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Developments in Environmental Radiochemistry*

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.

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Developments in Environmental Radiochemistry*

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  1. Developments in Environmental Radiochemistry* Environmental Radioactivity Measurement Facility Department of Oceanography Florida State University Tallahassee, Florida USA *Research funded by the PG Research Foundation

  2. Objectives • Study the distribution of U/Th decay-series nuclides to address problems in the earth/marine sciences. • Improve chemical and instrumental techniques for measurement of all radionuclides in the environment.

  3. 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 – TRU·Resin

  4. 222Rn 210Pb 222Rn 222Rn 234Th 226Ra 234U 238U 230Th var. ~10 dpm/100L: 237 <1 271 Seawater ~50 238U ~ 3.2 g/L 226Ra Sediments 230Th (234Th, 231Pa, 210Pb, etc.) U-Series Disequilibrium in the Ocean R/V Eichrom

  5. 234U 2.48 x 105y 238U 4.5 x 109 y 234Pa 1.18 m 234Th 24.1 d 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%)

  6. Th-234 in Marine Sediments: General Strategy • Add known amount Th-230 as yield tracer, leach sediment with HNO3 • Separate Th using TEVA·Resin • Count 234Th/230Th via LSC Options: (1) count resin directly (2) count TEVA elution (3) Cerenkov and/or LSC

  7. TEVA·Resin: 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 2-3M HNO3

  8. Th-234 in Marine Sediments: Separation of Th/U via TEVA Load Rinse U and Th loaded onto standard TEVA column in 2.5M HNO3

  9. Th-234 in Marine Sediments:Elution Curve total recovery (5 mL) ≥97% 1M H3PO4 lowers Th retention on TEVA by several orders of magnitude; combines well with cocktail; lowers quench

  10. Th-234 in Marine Sediments:Sample Preparation 1g Sediment HNO3/H2O2 2.5M HNO3 1M H3PO4 230Th tracer TEVA · Resin Hot Block 95o C, 2 hrs Hot Block Hot Block 95 95 o o C, 2 hrs. C, 2 hrs. discard LSC plastic vial Centrifuge, Rinse Up to 36 samples may be processed simultaneously on the “Hot Block” • Counting: • Cerenkov • LSC

  11. Th-234 in Marine Sediments:Results 8 sediment samples spiked with Th-234 -- all produced values within 10% of expected value, most within 4%.

  12. 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.

  13. Hold-Back of 90Sr

  14. 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 conical-shaped plastic tanks — processed for Am and Pu.

  15. Radium Isotopes via Rn Analysis 235U 7.13 x 108 y 232Th 1.39 x 1010 y 228Th 1.9 y 238U 4.49 x 109 y 228Ac 6.13 h Alpha Decay (MeV) 223Ra 11.4 d 226Ra 1600 y 224Ra 3.64 d 228Ra 6.7 y Beta Decay 5.71 5.60 5.68 4.78 219Rn 3.92 s 220Rn 54.5 s 222Rn 3.825 d 6.81 6.55 6.28 5.49 215Po 1.83 x 10-3 s 216Po 0.158 s 212Po 3.0 x 10-7 s 218Po 3.05 m 214Po 1.6x10-4 s 214Bi 2.16 m 212Bi 60.5 m 214Bi 19.7 m 7.37 6.78 6.00 7.69 8.78 214Pb 36.1 m 207Pb Stable 6.62 6.28 212Pb 10.6 h 208Pb Stable 214Pb 26.8 m 210Pb 22.3 y 6.08 208Tl 3.1 m 207Tl 4.79 m

  16. Detection on Radon Monitor Alpha Detector - - - 214Po 216Po 215Po 218Po Air Pump Drierite 222Rn 220Rn 219Rn RAD7 MnO2-Fiber (226,228,224,223Ra) 222Rn, 220Rn, 219Rn

  17. Ra-228 viaDiphonix-TRU MnO2 co-precipitation Centrifuge Dissolve in 2 M HCl 1 1 2 2 Process Actinide Elements Load sample in 2M HCl Load sample in 2M HNO3 TRU 1 1 Diphonix Rinse 2M HCl Rinse 2M HNO3 2 2 1 2 Elute 228Ac with 4 M HCl • Collect • Ba-133 yield • Hold >30 hrs. Beta source preparation CeF3 co-precipitation GFPC

  18. Half-Life Determination(228Ra sample) 228Ac t1/2 = 6.14 ± 0.13 hrs.

  19. Half-Life Determination(228Ra + 90Sr sample) 228Ac t1/2 = 6.10 ± 0.15 hrs.

  20. Ra-228 Test Results Ra-228 + Sr-90 Ra-228 + Ra-226 Ra-228 Expected Ra-228

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