Measurements of Ra Isotopes via MnO2 Resin

Bill Burnett, Natasha DimovaFlorida State University

E. Philip HorwitzPG Research Foundation

AcknowledgmentsFSU Graduate Students: Natasha Dimova Henrieta Dulaiova Ricky Peterson Benjamin Mwashote Christina StringerPGRF: Phil Horwitz Andy Bond Dan McAlster

IsotopeIsotope DirectDirectParentParent

Half-Half-lifelife

Decay Decay ModeMode

EnergyEnergyMeVMeV

223223RaRa 227227ThTh 11.4 d11.4 d 5.615.615.725.72

224224RaRa 228228ThTh 3.66 d3.66 d 5.695.69226226RaRa 230230ThTh 1600 y1600 y 4.784.78228228RaRa 232232ThTh 5.75 y5.75 y 0.0460.046

Natural Radium Isotopes

MnO2 ResinDeveloped by PGRFHigh adsorption of Ra, trivalent and

tetravalent actinides (Ac, Am, Pu, Th)Preconcentration approach in batch,

column, or pump (filtration) modes

Adsorption vs. pH• pH = variable• Resin = 25 mg• Solution = 10

mL• Reaction time

= 90 min

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

0 2 4 6 8 10 12 14

0

20

40

60

80

100

120

Ads

orpt

ion

Yiel

d of

133 B

a (%

)

pH

KD Determination

WV

AAA

Kf

foD

Ao = initial activity solution, cpmAf = final activity solution, cpmV = volume solution, mLW = weight of resin, g

KD and Kinetics, pH = 7

Floridan Aquifer groundwater ~40-200 mg/L (0.04-0.2 o/oo)

Moon et al. / Applied Radiation & Isotopes 59 (2003) 255-262

-20 0 20 40 60 80 100 120 140 160

200

400

600

800

1000

1200

pH=7,25mg MnO

2 resin

10 mL solution

133 Ba

Act

ivity

(CPM

-NaI

)

Time (min)

0.0 0.2 3.5 35.0

Kd=2.8x104

Salinity (‰)

50

60

70

80

90

100

110

0 200 400 600 800 1000

Volume of Solution (mL)

% R

ecov

ery

1.0 g0.5 g0.1 g

Percent Recovery

lnsin

sin100covRe%soreD

reDVMK

MKery

KD = 2.8 x 104 mL/g

Possible Analytical Uses1. Drinking water analysis of Ra-226

and Ra-228 via preconcentration and -spectrometry (well detector best)

2. Preconcentration of Ra isotopes and analysis of -emitters via -spect

3. Automated analysis of -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 -spect analysis

Gamma Spectrum

226Ra peak 186 keV no U

via 214Pb + 214Bi 228Ra via 228Ac

226Ra186

214Bi609

228Ac911

228Ac338

214Pb295

214Pb352

MDA Gamma Spect ~100-cc Ge well

detector 2-liter volume 295+352+609

keV assumes 50% equilibrium (4-day ingrowth)

volintensityeffT2.22TB4.66 2.71 (pCi/L)MDA

0

1

2

3

4

5

6

7

8

0 500 1000 1500 2000

Count Time (min)

MD

A (p

Ci/L

)

186 keV

338 keV

295+352+609 keV

Alpha Spectrometric Analysis

2

1 2

Rinse 2M HCl1

2

DiphonixI

1

2

Load sample in 2M HCl

•Collect•Ba-133 yield•Hold >30 hrs.

Process Actinide Elements

Rinse 2M HCl1 M HEDPA

1

2

Load sample in 2M HCl

Elute 228Ac into plastic vial; add cocktail, count

via LSC

MnO2 Resin

Dissolve in 2 M HCl

Centrifuge

1

DiphonixII

3

3

1 2

ppt BaSO4133Ba yield

223,224,226Ra via-spectrometry

3

50-100 mesh7 cm; 0.7 mm id

100-200 mesh2.5 cm; 0.7 mm id

2

1 2

Rinse 2M HCl1

2

DiphonixI

1

2

Load sample in 2M HCl

•Collect•Ba-133 yield•Hold >30 hrs.

Process Actinide Elements

Rinse 2M HCl1 M HEDPA

11

22

Load sample in 2M HCl

Elute 228Ac into plastic vial; add cocktail, count

via LSC

MnO2 Resin

Dissolve in 2 M HCl

Centrifuge

1

DiphonixII

3

3

1 211 2

ppt BaSO4133Ba yield

223,224,226Ra via-spectrometry

3

50-100 mesh7 cm; 0.7 mm id

100-200 mesh2.5 cm; 0.7 mm id

Nour et al., in press

Ra-226 via BaSO4 micro ppt

226Ra

222Rn 218Po 214Po

-Spectrometry

S. Purkl, A. Eisenhauer / Applied Radiation and Isotopes 59 (2003) 245–254

Ra-224 + daughters Natural Ra isotopes and Ra-225 tracer

Automated Measurements

inout (pump)

inner

outer

drying tube

RAD-7dryi

ng tu

be “DRYSTIK”

sample

0

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

A B

C= stopcockx

x

x

x

x

filter

moisture

Gas Handling System

All the necessary tubing, valves, and drying system fits easily into a small cabinet

Front Back

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 Protocol1. 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

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.

Results: Ra-226 (222Rn Ingrowth)

Several standards prepared with NIST 226Ra solution. Theoretical line drawn with decay constant for 222Rn.

Ingrowth (hrs.)0 50 100 150 200 250 300 350 400

cpm

0

50

100

150

200

250

300

y = 280(1-e-0.00752x)T1/2 = 3.84 days

ch A+C

ch A

226Ra MDAs: Auto Counting1 liter 2

liters

MDAs calculated assuming 96% yield, typical blanks for A and C channels, and an equilibrium fraction of 0.5 (4 days ingrowth)

0

1

2

3

4

5

0 250 500 750 1000

Count Time (min)

MD

A (p

Ci/L

)

ch A

ch A+C

0

1

2

3

4

5

0 250 500 750 1000

Count Time (min)M

DA

(pC

i/L)

ch A

ch A+C

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