Events by LUKA VIDMAR Treasurer of BEST BEST PARTNERS ROUND TABLE 26 January 2007 Turin, Italy.
10 nov Vidmar Efficiency transfer
Transcript of 10 nov Vidmar Efficiency transfer
Tim Vidmar
SCK•CEN, Belgian Nuclear Research Centre
Workshop “Metodi Avanzati di spettrometria gamma”
Milan, 10-12 November 2010
Efficiency Transfer
Milan 2010
#2 / 8
T. Vidmar (Belgium)
Introduction
� Samples may vary in size, composition and density
� Preparation of standards time consuming and costly
� Can we use a computational approach?
� Efficiency transfer – “transfer” of the efficiency of a
standard to another sample
Milan 2010
#3 / 8
T. Vidmar (Belgium)
Introduction
� Standards still required - but only a few!
� The efficiency of the measured sample is calculated
� The measured sample can differ from the standard in:
� Size – geometry correction
� Density – density correction
� Composition
� Any given combination of these
� Calculation can only be done with a computer
� Model of the detector and the sample are required
Milan 2010
#4 / 8
T. Vidmar (Belgium)
Moens theorem
� Virtual peak-to-total ratio independent of the sample for a given
gamma-ray energy
� Virtual efficiencies do not take scattering into account
� Virtual peak efficiency equivalent to the usual full-energy-peak
efficiency
� Virtual total efficiency can only be calculated (except for a point
source)
� P1/T1 = P2/T2 for two different samples 1 and 2
Milan 2010
#5 / 8
T. Vidmar (Belgium)
Moens theorem
� P/T = (τ+κσ)/µ
� τ = photo-effect absorption coefficient
� σ = Compton absorption coefficient
� µ = Total absorption coefficient
� κ κ = percentage of Compton scattered gamma-rays which eventually end
up in the full-energy peak (do not escape)
� κ can be shown to be independent of the source position
� T.Vidmar, A. Likar On the invariability of the total-to-peakratio
in gamma-ray spectrometry. Applied Radiation and Isotopes 60
(2004) 191–195
� Moens theorem not valid for planar detectors!
Milan 2010
#6 / 8
T. Vidmar (Belgium)
The Method
� P2 / T2 = P1 / T1 � P2 = P1 ( T2 / T1 )
� P1 measured, Reference sample (calibrated standard)
� T2 and T1 calculated
� P2 efficiency for the desired (analyzed) sample
� In the calculated ratio (T2/T1) many inaccuracies of the detector
model cancel out!
� Detector data can be taken from the manufacturers sheet
� Simultaneous “correction” for geometry and self absorption
� Alternative: P2 = P1 (ε2/ε1)
� ε2, ε1 full-energy-peak efficiencies � Monte Carlo simulation
Milan 2010
#7 / 8
T. Vidmar (Belgium)
Virtual Total Efficiency
Absorption:
F = exp(-µss) exp(-µww) …
Interaction:
R = 1-exp(-µGeL)
Registration:
pi = Fi Ri
Efficiency:
T = (1/N) Σ pi
Milan 2010
#8 / 8
T. Vidmar (Belgium)
Study
� M-C. Lepy et al., EUROMET Action 428: Transfer of Ge detector efficiency
calibration from point source geometry to other sources
� Various approaches
� Direct Monte Carlo with and without optimization
� Efficiency transfer with Monte Carlo efficiencies
� Efficiency transfer with the Moens method
� Semi-empirical methods
� Point-to-point, point-to-extended and extended-to-extended source transfers
� Efficiency transfer found to be much more consistent and reliable than direct
calculation
� Transfer with peak efficiencies (involves Monte Carlo calculations) best
� Accuracy sufficient for environmental measurements, especially for self-
absorption correction
Milan 2010
#9 / 8
T. Vidmar (Belgium)
The Originators
� Moens, L., De Donder, J., Xi-lei, L., De Corte, F., De
Wispelaere, A., Simonits, A., Hoste, J., 1981. Calculation of the
absolute peak efficiency of gamma-ray detectors for different
counting geometries. Nuclear Instruments and Methods in
Physics Research, 187, 451-472.
� Point-source reference measurements
� Sensitivity study
� Method very sensitive to the detector diameter!
