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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

Coincidence-summing in Gamma-ray spectrometry.IEC 1452 StandardGESPECOR software

Octavian Sima

Physics Department

Bucharest University

IWIRAD 2005

overview
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
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

slide4

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

2 coincidence summing effects
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
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
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
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

gespecor coincidence summing11
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

gespecor coincidence summing well type hpge detector ptb braunschweig
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%)
gespecor coincidence summing corrected efficiency vs mono gamma efficiency well type hpge detector
GESPECOR: coincidence-summingCorrected efficiency vs. mono-gamma efficiency (well-type HPGe detector)
slide17
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
GESPECOR: coincidence-summingSum 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 hpge19
GESPECOR: coincidence-summingSum peaks with X-rays (n-type HPGe)
  • Ba-133 point source
  • Corrections in good agreement with experimental data (PTB)
4 summary and conclusions
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