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Measurements of Ra Isotopes via MnO2 Resin

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Presentation on theme: "Measurements of Ra Isotopes via MnO2 Resin"— Presentation transcript:

1 Measurements of Ra Isotopes via MnO2 Resin
Bill Burnett, Natasha Dimova Florida State University E. Philip Horwitz PG Research Foundation

2 Acknowledgments FSU Graduate Students: Natasha Dimova
Henrieta Dulaiova Ricky Peterson Benjamin Mwashote Christina Stringer PGRF: Phil Horwitz Andy Bond Dan McAlster

3 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

4 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

5 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)

6 KD Determination Ao = initial activity solution, cpm
Af = final activity solution, cpm V = volume solution, mL W = weight of resin, g

7 KD and Kinetics, pH = 7 Floridan Aquifer groundwater ~ mg/L ( o/oo) Moon et al. / Applied Radiation & Isotopes 59 (2003)

8 Percent Recovery KD = 2.8 x 104 mL/g

9 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

10 Gamma-Spect Analysis React MnO2 Resin in a batch mode, let settle, decant/ centrifuge, transfer to counting vial for g-spect analysis

11 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

12 MDA Gamma Spect ~100-cc Ge well detector 2-liter volume
keV assumes 50% equilibrium (4-day ingrowth)

13 Alpha Spectrometric Analysis
Nour et al., in press

14 Ra-226 via BaSO4 micro ppt 226Ra 222Rn 218Po 214Po

15 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

16 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

17 Gas Handling System Front Back
All the necessary tubing, valves, and drying system fits easily into a small cabinet

18 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.

19 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.

20 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%.

21 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.

22 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

23 Results: Ra-224 Counting Water sample passed through MnO2 Resin and 220Rn counted periodically over many days produced the correct half-life for 224Ra.

24 Results: Ra-226 (222Rn Ingrowth)
Several standards prepared with NIST 226Ra solution. Theoretical line drawn with decay constant for 222Rn.

25 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)

26 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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