Developments in Environmental Radiochemistry* Environmental Radioactivity Measurement Facility Department of Oceanography Florida State University Tallahassee, Florida USA *Research funded by the PG Research Foundation Objectives Study the distribution of U/Th decayseries nuclides to address problems in the earth/marine sciences. Improve chemical and instrumental techniques for measurement of all radionuclides in the environment. Current Projects Tracing of groundwater discharge into the coastal zone via Rn-222, radium isotopes Th-234 in marine sediments via extraction chromatography - LSC Automated Rn-222 in water and improved Ra isotopes via Mn-fiber/Rn counting Ra-228 via Diphonix – TRUResin U-Series Disequilibrium in the Ocean 222Rn 222Rn 210Pb 222Rn R/V Eichrom 238U dpm/100L: 237 234Th var. 234U 230Th 226Ra 271 <1 ~10 Seawater 238U ~50 ~ 3.2 g/L 226Ra Sediments 230Th (234Th, 231Pa, 210Pb, etc.) Th-234 in Marine Sediments: 234Th Characteristics Half-life = 24.1 d Maximum beta energies: 198 keV (73%), 104 keV (27%) Pa-234m energies: 2290 keV (98%), 1530 keV (2%) 234U 238U 4.5 x 109 y 234Pa 1.18 m 234Th 24.1 d 2.48 x 105 y Th-234 in Marine Sediments: General Strategy Add known amount Th-230 as yield tracer, leach sediment with HNO3 Separate Th using TEVAResin Count 234Th/230Th via LSC Options: (1) count resin directly (2) count TEVA elution (3) Cerenkov and/or LSC TEVAResin: Acid Dependency TEVA·Resin = Aliquot 336 (2:1 mixture, trioctyl: tridecyl methyl ammonium chlorides on nonionic polymeric support Th(IV) has very high retention at 23M HNO3 Th-234 in Marine Sediments: Separation of Th/U via TEVA U-233 and Th-230 breakthrough TEVA column activty,cpm 2500 Rinse 2000 1500 Load 1000 500 0 0 10 20 30 40 Cumulative volume of 2.5 M HNO3 U-233 Th-230 U and Th loaded onto standard TEVA column in 2.5M HNO3 50 Th-234 in Marine Sediments: Elution Curve % of the eluted Th234 activity % of Th-234 eluted activity 100 total recovery (5 mL) ≥97% 50 0 1 2 3 4 5 6 7 8 9 10 Cumulative Volume of 1M H3PO4, mL 1M H3PO4 lowers Th retention on TEVA by several orders of magnitude; combines well with cocktail; lowers quench Th-234 in Marine Sediments: Sample Preparation 1g Sediment HNO3/H2O2 230Th 2.5M HNO3 tracer TEVA Resin Hot Hot Block Block o o C, C, 22hrs. 9595 hrs Centrifuge, Rinse Up to 36 samples may be processed simultaneously on the “Hot Block” 1M H3PO4 discard LSC plastic vial Counting: • Cerenkov • LSC Th-234 in Marine Sediments: Results Ratio Measured/Standard 0.00 0.20 0.40 0.60 0.80 1.00 1.20 2-1 4-1 6-1 8-1 10-1 12-1 14-1 16-1 LCS-1 LCS-2 8 sediment samples spiked with Th234 -- all produced values within 10% of expected value, most within 4%. Laboratory-Scale MnO2 ppt Concentrates Am, Pu, Th, Ra… MnO4 (purple) is reduced by added MnCl2 to precipitate MnO2 (brown). MnO2 precipitate settles relatively quickly. Hold-Back of 90Sr 100 holdback, % 80 60 40 20 0 0 1 2 Sr(NO3)2 in mg/L 3 4 MnO2 ppt: 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 conicalshaped plastic tanks — processed for Am and Pu. Radium Isotopes via Rn Analysis 238U 232Th 228Th 235U 4.49 x 109 y 1.39 x 1010 y 1.9 y 7.13 x 108 y 228Ac Alpha Decay (MeV) 226Ra 1600 y Beta Decay 6.13 h 228Ra 224Ra 6.7 y 3.64 d 11.4 d 5.71 5.60 5.68 4.78 223Ra 222Rn 220Rn 219Rn 3.825 d 54.5 s 3.92 s 6.81 6.55 6.28 5.49 218Po 214Po 216Po 212Po 215Po 3.05 m 1.6x10-4 s 0.158 s 3.0 x 10-7 s 1.83 x 10-3 s 6.00 214Bi 19.7 m 7.69 6.78 214Pb 210Pb 212Pb 26.8 m 22.3 y 10.6 h 212Bi 60.5 m 6.08 8.78 7.37 208Pb 214Pb Stable 36.1 m 214Bi 2.16 m 6.62 6.28 208Tl 207Tl 3.1 m 4.79 m 207Pb Stable Detection on Radon Monitor Alpha Detector 214Po 216Po 218Po 222Rn 220Rn 215Po 219Rn Drierite Air Pump --- RAD7 MnO2-Fiber (226,228,224,223Ra) 222Rn, 220Rn, 219Rn MnO2 co-precipitation Ra-228 via Diphonix-TRU Centrifuge Dissolve in 2 M HCl 1 1 2 2 Process Actinide Elements 1 Diphonix 1 2 Load sample in 2M HCl Rinse 2M HCl TRU 1 2 Load sample in 2M HNO3 Rinse 2M HNO3 2 •Collect •Ba-133 yield •Hold >30 hrs. Elute 228Ac with 4 M HCl Beta source preparation CeF3 co-precipitation GFPC Half-Life Determination (228Ra sample) 5.00 y = -0.113x + 4.8635 R2 = 0.9973 ln A 4.60 4.20 3.80 3.40 0.0 2.0 4.0 6.0 time, hours 228Ac 8.0 10.0 12.0 t1/2 = 6.14 ± 0.13 hrs. Half-Life Determination (228Ra + 90Sr sample) 5.00 y = -0.1137x + 4.7582 R2 = 0.987 ln A 4.60 4.20 3.80 3.40 0.0 2.0 4.0 6.0 time, hrs 228Ac 8.0 10.0 12.0 t1/2 = 6.10 ± 0.15 hrs. Ra-228 Test Results Ra-228 + Sr-90 Ra-228 + Ra-226 Ra-228 Expected Ra-228 0 50 100 150 200 Ra-228 (dpm) 250 300