Octavian Sima Physics Department Bucharest University 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 - examples Summary and conclusions IWIRAD 2005

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 IEC 973 (1989) – Tests of Ge detectors IEC 1151 (1992) – Amplifiers and preamplifiers for detectors of ionizing radiation IEC 1342 (1995) – Multichannel analysers IWIRAD 2005

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 Les Annexes (A-E) sont donees uniquement a titre d’informaion IWIRAD 2005

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

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

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

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

GESPECOR: coincidence-summing Corrected efficiency vs GESPECOR: coincidence-summing Corrected efficiency vs. mono-gamma efficiency (well-type HPGe detector)

- nuclide identification problems 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

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

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

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