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textbook:nrctextbook:chapter8 [2025-04-16 13:57]
Merja Herzig 		textbook:nrctextbook:chapter8 [2025-09-01 13:46] (current)
Merja Herzig
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 There are two principal means to measure radionuclide activities: radiometric and mass  There are two principal means to measure radionuclide activities: radiometric and mass 
-spectrometric. Radiometric methods are based on detection and measurement of radiation emitted by radionuclides whereas in mass spectrometric methods number of atoms are counted. The results of these methods, [[textbook:nrctextbook:chapter6#activity|activity]] (//A//) in case of radiometry and number of radioactive atoms (//N//) in mass spectrometry, can be can be converted to each other by the radioactive decay law equation+spectrometric. Radiometric methods are based on detection and measurement of radiation emitted by radionuclides whereas in [[textbook:nrctextbook:chapter8#mass_spectrometry|mass spectrometric methods]] number of atoms are counted. The results of these methods, [[textbook:nrctextbook:chapter6#activity|activity]] (//A//) in case of radiometry and number of radioactive atoms (//N//) in mass spectrometry, can be can be converted to each other by the radioactive decay law equation
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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.
  
 ### ###
-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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 ### ###
-If the sample contains several [[textbook:nrctextbook:chapter4|radionuclides]] and their individual activities are to be measured energy spectrometry is needed. [[textbook:nrctextbook:chapter9#semiconductor_detectors_gamma|Gamma spectrometers with semiconductor detectors]], having very good energy resolution, can differentiate tens of radionuclides from the same sample and their activities are measured from the areas of specific peaks belonging to each nuclide. Solid scintillation detectors can also be used for energy spectrometry but are seldom used for that due to their limited energy resolution. Gamma spectrometry is also used for radionuclide identification in  +If the sample contains several [[textbook:nrctextbook:chapter4|radionuclides]] and their individual activities are to be measured energy spectrometry is needed. [[textbook:nrctextbook:chapter9#semiconductor_detectors_gamma|Gamma spectrometers with semiconductor detectors]], having very good [[textbook:nrctextbook:chapter8#energy_resolution|energy resolution]], can differentiate tens of radionuclides from the same sample and their [[textbook:nrctextbook:chapter6#activity|activities]] are measured from the areas of specific peaks belonging to each nuclide. [[textbook:nrctextbook:chapter9#solid_scintillators|Solid scintillation detectors]] can also be used for energy spectrometry but are seldom used for that due to their limited [[textbook:nrctextbook:chapter8#energy_resolution|energy resolution]]. [[textbook:nrctextbook:chapter9|Gamma spectrometry]] is also used for radionuclide identification in which positions of peaks and their relative intensities are made use of. [[textbook:nrctextbook:chapter11#alpha_spectrometry|Alpha spectrometry]] with[[textbook:nrctextbook:chapter11#semiconductor_detectors_alpha|semiconductor detectors (alpha)]] is used to measure both activities of alpha emitters and their isotopic ratios, the latter bringing often valuable information, for example, on the source or origin of the alpha emitter. Alpha measurements, however, require radiochemical separations and typically only one element is measured at a time. Beta spectrometry is most often carried out by using a [[textbook:nrctextbook:chapter12|liquid scintillation counter]], but also with [[textbook:nrctextbook:chapter10#proportional_counter|proportional counter]]. Due to continuous nature of beta spectra, however, only one beta emitter is measured at a time. Sometimes it is possible to measure two beta emitters from the same samples if the energy difference of the two beta emissions is high enough.
-which positions of peaks and their relative intensities are made use of. Alpha spectrometry with semiconductor detectors is used to measure both activities of alpha emitters and their isotopic ratios, the latter bringing often valuable information, for example, on the source or origin of the alpha emitter. Alpha measurements, however, require radiochemical separations and typically only one element is measured at a time. Beta spectrometry is most often carried out by using a liquid scintillation counter, but also with proportional counter. Due to continuous nature of beta spectra,  +
-however, only one beta emitter is measured at a time. Sometimes it is possible to measure two beta emitters from the same samples if the energy difference of the two beta emissions is high enough.+
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 Radiation measurement equipment systems consist of the following components (Figure VIII.4): Radiation measurement equipment systems consist of the following components (Figure VIII.4):
  
