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 decay- series 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  Automated Rn-222 in water and improved Ra isotopes via Mn-fiber/Rn counting  Th-234 in marine sediments via extraction chromatography - LSC  Ra-228 via Diphonix – TRU  Resin

U-Series Disequilibrium in the Ocean R/V Eichrom

Th-234 in Marine Sediments: 234 Th Characteristics  Half-life = 24.1 d  Maximum beta energies: 198 keV (73%), 104 keV (27%)  Pa-234m energies: 2290 keV (98%), 1530 keV (2%) 238 U 4.5 x 10 9 y 234 Th 24.1 d 234 Pa 1.18 m 234 U 2.48 x 10 5 y

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

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 HNO 3

Th-234 in Marine Sediments: Separation of Th/U via TEVA U and Th loaded onto standard TEVA column in 2.5M HNO 3 Rinse Load

Th-234 in Marine Sediments: Elution Curve total recovery (5 mL) ≥97% 1M H 3 PO 4 lowers Th retention on TEVA by several orders of magnitude; combines well with cocktail; lowers quench

Th-234 in Marine Sediments: Sample Preparation Hot Block 95 o C, 2 hrs. Hot Block 95 o C, 2 hrs. 230 Th tracer Hot Block 95 o C, 2 hrs Centrifuge, Rinse 1g Sediment HNO 3 /H 2 O 2 LSC plastic vial 2.5M HNO 3 1M H 3 PO 4 TEVA  Resin Counting: Cerenkov LSC discard Up to 36 samples may be processed simultaneously on the “Hot Block”

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

Laboratory-Scale MnO 2 ppt MnO 4 (purple) is reduced by added MnCl 2 to precipitate MnO 2 (brown). MnO 2 precipitate settles relatively quickly. Concentrates Am, Pu, Th, Ra…

Hold-Back of 90 Sr

MnO 2 ppt: 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.

238 U 4.49 x 10 9 y 226 Ra 1600 y 222 Rn d 218 Po 3.05 m 214 Pb 26.8 m 214 Bi 19.7 m 214 Po 1.6x10 -4 s 210 Pb 22.3 y 232 Th 1.39 x y 228 Ra 6.7 y 220 Rn 54.5 s 216 Po s 212 Pb 10.6 h 212 Bi 60.5 m 212 Po 3.0 x s 208 Pb Stable 235 U 7.13 x 10 8 y 223 Ra 11.4 d 219 Rn 3.92 s 215 Po 1.83 x s 214 Pb 36.1 m 214 Bi 2.16 m 207 Pb Stable 208 Tl 3.1 m 207 Tl 4.79 m Alpha Decay (MeV) Beta Decay 228 Th 1.9 y 228 Ac 6.13 h 224 Ra 3.64 d Radium Isotopes via Rn Analysis

MnO 2 -Fiber ( 226,228,224,223 Ra) Alpha Detector Rn 220 Rn 219 Rn 222 Rn, 220 Rn, 219 Rn 215 Po 216 Po 214 Po 218 Po Drierite Air Pump RAD7 Detection on Radon Monitor

TRU Rinse 2M HCl 1 2 Diphonix 1 2 Load sample in 2M HCl Collect Ba-133 yield Hold >30 hrs. Process Actinide Elements Rinse 2M HNO Load sample in 2M HNO 3 Elute 228 Ac with 4 M HCl Beta source preparation CeF 3 co-precipitation GFPC MnO 2 co-precipitation Dissolve in 2 M HCl Centrifuge Ra-228 via Diphonix-TRU

228 Ac t 1/2 = 6.14 ± 0.13 hrs. Half-Life Determination ( 228 Ra sample)

Half-Life Determination ( 228 Ra + 90 Sr sample) 228 Ac t 1/2 = 6.10 ± 0.15 hrs.

Ra-228 Test Results Ra Sr-90 Ra Ra-226 Ra-228 Expected Ra-228