1 / 19

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.

meda
Download Presentation

An Improved Method for Determination of Ra-228 *

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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.

More Related