The Determination of 226 Ra in Water Samples

The Determination of 226Ra in Water Samples

Anil H. Thakkar & Michael Fern

Eichrom Technologies, Inc.

David McCurdy

Duke Engineering & Services

Objectives

• To design a procedure for radium in water which would: – be a simple, short and quick procedure

– allow to measure Ra-226 and Ra-224 via alpha spectroscopy and Ra-228 via Ac-228 measurements

– eliminate the tedious steps of precipitation and metathesis

Current Procedure Used

• Barium sulfate precipitation

• Conversion to BaCO3- tedious and time consuming

Sample + Ba carrier + Ba-133 + Conc.H2SO4_+ Heat BaSO4

Precipitate allowed to settle for several hours or overnight

Precipitate collected and converted to BaCO3

Current Procedure Used

New Approach

Water samples

Cation exchange resin column

Eichrom Ln Resin column

Preparation of Water Samples

• 0.5 L / 1.0 L water samples

• Acidified to pH 2

• Add 133Ba as a tracer

Eichrom Cation Exchange Column

• Load solution: 0.5 L/ 1.0 L of sample

• Rinse with 50 mL of 0.1M HNO3

• Strip Ra and Ba with 50 mL of 8M HNO3

Preparation of Load Solution for Ln Resin Column

• Evaporate eluent from cation exchange column to dryness

• Dissolve residue in 10 ml of 0.095M HNO3 acid

• Load on Eichrom Ln Resin column

Ln Resin Column Separation

(1) Load: 10 mL of 0.095M HNO3,

(3) Strip: 10 mL of 0.35M HNO3

collect (3) for 228Ac

(2) Rinse: 15 mL of 0.095M HNO3

Collect (1) and (2) for Ba & 226Ra

226Ra Via Alpha Spectrometry

• Evaporate 226Ra/133Ba fraction to 10 mL volume

• Add 0.1 ml of 0.75 mg/ml barium carrier

• Add 3 mL of 40% sodium sulfate, 4 drops of 1:1 acetic acid. Swirl

• Add 0.2 mL of seeding suspension. Mix

• Place tubes in cold water bath for 30 minutes

• Filter on 0.1 micron filters, count via alpha spectrometry

133Ba Via Gamma Counter

• Count 133Ba tracer yield via gamma spectrometry

eichrom

228Ac Via Gas-Flow Proportional Counter

• Add 50 micrograms of cerium carrier

• Add 1.0 mL of HF

• Filter on 0.1 micron filters

• Measure for beta radiation

226Ra % Recoveries-0.5L DI Water

0102030405060708090

100

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Sample #

226Ra Alpha Spectrum

133Ba Gamma Spectrum

226Ra, 224Ra, and Daughters

226 Ra222Rn

224Ra

218Po220Rn

226Ra % Recoveries in Tap water

0

20

40

60

80

100

120

1 2 3 4 5

Sample #

4 Tap Water (0.5L)5 Tap Water (1.0 L)

226Ra in EPA SampleSept.18, 1998

Sample # Ba-133 %Yield

EichrompCi/L

1 89 1.56

2 100 1.23

3 98 1.45

Average 95.7 + 6 1.41 + 0.17

Expected EPAValue

1.7 + 0.5

226Ra in NJ Sample

Sample # Ba-133 %Yield

EichrompCi/L

1 100 8.18 + 0.99

2 82 9.10 + 1.2

Average 91 8.64 + 1

Expected NJValue

- 9.1 + 0.5

226Ra in Georgia Inst. Of Tech. Sample# S8933

Sample # Ba-133 %Yield

EichrompCi/L

S8933 88 22.6 + 3.0

Expected Value - 18.0 + 2.0

226Ra in Georgia Inst. Of Tech. Sample# WS 14776

Sample # Ba-133 %Yield

EichrompCi/L

WS 14776 88 4.14 + 0.58

Expected Value - 3.3 + 0.3

Ca and Mg Interference

• 50, 100, 200, 400 and 500 ppm of Ca and Mg solutions were tested

• 500 mL and 100 mL volumes tested

Ca and Mg Interference in 500 mL Samples

Effect of Ca & Mg on Ra-226 Recoveries

75%61%

54%

0.00% 0.00%

87% 82%71% 70% 74%

0%

20%

40%

60%

80%

100%

0.00 100.00 200.00 600.00 1000.00

Ca & Mg ppm

% R

a-22

6 Ca PPM

Mg PPM

Ca Interference in 100 mL of Sample

Effect of Ca on Ba-133 and Ra-226 Recoveries100 mL Sample

99% 99%97%

101%

90%

97%99%

95%

103%

87%

75%

80%

85%

90%

95%

100%

105%

100.00 200.00 300.00 400.00 500.00

Ca ppm

% B

a-13

3/R

a-22

6

Ba-133

Ra-226

Detection Limits

Samplevolume Count Time

Detection.Limit

0.5 L 1000 min 0.09 pCi/L

0.5 L 240 min0.3 pCi/L

0.2 L 240 min 0.9 pCi/L

0.1 L 480 min 0.9 pCi/L

Summary

• <1.0 pCi/L detection limits achievable

• A good replacement for BaSO4 precipitation

• Eliminates inconsistent metathesis steps

• Reduces usage of chemicals/reagents

• Provides consistency and saves time

• High amounts of Ca and Mg interferences handled well with 100 mL samples

• Acceptable 226Ra recoveries

Special thanks to

Dr. B. Parsa, New Jersey department of health, NJ

Dr. B. Kahn, Georgia Institute of Technology, GA

Acknowledgements