MnO2 Resin and Automated Measurements of Ra Isotopes

1
MnO2 Resin and Automated Measurements of Ra
Isotopes

• Bill Burnett
• Dept. Oceanography
• Florida State University

2
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

3
Natural Radium Isotopes
Isotope Direct Parent Half-life Decay Mode Energy MeV
223Ra 227Th 11.4 d a 5.61 5.72
224Ra 228Th 3.66 d a 5.69
226Ra 230Th 1600 y a 4.78
228Ra 232Th 5.75 y b 0.046
4
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

5
Distribution Coefficient
C1 amount adsorbed per gram dry resin and C2
amount that remains in solution after equilbrium
has been reached. Units mL/g
6
KD Determinations w Tracers
Ao initial activity solution, cpm Af final
activity solution, cpm V volume solution, mL W
weight of resin, g
7
Percent Recovery
KD 2.8 x 104
8
Kinetics, pH 7

• pH 7
• Resin 25 mg
• Solution 10 mL

Floridan Aquifer groundwater 40-200 mg/L
(0.04-0.2 o/oo)
9
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.
10
Pump Tests
Peristaltic pump cartridge loaded with 1 g MnO2
Resin single pass
11
Pump Video
Fresh waters can be processed at high flow rates
(³300 mL/min) without any loss. Highly salted
waters require longer equilibration times
12
Ra Isotopes via RAD-7
13
Optimum Moisture Content
Water/Fiber Ratio (xi-xo)/xo where xi mass
at each stage and xo mass when completely dry
14
Recoil Effect on Rn Emanation
Recoil range in air 0.07 cm Recoil Range in
water 9.1 x 10-5 cm
15
DRYSTIK Approach
Drierite
16
Moisture Control During Counting
17
Effect on Countrate
18
Results Ra-224 Counting
Water sample passed through MnO2 Resin and 220Rn
counted periodically over many days produced the
correct half-life for 224Ra.
19
Results Ra-226 (222Rn Ingrowth)
T1/2 3.84 days
Several standards prepared with NIST 226Ra
solution. Theoretical line drawn with decay
constant for 222Rn.
20
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