-  * Detector, the function of which is to transform the energy of radiation into an electric pulse (gas ionization detectors and semiconductor detectors) or to a light pulse (scintillation detectors). Various detectors are discussed in later chapters in more detail.+  * Detector, the function of which is to transform the energy of radiation into an electric pulse ([[textbook:nrctextbook:chapter10|gas ionization detectors]] and [[textbook:nrctextbook:chapter9#semiconductor_detectors_gamma|semiconductor detectors for gamma]] and [[textbook:nrctextbook:chapter11|alpha]] radiation) or to a light pulse ([[textbook:nrctextbook:chapter12|liquid scintillation detectors]] and [[textbook:nrctextbook:chapter9#solid_scintillators|solid scintillators]] ). Various detectors are discussed in later chapters in more detail.
   * Voltage source which collects the initial electric pulses into electrodes.   * Voltage source which collects the initial electric pulses into electrodes.
   * Preamplifier which amplifies the weak pulses coming from semiconductor detectors to enable the pulse transfer through cables into the main amplifier.   * Preamplifier which amplifies the weak pulses coming from semiconductor detectors to enable the pulse transfer through cables into the main amplifier.
   * Main amplifier is called linear amplifier since its function is not only to increase the pulse height to a measureable one but also preserve the energy information. This is done by amplifying each initial pulse with the same factor so that the observed pulse heights are linearly related to the heights of the initial pulses coming from the detector and the preamplifier.   * Main amplifier is called linear amplifier since its function is not only to increase the pulse height to a measureable one but also preserve the energy information. This is done by amplifying each initial pulse with the same factor so that the observed pulse heights are linearly related to the heights of the initial pulses coming from the detector and the preamplifier.
-  * In scintillation detectors there is, instead of preamplifier and linear amplifier, a photomultiplier tube (PMT) which converts the light pulse into an electric pulse and amplifies the initial pulse into a measureable electric pulse.+  * In scintillation detectors there is, instead of preamplifier and linear amplifier, a [[textbook:nrctextbook:chapter9#photomultiplier_tube|photomultiplier tube]] (PMT) which converts the light pulse into an electric pulse and amplifies the initial pulse into a measurable electric pulse.
  
 ### ###
-After this there are two options depending on whether the equipment is used as a multichannel analyzer or as a single-channel analyzer. The former is used in energy spectrometry and the latter in pulse counting.+After this there are two options depending on whether the equipment is used as a [[textbook:nrctextbook:chapter8#multichannel_analyzer|multichannel analyzer]] or as a [[textbook:nrctextbook:chapter8#single_channel_analyzer|single-channel analyzer]]. The former is used in energy spectrometry and the latter in pulse counting.
 ### ###
 {{anchor:multichannel_analyzer}} {{anchor:multichannel_analyzer}}
  
-  * A multichannel analyzer (MCA) sorts the pulses into various channels depending on their pulse height which is proportional to the energy of the particle or ray. For example 1 mV pulse goes to channel 1, 12 mV pulse to channel 12 and 715 mV pulse to channel 715. This results in the formation of an energy spectrum. A multichannel analyzer may have even thousands of channels. Prior to sorting the pulses into channels the analog-to-digital converter (ADC) transforms the analogical pulses into digital form. +  * A multichannel analyzer (MCA) sorts the pulses into various channels depending on their pulse height which is proportional to the energy of the particle or ray. For example 1 mV pulse goes to channel 1, 12 mV pulse to channel 12 and 715 mV pulse to channel 715. This results in the formation of an energy spectrum. A multichannel analyzer may have even thousands of channels. Prior to sorting the pulses into channels the analog-to-digital converter (ADC) transforms the analogical pulses into digital form. {{anchor:single_channel_analyzer}} 
-  * 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 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 photopeak is between them. Single channel mode is typically used in gamma counters with 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 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 =====
  
