MnO2 Resin and Automated Measurements of Ra Isotopes

Bill BurnettDept. Oceanography

Florida State University

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

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

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

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

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

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

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)

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.

Pump Tests

Peristaltic pump; cartridge loaded with 1 g MnO2 Resin;

single pass

Pump Video

Fresh waters can be processed at high flow rates (300 mL/min) without any loss. Highly salted waters require longer equilibration times

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

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

Recoil Effect on Rn Emanation

Recoil range in air = 0.07 cm

Recoil Range in water = 9.1 x 10-5 cm

“DRYSTIK” ApproachMethods to increase moisture in cartridge

DRYSTIK-1Methods to increase moisture in cartridge

DRYSTIK-1

Drierite

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

Effect on Countrate

Time (min)

0 100 200 300 400 500

cpm

0

20

40

60

80

100

DrystikNo Drystik

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)

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.

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