1. 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

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
IEC 973 (1989) – Tests of Ge detectors
IEC 1151 (1992) – Amplifiers and preamplifiers for detectors of ionizing radiation
IEC 1342 (1995) – Multichannel analysers
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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
Les Annexes (A-E) sont donees uniquement a titre d’informaion
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
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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
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15. 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%)

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

17. - 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

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

19. GESPECOR: coincidence-summing Sum 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