 ### ###
 In energy spectrometry it is essential that the measurement system can differentiate different particle or ray energies as efficiently as possible. This is mostly dependent on the type of detector. The better the energy resolution the better the system can differentiate energies close to each other and the narrower are the observed peaks in a spectrum. Resolution (//R//) is expressed as the peak width at half of the height of peak maximum (FWHM = full width at half maximum) (Figure  In energy spectrometry it is essential that the measurement system can differentiate different particle or ray energies as efficiently as possible. This is mostly dependent on the type of detector. The better the energy resolution the better the system can differentiate energies close to each other and the narrower are the observed peaks in a spectrum. Resolution (//R//) is expressed as the peak width at half of the height of peak maximum (FWHM = full width at half maximum) (Figure 
-VIII.5). Instead of the absolute value the energy resolution can also expressed as the relative value //(ΔE/E)×100%//, where //E// is the energy of the peak maximum and //ΔE// is FWHM. For example, for <sup>137</sup>Cs the energy resolution of the 662 keV peak is typically 60 keV and the relative resolution value (60/662)×100% = 9%. For semiconductor gamma detectors, which are superior with respect to energy resolution compared to solid scintillation detectors the energy resolution is often expressed  +VIII.5). Instead of the absolute value the energy resolution can also expressed as the relative value //(ΔE/E)×100%//, where //E// is the energy of the peak maximum and //ΔE// is FWHM. For example, for <sup>137</sup>Cs the energy resolution of the 662 keV peak is typically 60 keV and the relative resolution value (60/662)×100% = 9%. For [[textbook:nrctextbook:chapter9#semiconductor_detectors_gamma|semiconductor gamma detectors]], which are superior with respect to energy resolution compared to [[textbook:nrctextbook:chapter9#solid_scintillators|solid scintillation detectors]] the energy resolution is often expressed as the FWHM of the <sup>60</sup>Co peak at 1332 keV. The energy resolution of semiconductor gamma detectors is clearly below 2 keV. Energy resolution is also dependent on the energy, the absolute values being better for low energy gamma rays, and therefore the resolution value should always refer to the energy for which is given. The energy resolution for 2 MeV gamma rays of germanium semiconductors is below 2 keV (0.1%), below 1.5 keV (0.15%) for 1 MeV rays and below 1 keV (0.2%) for 0.5 MeV rays.  For NaI(Tl) solid scintillation detector the corresponding values are about 100 keV (5%) for 2 MeV rays, 70 keV (7%) for 1 MeV rays and about 50 keV (10%) for 0.5 MeV rays. Thus the germanium detectors have about 50-times better resolution compared to the NaI(Tl) detectors. Silicon semiconductor alpha detectors have resolutions between 20-30 keV (0.4-0.6% for typical alpha energies of 4-7 MeV) which are about ten times lower than values obtainable with liquid scintillation counters.
-as the FWHM of the <sup>60</sup>Co peak at 1332 keV. The energy resolution of semiconductor gamma detectors is clearly below 2 keV. Energy resolution is also dependent on the energy, the absolute values being better for low energy gamma rays, and therefore the resolution value should always refer to the energy for which is given. The energy resolution for 2 MeV gamma rays of germanium semiconductors is below 2 keV (0.1%), below 1.5 keV (0.15%) for 1 MeV rays and below 1 keV (0.2%) for 0.5 MeV rays.  For NaI(Tl) solid scintillation detector the corresponding values are about  +
-100 keV (5%) for 2 MeV rays, 70 keV (7%) for 1 MeV rays and about 50 keV (10%) for 0.5 MeV rays. Thus the germanium detectors have about 50-times better resolution compared to the NaI(Tl) detectors. Silicon semiconductor alpha detectors have resolutions between 20-30 keV (0.4-0.6% for typical alpha energies of 4-7 MeV) which are about ten times lower than values obtainable with liquid scintillation counters.+
 ### ###
  
  
-{{: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.
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 1. Gas ionization detectors 1. Gas ionization detectors
-  * Ionisation chamber +  * [[textbook:nrctextbook:chapter10#ionization_chamber|Ionization chamber]] 
-  * Proportional counter +  * [[textbook:nrctextbook:chapter10#proportional_counter|Proportional counter]] 
-  * Geiger-Muller (GM) tube+  * [[textbook:nrctextbook:chapter10#gm_counter|Geiger-Muller (GM) tube]]
  
 2. Scintillation detectors 2. Scintillation detectors
-  * Liquid scintillation +  * [[textbook:nrctextbook:chapter12|Liquid scintillation]] 
-  * Solid scintillation detectors+  * [[textbook:nrctextbook:chapter9#solid_scintillators|Solid scintillation detectors]]
  
-3. Semiconductor detectors+3. Semiconductor detectors ([[textbook:nrctextbook:chapter11#semiconductor_detectors_alpha|semiconductor detectors for alpha spectrometry]] and [[textbook:nrctextbook:chapter9#semiconductor_detectors_gamma|semiconductor detector for gamma spectrometry]])
  
