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Verification of Carbon-14 Standards used in Proficiency Testing Materials

Verification of Carbon-14 Standards used in Proficiency Testing Materials. Shane Steidley. Radiological and Environmental Sciences Laboratory U.S. Department Of Energy. Outline. Properties of PE Materials Verification of Standards Applications Questions. Properties PE Material Must Have:.

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Verification of Carbon-14 Standards used in Proficiency Testing Materials

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  1. Verification of Carbon-14 Standards used in Proficiency Testing Materials Shane Steidley Radiological and Environmental Sciences Laboratory U.S. Department Of Energy

  2. Outline • Properties of PE Materials • Verification of Standards • Applications • Questions

  3. Properties PE Material Must Have: • Scientifically defensible • NIST Traceable Standard • No Laboratory Bias • Smaller Uncertainties • Synthetically Spiked Natural Matrices • Not analyzed • Verify Final Product • Unimpeachable Integrity • Verification of standards

  4. Independent Verification Intercompare C-14 against Tc-99, & I-129

  5. C-14 Std Verification using I-129 Std Known (dpm) Expt’l (dpm) Ratio E C14_V 9.24 ± 0.11 E3 9.3 ± 0.3 E3 0.99 ± 0.03 0.97 ± 0.01 C14_A 5.00 ± 0.05 E4 5.06 ± 0.16 E4 0.99 ± 0.03 0.97 ± 0.01 Tc99_V 9.98 ± 0.12 E3 1.00 ± 0.03 E4 1.00 ± 0.03 0.96 ± 0.01 I-129_V 1.000 ± 0.012 E3 - - 0.96 ± 0.01

  6. LISA • Linear Integral Spectral Analysis • Verify Laboratory Standards. • Quench curves not required. • Integral Counting is NOT based on comparison of a known standard • Validated • Similar to Efficiency Tracing, instead the count rate is extrapolated to 0.

  7. Further independence, LISA Linear Integral Spectral Analysis Provides an additional check Not based on comparison of a known std LISA extrapolates to 0% effciency, not 100% Uses/Benefits Quench curves not required Verify laboratory standards, independently

  8. LISA Method (cont) • External Blind NIST Performance Test -0.2 -0.1

  9. LISA Method (cont) • LISA standardized I-129 & I-131 solutions used for gamma spec calibration • XAW waters are prepared with an independent NIST traceable solution of I-129 • Blind RESL verification results: Std Known (pCi/L) Exp (pCi/L) Ratio I-129- XAW-A 2.56 ± 0.04 E2 2.55 ± 0.04 E2 1.00 ± 0.02 I-129- XAW-B 3.30 ± 0.05 E2 3.36 ± 0.03 E2 1.01 ± 0.02

  10. C-14 PE Performance

  11. Verification of customers standards • Ratio of known to experimental Std Type Ratio LISA Ratio C14_E Ratio Tc99_E C14 Carbonate 0.82 ± 0.04 0.81 ± 0.04 0.82 ± 0.04 C14 Glucose 1.03 ± 0.05 1.03 ± 0.05 1.04 ± 0.05 C14 Carbonate 0.88 ± 0.04 0.87 ± 0.04 0.89 ± 0.04 Other examples of inaccurate reference values include: U-233, H-3, Th-230, Sr-90 Conclusion: Multiple cross checks and intercomparisons needed to verify the accuracy of standards

  12. Questions??

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