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 minThe 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, cpmV = volume solution, mLW = weight of resin, 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-spectAutomated analysis of a-emitting Ra isotopes via a radon-in-air analyzer
10 Gamma-Spect AnalysisReact 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 352226Ra peak 186 keV no Uvia 214Pb + 214Bi228Ra via 228Ac214Pb295214Bi609226Ra186228Ac911228Ac338
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
17 Gas Handling System Front Back All the necessary tubing, valves, and drying system fits easily into a small cabinet
18 Loading the SampleFresh 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 ProtocolLoad sample on resin, measure Ra-224, close stopcocks, allow ~5 days ingrowth for Ra-226Attach to RAD-7 manifold, purge RAD-7, pump air through cartridge/RAD-7 for 5 minutes, close valvesCount 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 CountingWater 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