Presentation on theme: "Measurements of Ra Isotopes via MnO 2 Resin Bill Burnett, Natasha Dimova Florida State University E. Philip Horwitz PG Research Foundation."— Presentation transcript:
Measurements of Ra Isotopes via MnO 2 Resin Bill Burnett, Natasha Dimova Florida State University E. Philip Horwitz PG Research Foundation
Acknowledgments FSU Graduate Students: Natasha Dimova Henrieta Dulaiova Ricky Peterson Benjamin Mwashote Christina Stringer PGRF: Phil Horwitz Andy Bond Dan McAlster
IsotopeDirectParentHalf-life Decay Mode EnergyMeV 223 Ra 227 Th 11.4 d Ra 228 Th 3.66 d Ra 230 Th 1600 y Ra 232 Th 5.75 y 0.046 Natural Radium Isotopes
MnO 2 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
Adsorption vs. pH pH = variable Resin = 25 mg Solution = 10 mL Reaction time = 90 min The optimum pH for adsorption of Ra 2+ is from 4 to 8 – nearly all natural waters fall into this range. Moon et al. / Applied Radiation & Isotopes 59 (2003)
K D Determination A o = initial activity solution, cpm A f = final activity solution, cpm V = volume solution, mL W = weight of resin, g
K D and Kinetics, pH = 7 Floridan Aquifer groundwater ~ mg/L ( o / oo ) Moon et al. / Applied Radiation & Isotopes 59 (2003)
Percent Recovery K D = 2.8 x 10 4 mL/g
Possible Analytical Uses 1.Drinking water analysis of Ra-226 and Ra-228 via preconcentration and - spectrometry (well detector best) 2.Preconcentration of Ra isotopes and analysis of -emitters via -spect 3.Automated analysis of -emitting Ra isotopes via a radon-in-air analyzer
Gamma-Spect Analysis React MnO 2 Resin in a batch mode, let settle, decant/ centrifuge, transfer to counting vial for -spect analysis
Gamma Spectrum 226 Ra peak 186 keV no U via 214 Pb Bi 228 Ra via 228 Ac 226 Ra Bi Ac Ac Pb Pb 352
MDA Gamma Spect ~100-cc Ge well detector 2-liter volume keV assumes 50% equilibrium (4-day ingrowth)
Alpha Spectrometric Analysis Nour et al., in press
Ra-226 via BaSO 4 micro ppt 226 Ra 222 Rn 218 Po 214 Po
-Spectrometry S. Purkl, A. Eisenhauer / Applied Radiation and Isotopes 59 (2003) 245–254 Ra daughters Natural Ra isotopes and Ra-225 tracer
Automated Measurements in out (pump) inner outer drying tube RAD-7 drying tube “DRYSTIK” sample A B C = stopcock x x x x x filter moisture
Gas Handling System All the necessary tubing, valves, and drying system fits easily into a small cabinet Front Back
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.
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.
Validating Standard Ra Activity Our standards are made by passing NIST-traceable Ra-226 solution standards through the MnO 2 Resin. Any Ra remaining is measured by Rn emanation. Results confirm retention >96%.
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.
Suggested Protocol 1.Load sample on resin, measure Ra-224, close stopcocks, allow ~5 days ingrowth for Ra Attach to RAD-7 manifold, purge RAD-7, pump air through cartridge/RAD-7 for 5 minutes, close valves 3.Count for a few 15-min cycles for quick analysis (Po-218) or several hours for more sensitive analysis (Po Po-214) 4.Calculate results
Results: Ra-224 Counting Water sample passed through MnO 2 Resin and 220 Rn counted periodically over many days produced the correct half-life for 224 Ra.
Results: Ra-226 ( 222 Rn Ingrowth) Several standards prepared with NIST 226 Ra solution. Theoretical line drawn with decay constant for 222 Rn.
226 Ra MDAs: Auto Counting 1 liter2 liters MDAs calculated assuming 96% yield, typical blanks for A and C channels, and an equilibrium fraction of 0.5 (4 days ingrowth)
Summary MnO 2 Resin is an excellent adsorber of Ra from natural waters May be used for preconcentration to combine with traditional techniques (e.g., -spect, -spect) Interfacing with a RAD-7 Radon analyzer allows determination of 224 Ra and 226 Ra without chemical separations