AN-2102

Determination of 225Ac in
Geological Samples

Summary of Method Soil or rock samples are pulverized to <1mm and dissolved, either by acid digestion orsodium hydroxide fusion. 225Ac (t1/2 = 10 days) is separated from matrix ions using a ferric hydroxide precipitation.
Following dissolution in 4M HCl, 225Ac is separated from radiometric impurities using 2 mL cartridges of TRU and DGA,
Normal resin. 225Ac is prepared for measurement using a CeF3 or LaF3
Sample Preparation
microprecipitation on Resolve(R) Filters. Chemical recovery of actinium can betraced using 227Ac (alpha spectrometry) or stable La (ICP-MS or ICP-AES). 225Ac
0.25-50g Soil or Rockmay be measured by alpha spectrometry (5.54-5.83 MeV) or gamma
Pulverize to <1mm.
spectrometry (via its 221Fr daughter, 218 keV, 11.44%).The alpha emission fromthe 227Ac tracer (4.71-4.90 MeV) only occurs in 1.38% of decays.
Aliquot Sample.
Therefore, use of 227Ac tracer may be more efficient by measuring its
Add 227Ac tracer or 55 g La.
227Th (5.59-6.04 MeV) or 223Ra (5.24-5.87 MeV) daughters after a period
Acid Digestion Optionof ingrowth and decay of 225Ac. The mass of La that can be added to use aDigest in Teflon beaker on hotplate withyield tracer must be minimized (55 g) to prevent degradation of the alpha2:1 conc. HNO3:HF to near dryness.
spectra through self-absorption. However, this amount of La should be
sufficient to measure via ICP-MS or ICP-AES.
Digest in Teflon beaker on hotplate withconc. HNO3 + Boric Acid.
Reagents
DGA Resin, 2 mL Cartridges (Eichrom DN-R50-S)
TRU Resin, 2 mL cartridges (Eichrom TR-R50-S)
Iron Carrier (50 mg/mL Fe, as ferric nitrate)
Cerium carrier (10 mg/mL)
227Ac tracer or Lanthanum Carrier (10 mg/mL)
Hydrofluoric Acid (49%) or Sodium Fluoride
Boric acid
HNO3 (70%)
HCl (37%)
NaOH
Deionized Water
H2O2 (30%)
Equipment
Vacuum Box (Eichrom AR-24-BOX or AR-12-BOX)
Cartridge Reservoir, 20 mL (Eichrom AR-200-RV20)
Inner Support Tubes-PE (Eichrom AR-1000-TUBE-PE)
Yellow Outer Tips (Eichrom AR-1000-OT)
Resolve Filters in Funnel (Eichrom RF-DF25-25PP01)
50 mL and 250 mL Centrifuge TubesAlpha Spectrometry System
Ball mill grinder or equivalent
Centrifuge
Vacuum Pump
Heat Lamp
Analytical Balance
Fusion Option
250 mL Zirconium crucibles with zirconium lids
Muffle Furnace
Digestion Option
Hot Plate
Teflon Beakers

Dissolve Residue in 4M HCl + 0.25M Boricacid. If solids remain. Repeat digestion.
Proceed to ferric hydroxide precipitation.
Fusion Option
In Zr crucible. Add 10-15g NaOH
Muffle at 600oC for 15-30 minutes.
Cool. Dissolve fusion cake with 50mL water.
Heat as necessary. Rinse crucible with 50mL 4M HCl.
Proceed to ferric hydroxide precipitation.
Ferric Hydroxide Precipitation
Transfer sample to 250mL centrifuge tube.
Dilute to 150mL with water.
Add 25mg Fe carrier. Mix well.
Centrifuge 2500 rpm for 10 minutes.
Decant Supernate.
Rinse ppt with 50mL water. Centrifuge.
Decant Supernate.
Dissolve precipitate with 10mL conc. HNO3.
Dilute to 25mL.

Ac Separation on TRU-DGA(1) Precondition 2mL TRU and
DGA with 10mL 6M HNO3.
TRU(2) Load sample solution.
(3) Rinse sample tube with5mL 6M HNO3. Add tube
rinse to TRU-DGA.
DGA(4) Rinse TRU-DGA with 10mL
3M HNO3.

(5) Rinse TRU-DGA with 15mL 2M
HCl (transfers La/Ac to DGA).
(6) Discard TRU. Rinse DGA with
20mL 0.5M HNO3.
(7) Strip Ac from DGA with
20 mL 2M HCl. (2M HCl is used
to achieve additional
decontamination from Th.)
*If using stable La as the yield tracer,
remove 2 mL aliquot and dilute to
10 mL for recovery measurement byICP-MS or ICP-AES.

(7) Add 0.5mL 30% H2O2 to samples.
(8) Add 50ug Ce carrier** to samples.
Mix well. Add 1mL 49% HF.
Mix well. Wait 15-20 minutes.

(13) Rinse filter funnel with 3mL DI
water and 2mL 100% ethanol.

(14) Draw vacuum until filter is dry.
(15) Remove filter from funnel
assembly and mount filter on
stainless steel planchet with**If stable La is used as the yield tracer,2-sided tape.
omit the addition of 50 ug of Ce.
The La will serve as the carrier forthe rare earth fluoride micro-ppt.

(9) Set up Resolve® Filter Funnel on
vacuum box.
(10) Wet filter with 3mL 80% ethanol
followed by3mL DI water.

(16) Dry filter under heat lamp for
3-5 minutes.

(11) Filter sample.
(12) Rinse sample
tube with 5mL
DI water andadd to filter.

(17) Measure actinides by alphaspectrometry.

References
1) H. Dulaiova, K.W.W. Sims, M.A. Charette, J. Prytulak, J.S. Blusztajn “A new method for the determination ofactinium-227 in geological samples,” J. Radioanal. Nucl. Chem., 296, 279-283 (2013).
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