A sample of two hundred kg of contaminated bulk soil was collected in September 2007 from a Syrian oil field by staff of the Atomic Energy Commission of Syria, an IAEA collaborating centre. Stones and undesired parts were manually removed; the soil was evenly distributed on stainless steel plates in laboratory environment for primary drying at room temperature. Then it was dried in a closed oven at 105°C for 48 hours and the content of moisture was determined and found to be (3.4 ± 0.3)% with a coverage factor k =1.
The material was milled to a powder in a rotary ball mill. The powder was then sieved through a 100 μm sieve. The sieved material, with a particle size of less than 100 µm, was further homogenized by using a plastic rotating drum for 7 days in a clean atmosphere at approximate room temperature of 24°C and relative humidity of 50%. To check the level of bulk material homogeneity, three samples from bottom, middle and top of the homogenizer were analyzed using gamma-ray spectrometry. The material mixing was stopped when a relative standard deviation of the three samples less than 4 % was attained.
The IAEA-448 soil CRM was bottled under normal laboratory conditions; 500 bottles were filled in one day. The bottles were labeled, arranged into plastic boxes and sterilized using gamma-ray irradiation with a total dose of 25 kGy using a 60Co source.
Certified values for massic activities (Based on dry mass)
Reference date for decay correction: 01 January 2009
|Radionuclide||Certified value [Bq kg-1]||Uncertainty* [Bq kg-1]|
|226Ra||19.05 x 103||0.26 x 103|
* The uncertainty is expressed as a combined standard uncertainty with a coverage factor k = 1 estimated in accordance with the JCGM 100:2008 Evaluation of measurement data – Guide to the expression of uncertainty in measurement.
Information values for massic activities (Based on dry mass)
|Radionuclide||Information value* [Bq kg-1]||Uncertainty** [Bq kg-1]|
* As clearly shown from the information values, reported radionuclides part of natural decay series are not in secular equilibrium and therefore decay corrections should be applied using the appropriate Bateman equations. The information values are given at the following date : 08 October 2012.
**The uncertainty is expressed as a combined standard uncertainty with a coverage factor k = 1 estimated in accordance with the JCGM 100:2008 Evaluation of measurement data – Guide to the expression of uncertainty in measurement.
The reference value of 226Ra in the IAEA-448 CRM was derived as a consensus of all reported results estimated using the median as described in ISO Guide 35 and ISO 13528. The arithmetic mean, Algorithm A mean and Hampel mean were also calculated and compared with the median. No significant difference was observed between the median and other mean value estimators.
The reference value obtained using the median estimator was adopted. This value is a reliable estimation of the property value.
In addition, the derived reference value of 226Ra was confirmed by the IAEA Terrestrial Environment Laboratory using alpha spectrometry after radiochemical separation.
This Certified Reference Material is intended to be used for quality assurance and quality control purposes in the determination of massic activity of 226Ra in soil. The IAEA-448 CRM is also suitable for method development and validation of analytical procedures, including potential bias evaluation, and for training purposes. This material is not to be used as a calibrator.