ac ical assump ion, since in mos o he expe imen al s udies his po e size
is
used
o sepa a e bo h ac ions.
2.2 Expe imen al p ocedu e
The objec i e o his wo k was o e alua e he up ake o 239Pu,241 Am and "Tc by suspended
ma e
in en i onmen al esh wa e s. In each expe ience, a ypical olume o 1.0
1
o wa e was ans e ed
in o
a glass beake . The e, he sample was spiked wi h 239Pu, 241 Am o "Tc and con inuously s i ed
in
o
a oid any decan a ion o he suspended ma e .
We ollowed he ime e olu ion o he ac i i y concen a ion in he dissol ed phase by aking
aliquo s a di e en imes a e spiking. A ypical olume o 45 ml was selec ed o e e y
aliquo .
Suspended ma e was emo ed by cen i uga ion (20 minu es a 4000 pm). Then, 35 ml o
supe na an
we e ans e ed in o aplas ic con aine and acidula ed wi h 1ml o HN03 o a oid loses o plu oniumby
adso p ion on o he con aine walls. Finally, 5 ml o acidula ed sample was ans e ed in o a
plas ic
ial
and mixed wi h 15 ml o liquid scin illa ion cock ail Pha macia Op iphase 3.
Nephelome ic measu emen s p o ed ha he u bidi y o he supe na an wa e s a e cen i uga ion
we e simila o he measu ed ones in he il a ed ac ion. Consequen ly, cen i uga ion is an e icien
p ocess o sepa a e almos he same ac ion ha we could ob ain by il a ion. Fil a ion canno
be used
as al e na i e echnique o sepa a e bo h ac ions om each aliquo e, since app oxima ely some
10% in
he case o he Pu was e ained by he il e
i sel ,
as p o ed by il a ing dis illa e wa e spiked
wi h
Pi
Al hough cen i uga ion is ou bes choice, i is no a pe ec p ocess, and in some samples we
go an
incomple e sepa a ion, p o oking some o e -es ima ions o he speci ic ac i i y in he dissol ed ( il e ed)
phase.
2.3 G anulome ic analysis and mine al composi ion s udy
I is known [4, 5] ha he kine ic ans e coe icien o di ec so p ion depends on he o al a ail
su ace o pa icles pe uni olume o solu ion, and on he concen a ion o ac i e si es in he sui
ECORAD 2001 Cl-1017
laye o
solids.
This las depends on he mine al composi ion, ee edges, po es, coa ings, e c. Thus, i is
necessa y o handle he pa icle size spec a and he mine al composi ion o na u al occu ing suspended
loads o compa e esul s om di e en en i onmen s and o ix he condi ions o applicabili y o he
de i ed coe icien s.
A g anulome ic analysis o all he samples was ca ied ou by using a Ma e Size ins umen wi h
100 size
bands,
om 0.01 o 1000 um.
A Scanning elec on mic oscope (SEM) was used o s udy he mo phology o na u al pa icles om
all
he samples. The SEM mic og aph o he ou samples e ealed ha he mos common shape is he
sphe ical one. We can app ecia e some agg ega ion o pa icles owing o he p epa a ion p ocedu e. Sal -
c ys als a e p een in mos o he samples. Finally, he mine al composi ion was de e mined by X- ay
di ac ion (XRD). Some esul s a e summa ised in Table 2.
Table 2.- Resul s om g anulome ic and miné alogie analysis. Diame e in (im, co esponds o he mos equen
diame e , and d)2 is he diame e co esponding o pa icles wi h he highes pe cen age o olume. The speci ic su ace a ea
(S.S.A.)
is compu ed assuming a densi y o 2.10 g cm-3 o all he solids.
En i onmen Diame e
dp.
Diame e
<b2
S.S.A. Main mine alogical
(u n) (um) (m2/g) composi ion
Ge gal ese oi 0.30 19 0.28
CaC03
Calci e, Musco i e
Guadalqui i i e 0.22 15 1.63
CaC03
Calci e
T in o es ua y 0.18 28 0.78 CaS042H20, Bassani e
2.4
Liquid scin illa ion coun e
A liquid scin illa ion spec ome e Wallac Quan ulus 1220™ was used o 239Pu, 241 Am and "Tc
ac i i y measu emen s. The low backg ound o he de ec o allows he measu emen o low-le el
ac i i ies. Mo eo e , alpha and be a ac i i y om he same sample can be measu ed simul aneous and
sepa a ely (alpha and be a spec a) by using i s pulse shape analyse (PSA) [6]. The PSA was op imised
by
measu ing a 239Pu and 241 Am s anda d samples, unde he ypical measu emen condi ions, a di e en
alues o he PSA h eshold le el. Resul s a e shown in Fig.l, whe e alpha in e e ence is plo ed e sus
PSA
le el.