� Otherwise quite robust
� Sensitivity increases with decreasing energy
Tim Vidmar
SCK•CEN, Belgian Nuclear Research Centre
Workshop “Metodi Avanzati di spettrometria gamma”
Milan, 10-12 November 2010
Efficiency Transfer –
Experimental Verification
Milan 2010
#11 / 8
T. Vidmar (Belgium)
Study
� Water solution samples with known activities: Am-241, Cd-109,
Ce-139, Sn-113, Co-57, Cr-51, Sr-85, Co-60 and Y-88
� Point source measurements
� Transfer from point source and between different extended
samples
� Efficiency transfer between extended sources.
Tim Vidmar, Branko Vodenik, Marijan Nečemer, Applied
Radiation and Isotopes, 68 (2010) 2352–2354
Milan 2010
#12 / 8
T. Vidmar (Belgium)
Standard solutions
39.4111387.2I
37.390240.9G
19.990128.3F
10.19065.2E
19.36055.5D
11.76033.6C
4.96014.0B
5.05010.0A
h [mm]d [mm]m [g]Sample
Milan 2010
#13 / 8
T. Vidmar (Belgium)
Detector Data
AlHousing material
1Housing thickness
5Crystal-to-window distance
AlWindow material
1Window thickness
80Window diameter
45Central cavity depth
10Central cavity diameter
1Side dead layer thickness
1Top dead layer thickness
0Crystal rounding (bulletization)
58.8Crystal length (including the top dead layer)
60.5Crystal diameter (including the side dead layer)
GeCrystal material
pCrystal type
Value Parameter
Milan 2010
#14 / 8
T. Vidmar (Belgium)
Point source measurements
Milan 2010
#15 / 8
T. Vidmar (Belgium)
Transfer from point source
7.25.78.97.29.09.18.67.31836
5.65.67.28.07.47.86.25.91333
5.74.15.44.66.47.87.24.91173
6.65.99.87.89.011.910.28.1898
7.16.68.38.69.710.510.28.9662
8.98.610.710.911.312.611.811.0392
8.37.89.29.29.210.810.58.9320
15.112.714.615.015.917.416.614.2166
17.016.018.018.018.019.519.017.2122
11.19.911.314.512.812.215.112.788
10.08.08.811.29.08.811.25.560
IGFEDCBAE [keV]
Milan 2010
#16 / 8
T. Vidmar (Belgium)
Transfer between extended samples
1.2-2.91.6-1.6-0.10.51.11836
0.0-1.5-0.80.6-0.31.50.31333
1.5-1.20.8-1.7-1.30.52.21173
0.6-3.61.9-1.1-2.61.61.9898
0.6-1.6-0.3-1.0-0.80.21.3662
0.3-2.0-0.2-0.3-1.20.70.7392
0.5-1.20.0-0.1-1.40.31.4320
2.1-1.6-0.3-0.8-1.30.72.1166
0.8-1.70.1-0.1-1.20.41.5122
1.0-1.2-2.81.50.5-2.52.188
2.0-0.6-2.21.90.2-2.25.460
I/GG/FF/EE/DD/CC/BB/AE [keV]
Tim Vidmar
SCK•CEN, Belgian Nuclear Research Centre
Workshop “Metodi Avanzati di spettrometria gamma”
Milan, 10-12 November 2010
Efficiency Transfer –
Computer Codes
Milan 2010
#18 / 8
T. Vidmar (Belgium)
General purpose packages
� Written for large experiments in particle physics, medical
physics, shielding applications, criticality calculations, etc
� Mostly require programming, quite complex to use
� Track various kinds of particles
� Perform full Monte Carlo calculations
� Can handle arbitrary geometries – unusual objects
� Run times between minutes and hours
� Variance reduction techniques available
Milan 2010
#19 / 8
T. Vidmar (Belgium)
General purpose packages
� MCNP – 40 years of development, no programming (input decks only
� GEANT3 - Fortran, geometry description in terms of volumes, no longer developed
� GEANT4 – C++, general purpose, developed at CERN, no input decks
� PENELOPE – Fortran, e- and gamma, very precise interaction treatment, limited programming required
� EGS – Mortran, popular in medical community
� FLUKA – developed at CERN, Fortran, rather recent
Milan 2010
#20 / 8
T. Vidmar (Belgium)
Specialized codes
� Specifically aimed at gamma-ray spectrometry
� No programming, user friendly interfaces
� Various approaches
� Full Monte Carlo (spectra available)
� Virtual total efficiencies – Effective solid angle
� Much quicker than general packages
� Limited geometry
� Not all of them (yet) integrated with major manufacturer’s
platforms
Milan 2010
#21 / 8
T. Vidmar (Belgium)
Specialized codes
� SOLANG – “grand daddy” of coincidence correction codes,
developed by the method’s originators
� GESPECOR – developed in the 90’s, commercial, widely used,
also by NMIs, constant improvements, all major detector and
sample types covered, abundant references, full Monte Carlo
� ETNA – Effective solid angle, well-type and cylindrical
detectors, Marinelli beakers
� DETEFF – Monte Carlo, special attention to low energies
� EFFTRAN – Effective solid angle, fast, limited to cylindrical
symmetry
� Your own code? – use XCOM material data!
