MnO 2 Resin and Automated Measurements of Ra Isotopes
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Transcript of MnO 2 Resin and Automated Measurements of Ra Isotopes
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MnO2 Resin and Automated Measurements of Ra Isotopes
Bill BurnettDept. Oceanography
Florida State University
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MnO2 Resin Developed by PGRF 80-160 mesh High adsorption of Ra, trivalent and
tetravalent actinides (Ac, Am, Pu, Th) Preconcentration approach in batch,
column, or pump (filtration) modes
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IsotopeIsotope DirectDirect
ParentParentHalf-Half-lifelife
Decay Decay ModeMode
EnergyEnergy
MeVMeV223223RaRa 227227ThTh 11.4 d11.4 d 5.615.61
5.725.72224224RaRa 228228ThTh 3.66 d3.66 d 5.695.69
226226RaRa 230230ThTh 1600 y1600 y 4.784.78
228228RaRa 232232ThTh 5.75 y5.75 y 0.0460.046
Natural Radium IsotopesNatural Radium Isotopes
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Tracers for Characterization
Ba-133 (commercial, nominal activity)
Ra-228, Ra-224 (separated from 40-year old Th(SO4)2,
calibrated by gamma spect Ra-226 NIST solution standard
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Distribution Coefficient
solution /Cresin /
2
1
mLgC
KD
C1 = amount adsorbed per gram dry resin; and C2 = amount that remains in solution after equilbrium has been reached.
Units = mL/g
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KD Determinations w Tracers
W
V
A
AAK
f
foD
Ao = initial activity solution, cpm
Af = final activity solution, cpm
V = volume solution, mL
W = weight of resin, g
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0
20
40
60
80
100
120
0 2000 4000 6000 8000 10000
Volume of Solution (mL)
% R
ec
ov
ery
1.0 g
0.5 g
0.1 g
50
60
70
80
90
100
110
0 200 400 600 800 1000
Volume of Solution (mL)
% R
ec
ov
ery
1.0 g
0.5 g
0.1 g
Percent Recovery
lnsin
sin100covRe%
soreD
reD
VMK
MKery
KD = 2.8 x 104
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Kinetics, pH = 7
• pH = 7• Resin = 25 mg• Solution = 10
mL
-20 0 20 40 60 80 100 120 140 160
200
400
600
800
1000
1200
DDW SW (35) ISW (3.5) GW (0.2)
pH=7, 25mg Mn resin
Kd=2.8x104
133 B
a A
ctiv
ity (
CP
M-N
aI)
Time (min)
Floridan Aquifer groundwater ~40-200 mg/L (0.04-0.2 o/oo)
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0 2 4 6 8 10 12 14
0
200
400
600
800
1000
1200
DDW SW
133 B
a a
ctiv
ity in
Mn
O2
resi
n (
CP
M)
pH
pH Variation
• pH = variable• Resin = 25 mg• Solution = 10
mL• Reaction time
= 90 min
Surface charge
Ra2+ speciation
The optimum pH for adsorption of Ra2+ is from 5 to 8 – nearly all natural waters fall into this range.
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Pump Tests
Peristaltic pump; cartridge loaded with 1 g MnO2 Resin;
single pass
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Pump Video
Fresh waters can be processed at high flow rates (300 mL/min) without any loss. Highly salted waters require longer equilibration times
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Ra Isotopes via RAD-7
MnO2-Resin(226,228,224,223Ra)
Alpha Detector
- - -
222Rn 220Rn 219Rn
222Rn, 220Rn, 219Rn
215Po216Po
214Po
218Po
Dri
erit
e
Air
Pum
p
RAD70
2000
4000
6000
8000
2000 4000 6000 8000 10000
Energy (keV)
Cou
nts
218Po
214Po
0
2000
4000
6000
8000
2000 4000 6000 8000 10000
Energy (keV)
Cou
nts
218Po
214Po
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Optimum Moisture Content
Water/Fiber Weight Ratio
0 1 2 3 4 5
220 R
n (c
pm)
0
20
40
60
80
66.1±2.4 cpmn=7
Water/Fiber Ratio = (xi-xo)/xo ; where xi = mass at each stage; and xo = mass when completely dry
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Recoil Effect on Rn Emanation
Recoil range in air = 0.07 cm
Recoil Range in water = 9.1 x 10-5 cm
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“DRYSTIK” ApproachMethods to increase moisture in cartridge
DRYSTIK-1Methods to increase moisture in cartridge
DRYSTIK-1
Drierite
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Moisture Control During Counting
Time (min)
0 100 200 300 400 500
Moi
stur
e/R
esin
0.0
0.2
0.4
0.6
0.8
DrystikNo Drystik
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Effect on Countrate
Time (min)
0 100 200 300 400 500
cpm
0
20
40
60
80
100
DrystikNo Drystik
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Results: Ra-224 Counting
Time (hours)
0 100 200 300 400 500
224 R
a (c
pm)
0
2
4
6
8
10
y = 9.5 x e-0.00793x
t1/2 = 3.64 days
Water sample passed through MnO2 Resin and 220Rn counted periodically over many days produced the correct half-life for 224Ra.
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Results: Ra-226 (222Rn Ingrowth)
Time (hrs.)
0 50 100 150 200 250 300
cpm
0
50
100
150
200
250
300
Equation plotted:y = 281.5(1-e-0.00752x)
T1/2 = 3.84 days
Several standards prepared with NIST 226Ra solution. Theoretical line drawn with decay constant for 222Rn.
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Summary
MnO2 Resin is an excellent adsorber of Ra from natural waters
May be used for preconcentration to combine with traditional techniques (e.g., -spect, -spect)
Interfacing with a RAD-7 Radon analyzer allows determination of 224Ra and 226Ra without chemical separations