A soil from China was used to prepare the IAEA-444 soil certified reference material spiked with gamma emitting radionuclides. Before using the soil for spiking, it was milled and sieved to collect the appropriate fraction at mesh size less than 0.3 mm, and then homogenized. The matrix of Chinese soil was characterized and a number of samples were pre-screened for the radionuclides of interest prior to spiking. The results have shown that the material is free from artificial radionuclides, except for Cs-137, which was present at 2.6±0.2 Bq kg-1 based on dry mass. (Ref. date: 2006-01-01). The moisture content was found to be 2.3±0.2 %.
The preparation of the spiked soil CRM was performed according to a validated procedure [1]. In total, 400 bottles of 200 grams each were prepared. After bottling the material was sterilized by gamma ray irradiation with a total dose of 25 kGy using a Co-60 source according to EN ISO 13485:2003 to ensure long-term stability of the material by inhibiting microbial action.
Reference date for decay correction: 2007-10-15
| Analyte | Certified value1,2 [Bq kg-1] | Uncertainty* [Bq kg-1] |
| 54Mn | 61.0 | 1.3 |
| 60Co | 82.6 | 2.0 |
| 65Zn | 29.9 | 1.0 |
| 109Cd | 248.7 | 5.2 |
| 134Cs | 59.4 | 1.7 |
| 137Cs | 68.5 | 1.4 |
| 210Pb3 | 48.0 | 1.6 |
| 241Am | 55.6 | 1.6 |
1Established based on the certified activity value of the standard solutions used for spiking
2The certified values of massic activities are traceable to the SI through the radioactivity standard solutions used for spiking
3Information value
*Uncertainty is expressed as a Mixture model median based standard deviation S (MM-median) at 95 % confidence level
The reference values of the massic activities of each nuclide and their associated standard uncertainties were established based on the certified activity value of the standard solutions used for spiking the soil, taking into account the successive dilution steps, the mass of spiking solutions and the dry mass of the soil being spiked.
The information property value of 210Pb was established based on a consensus value derived from measurement results of 10 test portions measured using a broad energy type Ge detector. The obtained consensus value from measurement results was comparable to the median (48.9 ± 1.7) calculated from 172 measurement results reported in the IAEA-CU-03-2007 world wide proficiency test [2]. This information value of 210Pb massic activity should not be used for calibration purposes and it could only be used for quality control purposes.
References
[1] Shakhashiro, A., Gondin da Fonseca Azeredo, A. M., Sansone, U., Fajgelj, A. (2007): Matrix materials for proficiency testing: optimization of a procedure for spiking soil with gamma-emitting radionuclides, Analytical and bioanalytical chemistry, 387 (7), 2509-2515.
[2] International Atomic Energy Agency (2009): Worldwide Open Proficiency Test on the Determination of Radionuclides in Spinach, Soil and Water, IAEA-CU-2007-03, IAEA Analytical Quality in Nuclear Applications Series No. 8.
