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An Improved Method for Determination of Ra-228 *

An Improved Method for Determination of Ra-228 *. “The Double-Pass Approach”. Jamie Christoff & Bill Burnett Department of Oceanography Florida State University. * Research funded by the PG Research Foundation. Naturally-Occurring Radium Isotopes. Problems in the Assay of Radium.

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An Improved Method for Determination of Ra-228 *

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  1. An Improved Method for Determination of Ra-228* “The Double-Pass Approach” Jamie Christoff & Bill Burnett Department of Oceanography Florida State University *Research funded by the PG Research Foundation

  2. Naturally-Occurring Radium Isotopes

  3. Problems in the Assay of Radium

  4. Flow Chart - Ln•Resin Method 1 2 0.5-2 L acidified sample Ba-133 3 Load sample in 0.09M HNO3 1 Ln BaSO4 ppt Rinse 0.09M HNO3 2 • 0.35M HNO3 3 Resin Conversion to BaCO3 226Ra via Rn emanation 223,224Ra via a-spectrometry 1 2 3 0.09M HNO3 228Ra via 228Ac {proportional or HPGe counter} {hold for ~30 hrs.} g-ray measurement Ba-133 Burnett et al., 1993

  5. Calculations A = net cpm; E = detector efficiency; Y = yield;  = decay constant of 228Ac; V = volume; t1 = time from separation until start of counting; and t2 = counting time

  6. Elution Curve — Ln•Resin The Ac fraction is collected and a CeF3 precipitate prepared for low-level gas-flow proportional counting.

  7. Problems/Improvements • BaSO4 conversion (metathesis) time- consuming and not quantitative; • Samples heavily contaminated with Sr-90 (Y-90) have produced false positives; • Ln•Resin and TRU•Resin approach for Ra-228 not suitable for soil samples — additional clean-up required.

  8. New “Combined” Approach • Water samples — ppt MnO2 —> scavenges actinides, Ra, Ba (Sr stays in solution) • Soil samples: convert matrix to 2M HCl • Pass sample (2M HCl) over Actinide Resin to remove actinides — collect load/rinse (Ra, Ba) • Process Actinide Resin fraction for Pu, Am, etc. • Store load/rinse ~30 hrs. for Ac-228 ingrowth; pass over 2nd column for Ac separation • Several options for counting including direct counting of Actinide Resin via LSC

  9. Uptake of Ac viaActinide Resin At 2-6M HCl, Ac and Ra have k' values differing by ~5 orders of magnitude ensuring complete separation

  10. The “Double-Pass” Approach First Pass: Second Pass: 1 1 2 2 Load sample in 2M HCl Load sample in 2M HCl 1 1 Actinide Actinide Rinse 2M HCl Rinse 2M HCl 2 2 • • Resin #2 Process Actinide Elements Resin #1 1 2 226Ra via Rn emanation 1 2 223,224Ra via -spectrometry • Collect • Ba-133 yield • Hold >30 hrs. Extrude resin into plastic vial; add cocktail, count via LSC 2nd column options: TRU.Resin — load 2.5M HNO3; elute Ac 1M HCl, ppt CeF3, count Diphonix — load 2M HCl; elute Ac 0.5M HEDPA, evap., count

  11. Water Samples: MnO2 ppt • Seawater, 100-400 liters • Acidify to pH 2, add Pu/Am tracers, stir/hold • For 100L sample, add 35 mL sat KMnO4 (~2.1g); Pu-->Pu(VI), org oxid, purple color • Adjust pH to 8-9 with NaOH • Add 0.5M MnCl2 (2x vol of KMnO4); --> MnO2 ppt, dark brown Seawater MnO2 Suspension 2MnO4- + 3Mn2+ + 2H2O = 5MnO2 + 4H+ • Re-adjust pH to 8-9 as necessary • Stir occasionally to keep MnO2 suspended for few hours • Allow Mn02(Pu, Am) ppt to settle overnight • Pump supernatant into clean tank for Cs, Sr processing • Drain MnO2 slurry from bottom tap centrifuge/ filter MnO2 ppt (Pu, Am, Ra, Ba) supernatant Cs, Sr,...

  12. Hold-back of 90Sr Reference MnO2 ppt

  13. Large Volume Seawater Samples Supernatant seawater transferred from one plastic tank to another via pumping — this will be used for 90Sr and 137Cs. MnO2 suspension withdrawn from bottom of conical-shaped plastic tanks — processed for Am and Pu.

  14. Smaller-Scale MnO2 ppt MnO4 (purple) is reduced by added MnCl2 to precipitate MnO2 (brown). MnO2 precipitate settles relatively quickly.

  15. Count Overnight Analysis of rate of decay indicated a half-life ~8% too low Ac-228 t1/2 = 6.13 hrs.

  16. Decay Component Analysis Ao = 135 cpm Ao = 95.4 cpm

  17. Ba Yields: MnO2 ppt Sample spilled

  18. Ra-228 Test Results

  19. Summary • MnO2 ptt effectively scavenges Ra isotopes as well as actinides; • Radium recoveries very high, dissolution of MnO2 simple; • “Double Pass” approach provides way to combine Ra-228 with actinide element analysis; and • Direct counting of Actinide Resin via LSC provides high efficiency & ease of analysis.

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