the determination of 226 ra in water samples
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The Determination of 226 Ra 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 - PowerPoint PPT PresentationTRANSCRIPT
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The Determination of 226Ra in Water Samples
Anil H. Thakkar & Michael Fern
Eichrom Technologies, Inc.
David McCurdy
Duke Engineering & Services
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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
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Current Procedure Used
• Barium sulfate precipitation
• Conversion to BaCO3- tedious and time consuming
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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
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New Approach
Water samples
Cation exchange resin column
Eichrom Ln Resin column
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Preparation of Water Samples
• 0.5 L / 1.0 L water samples
• Acidified to pH 2
• Add 133Ba as a tracer
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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
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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
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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
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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
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133Ba Via Gamma Counter
• Count 133Ba tracer yield via gamma spectrometry
eichrom
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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
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226Ra % Recoveries-0.5L DI Water
0102030405060708090
100
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Sample #
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226Ra Alpha Spectrum
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133Ba Gamma Spectrum
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226Ra, 224Ra, and Daughters
226 Ra222Rn
224Ra
218Po220Rn
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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)
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Special thanks to
Dr. B. Parsa, New Jersey department of health, NJ
Dr. B. Kahn, Georgia Institute of Technology, GA
Acknowledgements