1. Measurement Uncertainty

2. Measurements Accuracy - hitting the center of the target Precision - tight pattern of hits Bias - all two inches high Uncertainty - circle containing 95% hits

4. Traceability Accuracy - close to system limitation Precision - range Bias - identified and corrected for Acceptable Uncertainty - 2 sigma Unbroken links to national standards

5. Calibration Traceability Unbroken linkage to national standards Uncertainty - elements identified and quantified Strong QC/QA program Periodic MQA testing

6. Measurement Traceability Starts with calibration uncertainty Identifies and quantifies all factors that affect the quality of a measurement Requires reproducibility Testing usually required to validate values

7. How this affects you Did I make the measurement right? Is it reproducible? What uncertainty is involved? Can I cite them for a violation?

8. 2 cases, more than 2 results Package survey of radioactive material Mammography machine measurements

9. Package 31x31x27 cm Bicron RSO-50E Calibrated by secondary laboratory Maximum surface dose rate measured is 0.4 uSv/h (0.4 mR/h) Traveling by air

11. IATA (ST-1 Requirements) Accuracy - so that correctly labeled Precision/uncertainty - based on package surface to detector center distance Bias - as high as a factor of 4 low

12. ST-2 Measurement Guidance Correction factors for package and detector sizes

13. Mammography Measurements Exposure at skin entrance Half value layer Non-invasive kVp measurements Mean glandular dose calculation

14. X-ray vs. Mammo Probes

15. Phantom Variability

16. Temperature Effects

17. HVL Measurements

18. Non Invasive kVp Measurements

19. Example of How Combined Uncertainties Effect Measurement 0.03Machine Repro. 0.01Rate Dependence 0.01Energy Dependence 0.01Temp/Pressure 0.015Meter Calibration Estimated Std. Dev. Component (Cont.)

20. Example of How Combined Uncertainties Effect Measurement 0.0070.02kVp (+/- 1 kVp) 0.020.06HVL(+/-0.02mmAl) 0.020.06Phantom Variability 0.020.06Probe Placement Estimated Std. Dev. Estimated Max. Dev. Component Estimate Std Deviation as Max Deviation/3 (NCRP Report 112) (Cont.)

21. Combined Uncertainty Total estimated uncertainty ( 1.5 2 + 1 2 + 1 2 +1 2 + 3 2 + 2 2 + 2 2 + 2 2 + 0.7 2 ) 1/2 = 5.2 To estimate a confidence level of 95% use a coverage factor of 2 = 2 x 5.2 = 10.4 %