AN-1421

Rapid Determination of 226Ra
in 1g Soil Samples

Summary of Method 226Ra is separated from 1 gram samples of soil and measured by alpha spectrometry.
Samples are fused with sodium hydroxide at 600°C. The fusion cake is dissolved in water, and radium is precipitatedfrom samples with calcium carbonate. The calcium carbonate precipitate is dissolved in hydrochloric acid, and cationexchange chromatography is used to purify radium and barium from matrix ions. Barium is removed from samples using
Eichrom Sr Resin. Eichrom DGA Resin is used to reomve other alpha emitting nuclides from radium. Samples areprepared for alpha spectrometry by barium sulfate micro-precipitation onto Eichrom® Resolve Filters. Sample
preparation, including alpha spectrometry source preparation, for batches of 12-24 samples can be completed by asingle operator in as little as 6 hours. Yields are traced with 225Ra(229Th) by alpha spectrometry. At least 8 hours ofingrowth time for the alpha emitting 217At daughter of 225Ra is required prior to measurement by alpha spectrometry.
Reagents
Cation Exchange Resin (Eichrom C8-B500-F-H)
Sr Resin, 2mL Cartridges (Eichrom SR-R50-S)
DGA Resin, Normal 2mL Cartridges (Eichrom DN-R50-S)
Nitric Acid (70%)
Hydrochloric Acid (37%)
225
Deionized Water
Ra(229Th) Tracer
1.25M Ca(NO3)2
2M Na2CO3
Barium Carrier (1mg/mL)
Isopropyl Alcohol
Ammonium Sulfate
Denatured Ethanol
Ascorbic Acid
Sodium Hydroxide
H2O2(30%)

Figure 1. Sample Preparation
1g finely milled dry soil
+Tracer 225Ra(229Th)+10g NaOH in Zr crucible.
Fuse at 600°C in muffle furnace for 15 minutes.

Equipment
Plastic Chromatography Column (Eichrom AC-50E-5M)
Column Extension Funnel (Eichrom AC-20X-20M)
Vacuum Box (Eichrom AR-24-BOX or AR-12-BOX)
Cartridge Reservoir, 20mL (Eichrom AR-200-RV20)
Inner Support Tubes-PE (Eichrom AR-1000-TUBE-PE)
Yellow Outer Tips (Eichrom AR-1000-OT)
Resolve Filter in Disposable Funnel (Eichrom RF-DF-25-25PP01)
50mL and 250mL Centrifuge Tubes
Centrifuge
Stainless Steel Planchets with adhesive tape
Hotplate
Alpha Spectrometry System
150mL Glass beakers
Vacuum Pump
250mL Zirconium Crucible w/ lid
Muffle Furnace

Remove from furnace. Cool 10 minutes.
Dissolve fusion cake with 100mL DI water.
Transfer to 250mL centrifuge tube. Add
10mL 37% HCl. Dilute to 150mL.
Add 0.5mL 1.25M Ca(NO3)2 and10mL 2M Na2CO3. Mix well.
Place in ice bath for 10 minutes.
Centrifuge 3500 rpm, 10 min
Dissolve precipitate in20mL 1.5M HCl and3mL 1.5M ascorbic acid.
Proceed to Column Purification

DecantSupernateTo WasteFigure 2. Column Purification and Alpha Source Preparation(11) Add 50ug Ba carrier. Mix well.

(1) Prewash 5.0g 50Wx8200-400 mesh, cationexchange resin column:-10mL deionized water-20mL 6M HCl-10mL 0.5M HCl(12) Add 3g (NH4)2SO4 and 5mL isopropanol. Mix well.
(13) Place in ice bath for 30 minutes.
(14) Set up Resolve® Filter Funnel
on vacuum box.

(2) Load Sample(3) Rinse 30mL 3M HCl(4) Strip Ra/Ba with 25mL 5M HNO3.
(5) Add 2mL 30% H2O2.
Evaporate to dryness.
(6) Dissolve residue in 5mL
3M HNO3.
(7) Pass through 2mL Sr +DGA Resin Cartridges.
(8) Rinse Sr + DGA with
6mL 3M HNO3.
(9) Evaporate (7) +(8) to dryness.
226(10) Dissolve residue
in 10mL 1.5MHCl.

(21) Remove filter from funnel
assembly and mount filter on
stainless steel planchet withadhesive tape.

(15) Wet filter with 3mL 80% ethanol
followed by 3mL DI water.
(16) Filter sample.

SrDGA(17) Rinse sample
tube with 5mL
DI water andadd to filter.

(22) Dry filter under heat lamp for
3-5 minutes.
(23) Measure 226Ra and 225Ra(217At)
by alpha spectrometry after >8hours 217At ingrowth.

(18) Rinse filter funnel
with 3mL DI water.
(19) Rinse filter funnel
with 1-2mL 100%ethanol.

Ra(20) Draw vacuum until filter is dry.

1If using 133Ba tracer, 3.0g of cation exchange resin and proportionally smaller rinse volumes may be used.
2If tracing with 229Th, a 20mL 1M HCl-1M H3PO4 rinse following the sample load can improve purity of final 226Ra fraction.

Method Performance
225

Sample
12
3
4
AVG
225

*

217

Ra in 1g Soil Samples

226

Ra( At)% Yield*
75.2
77.9
74.8
73.3
75 + 2Ra tracer is added as226

Ra(mBq/g)
Reference
184.5
184.5
184.5
184.5
184.5

226

Ra(mBq/g)
Measured
185.9
192.0
176.9
184.7
185 + 6% Bias
0.8
4.1-4.1
0.1
0.3

229

Th in equilibrium with its daughters andmeasured by its alpha emitting>8 hr ingrowth.

217

At daughter (7.066MeV) after

References
1) Sherrod L. Maxwell, Brian K. Culligan, “Rapid Determination of 226Ra in Environmental Samples,” J. Radioanal.
Nucl. Chem., 293(1), 149-155 (2012).
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