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Coincidence-summing in Gamma-ray spectrometry. IEC 1452 Standard GESPECOR software

Coincidence-summing in Gamma-ray spectrometry. IEC 1452 Standard GESPECOR software. Octavian Sima Physics Department Bucharest University. IWIRAD 2005. Overview. IEC 1452 standard Coincidence-summing effects GESPECOR software - decay scheme data - Monte Carlo simulation

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Coincidence-summing in Gamma-ray spectrometry. IEC 1452 Standard GESPECOR software

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  1. Coincidence-summing in Gamma-ray spectrometry.IEC 1452 StandardGESPECOR software Octavian Sima Physics Department Bucharest University IWIRAD 2005

  2. Overview • IEC 1452 standard • Coincidence-summing effects • GESPECOR software • - decay scheme data • - Monte Carlo simulation • - examples • Summary and conclusions IWIRAD 2005

  3. 1. IEC STANDARD 1452 (1995) • Purpose: - to establish methods for the calibration and measurement of energy and  emission rate with Ge detectors and on this basis to assess the activity - to provide tests for checking that the system and the analysis are adequate • Calibration and peak analysis • Energy and emission rate measurement (corrections) • Quality control of the spectrometry system • Quality control of the analysis software • Quality control of the complete system IWIRAD 2005

  4. Emission rate measurement => required corrections: • - count rate in the interfering background peaks • - decay corrections • - random summing, pile-up corrections • - true coincidence-summing corrections • - attenuation (self-attenuation + external) • True coincidence-summing • - magnitude of the effect N(E1)/N(E2) =f(distance) • E1E2, E1 with coincidence, E2 without • - Appendix C – principles and examples (1-st order) • Nuclide identification • - peak search, library data IWIRAD 2005

  5. 2. Coincidence-summing effects • Summing out => losses from peaks (apparent efficiency is lower than correct efficiency) • Summing in => additional counts due to1+2 in the peak of 3 (apparent efficiency for 3 is higher than correct efficiency) IWIRAD 2005

  6. Magnitude of coincidence-summing effects • Enhanced in high efficiency measurement conditions => more important in present day measurements (tendency to use high efficiency) • Depend on the detailed decay scheme of the nuclide (peak energy, probability of emission of other photons in cascade, energy of the cascading photons) => nuclide dependent efficiency • Depend on the geometry (including surrounding materials), matrix => Difficult to evaluate: nuclear data + radiation transport IWIRAD 2005

  7. 3. GESPECOR • GERMANIUM SPECTROSCOPY CORRECTION FACTORS, authors Sima, Arnold, Dovlete Realistic Monte Carlo calculation of: - self-attenuation - coincidence-summing corrections - efficiency (including non-uniform activity distribution) IWIRAD 2005

  8. GESPECOR: coincidence-summing • Nuclear data: - sources: NUCLEIDE, ENSDF (Oct. 2004) - 200 nuclides, 250 records - completely automatic evaluation - arbitrary decay scheme - based on graph theory - better than Monte Carlo simulation of the decay scheme - without the limitations of the matrix formalism - user friendly interfaces IWIRAD 2005

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  11. GESPECOR: coincidence-summing • Radiation transport: - realistic Monte Carlo simulation - powerful variance reduction techniques - detailed detector description (including a complex structure of the dead layer) - detailed description of the sample (geometry, matrix) and surrounding materials • User friendly interfaces IWIRAD 2005

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  15. GESPECOR: coincidence-summingWell-type HPGe detector (PTB, Braunschweig) • Higher order effects • Count-rate reduction: 6 (1275 keV), 7.5 (511 keV) • Good agreement with exp. (5%)

  16. GESPECOR: coincidence-summingCorrected efficiency vs. mono-gamma efficiency (well-type HPGe detector)

  17. Corrections factors for the main peaks required for activity determination, but: • All features of the spectra should be correctly described (including small peaks and pure sum peaks) - peak interference - nuclide identification problems • Present day tendency: completely automatic analysis of spectra => requires improvement [Arnold, Blaauw, Fazinic, Kolotov, Nucl. Instrum. Meth. A 536 (2005) 196 ] IWIRAD 2005

  18. GESPECOR: coincidence-summingSum peaks with X-rays (n-type HPGe) • Ba-133 point source • Corrections in good agreement with experimental data (PTB)

  19. GESPECOR: coincidence-summingSum peaks with X-rays (n-type HPGe) • Ba-133 point source • Corrections in good agreement with experimental data (PTB)

  20. 4. Summary and conclusions • Coincidence-summing effects enhanced in present day measurements • All features present in the spectra should be properly described • GESPECOR is able to provide correction factors in agreement with experimental values (5% simple decay schemes, 10-15% complex decay schemes, with important higher order corrections) • High quality nuclear data required, including the covariance matrix (not yet available) to satisfy the ever increasing quality requirements. IWIRAD 2005

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