Stan Chałupnik

Silesian Centre for Environmental Radioactivity

Central Mining Insitute

Katowice, Poland

schalupnik@gig.eu

Gross alpha and gross beta activity measurements

in drinking and mineral waters

Drinking Water Directive 98/83/EC

• Direct addressing tritium level only (100 Bq/l)

• Total indicative dose (TID) due to ingestion of all other

radionuclides, except K-40 and radon decay products

• TID should be estimated accordingly to the Directive

96/29/Euratom (BSS)

• Radon and decay products – Directive

2001/928/Euratom The Protection of the Public

against Exposure to Radon in Drinking Water

Supplies

• Draft of Euratom Drinking Water Directive

– Gross alpha/beta measurement as screening method

– Dose asssessment for adults only

Gross alpha/beta

• This technique is only a screening method.

• Till now there is no regulations, concerning

it’s application, only recommendations.

• A source – WHO recommendations:

– 2004 α < 0.5 Bq/l β < 1.0 Bq/l

– Previously α < 0.1 Bq/l β < 1.0 Bq/l

Gross alpha/beta

• Useful method for screening of the

contamination of the environment, caused by

man-made radioactivity.

• Seems to be that application of the method is

simple and possible for natural radioactivity, for

instance in water samples.

• LSC is a very good technique for measurements

of gross alpha/beta.

Procedures for gross α/β

– We try to test two different procedures for gross alpha/beta measurements

– ISO 11704:2010(E) „Water quality – Measurement of gross alpha and gross beta activity concentration in non-saline water – Liquid Scintillation Counting Method”

– H-α-GESAMT-TWASS-02 “Schnellverfahren zur Bestimmung der Gesamt-Alpha-Aktivitätkonzentration im Trinkwasser” Beyermann, Bünger

ISO Method

• Sample of water (up to 200 ml)

• Evaporation to dryness or very small volume (2-4 ml)

• Addition of deionised water (up to 6 ml + small amount of HCl, if necessary)

• 12 ml of LS cocktail added – preferably Ultima Gold AB

• Measurement

• Advantage – no lost nuclides

• Disadvantage – problem with K-40

Fast method

• Sample volume up to 500 ml

• Admixture of 2 ml 3,2 M (NH4) 2HPO4

• Precipitation – Important – no precititation of I group cations (K-40,

but also Cs isotopes)

• Dissolution of the precipitate in 4,4M HCl

• Addition of deionised water (up to 6 ml)

• 12 ml of Ultima Gold AB

• Measurement

• Advantage – no influence of K-40

• Disadvantage – lost Cs, if present

Detection Limit

• Decision threshold

– Ld = [k1-α/(V*η)]*SQRT[IB(1/tB+1/tp)]

• Detection Limit

– LLD =

)*(*1

/))*/((*222

2

Vsk

tpVkLd

Threshold levels

• WHO (Guidelines for drinking water quality 2004): – Gross alpha < 0.5 Bq/l (500 mBq/l)

– Gross beta < 1.0 Bq/l (1000 mBq/l)

• Poland: – Gross alpha < 0.1 Bq/l (100 mBq/l)

– Gross beta < 1.0 Bq/l (1000 mBq/l)

• New draft od Euratom Directive: – Gross alpha < 0.1 Bq/l (100 mBq/l)

– Gross beta < 1.0 Bq/l (1000 mBq/l)

• Further measurements required, if screening values are above threshold levels.

Gross alpha/beta and LSC

• LSC technique is used very commonly for this purpose

• Preparation of samples and measurements

– Evaporation of the liquid sample

– Mixing with the scintillator

– Measurement

– The most important problem – misclassified particles!!

LSC spectrometer

Detection limits:

Gross alpha =

0.01 Bq/l

Gross beta =

0,05 Bq/l

Sample volume

200 ml

Counting time 1 h

QUANTULUS

PSA and SQP(E)

• Effieciency of alpha/beta separation is also dependent on quenching;

• SQP(E) – indicator of the quenching in Quantulus, good for pure beta emitters.

• No simple correction for PSA versus SQP(E) .

• A kind of a „mysterious” behaviour of samples with obvious quenching and high SQP(E)

„Misclassified particles”

• Just a reminder – alpha/beta separation is

done electronically.

