Both, IAEA-RGU-1 and IAEA-RGTh-1 reference materials were prepared on behalf of the International Atomic Energy Agency by the Canada Centre for Mineral and Energy Technology by dilution of a uranium ore BL-5 (7.09% U) and a thorium ore OKA-2 (2.89% Th, 219 μg U/g) with floated silica powder of similar grain size distribution, respectively. No evidence for between-bottles inhomogeneity was detected after mixing and bottling. BL-5 has been certified for uranium, 226Ra and 210Pb confirming that it is in radioactive equilibrium. The agreement between radiometric and chemical measurements of thorium and uranium in OKA-2 shows both series to be in radioactive equilibrium.
Certified values for massic activities (based on dry mass)
| Radionuclide | Certified Value {Bq/kg] | Uncertainty [Bq/kg] | Half-life (years) |
|---|
| 232Th | 3250 | 180 | 1.402 (6).1010 |
Reference date for decay correction: 1 June 2016
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 [2].
Information values for massic activities (based on dry mass)
| Radionuclide | Certified Value {Bq/kg] | Uncertainty [Bq/kg] | Half-life (years) |
|---|
| 40K | 6.3 | 3.2 | 1.2504 (30).109 |
| 235U | 3.6 | 0.3 | 7.04 (1).108 |
| 238U | 78 | 6 | 4.468 (5).109 |
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 [2].
The values listed above were established on the basis of a gravimetric dilution of materials with known uranium, thorium and potassium composition. The details concerning the criteria for qualification as a recommended or information value can be found in the respective report (attached).
