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

Naturally-Occurring Radium Isotopes

Problems in the Assay of Radium

Flow Chart - Ln Resin Method 12 Load sample in 0.09M HNO 3 Rinse 0.09M HNO M HNO Ln Resin 1 2 Burnett et al., L acidified sample Ba-133 BaSO 4 ppt Conversion to BaCO 3 {hold for ~30 hrs.} 0.09M HNO 3  -ray measurement Ba Ra via 228 Ac {proportional or HPGe counter} 226 Ra via Rn emanation 223,224 Ra via  -spectrometry

Calculations A = net cpm; E = detector efficiency; Y = yield; = decay constant of 228 Ac; V = volume; t 1 = time from separation until start of counting; and t 2 = counting time

Elution Curve — Ln Resin The Ac fraction is collected and a CeF 3 precipitate prepared for low-level gas-flow proportional counting.

Problems/Improvements BaSO 4 conversion (metathesis) time- consuming and not quantitative; Samples heavily contaminated with Sr- 90 (Y-90) have produced false positives; LnResin and TRUResin approach for Ra-228 not suitable for soil samples — additional clean-up required.

New “Combined” Approach Water samples — ppt MnO 2 —> 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

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

The “Double-Pass” Approach 12 Actinide Resin # Ra via Rn emanation 223,224 Ra via  -spectrometry 12 Rinse 2M HCl 1 2 Actinide Resin #1 1 2 Load sample in 2M HCl Collect Ba-133 yield Hold >30 hrs. Process Actinide Elements First Pass: Rinse 2M HCl 1 2 Load sample in 2M HCl Extrude resin into plastic vial; add cocktail, count via LSC Second Pass: 2nd column options: TRU. Resin — load 2.5M HNO 3 ; elute Ac 1M HCl, ppt CeF 3, count Diphonix — load 2M HCl; elute Ac 0.5M HEDPA, evap., count

Water Samples: MnO 2 ppt Seawater, liters Acidify to pH 2, add Pu/Am tracers, stir/hold For 100L sample, add 35 mL sat KMnO 4 (~2.1g); Pu-->Pu(VI), org oxid, purple color Adjust pH to 8-9 with NaOH Add 0.5M MnCl 2 (2x vol of KMnO 4 ); --> MnO 2 ppt, dark brown 2MnO Mn H 2 O = 5MnO 2 + 4H + Re-adjust pH to 8-9 as necessary Stir occasionally to keep MnO 2 suspended for few hours Allow Mn0 2 (Pu, Am) ppt to settle overnight Pump supernatant into clean tank for Cs, Sr processing Drain MnO 2 slurry from bottom tap Seawater MnO 2 Suspension MnO 2 ppt (Pu, Am, Ra, Ba) supernatant Cs, Sr,... centrifuge/ filter

Hold-back of 90 Sr MnO 2 ppt Reference

Large Volume Seawater Samples Supernatant seawater transferred from one plastic tank to another via pumping — this will be used for 90 Sr and 137 Cs. MnO 2 suspension withdrawn from bottom of conical-shaped plastic tanks — processed for Am and Pu.

Smaller-Scale MnO 2 ppt MnO 4 (purple) is reduced by added MnCl 2 to precipitate MnO 2 (brown). MnO 2 precipitate settles relatively quickly.

Count Overnight Analysis of rate of decay indicated a half-life ~8% too low Ac-228 t 1/2 = 6.13 hrs.

Decay Component Analysis A o = 135 cpm A o = 95.4 cpm

Ba Yields: MnO 2 ppt Sample spilled

Ra-228 Test Results

Summary MnO 2 ptt effectively scavenges Ra isotopes as well as actinides; Radium recoveries very high, dissolution of MnO 2 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.