Determination of 227Ac in
Geological Samples

AN-1601-10
Summary of Method Soil or rock samples are pulverized to <1mm and dissolved, either by acid digestion orsodium hydroxide fusion. 227Ac is separated from matrix ions using a ferric hydroxide precipitation step. Following
dissolution in 4M HCl, 227Ac is separated from radiometric impurities using a 2mL cartridge of DGA, Normal resin. 227Ac
is prepared for measurement using a CeF3 microprecipitation onto Resolve(R) Filters. An 225Ac(229Th) tracer is used tomeasure chemical recovery of actinium. After a 30 minute ingrowth
Sample Preparation
225time, the Ac tracer yield is measured via alpha spectrometry using
0.25-50g Soil or Rockthe 221Fr and 217At daughters of 225Ac. 227Ac is measured via its 227Th and223Ra daughters after a longer period of ingrowth (30-90 days). Ac yields

Pulverize to <1mm.

are typically 70-90%. MDA for 227Ac was 0.05Bq/kg for 3 day count times
after 90 days ingrowth period.
Reagents
DGA Resin, 2mL Cartridges (Eichrom DN-R50-S)
Iron Carrier (50mg/mL Fe, as ferric nitrate)
Cerium Carrier (10mg/mL)
229Th(225Ac) tracer
Hydrofluoric Acid (49%) or Sodium Fluoride
Boric acid
HNO3 (70%)
HCl (37%)
NaOH
Deionized Water
H2O2 (30%)
Optional for additional Th/U removal:
TRU Resin, 2mL cartridges (Eichrom TR-R50-S)
Equipment
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 Filters in Funnel (Eichrom RF-DF25-25PP01)
50mL and 250mL Centrifuge Tubes
Alpha Spectrometry System
Ball mill grinder or equivalentCentrifuge
Vacuum Pump
Heat Lamp
Analytical Balance
Fusion Option
250mL Zirconium crucibles with zirconium lids
Muffle Furnace
Digestion Option
Hot Plate
Teflon Beakers

Aliquot Sample. Add 229Th(225Ac) tracer.
Acid Digestion Option
Digest in Teflon beaker on hotplate with
2:1 conc. HNO3:HF to near dryness.
Digest in Teflon beaker on hotplate withconc. HNO3 + Boric Acid.
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. HCl.
Dilute to 30mL.

Ac Separation on DGA(1) Precondition 2mL DGA
with 10mL 4M HCl.*(2) Load sample solution.

DGA(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.

(3) Rinse sample tube with5mL 4M HCl. Add tube
rinse to DGA. (If TRU
cartridge is used, remove
following this step.)(10) Wet filter with 3mL 80% ethanol
followed by 3mL DI water.

(4) Rinse DGA with 10mL 3M HNO3.

(11) Filter sample.

(5) Rinse DGA with 20mL 0.5M
HNO3.

(9) Set up Resolve® Filter Funnel on
vacuum box.

(12) Rinse sample tube with 5mL DI
water and add to filter.
(16) Dry filter under heat lamp for
3-5 minutes.

(6) Strip Ac from DGA with
20mL 2M HCl. (2M HCl is used
to achieve additional
decontamination from Th.)

* A 2mL cartridge of TRU resin may
be added above DGA for additional
decontamination from U/Th.

(14) Draw vacuum until filter is dry.
(15) Remove filter from funnel
assembly and mount filter on
stainless steel planchet with 2sided tape.

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

(17) Measure actinium or daughtersby alpha spectrometry.

Method Performance
227

RockStandard
BCR-2
BHVO-1
HK-018HK-019HK-021
HK-022SAV B6Ac
Measured
Bq/kg
0.955 + 0.083
0.299 + 0.017
0.965 + 0.009
0.962 + 0.073
0.559 + 0.055
0.887 + 0.080
0.677 + 0.067

227

Ac
Reference
Bq/kg
0.967
0.283
0.948
0.966
0.572
0.862
0.680

% Bias-1.2
5.7
1.8
-0.4
-2.3
2.9-0.4

TracerRecovery
83718691
80
6866

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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