MnO 2 Resin and Automated Measurements of Ra Isotopes Bill Burnett Dept. Oceanography Florida State University

MnO 2 Resin Developed by PGRF mesh High adsorption of Ra, trivalent and tetravalent actinides (Ac, Am, Pu, Th) Preconcentration approach in batch, column, or pump (filtration) modes

IsotopeDirectParentHalf-life Decay Mode EnergyMeV 223 Ra 227 Th 11.4 d  Ra 228 Th 3.66 d  Ra 230 Th 1600 y  Ra 232 Th 5.75 y 0.046 Natural Radium Isotopes

Tracers for Characterization Ba-133 (commercial, nominal activity) Ra-228, Ra-224 (separated from 40-year old Th(SO 4 ) 2, calibrated by gamma spect Ra-226 NIST solution standard

Distribution Coefficient C 1 = amount adsorbed per gram dry resin; and C 2 = amount that remains in solution after equilbrium has been reached. Units = mL/g

K D Determinations w Tracers A o = initial activity solution, cpm A f = final activity solution, cpm V = volume solution, mL W = weight of resin, g

Percent Recovery K D = 2.8 x 10 4

Kinetics, pH = 7 pH = 7 Resin = 25 mg Solution = 10 mL Floridan Aquifer groundwater ~ mg/L ( o / oo )

pH Variation pH = variable Resin = 25 mg Solution = 10 mL Reaction time = 90 min Surface charge Ra 2+ speciation The optimum pH for adsorption of Ra 2+ is from 5 to 8 – nearly all natural waters fall into this range.

Pump Tests Peristaltic pump; cartridge loaded with 1 g MnO 2 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 MnO 2 -Resin ( 226,228,224,223 Ra) Alpha Detector Rn 220 Rn 219 Rn 222 Rn, 220 Rn, 219 Rn 215 Po 216 Po 214 Po 218 Po Drierite Air Pump RAD7

Optimum Moisture Content Water/Fiber Ratio = (x i -x o )/x o ; where x i = mass at each stage; and x o = mass when completely dry

Recoil Effect on Rn Emanation Recoil range in air = 0.07 cm Recoil Range in water = 9.1 x cm

“DRYSTIK” Approach Drierite

Moisture Control During Counting

Effect on Countrate

Results: Ra-224 Counting Water sample passed through MnO 2 Resin and 220 Rn counted periodically over many days produced the correct half-life for 224 Ra.

Results: Ra-226 ( 222 Rn Ingrowth) T 1/2 = 3.84 days Several standards prepared with NIST 226 Ra solution. Theoretical line drawn with decay constant for 222 Rn.

Summary MnO 2 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 224 Ra and 226 Ra without chemical separations