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MnO 2 Resin and Automated Measurements of Ra Isotopes

MnO 2 Resin and Automated Measurements of Ra Isotopes. Bill Burnett Dept. Oceanography Florida State University. MnO 2 Resin. Developed by PGRF 80-160 mesh High adsorption of Ra, trivalent and tetravalent actinides (Ac, Am, Pu, Th)

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MnO 2 Resin and Automated Measurements of Ra Isotopes

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  1. MnO2 Resin and Automated Measurements of Ra Isotopes Bill Burnett Dept. Oceanography Florida State University

  2. MnO2 Resin • Developed by PGRF • 80-160 mesh • High adsorption of Ra, trivalent and tetravalent actinides (Ac, Am, Pu, Th) • Preconcentration approach in batch, column, or pump (filtration) modes

  3. Natural Radium Isotopes

  4. Tracers for Characterization • Ba-133 (commercial, nominal activity) • Ra-228, Ra-224 (separated from 40-year old Th(SO4)2, calibrated by gamma spect • Ra-226 NIST solution standard

  5. Distribution Coefficient C1 = amount adsorbed per gram dry resin; and C2 = amount that remains in solution after equilbrium has been reached. Units = mL/g

  6. KD Determinations w Tracers Ao = initial activity solution, cpm Af = final activity solution, cpm V = volume solution, mL W = weight of resin, g

  7. Percent Recovery KD = 2.8 x 104

  8. Kinetics, pH = 7 • pH = 7 • Resin = 25 mg • Solution = 10 mL Floridan Aquifer groundwater ~40-200 mg/L (0.04-0.2 o/oo)

  9. pH Variation • pH = variable • Resin = 25 mg • Solution = 10 mL • Reaction time = 90 min Surface charge Ra2+ speciation The optimum pH for adsorption of Ra2+ is from 5 to 8 – nearly all natural waters fall into this range.

  10. Pump Tests Peristaltic pump; cartridge loaded with 1 g MnO2 Resin; single pass

  11. Pump Video Fresh waters can be processed at high flow rates (³300 mL/min) without any loss. Highly salted waters require longer equilibration times

  12. Alpha Detector - - - 214 Po 216 215 Po Po 218 Po Air Pump Drierite 222 220 219 Rn Rn Rn RAD7 MnO - Resin 2 ( Ra) 226,228,224,223 222 220 219 Rn , Rn, Rn Ra Isotopes via RAD-7

  13. Optimum Moisture Content Water/Fiber Ratio = (xi-xo)/xo ; where xi = mass at each stage; and xo = mass when completely dry

  14. Recoil Effect on Rn Emanation Recoil range in air = 0.07 cm Recoil Range in water = 9.1 x 10-5 cm

  15. “DRYSTIK” Approach Drierite

  16. Moisture Control During Counting

  17. Effect on Countrate

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

  19. Results: Ra-226 (222Rn Ingrowth) T1/2 = 3.84 days Several standards prepared with NIST 226Ra solution. Theoretical line drawn with decay constant for 222Rn.

  20. 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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