Table 8.
Uncertainty budgets for the absolute emission intensity for the 241 keV γ-ray, Iγ, determined at NIST with the x-detector and at NPL using the S3 solution.
| NPL |
NIST |
||
|---|---|---|---|
| LET + HET | GENIE | LET + HET | |
|
|
|
|
|
| /% | /% | /% | |
| Standard uncertainty of weighted mean | 0.11 | ||
| Peak fitting and counting statistics | 0.41 | 0.22 | 0.21 |
| Source activity | 0.27 | 0.31 | 0.31 |
| Full-energy peak detection efficiency | 0.34 | 0.71 | 0.71 |
| Decay correction during measurement (NPL combined this component with “Decay factor to reference time” for a single component) | – | 0.037 | 0.037 |
| Decay factor to reference time | 0.069 | 0.066 | 0.066 |
| Dead time/Pile-up | 0.1 | 0.006 | 0.006 |
| Self-absorption (wholly embodied in NIST “Full-energy peak detection efficiency”) | 0.065 | – | – |
| Stability (wholly embodied in NIST “Full-energy peak detection efficiency”) | 0.1 | – | – |
| Gravimetric (wholly embodied in NIST “Source activity”) | 0.02 | – | – |
| 228Th impurity | <0.001 | 0.004 | 0.004 |
|
| |||
| Combined standard uncertainty, uc | 0.63 | 0.8 | 0.8 |
| uc using correlation calculation from the GUM | 0.59 | 0.59 | |