2.6.11 - Ca Isotopes in Biological Shield


Bioshield concrete is an important structural component of a nuclear reactor, as it acts as a radiological shield. However, when a nuclear reactor is decommissioned, the bioshield concrete presents a significant waste to be treated. The quantification of the long lived activation products is important for the long-term safety of final repositories for nuclear waste.

Some of the most important radionuclides generated in concrete are the Calcium-Isotopes 41Ca (T1/2 = 1.03 x 105 a) and 45Ca (T1/2 = 163 d), both with a long biological half-life. They are produced by thermal neutron capture from stable 40Ca and 44Ca, respectively. 45Ca as β-emitting radionuclide with Emax of 257 keV is easily measured by liquid scintillation. 41Ca decays by pure electron capture, emitting X-rays and Auger electrons with very low energies below 3.6 keV; hence its determination is more difficult due to the strong self-absorption.

Liquid scintillation counting represents an alternative methodology for 45Ca quantification and 41Ca determination in bioshield concretes. As standard, IRMM 3701 material with a known 41Ca activity of about 6 Bq/g 41Ca, produced by the Institute for Reference Materials and Methods (Geel, Belgium) is employed for LSC calibration [Warwick et al. 2009].

For measuring details of the electron capture nuclide, especially applying TDCR, see 2.3.11. Detailed descriptions for sample preparation are outlined below.

A second procedure is described, which has been used by Xaolin [Xaolin 2002] for the analysis of concrete samples for the decommissioning of research reactors. It consists of an alkaline fusion for the decomposition of the sample followed by a group separation and further specific separation steps for individual radionuclides (fig. 31).

PROCEDURE 1: Ca-41 in concrete bioshield [Warwick 2009] 

Materials and Equipment

  • Sr SPEC resin (EICHROM)

  • 41Ca standard solution (≈ 6 Bq/g 41Ca; IRMM 3701), Institute for Reference Materials and Methods (Geel, Belgium)

  • Lithium borate

  • Fe carrier

  • Ba carrier

  • Conc. HNO3; 8 M HNO3

  • Conc. HCl

  • Saturated Na2CO3

  • 4 % (NH4)2(COO)2

  • Acetate buffer

  • 6 M acetic acid

  • 1.5 M NaCrO4

  • Ammonia

  • Gelating cocktail

Procedure 1 

Pre-concentration steps:

  1. Mix the sample (dried ground concrete) with Lithium borate and fuse at 1100 ºC (dissolution of Ca), then dissolve the solid in 50 mL 8 M HNO3

  2. Add 20 mL 4 % (NH4)2-oxalate and adjust to pH 5 (precipitation of Ca-oxalate, 133Ba, 226Ra)

  3. Dissolve the precipitate in 5 mL conc. HCl; add 15 mL H2O and 5 mL 4 % (NH4)2-oxalate and adjust the pH to 5 (precipitation of Ca-oxalate)

  4. Ignite the precipitate at 500 ºC; dissolve the residue in 5 mL concentrate HCl and add 2 mL conc. HNO3 and 10 mg of Fe carrier; adjust the pH to 5 to precipitate the Fe(OH)3 (Ln(III), An(III, IV, V, VI))

  5. Add 15 mL of saturated Na2CO3 to precipitate CaCO3

  6. Dissolve the CaCO3 in 10 mL 8 M HNO3

41Ca separation:

  1. Wash the Sr resin column (4 x 0.5 cm) twice with 10 mL 8 M HNO3

  2. Drain the solution containing CaCO3 through the column; 90Sr is retained on the resin

  3. Evaporate the eluent to dryness and dissolve the residue by adding 0.5 mL conc. HCl and 15 mL H2O

  4. Add 10 mg of Ba and 3 mL of acetate buffer; adjust the pH to 5 using 6 M acetic acid

  5. Add 1 mL 1.5 M NaCrO4 and warm up in order to precipitate BaCrO4 (133Ba, 226Ra)

  6. Adjust the pH to 8 with ammonia; add 15 mL of saturated Na2CO3 to precipitate CaCO3

  7. Dissolve the precipitate in 1 mL of conc. HCl; warm up until a green color is observed and elute with 15 mL H2O; add 10 mg of Fe and adjust to pH 7 with ammonia to precipitate Fe(OH)3 (residual Cr(III))

  8. Add 15 mL of saturated Na2CO3 to precipitate CaCO3

  9. Transfer the solid into a LS vial, dry and weigh for recovery

  10. Dissolve CaCO3 in 1 mL conc. HCl, add 3 mL of H2O and 16 mL of gelating scintillation cocktail

Procedure 2 

Simultaneous determination of 41Ca in presence of 36Cl, 55Fe, 63Ni and 129I in concrete [Xaolin 2007]

Materials and Equipment

  • Fe, Ni, Ca, Cl and I carriers

  • 0.2 M HCl

  • NaOH

  • Gelating cocktail


  1. Add to the concrete sample Fe, Ni, Ca, Cl and I carriers and hold-back carriers, NaOH, NaCO3, and fuse at 500 ºC

  2. Leach with water, centrifuge and wash the precipitate with 0.2 M of Na2CO3 four times; the resulting supernatant contains Cl, I, Cs and K and can further be processed for 36Cl and 129I determination (see fig. 31, left side), while the precipitate contains metals, Ca and Sr.

  3. Dissolve the precipitate with HCl; add NaOH until pH 9 and centrifuge the M(OH)x; the precipitate can further be used for the determination of 63Ni and 55Fe (see fig. 31, right side)

  4. Add Na2CO3 to the solution containing Ca, Sr, and Ba, centrifuge and discard the supernatant

  5. Dissolve the precipitate (which contains Ca, Ba, Sr, BaCO3) in HCl and add NaOH to 0.5 M

  6. Centrifuge and repeat the procedure 3 times and discard the supernatant containing Sr and Ba

  7. Dissolve the 41Ca containing precipitate in HCl and use this solution for the LS measurement


LSC measurements were applied by the authors for 36Cl, 129I, 41Ca, 45Ca, 63Ni and 55Fe.

For yield determination the stable Cl, I and Ca tracers have been evaluated by ICP-MS or alternatively ICP-AES.

Lower Limit of Detection LLD: 50 mBq per sample (without preconcentration)

Figure 31: Procedure for the simultaneous determination of 36Cl, 129I, 41Ca, 45Ca, 63Ni and 55Fe in concrete [Xaolin 2007]

Warwick P. 2009: Effective determination of long-lived nuclide Ca-41 in nuclear reactor bioshield concretes: Comparison of LSC and Accelerator Mass Spectrometry; Anal. Chem. 81 (2009) 1901/1906

Xaolin H. 2007: Radiochemical analysis of radionuclides difficult to measure for characterization of waste in decommissioning of nuclear facilities; J. Radioanal. Nucl. Chem. 273 (2007) 43-8

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