developments in environmental radiochemistry* environmental radioactivity measurement facility...
TRANSCRIPT
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 – TRUResin
U-Series Disequilibrium in the
Ocean
238U ~ 3.2 g/L
230Th
226Ra
Seawater
Sediments
238U 234U
237 271
230Th 226Ra
<1 ~10dpm/100L:
(234Th, 231Pa, 210Pb, etc.)
~50
222Rn 210Pb222Rn 222Rn
234Th
var.
R/VEichrom
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%)
238U4.5 x 109 y
234Th24.1 d
234Pa1.18 m
234U2.48 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 2-3M HNO3
Th-234 in Marine Sediments:
Separation of Th/U via TEVA
U and Th loaded onto standard TEVA column in 2.5M HNO3
U-233 and Th-230 breakthrough TEVA column
0
500
1000
1500
2000
2500
0 10 20 30 40 50
Cumulative volume of 2.5 M HNO3
activ
ty,c
pm
U-233 Th-230
Rinse
Load
Th-234 in Marine Sediments:
Elution Curve% of Th-234 eluted activity
0
50
100
1 2 3 4 5 6 7 8 9 10
Cumulative Volume of 1M H3PO4, mL
% o
f the
elu
ted
Th-
234
activ
ity total recovery (5 mL) ≥97%
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
Hot Block95o C, 2 hrs.Hot Block
95o C, 2 hrs.
230Th tracer
Hot Block95o C, 2 hrs
Centrifuge,Rinse
1g
Sediment
HNO3/H2O2
LSCplastic
vial
2.5M HNO3
1M H3PO4
TEVA
Resin
Counting:• Cerenkov• LSC
discard
Up to 36 samples may be processed simultaneously on
the “Hot Block”
Th-234 in Marine Sediments:
Results0.00 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
Ratio Measured/Standard
8 sediment samples spiked with Th-234 -- all produced values
within 10% of expected value, most within 4%.
Laboratory-Scale MnO2 ppt
MnO4 (purple) is reduced by added MnCl2 to precipitate MnO2 (brown). MnO2 precipitate settles relatively
quickly.
Concentrates Am, Pu, Th, Ra…
Hold-Back of 90Sr
0
20
40
60
80
100
0 1 2 3 4
Sr(NO3)2 in mg/L
ho
ldb
ack,
%
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.
238U4.49 x 109 y
226Ra1600 y
222Rn3.825 d
218Po3.05 m
214Pb26.8 m
214Bi19.7 m
214Po1.6x10-4 s
210Pb22.3 y
232Th1.39 x 1010 y
228Ra6.7 y
220Rn54.5 s
216Po0.158 s
212Pb10.6 h
212Bi60.5 m
212Po3.0 x 10-7 s
208PbStable
235U7.13 x 108 y
223Ra11.4 d
219Rn3.92 s
215Po1.83 x 10-3 s
214Pb36.1 m
214Bi2.16 m
207PbStable
208Tl3.1 m
207Tl4.79 m
4.78
5.49
6.00
5.68
6.08
6.78
6.28
7.69 8.78
6.626.28
7.37
6.816.55
5.715.60
Alpha Decay (MeV)
Beta Decay
228Th1.9 y
228Ac6.13 h
224Ra3.64 d
Radium Isotopes via Rn Analysis
MnO2-Fiber(226,228,224,223Ra)
Alpha Detector
- - -
222Rn 220Rn 219Rn
222Rn, 220Rn, 219Rn
215Po216Po
214Po
218Po
Dri
erit
e
Air
Pum
p
RAD7
Detection on Radon Monitor
TRU
1
2
1 2
Rinse 2M HCl1
2Diphonix
1
2
Load sample in 2M HCl
•Collect•Ba-133 yield•Hold >30 hrs.
Process Actinide Elements
Rinse 2M HNO3
1
2
Load sample in 2M HNO3
Elute 228Ac with 4 M HCl
Beta source preparationCeF3 co-precipitation
GFPC
MnO2 co-precipitation
Dissolve in 2 M HCl
Centrifuge
Ra-228 viaDiphonix-
TRU
228Ac t1/2 = 6.14 ± 0.13 hrs.
Half-Life Determination
(228Ra sample)y = -0.113x + 4.8635
R2 = 0.9973
3.40
3.80
4.20
4.60
5.00
0.0 2.0 4.0 6.0 8.0 10.0 12.0time, hours
ln A
Half-Life Determination(228Ra + 90Sr sample)
228Ac t1/2 = 6.10 ± 0.15 hrs.
y = -0.1137x + 4.7582
R2 = 0.987
3.40
3.80
4.20
4.60
5.00
0.0 2.0 4.0 6.0 8.0 10.0 12.0time, hrs
ln A
Ra-228 Test Results
Ra-228 + Sr-90
Ra-228 + Ra-226
Ra-228
Ra-228 (dpm)
0 50 100 150 200 250 300
Expected Ra-228