True Coincidence Summing Correction in Gamma Spectroscopy

More documents

Recommendations

Info

1.3 Gamma-Ray Spectroscopy with Semiconductor Detector For a detector serving as a gamma-ray spectrometer, it must carry out two distinct functions; i.e. first it must act as a conversion medium with reasonable probability of gamma ray interaction yielding one or more fast primary electrons; second, it must function as a conventional detector for secondary electrons. The requirement of full absorption of the secondary electron rules out gas-filled detectors for the spectroscopy of gamma rays, other than those with very low energy. The penetration distance of a 1 MeV electron in standard temperature and pressure (STP) gases is several meters, so that detectors of any practical size can never come close to absorbing all the secondary electron energy. For the measurement of gamma rays above several hundred keV, there are two detector categories of major importance, inorganic scintillators as NaI(Tl) and semiconductor detectors. The scintillators have the advantage of availability in large size and high density which can result in high interaction probabilities for gamma-rays. Due to the high atomic number of iodine, a large number of all interactions will result in complete absorption of gamma-ray energy, so the photo fraction will be high. The energy resolution of scintillators is poor. Figure-1.1 shows comparative spectra with germanium and shows that it is better choice for separation of closely spaced gamma energies. The typical energy resolution of a good germanium system is few tenths of a percent compared to 5-10 % for sodium iodide. The smaller size available and the lower atomic number of germanium contribute to give photopeak efficiencies an order of magnitude lower in typical cases. Moreover the photofractions are low and thus the quanta in the pulse height spectra are more of a problem. On the other hand, the good resolution of the semiconductor detectors aids in the detection of weak sources of discrete energies when superimposed on a broad continuum. 3
Figure 1.1 Comparative pulse height spectra recorded using NaI and Ge(Li) [1] 1.4 High Purity Germanium Detector 1.4.1 Introduction The semiconductor materials are good for the electron-hole pair collection within the detector, this must be done within a reasonably short time. Moreover there must be no traps which can prevent them reaching the collecting contacts. Trapping centres can be due to • Impurities within the semiconductor lattice • Interstitial atoms and vacancies within the lattice due to structural defects • Interstitial atoms caused by radiation damage This implies that the detector material should be of high purity and nearly perfect crystalline state. 4
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: the photopeak area is related to el
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 and 48: ∫ ∫ ε r) ε t ( r) dV ( r) dV
Page 49 and 50: For equation (3.8); N p,g = measure
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
show all

True Coincidence Summing Correction in Gamma Spectroscopy

Create successful ePaper yourself

Delete template?

Save as template?