Milan 2010
#22 / 8
T. Vidmar (Belgium)
Major manufacturers
� CANBERRA – ISOCS and LABSOCS
� All imaginable sample geometries and materials
� Detector characterization required
� Sufficient accuracy?
� ORTEC – ANGLE, part of GammaVision
� Fully integrated with the spectrum analysis
� Planar, coaxial and well-type detectors
� Cylindrical, rectangular and Marinelli samples
� Calculates effective solid angle
Milan 2010
#23 / 8
T. Vidmar (Belgium)
The choice is yours …
� Do I really need efficiency transfer?
� Am I willing to do some programming?
� Would I rather stick to major manufacturers’ products?
� Do I work with an (semi)-automated analysis?
� How well do I know my detectors?
� Is there not a simple, tested, one-fit-all solution?
Tim Vidmar
SCK•CEN, Belgian Nuclear Research Centre
Workshop “Metodi Avanzati di spettrometria gamma”
Milan, 10-12 November 2010
Efficiency Transfer –
Computer Codes II
Milan 2010
#25 / 8
T. Vidmar (Belgium)
Study of efficiency transfer codes
� Codes were compared to each other for a set of well defined
detector and sample geometries
� No reference to experimental data
� Testing Efficiency Transfer Codes for Equivalence.
T. Vidmar et al., Applied Radiation and Isotopes, 68 (2010)
355-359.
Milan 2010
#26 / 8
T. Vidmar (Belgium)
Codes and Modes
xxPENELOPE PENCYL
xxPENELOPE 2008
xxPENELOPE 2003
xxMCNPX
xxMCNP5
xxMCNP4C
xxGESPECOR 4.2
xxxGEANT 3.21
xxEGS4
xxETNA
xxEFFTRAN
xxxDETEFF 4.2
xxANGLE
GeneralSpecializedTEFEPE
Code TypeET ImplementationComputer Code
Milan 2010
#27 / 8
T. Vidmar (Belgium)
Detector models
AlAlHousing material
11Housing thickness
8080Housing length
55Crystal-to-window distance
BeAlWindow material
0.51Window thickness
8080Window diameter
4040Hole depth
1010Hole diameter
0.00031Dead layer thickness (top and side)
6060Crystal length (including the top dead layer)
6060Crystal diameter (including the side dead layer)
GeGeCrystal material
npCrystal type
Detector BDetector AParameter
Milan 2010
#28 / 8
T. Vidmar (Belgium)
Samples
0.00.01.00.0Container-to-detector-window distance
CelluloseQuartz-WaterSample material
3400.020Sample height
(including the container)
80900.060Sample diameter
(including the container)
FilterSoilPointReferenceParameter
Milan 2010
#29 / 8
T. Vidmar (Belgium)
Materials
C8H
91.050Plastics (polystyrene)
C6H
12O
60.200Cellulose
SiO2
1.400Quartz
H2O1.000Water
Be1.848Be
Al2.700Al
Ge5.323Ge
Chemical formulaDensityMaterial
Milan 2010
#30 / 8
T. Vidmar (Belgium)
Water sample, Detector B
Milan 2010
#31 / 8
T. Vidmar (Belgium)
Results – Standard Deviations
0.80.80.60.71.00.72000
0.90.80.50.51.10.71000
0.90.60.30.80.90.8500
0.80.60.60.60.70.7200
0.60.60.50.70.40.5120
0.50.80.70.90.40.680
0.51.00.90.90.50.660
0.80.90.50.90.90.545
1.22.51.420
Filter BFilter ASoil BSoil APoint BPoint AEnergy
Milan 2010
#32 / 8
T. Vidmar (Belgium)
Results – Maximum Deviations
1.31.40.91.51.91.92000
1.51.41.20.92.01.61000
1.51.10.51.71.91.4500
1.41.21.61.21.41.1200
1.11.21.61.80.80.9120
1.12.01.62.01.01.280
1.02.52.31.91.11.260
1.42.21.33.11.71.245
3.4-7.6-3.1-20
Filter BFilter ASoil BSoil APoint BPoint AEnergy