14-12nov_gattinoni_software_genie_isocs_labsocs (1).pdf
TRANSCRIPT
-
Version 3.2
Cascade Summing
Correction
Gamma Spectroscopy Software Solutions
ISOCS - LabSOCS Version 4.2
Monica Gattinoni
-
Summing Effects Definition
Random Summing loss of observable peak area as a function increasing count rate independent of energy, sample-to-detector distance, number of
nuclides in the sample correctable with the use of a pulser or a stationary reference
source Cascade Summing (True Coincidence Summing)
loss or gain of observable peak area as a function of nuclide decay scheme and geometry
independent of count rate different effect for different gamma energies of even the same
nuclide
-
Distance Result, 22% Detector
Example of coincidence summing effect for some of the Eu-152 gamma lines as a function of sample - detector distance using a small 22% relative efficiency detector. Note the almost 50% loss of area for peak 244 keV at
close distances.0 5 10 15
0.5
1
1.5
Source - Detector Distance (cm)
Rat
io o
f Obs
erve
d vs
. Cor
rect
Pea
k A
rea
244 keV
1085 keV
1112 keV
-
Simple Coincidence Theory
With no coincidence, the rate of pulses for peak1 is n = Ap11where A = activity, p1 = emission probability of1, and 1 = peak efficiency at E1
With coincidence, the rate of pulses in peak 1 isn* = Ap11-Ap11t2where t2 is the probability of observing a count due to 2 emitted at energy E2 anywhere in the spectrum, i.e. the total efficiency at energy E2.
The correction is C = n/n* = 1/(1-t2) Need to calibrate for total efficiency, or a
combination of peak efficiency and peak-to-total efficiency, which can be used to calculate the total efficiency.
1
2
Co-60
Ni-60
-
Total efficiency vs. Peak efficiency
Total efficiency: ratio of all counts in the spectrum to the gamma rays emitted by the source
Peak efficiency: ratio of all counts in the photopeak(at the emission energy) to the gamma rays emitted by the source.
P/T ratio is the Peak Efficiency divided by the Total Efficiency.
0 100 200 300 400 500 60020
30
50
100
200
300
500
1,000
Total efficiency
Peak efficiency
-
Peak-to-Total Calibration
The inherent P/T-ratio for all practical purposes, does not depend on
the source-to-detector distance it has been shown that for HPGe detectors up
to about 80% relative efficiency the use of the intrinsic P/T-calibration during the integration of the coincidence correction factor produces sufficiently accurate results.
-
P/T ratio is essentially independent of sample position relative to the detector
7
6
5
4
3
1 2
1 2 3 4 5 6 7
-2.2
-2.0
-1.8
-1.6
-1.4
-1.2
-1.0
-0.8
Model: ConstantChi 2 = 0.00303a-1.614
Model: ConstantChi 2 = 0.00103a-1.224
Mapping of P/T-ratio around detector(no separation)
Zn Mn
ln(P
/T)
Position of point around end cup
-
Empirical Peak -to-Total Curve
100 1000
-2,0
-1,8
-1,6
-1,4
-1,2
-1,0
-0,8
-0,6
-0,4
-0,2
20% Canberra, 1997
18% ORTEC, 1995
20% Canberra, 2000
P/T
Rat
io (
Ln)
Energy, keV
-
Cascade Summing effects
Efficiency calibration is also effected
-
Br-82, Sand Matrix, 15% detector
0.85
0.9
0.95
1
1.05
1.1
1.15
0 500 1000 1500 2000Energy (keV)
Rat
io to
Cor
rect
Act
ivity
Corrected Activity
Uncorrected Activity
-
Coincidence Correction for Voluminous Sources
The inherent P/T-ratio is a constant value (geometry independent):
But our sample has a certain geometry, so the peak efficiency is different We use LABSOCS to calculate for us the
PEAK EFFICIENCY for the used geometry Based on the above formula, the
TOTAL efficiency can next be calculated as follows:
(E)Constant (E) Efficiency Total
(E) EfficiencyPeak =
(E) Efficiency Total(E)Constant
(E) EfficiencyPeak =
-
Coincidence Correction forVoluminous Sources
divide source into 2n voxels place point source into each voxel in
random location compute efficiency at that point in space divide by inherent P/T ratio calculate the coincidence correction
factor do this for all voxels and totalize repeat with 2n+1 voxels continue doubling until no further
change in coincidence correction factor repeat for all energies and sources
source volume
generic attenuators 1 & 2
sample container
source attenuation correction pathway
collimator attenuation correction pathways
collimator
detector
point sources
-
Conclusion
Approximate detector characterization is acceptable to use for cascade summing corrections when the detector specific characterization is not available, at least above about 120 keV.
Genie 2000 (S501C) will be shipped with a selected range of detector characterizations, enabling the effectiveCoincidence Summing Correction for the vast majority of cases.
