the determination of 226 ra in water samples
DESCRIPTION
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
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