Transcript MnO2 Resin: Ra Isotopes w/o Radiochemistry

Measurements of Ra Isotopes via
MnO2 Resin
Bill Burnett, Natasha Dimova
Florida State University
E. Philip Horwitz
PG Research Foundation
Acknowledgments
FSU Graduate Students:
 Natasha Dimova
 Henrieta Dulaiova
 Ricky Peterson
 Benjamin Mwashote
 Christina Stringer
PGRF:
 Phil Horwitz
 Andy Bond
 Dan McAlster
Natural Radium Isotopes
Isotope
Half-life
Decay
Mode
223Ra
Direct
Parent
227Th
11.4 d
a
224Ra
228Th
3.66 d
a
Energy
MeV
5.61
5.72
5.69
226Ra
230Th
1600 y
a
4.78
228Ra
232Th
5.75 y
b
0.046
MnO2 Resin
 Developed
by PGRF
 High adsorption of Ra, trivalent and
tetravalent actinides (Ac, Am, Pu, Th)
 Preconcentration approach in batch,
column, or pump (filtration) modes
Adsorption vs. pH
120
• pH = variable
• Resin = 25 mg
• Solution = 10
mL
• Reaction time =
90 min
80
Adsorption Yield of
133
Ba (%)
100
60
40
20
0
0
2
4
6
8
10
12
14
pH
The optimum pH for adsorption of Ra2+ is from 4 to
8 – nearly all natural waters fall into this range.
Moon et al. / Applied Radiation & Isotopes 59 (2003) 255-262
KD Determination
 Ao  A f
KD  
 Af

 V 
 
 W 

Ao = initial activity solution, cpm
Af = final activity solution, cpm
V = volume solution, mL
W = weight of resin, g
KD and Kinetics, pH = 7
1200
Kd=2.8x104
Floridan Aquifer
groundwater ~40200 mg/L (0.04-0.2
o/ )
oo
800
Salinity (‰)
0.0
0.2
3.5
35.0
600
400
133
Ba Activity (CPM-NaI)
1000
pH=7,
25mg MnO2 resin
10 mL solution
200
-20
0
20
40
60
80
100
120
140
160
Time (min)
Moon et al. / Applied Radiation & Isotopes 59 (2003) 255-262
Percent Recovery
100  K D  M re sin
% Re cov ery 
K D  M re sin  Vso ln
110
mL/g
1.0 g
0.5 g
100
0.1 g
% Recovery
KD = 2.8 x
104
90
80
70
60
50
0
200
400
600
800
Volume of Solution (mL)
1000
Possible Analytical Uses
1. Drinking water analysis of Ra-226 and
Ra-228 via preconcentration and gspectrometry (well detector best)
2. Preconcentration of Ra isotopes and
analysis of a-emitters via a-spect
3. Automated analysis of a-emitting Ra
isotopes via a radon-in-air analyzer
Gamma-Spect Analysis
React MnO2 Resin in a batch mode, let settle, decant/
centrifuge, transfer to counting vial for g-spect analysis
Gamma Spectrum
214Pb
226Ra
352
peak 186 keV no U
via 214Pb + 214Bi
214Pb
214Bi
295
228Ra
609
226Ra
186
228Ac
228Ac
338
911
via 228Ac
MDA Gamma Spect
8
186 keV
338 keV
7
295+352+609 keV

~100-cc Ge well
detector

2-liter volume

295+352+609 keV
assumes 50%
equilibrium (4-day
ingrowth)
MDA (pCi/L)
6
5
4
3
2
1
0
0
500
1000
1500
2000
Count Time (min)
2.71  4.66 B  T
MDA (pCi/L) 
2.22  T  eff  intensity  vol
Alpha Spectrometric Analysis
Nour et al., in press
Ra-226 via BaSO4 micro ppt
226Ra
222Rn
218Po
214Po
a-Spectrometry
Ra-224 + daughters
Natural Ra isotopes and
Ra-225 tracer
S. Purkl, A. Eisenhauer / Applied Radiation and Isotopes 59 (2003) 245–254
Automated Measurements
drying tube
sample
x
x
“DRYSTIK”
x
x
filter
inner
moisture
in 218
Po
6000 out (pump)
8000
Counts
drying tube
4000
214Po
2000
outer
0
2000
RAD-7
4000 6000
8000 10000
Energy (keV)
B
A
x = stopcock
C
Gas Handling System
Front
Back
All the necessary tubing, valves, and drying system fits
easily into a small cabinet
Loading the Sample
Fresh water samples can be processed either by
gravity flow or by pumping at rates up to 300
mL/min without any loss of Ra.
Connecting Sample to RAD-7
The sample, inside the same cartridge used for
processing the sample, is hooked up to a radon-in-air
analyzer.
Validating Standard Ra Activity
Our standards are made by passing NIST-traceable
Ra-226 solution standards through the MnO2 Resin.
Any Ra remaining is measured by Rn emanation.
Results confirm retention >96%.
Setting Standard Ingrowth
The standards are re-set for ingrowth by passing
helium through the cartridge to ensure no Rn-222
is present at t=0. A small amount of water is then
added to enhance Rn emanation.
Suggested Protocol
1. Load sample on resin, measure Ra-224,
close stopcocks, allow ~5 days ingrowth
for Ra-226
2. Attach to RAD-7 manifold, purge RAD-7,
pump air through cartridge/RAD-7 for 5
minutes, close valves
3. Count for a few 15-min cycles for quick
analysis (Po-218) or several hours for
more sensitive analysis (Po-218 + Po-214)
4. Calculate results
Results: Ra-224 Counting
10
Ra (cpm)
8
224
Water sample passed
through MnO2 Resin
and 220Rn counted
periodically over many
days produced the
correct half-life for
224Ra.
y = 9.5 x e-0.00793x
t1/2 = 3.64 days
6
4
2
0
0
100
200
300
Time (hours)
400
500
Results: Ra-226 (222Rn Ingrowth)
300
ch A+C
-0.00752x
250
y = 280(1-e
)
T1/2 = 3.84 days
cpm
200
150
ch A
100
50
0
0
50
100 150 200 250 300 350 400
Ingrowth (hrs.)
Several standards prepared with NIST 226Ra
solution. Theoretical line drawn with decay
constant for 222Rn.
226Ra
MDAs: Auto Counting
1 liter
2 liters
5
ch A
4
ch A+C
MDA (pCi/L)
MDA (pCi/L)
5
3
2
2
1
0
0
250
500
750
Count Time (min)
1000
ch A+C
3
1
0
ch A
4
0
250
500
750
Count Time (min)
MDAs calculated assuming 96% yield, typical blanks
for A and C channels, and an equilibrium fraction of
0.5 (4 days ingrowth)
1000
Summary
MnO2 Resin is an excellent adsorber of
Ra from natural waters
 May be used for preconcentration to
combine with traditional techniques
(e.g., a-spect, g-spect)
 Interfacing with a RAD-7 Radon
analyzer allows determination of 224Ra
and 226Ra without chemical separations