Taking in o accoun ha alpha in e e ence is de ined as he ac ion o alpha coun s measu ed
in he
be a spec um, a A PSA le el o 55 was selec ed in ou wo king condi ions, because using highe
alues he alpha in e e ence canno be conside ed negligible and he coun ing e iciency dec eases. In
he
"Tc ac i i y measu emen s, i is no necessa y o use he PSA.
PSA
" e 1.- Op imisa ion o he PSA o he Wallac Quan ulus 1220™. Bes esul s do Pu and Am co esponds o PSA = 55
Cl-1018 RADIOPROTECTION - COLLOQUES
When PSA is selec ed on, backg ound coun s a e acqui ed in he be a spec um, because 40K
(a be a
emi e ) o ial walls is he main con ibu o o backg ound o de ec o . We ha e o no e ha
alpha
/
be a
sepa a ion is no o ally e icien , and a pa o he be a emissions can be coun ed in he alpha spec um,
This ac ion is known as he be a in e e ence and can be conside ed as he main con ibu ion o
he alpha
backg ound. Ob iously, his be a in e e ence dec eases when inc easing he PSA alue. Fo his
eason
he PSA alue was selec ed as he maximum alue a which he alpha in e e ence is s ill negligible.
On he o he hand, we also s udied he dependence o he alpha backg ound wi h he olume
o he
sample. Always he dis illed wa e /scin illa o olume a io was 1:1, and he sample olume anged
om
8 up o 20 ml. When he op imum PSA le el was selec ed, he alpha backg ound was simila in
all cases.
Fo ha eason, he sample accep ance o he scin illa o was conside ed as he main pa ame e
o
selec ing he sample olume. Fo example, he scin illa o used, he Wallac Op iphase Hisa e3,
has a
sample accep ance o 4 ml o 2M F£N03 in 10 ml o scin illa o . The samples ob ained in ou
expe imen s
can be conside ed as a 0.4M HN03 solu ion, bu ma e ial o iginally dissol ed in he en i onmen al
wa e
could be p esen also in he sample o be measu ed and could educe he sample accep ance o scin illa o .
This is he case o he Guadalqui i sample, whe e i is possible o app ecia e he p esence o
colloids.
Fo his eason, a olume o 5 ml was selec ed o he aqueous phase, which was mixed wi h
15 ml o
scin illa o . In hese condi ions, alpha backg ound and alpha e iciency we e de e mined in he
di e en
collec ed wa e samples. Alpha e iciency was de e mined spiking he 5 ml o he wa e samples
wi h
known amoun s o 239Pu, 241 Am o "Tc. Resul s a e lis ed in Table 3 o Pu measu emen s.
Alpha
coun ing e iciency anged om 0.67 up o 0.89 being no uni o m, p obably due o a di e en
chemical
quenching o he sample. Backg ound le el anged om 0.4 cpm in he ese oi wa e s, o 0.8
cpm o
he Guadalqui i wa e . A highe le el o 2.4 cpm was measu ed in wa e collec ed om he
Tin o
es ua y. This esul can be a ibu ed o he p esence o na u al alpha emi e s in he sample [7].
Table 3. Coun ing cha ac e is ics o a Wallac Quan ulus 1220™ in he case o "'Pu, using wa e samples collec ed in di e en
en i onmen al scena ios. LID is de de ec ion limi , and MDA is he minimum de ec able ac i i y; coun ing ime was
600 min
in all he cases.
En i onmen E iciency Backg ound MDA LID
(cpm) (Bq li e 1) (cpm)
Ge gal 0.67 ± 0.01 0.66 ± 0.03 0.23 0.047
Guadalqui i 0.89 ± 0.03 0.79 + 0.04 0.19 0.051
Tin o 0.67 ± 0.02 2.36 ± 0.06 0.44 0.089
3.
