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Measurements of Ra Isotopes via MnO2 Resin
Bill Burnett, Natasha Dimova Florida State University E. Philip Horwitz PG Research Foundation
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Acknowledgments FSU Graduate Students: Natasha Dimova
Henrieta Dulaiova Ricky Peterson Benjamin Mwashote Christina Stringer PGRF: Phil Horwitz Andy Bond Dan McAlster
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Natural Radium Isotopes
Direct Parent Half-life Decay Mode Energy MeV 223Ra 227Th 11.4 d a 5.61 5.72 224Ra 228Th 3.66 d 5.69 226Ra 230Th 1600 y 4.78 228Ra 232Th 5.75 y b 0.046
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MnO2 Resin Developed by PGRF
High adsorption of Ra, trivalent and tetravalent actinides (Ac, Am, Pu, Th) Preconcentration approach in batch, column, or pump (filtration) modes
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Adsorption vs. pH pH = variable Resin = 25 mg Solution = 10 mL
Reaction time = 90 min The optimum pH for adsorption of Ra2+ is from 4 to 8 – nearly all natural waters fall into this range. Moon et al. / Applied Radiation & Isotopes 59 (2003)
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KD Determination Ao = initial activity solution, cpm
Af = final activity solution, cpm V = volume solution, mL W = weight of resin, g
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KD and Kinetics, pH = 7 Floridan Aquifer groundwater ~ mg/L ( o/oo) Moon et al. / Applied Radiation & Isotopes 59 (2003)
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Percent Recovery KD = 2.8 x 104 mL/g
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Possible Analytical Uses
Drinking water analysis of Ra-226 and Ra-228 via preconcentration and g-spectrometry (well detector best) Preconcentration of Ra isotopes and analysis of a-emitters via a-spect Automated analysis of a-emitting Ra isotopes via a radon-in-air analyzer
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Gamma-Spect Analysis React MnO2 Resin in a batch mode, let settle, decant/ centrifuge, transfer to counting vial for g-spect analysis
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Gamma Spectrum 226Ra peak 186 keV no U via 214Pb + 214Bi
352 226Ra peak 186 keV no U via 214Pb + 214Bi 228Ra via 228Ac 214Pb 295 214Bi 609 226Ra 186 228Ac 911 228Ac 338
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MDA Gamma Spect ~100-cc Ge well detector 2-liter volume
keV assumes 50% equilibrium (4-day ingrowth)
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Alpha Spectrometric Analysis
Nour et al., in press
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Ra-226 via BaSO4 micro ppt 226Ra 222Rn 218Po 214Po
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Natural Ra isotopes and Ra-225 tracer
a-Spectrometry Natural Ra isotopes and Ra-225 tracer Ra daughters S. Purkl, A. Eisenhauer / Applied Radiation and Isotopes 59 (2003) 245–254
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Automated Measurements
drying tube filter sample in x “DRYSTIK” x out (pump) x inner drying tube moisture x outer RAD-7 A B C = stopcock x
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Gas Handling System Front Back
All the necessary tubing, valves, and drying system fits easily into a small cabinet
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Loading the Sample Fresh water samples can be processed either by gravity flow or by pumping at rates up to 300 mL/min without any loss of Ra.
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Connecting Sample to RAD-7
The sample, inside the same cartridge used for processing the sample, is hooked up to a radon-in-air analyzer.
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Validating Standard Ra Activity
Our standards are made by passing NIST-traceable Ra-226 solution standards through the MnO2 Resin. Any Ra remaining is measured by Rn emanation. Results confirm retention >96%.
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Setting Standard Ingrowth
The standards are re-set for ingrowth by passing helium through the cartridge to ensure no Rn-222 is present at t=0. A small amount of water is then added to enhance Rn emanation.
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Suggested Protocol Load sample on resin, measure Ra-224, close stopcocks, allow ~5 days ingrowth for Ra-226 Attach to RAD-7 manifold, purge RAD-7, pump air through cartridge/RAD-7 for 5 minutes, close valves Count for a few 15-min cycles for quick analysis (Po-218) or several hours for more sensitive analysis (Po Po-214) Calculate results
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Results: Ra-224 Counting Water sample passed through MnO2 Resin and 220Rn counted periodically over many days produced the correct half-life for 224Ra.
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Results: Ra-226 (222Rn Ingrowth)
Several standards prepared with NIST 226Ra solution. Theoretical line drawn with decay constant for 222Rn.
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226Ra MDAs: Auto Counting 1 liter 2 liters
MDAs calculated assuming 96% yield, typical blanks for A and C channels, and an equilibrium fraction of 0.5 (4 days ingrowth)
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Summary MnO2 Resin is an excellent adsorber of Ra from natural waters
May be used for preconcentration to combine with traditional techniques (e.g., a-spect, g-spect) Interfacing with a RAD-7 Radon analyzer allows determination of 224Ra and 226Ra without chemical separations
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