• When quenching occurs, some alpha

particles are classified as beta pulses.

• Theoretically – we should apply low PSA,

but as a result some beta particles are

classified as alpha ones!!!!

Am-241 + Sr-90/Y-90

...AL\LIN5\S53.sum 11

...AL\LIN5\S53.sum 21

...AL\LIN5\S53.sum 22

Sample Spectrum

1 000950900850800750700650600550500450400350300250200150100500

5

4

3

2

1

0

UG AB

PSA=90

Misclassified... cd.

• Another problem is related to the fact, that

alpha/beta separation is also dependent

on „generation” of LS spectrometer.

• For instance, in case of older Quantuli,

separation is energy dependent (big

problem is proper separation for K-40)

• Much better for „new vintage” of

spectrometers.

Misclassified particles (at least 5-7%)

Missclassified particles for Quantulus (1990)

0

5

10

15

20

25

30

35

40

90 100 110 120

PSA

[%]

UG alfa UG beta Optiscint alfa

Optiscint beta LumaGel alfa LumaGel beta

Misclassified particles (1,5 % only)

Misclassified particles Quantulus (2006)

0

5

10

15

20

25

30

35

40

60 65 70 75 80 85 90 95 100

PSA

[%]

UG alfa UG beta Opti alfa Opti beta LumaGel alfa LumaGel beta

Linearity – O.K.!

Linear response Sr-90

-1

0

1

2

3

4

5

6

00,

30,

60,

91,

21,

51,

82,

12,

42,

7 33,

33,

63,

94,

24,

54,

85,

15,

45,

7 6

objętość [ml]

często

ść [

cp

s]

Sr-90 beta Liniowy (Sr-90 beta)

Linear response Am-214

0

0,5

1

1,5

2

2,5

3

3,5

0

0,0

2

0,0

4

0,0

6

0,0

8

0,1

0,1

2

0,1

4

0,1

6

0,1

8

0,2

0,2

2

0,2

4

0,2

6

0,2

8

0,3

0,3

2

0,3

4

0,3

6

0,3

8

0,4

0,4

2

0,4

4

0,4

6

0,4

8

0,5

0,5

2

0,5

4

objętość [ml]

często

ść [

cp

s]

Am-214 Liniowy (Am-214)

Misclassified....

• Again a reminder – alpha/beta separation

is dependent on the type of coctail.

• For any type of sample PSA must be set

separately!!

• Moreover, even for the same type of the

spectrometer it must be done separately,

„vintage” is important again.

Lost nuclide(s) Pb-210

...AL\LIN5\S49.sum 11

...AL\LIN5\S49.sum 21

...AL\LIN5\S49.sum 22

Sample Spectrum

1 000950900850800750700650600550500450400350300250200150100500

1

0

Lost nuclide(s) Ra-228

...\QUICK1\S25.sum 11

...\QUICK1\S25.sum 21

...\QUICK1\S25.sum 22

...\QUICK1\S26.sum 11

...\QUICK1\S26.sum 21

...\QUICK1\S26.sum 22

Sample Spectrum

1 000950900850800750700650600550500450400350300250200150100500

37

36

35

34

33

32

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Fast method – additional problem

• Too much acid or big amount of precipitate

leads to significant quenching

• Alpha/beta separation is different

• SQP(E) characteristics is a bit peculiar

– The highest value found for the most

quenched sample???

Fast method – additional problem

...\SR_AM1\S41.sum 11

...\SR_AM1\S41.sum 21

...\SR_AM1\S41.sum 22

...\SR_AM1\S46.sum 11

...\SR_AM1\S46.sum 21

...\SR_AM1\S46.sum 22

Sample Spectrum

1 000950900850800750700650600550500450400350300250200150100500

4

3

2

1

0

Conclusions

• Application of LSC for measurements of gross alpha/beta activities must be done carefully.

• ISO method is reliable but K-40 influence is important, especially for mineral waters.

• Fast method seems to be better for screening, except cases, when Cs presence is predicted.

• Some radionuclides are simply excluded by gross alpha/beta (Ra-228, Pb-210).

• Concerning the dose, Ra-228 is the most important radionuclide.

• Therefore gross alpha/beta measurements should be treated only as an additional tool!!

Muchas gracias!!

Stan