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 – TRUResin
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 TEVAResin
 Count 234Th/230Th 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 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