RESULTS AND DISCUSSION
In igu es 2, 3, 4, 5 and 6 we show he ime e olu ion o 239Pu, 241 Am and "Tc ac i i ies
in he
dissol ed phase co esponding o he ou se ies o expe imen s. Measu ed alues a e ep esen ed
wi h
e o ba s. F om Fig. 2, 3, 4 and 5, in loga i hmic scale, h ee di e en egions cha ac e ised by
di e en
slopes can be dis inguished: i s egion co esponds o a as eac ion, las ing o ew minu es,
du ing
which ime up o 30% o dissol ed Pu o Am is ans e ed on o suspended solids. This co esponds
o a
as physical-adso p ion eac ion (Pu o Am is ixed by coulombian o ces on o he ex e nal ee
su ace
o pa icles); in second egion, o he eac ion go e ns he Pu o Am up ake du ing 10-20
hou s ime,
ans e ing up o 30% o emaining Pu in dissol ed o m. This eac ion co esponds o
physical
adso p ion on o he inne su ace o po es and ee-edges, and o he o ma ion o e e sible
unions o a
di e en na u e and/o s eng h. In hi d egion, he up ake (up o 50% o he emaining Pu
o Am in
solu ion) con inues du ing se e al days ( he du a ion o he expe imen s was oo sho o
allow a
conclusion conce ning he inal cou se o he eac ion). This eac ion may co espond o a slowe
p ocess
in which p e iously adso bed Pu o Am is ans e ed in o he inne ma ix o he pa icles
o o ms
o he non- e e sible unions.
ECORAD 2001 CT-1019
2.5
2
1.5
1
0.5
0
2.4
2.2
2
1.8
1.6
1.4
1.2
1
0.8
0.6
2.4
2.2
2
1.8
1.6
1.4
1.2
1
0.8
0.6
200
Fig.2 Ri e ~—•
* I •
0 5 10 15 20 25 30
Time (hou s)
35 40 45 50
;
Fig.3 Es ua y -•—«
I J I
0 5 10 15 20 25 30
Time (hou s)
35 40 45 50
•
Fig.
4 Rese oi .
I
I
10
15
20
25 30
Time (hou s)
35 40 45 50
20 80 100
40 60
j.
Time (hou s)
'?'*'..'3'4.'
Time e olu ion o 239-Pu and 241 -Am ac i i ies (in cpm and mBq) in he dissol ed phase co esponding o
e ou senes o expe imen s on 239-Pu and 241-Am up ake (non-conse a i e adio ace s) in na u al aqueous suspensions.

Cl-1020 RADIOPROTECTION - COLLOQUES
Fig.
6
Ri e
¡ i l i I l
0
50 100 150 200 250
Time
(hou s)
Fig. 6: Time e olu ion o 99-Tc ac i i ies (in mBq) in he dissol ed phase co esponding o he se ie o expe imen s on
conse a i e adio ace (99-Tc) up ake in na u al aqueous suspensions o un il e ed wa e s om Guadalqui i i e .
F om Fig.6, he 99-Tc is conside ed as conse a i e adionuclide, he ac ion o he 99-Tc abso bed
by
he suspended ma e is negligible.
4.
CONCLUSIONS
In his wo k we applied a use ul expe imen al p ocedu e o s udy he up ake o Pu, Am and
Tc by
na u al aqueous suspensions, based on he use o liquid scin illa ion echnique.
Acknowledgemen s
This wo k has been pa ially suppo ed by I+D con ac wi h ENRESA, Spain.
Re e ences
1.
Laissaoui A., Ab il J.M., Pe iá iez R., Ga cía León M., Ga cía Mon ano E. Jou nal o Radioanaly ical
and Nuclea Chemes y. 237 (1-2) (1998)
55-61.
2.
R. El M abe , J.M Ab il, G. Manjón and R. Ga cía Teno io. Wa e Resea ch (2001) (accep ed o
publica ion).
3.
J. Auplais Jou nal o Radioanaly ical and Nuclea Chemis y 218 (1997) 201-207.
4.
J.M. Ab il Jou nal o En i onmen al Radioac i i y. 41 (1998a)307-324, Pa I: heo y de elopmen
5.
J.M. Ab il Jou nal o En i onmen al Radioac i i y. 41 (1998b) 325-342, Pa II: applica ions
6. G. Manjón, I. Vioque, H. P. Mo eno, R. Ga cía-Teno io and M. Ga cía-León. Applied Radia ion
Iso opes. 48 (1997) 535-540
7.
H. P. Mo eno, I. Vioque, G. Manjón and R. Ga cía-Teno io. Czechoslo ak Jou nal o Physics
(1999)
(accep ed o publica ion)
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