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textbook:nrctextbook:chapter8 [2025-04-22 10:41]
Merja Herzig 		textbook:nrctextbook:chapter8 [2025-09-01 13:46] (current)
Merja Herzig
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 ;;# ;;#
  
-{{:textbook:nrctextbook:effect_of_counting_geometry_on_radiation_detection_fig_8_1.png?400|}} 
  
 +{{:textbook:nrctextbook:effect_of_counting_geometry_on_radiation_detection_of_a_point_source_light.png?200 |}}
 Figure VIII.1. Effect of counting geometry on radiation detection of a point source. Figure VIII.1. Effect of counting geometry on radiation detection of a point source.
  
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-In practice the situation is more complicated since the sources are seldom point sources. As a rule the geometry factor is the higher the closer is the source to the detector. To improve geometry in [[textbook:nrctextbook:chapter9|gamma spectrometry]] well-type detectors, instead of planar, are used. In these the source is placed inside a hole in the detector and a larger fraction of gamma rays are thus detected. The best geometry in obtained in [[textbook:nrctextbook:chapter12|liquid scintillation counting]] where the [[textbook:nrctextbook:chapter4|radionuclide]] is uniformly distributed in liquid [[textbook:nrctextbook:chapter12#scintillator_molecule|scintillation cocktail]] and in principal all [[textbook:nrctextbook:chapter5#beta_particle|beta]] and [[textbook:nrctextbook:chapter5#alpha_particle|balpha particles]] can lead to formation of light pulses when exciting [[textbook:nrctextbook:chapter12#scintillator_molecule|scintillator molecules]] are surrounding them in all directions.+In practice the situation is more complicated since the sources are seldom point sources. As a rule the geometry factor is the higher the closer is the source to the detector. To improve geometry in [[textbook:nrctextbook:chapter9|gamma spectrometry]] well-type detectors, instead of planar, are used. In these the source is placed inside a hole in the detector and a larger fraction of gamma rays are thus detected. The best geometry in obtained in [[textbook:nrctextbook:chapter12|liquid scintillation counting]] where the [[textbook:nrctextbook:chapter4|radionuclide]] is uniformly distributed in liquid [[textbook:nrctextbook:chapter12#scintillator_molecule|scintillation cocktail]] and in principal all [[textbook:nrctextbook:chapter5#beta_particle|beta]] and [[textbook:nrctextbook:chapter5#alpha_particle|alpha particles]] can lead to formation of light pulses when exciting [[textbook:nrctextbook:chapter12#scintillator_molecule|scintillator molecules]] are surrounding them in all directions.
 ### ###
  
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-{{:textbook:nrctextbook:observed_count_rate_as_a_function_of_count_rate_with_deadtime_fig_7_2.png|}}+{{:textbook:nrctextbook:observed_count_rate_r_as_a_function_of_count_rate_with_dead_time.png?400 |}}
  
 Figure VIII.2. Observed count rate (R) as a function of count rate taking into account 10 µs dead-time of the detector. Figure VIII.2. Observed count rate (R) as a function of count rate taking into account 10 µs dead-time of the detector.
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-{{:textbook:nrctextbook:gamma_spec_of_137cs_solid_scintillation_fig_8_3.png|}}+{{:textbook:nrctextbook:gamma_spectrum_of_137cs_measured_with_a_solid_scintillation_detector.png?400 |}}
  
 Figure VIII.3. Gamma spectrum of <sup>137</sup>Cs measured with a solid scintillation detector. Figure VIII.3. Gamma spectrum of <sup>137</sup>Cs measured with a solid scintillation detector.
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   * A single channel analyzer (SCA) counts only pulses at a defined height range. As described above, selection of pulse height range is accomplished with voltage discriminators, lower and upper. In addition, there is a pulse counter that sums all pulses coming to the discriminator window. For example, single channel can be set to count only pulses with heights between 50 mV and 150 mV, i.e. pulses that would go channels 50-150 in the multichannel analyzer, presuming same settings. Single-channel analyzer is used to measure only one [[textbook:nrctextbook:chapter4|radionuclide]] at the time. The discriminators are set by measuring the spectrum of the desired radionuclide by using a narrow discriminator window at increasing mV range. Plotting the counts at increasing mV results in the formation of an energy spectrum. The measurement window is set by measuring the spectrum of the desired radionuclide and selecting from the spectrum the lower and upper discriminator voltage values so that the pulses from the [[textbook:nrctextbook:chapter9#photopeak|photopeak]] is between them. Single channel mode is typically used in gamma counters with [[textbook:nrctextbook:chapter9#solid_scintillators|solid scintillation detectors]].   * A single channel analyzer (SCA) counts only pulses at a defined height range. As described above, selection of pulse height range is accomplished with voltage discriminators, lower and upper. In addition, there is a pulse counter that sums all pulses coming to the discriminator window. For example, single channel can be set to count only pulses with heights between 50 mV and 150 mV, i.e. pulses that would go channels 50-150 in the multichannel analyzer, presuming same settings. Single-channel analyzer is used to measure only one [[textbook:nrctextbook:chapter4|radionuclide]] at the time. The discriminators are set by measuring the spectrum of the desired radionuclide by using a narrow discriminator window at increasing mV range. Plotting the counts at increasing mV results in the formation of an energy spectrum. The measurement window is set by measuring the spectrum of the desired radionuclide and selecting from the spectrum the lower and upper discriminator voltage values so that the pulses from the [[textbook:nrctextbook:chapter9#photopeak|photopeak]] is between them. Single channel mode is typically used in gamma counters with [[textbook:nrctextbook:chapter9#solid_scintillators|solid scintillation detectors]].
  
-{{:textbook:nrctextbook:components_and_scheme_of_radiation_measurement_equipment_systems_fig_8_4.png|}}+{{:textbook:nrctextbook:components_and_scheme_of_radiation_measurement_equipment_systems.png|}}
  
 Figure VIII.4. Components and scheme of radiation measurement equipment systems. PMT is [[textbook:nrctextbook:chapter9#photomultiplier_tube|photomultiplier tube]]. Figure VIII.4. Components and scheme of radiation measurement equipment systems. PMT is [[textbook:nrctextbook:chapter9#photomultiplier_tube|photomultiplier tube]].
  
 {{anchor:energy_resolution}}  {{anchor:energy_resolution}} 
 +{{anchor:fwhm_full_width_at_half_maximum}} 
 ===== 8.4. Energy resolution ===== ===== 8.4. Energy resolution =====
  
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-{{:textbook:nrctextbook:energy_resolution_of_spectrum_peak_fig_7_5.png?400|}}+{{:textbook:nrctextbook:energy_resolution_of_spectrum_peak.png?400|}}
  
 Figure VIII.5. Energy resolution of spectrum peak. Figure VIII.5. Energy resolution of spectrum peak.
textbook/nrctextbook/chapter8.1745311265.txt.gz · Last modified: 2025-04-22 10:41 by Merja Herzig

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