True Coincidence Summing Correction in Gamma Spectroscopy

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position will not have a significant impact on the final cascade summing correction factor 6 . The P/T calibration measurements can be performed using a series of individual point sources of nuclides that emit only one gamma ray located at a given source-detector distance since the P/T calibration curve is a property of the detector and not the sample geometry. Table 3.1 Measured Computed P/T ratios for detector 3 at different geometries Energy (keV) P/T ratio at 11cm Error (%) P/T ratio at 6cm Error (%) 59.6 0.506 0.612 0.517 0.612 88 0.816 0.690 0.829 1.239 121.97 0.779 0.158 0.797 0.22 391.46 0.336 0.323 0.352 0.513 661.67 0.244 0.256 0.267 0.172 835.19 0.237 0.419 0.246 0.373 1115.68 0.199 0.143 0.208 0.111 Knowing the P/T ratios for a detector and the total efficiency ε t at a given gamma ray energy and point inside a sample, the full peak efficiency ε p at these point can be computed according ε p ε t = (3.7) P / T 3.4 Cascade Correction Theory A discussion about the computation of true coincidence correction for voluminous sources can be based on the work of V.P. Kolotov et al 13 . Based on FEP (full energy peak) measurement, for a certain emitted gamma ray “g”, the activity of a radionuclide, can be written as follows. N p, g A = (3.8) ε . f g g 39
For equation (3.8); N p,g = measured full energy peak count rate of the gamma line g, ε g f g = full energy peak efficiency of the whole source, and =yield of the gamma line. As the voluminous source consists of “n” subsources of equal volumes. So the activity of the ith subsource is given by, A i N p, g = (3.9) e . f . n g g Each subsource ``i´´ contributes to the measured count rate that is given by, N ( p, g) i Ai f g. g, i = . ε (3.10) Here; A i ε g,I = activity of the ith subsource, and = full energy peak efficiency of the ith subsource. To determine partial count rate due to the subsource ´´i``, substitution for A i from Equation (3.9) results in, N ( p, g ) i ( N p, g . ε g, i ) = (3.11) ( ε . n) g If the peak count rate for each subsource is known, and the peak efficiencies and P/T ratios for each gamma line within a given subsource are assumed to be constant, then the coincidence correction (COI g,i ) for each subsource can be computed. Consequently the correction for the whole source is obtained by summation. N' p, g = n ∑ N p, g . ε g, i ε . n. COI i= 1 g g, i = N p, g ε . n g n ∑ ε g, i COI i= 1 g, i (3.12) Where, N′ p,g = peak count rate corrected for cascade summing or true coincidence effects. Hence, for the voluminous source, the overall true coincidence correction is, 40
Page 1 and 2: Universität Bremen Faculty of Envi
Page 3 and 4: 2.2 The Origin of Summing 19 2.3 Su
Page 5 and 6: Acknowledgements My recognition to
Page 7 and 8: List of Figures: Figure 1.1 - Compa
Page 9 and 10: List of Tables: Table 1.1 - Typical
Page 11 and 12: the photopeak area is related to el
Page 13 and 14: Figure 1.1 Comparative pulse height
Page 15 and 16: 1.4.2 Packing of the Detector HPGe
Page 17 and 18: Table 1.1 Typical FWHM values as a
Page 19 and 20: The gamma photons produce electron-
Page 21 and 22: Figure 1.7 Peak and background area
Page 23 and 24: • Absolute full-peak energy effic
Page 25 and 26: p c =1-e -2Rτ (1.6) R is the mean
Page 27 and 28: amplifier output pulses shapes are
Page 29 and 30: Figure 2.3 Simplified decay scheme
Page 31 and 32: Counts 5000 4000 3000 2000 1000 Eu-
Page 33 and 34: Figure 2.6 Ratio of count rates in
Page 35 and 36: participate in summing. However, ca
Page 37 and 38: Figure 2.8 The efficiency curve con
Page 39 and 40: The above discussion leads to the c
Page 41 and 42: The ratio n 2 /n’ 2 would be used
Page 43 and 44: • The larger Eu-152 factors for t
Page 45 and 46: As discussed in chapter 2, the emis
Page 47: ∫ ∫ ε r) ε t ( r) dV ( r) dV
Page 51 and 52: comprehensive spectrum analysis for
Page 53 and 54: Tentative Nuclide Identification An
Page 55 and 56: correction uses LabSOCS technology
Page 57 and 58: 4 Results, Validations and Discussi
Page 59 and 60: assumed to be constant for detector
Page 61 and 62: 4.2.3 Geometry Description The prop
Page 63 and 64: Table 4.4- Cascade correction facto
Page 65 and 66: Table 4.6- Cascade correction facto
Page 67 and 68: Figure 4.8 Comparison between the f
Page 69 and 70: 4.4 Validations and Discussion To v
Page 71 and 72: 0.900 0.850 0.800 0.750 0.700 0.650
Page 73 and 74: The sediment sample obtained from B
Page 75 and 76: Appendix A Detector 3: Marinelli be
Page 77 and 78: Detector 3: Pellets (1g/cm 3 ) 5 mm
Page 79 and 80: Nuclide Energy (keV) Detector 4: Ma
Page 81 and 82: Nuclide Energy (keV) Detector 4: Pe
Page 83 and 84: Detector 5: Marinelli beaker 0.5 L
Page 85 and 86: Detector 5: Pellets (1g/cm 3 ) Nucl
Page 87 and 88: Detector 6: Marinelli beaker Nuclid
Page 89 and 90: Detector 6: Pellets (1g/cm 3 ) 5 mm
Page 91 and 92: References [1] Radiation Detection

True Coincidence Summing Correction in Gamma Spectroscopy

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