-
Cascade Summing Correction
CascadeSummingCorrection
P/TCalibration
GeometryDescription
NID Results
CorrectedNID
Results
-
P/T (Peak to Total) Calibration
P/T calibration curve
241Am
109Cd
54Mn
137Cs
113Sn
65Zn
-
P/T (Peak to Total) Calibration
-
Genie 2000
Pre loaded P/T calibrations per detector type. Either do a detector specific P/T calibration
Or use one of the pre-loaded files
-
Geometry Description
GeometryComposer
GeometryDescription
(*.GEO)
-
Geometry Composer
-
Geometry Composer
-
Cascade Summing Correction
1. Perform P/T Calibration (only once for eachdetector) or use a pre-loaded one.
2. Define counting geometry and select similardetector from supplied LabSOCS templates
3. Perform Cascade Summing Correctionduring NID
-
Cascade Summing Correction
-
Nuclide Id Energy Yield Activity Activity Coinc
Name Confidence (keV) (%) (Bq /Filt) Uncertainty Corr
K-40 0.946 1460.81* 10.67 1.037731E+00 6.206464E-01 miss
Co-60 0.947 1173.22* 100.00 9.617665E+00 3.544436E-01 0.949
1332.49* 100.00 9.375374E+00 3.637913E-01 0.946
Se-75 0.982 96.73* 3.41 1.564261E+01 1.424260E+00 free
121.11* 16.70 1.444366E+01 7.741458E-01 0.909
136.00* 59.20 1.326770E+01 7.399303E-01 0.907
198.60* 1.45 1.772982E+01 3.722104E+00 0.869
264.65* 59.80 1.353332E+01 6.656023E-01 0.901
279.53* 25.20 1.414516E+01 7.395598E-01 0.930
303.91 1.32
400.65* 11.40 2.288417E+01 1.124830E+00 1.531
Kr-85 0.972 513.99* 0.43 1.820692E+03 5.812067E+01 miss
Ba-133 0.949 79.62 2.55
81.00* 33.00 5.994030E+00 5.042487E-01 0.912
276.40* 6.90 5.584701E+00 6.266892E-01 0.931
302.84* 17.80 6.196358E+00 5.741855E-01 0.962
356.01* 60.00 5.427056E+00 3.817154E-01 0.966
free = No coincidence correction required.
miss = Nuclide energy was not found in the coincidence library.
-
Distance Effect
To correct/avoid for coincidence summing you could move the sample further away from the detector.
If you move a 5 cm diameter x 1 cm high disk source from being on the end cap to 15 cm away to eliminate true coincidence effects the MDA will increase by a factor 22.
To reach the same MDA you are able to achieve at the end cap you must count the sample at 15 cm for 500 times longer!
-
Real examples, pointsource
XTRa, GX4018, Pointsource Pointsource at contact
Co-60: 21% correction
Pointsource at 2 cm Co-60: 8% correction
Pointsource at 5 cm Co-60: 3% correction
-
Real examples, filter paper
XTRa, GX4018, filter paper Filter at contact
Co-60: 17,5% correction
Filter at 2 cm Co-60: 7% correction
Filter at 5 cm Co-60: 3% correction
-
Real examples, Beaker
XTRa, GX4018, Beaker Beaker at contact
Co-60: 7,5% correction
Beaker at 2 cm Co-60: 3,5% correction
Beaker at 5 cm Co-60: 1,85% correction
-
Overview
XTRa, GX4018, b01166, Co-60, % loss
Pointsource Filter Beaker0 cm 21 17,5 7,52 cm 8 7 3,55 cm 3 3 1,85
-
NEW Cascade Summing v3.2Total efficiency automatically calculated
Now TE can be calculated internally [P/T method still retained].
Using a characterizeddetector the Peak-to-Total calibration is no longer needed
Total Efficiency algorithms include corrections for build-up.
Calibration sources are no longer required in order to take advantage of the Genie2Ks cascade summing corrections.
CSC results are better
-
NEW Cascade Summing v3.2Total efficiency automatically calculated
-
NEW Cascade Summing v3.2
Correcting for gamma-gamma, X ray-and positron annihilation-gamma summing effects
Expansion of the library to include 200 nuclides (over 2050 lines).
-
NEW Cascade Summing v3.2Nuclear Data Automatically
extracted from ENSDF
-
Measured Activity of a filter paper on the detector endcap
without and with Canberra CSC
-
Cascade Summing Correctionwith Characterized Detector
-
Other LabSOCS Benefits
-
When calibration source is different density then sample
-
Sample is different Z than standard
-
3D Geometry Composer
-
LabSOCS and Traditional Efficiency Calibration agreement
-
Custom General Purpose Beaker Editor
-
Lab-ISOCS IUE for automated Sensitivity and uncertainty analyses
-
Lab-ISOCS IUE for automated Sensitivity and uncertainty analyses
-
ISOCSIIn Situ Object Counting System
-
ISOCS Application Example
Geometry Composer :
Characterized detector
User-selected collimator
H-Beam with external contamination