 ### ###
-**Alpha radiation** is most accurately measured with semiconductor detectors. Their background pulses are very low and their energy resolution is good, at 5 MeV energies even 15 keV. The energy resolution of liquid scintillation counting, another choice to measure alpha radiation, is about ten times poorer than that of semiconductor detectors. Sample preparation for liquid scintillation counting is, however, clearly less difficult since the sample is just dissolved in the liquid scintillation cocktail for measurement while for semiconductor detectors counting sources need to be prepared by electrodeposition or microcoprecipitation. Another benefit of liquid scintillation  +**[[textbook:nrctextbook:chapter5#alpha|Alpha radiation]]** is most accurately measured with [[textbook:nrctextbook:chapter11#semiconductor_detectors_alpha|semiconductor detectors]]. Their background pulses are very low and their [[textbook:nrctextbook:chapter8#energy_resolution|energy resolution]] is good, at 5 MeV energies even 15 keV. The energy resolution of [[textbook:nrctextbook:chapter12|liquid scintillation counting]], another choice to measure alpha radiation, is about ten times poorer than that of semiconductor detectors. Sample preparation for liquid scintillation counting is, however, clearly less difficult since the sample is just dissolved in the [[textbook:nrctextbook:chapter12#scintillator_molecule|liquid scintillation cocktail]] for measurement while for semiconductor detectors counting sources need to be prepared by electrodeposition or microcoprecipitation. Another benefit of liquid scintillation  
-counting is a very good, practically 100%, counting efficiency. In liquid scintillation counting the beta emitters present can cause problems by creating extra pulses to alpha peaks. In modern liquid scintillation counters this is overcome by alpha-beta discrimination system that differentiates alpha and beta pulses from each other and count them separately. Due to the poor energy resolution liquid +counting is a very good, practically 100%, [[textbook:nrctextbook:chapter8#counting_efficiency|counting efficiency]]. In liquid scintillation counting the beta emitters present can cause problems by creating extra pulses to alpha peaks. In modern liquid scintillation counters this is overcome by alpha-beta discrimination system that differentiates alpha and beta pulses from each other and count them separately. Due to the poor [[textbook:nrctextbook:chapter8#energy_resolution|energy resolution]] liquid 
 scintillation counting is not a proper method to determine the isotopic ratios of alpha emitters. For this purpose semiconductor detectors need to be used. scintillation counting is not a proper method to determine the isotopic ratios of alpha emitters. For this purpose semiconductor detectors need to be used.
 ### ###
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 ### ###
-For **beta radiation** the most often used method is liquid scintillation counting. It yields into high counting efficiencies and is suitable also for low energy beta radiation. Liquid scintillation counting also enables determination of beta spectra. Usually, however, due to the continuous nature of beta spectra, only one beta emitter can be measured at a time. Other options to measure beta radiation are the gas ionization detectors, GM tube and proportional counters, the latter of which can also  +For **[[textbook:nrctextbook:chapter5#beta|beta radiation]]** the most often used method is [[textbook:nrctextbook:chapter12|liquid scintillation counting]]. It yields into high [[textbook:nrctextbook:chapter8#counting_efficiency|counting efficiencies]] and is suitable also for low energy beta radiation. Liquid scintillation counting also enables determination of beta spectra. Usually, however, due to the continuous nature of beta spectra, only one beta emitter can be measured at a time. Other options to measure beta radiation are the [[textbook:nrctextbook:chapter10|gas ionization detectors]], [[textbook:nrctextbook:chapter10#gm_counter|GM tube]] and [[textbook:nrctextbook:chapter10#proportional_counter|proportional counters]], the latter of which can also produce beta spectra. The drawbacks of gas ionization detectors are more laborious counting source preparation, lower counting efficiency and the fact they cannot be easily used in measurement of beta emitters with the lowest energies, such as tritium. The benefit of gas ionization detectors is their clearly lower background compared to liquid scintillation counting and thus much lower detection limits are obtained.
-produce beta spectra. The drawbacks of gas ionization detectors are more laborious counting source preparation, lower counting efficiency and the fact they cannot be easily used in measurement of beta emitters with the lowest energies, such as tritium. The benefit of gas ionization detectors is their clearly lower background compared to liquid scintillation counting and thus much lower detection limits are obtained.+
 ### ###
  
  
 ### ###
-For the measurement of **gamma radiation** solid scintillation and semiconductor detectors are used. The benefit of solid scintillation detectors is their higher counting efficiency as the detectors can be produced in large sizes and they are often of well-type in which the sample is inside the detector.Solid scintillation detectors are usually utilized for gamma counting in single-channel mode. The benefit of semiconductor detectors is their superior energy resolution compared to solid scintillators and therefore they are typically used for gamma spectrometric measurements in radionuclide identifications and measurement of radionuclide activities from samples having several gamma-emitting nuclides.+For the measurement of **[[textbook:nrctextbook:chapter5#gamma|gamma radiation]]** [[textbook:nrctextbook:chapter9#solid_scintillators|solid scintillation]] and [[textbook:nrctextbook:chapter9#semiconductor_detectors_gamma|semiconductor detectors]] are used. The benefit of solid scintillation detectors is their higher [[textbook:nrctextbook:chapter8#counting_efficiency|counting efficiency]] as the [[textbook:nrctextbook:chapter8#detector|detectors]] can be produced in large sizes and they are often of well-type in which the sample is inside the detector. Solid scintillation detectors are usually utilized for gamma counting in single-channel mode. The benefit of semiconductor detectors is their superior [[textbook:nrctextbook:chapter8#energy_resolution|energy resolution]] compared to solid scintillators and therefore they are typically used for gamma spectrometric measurements in radionuclide identifications and measurement of radionuclide activities from samples having several gamma-emitting nuclides.
 ### ###
  
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-  * semiconductor detector(s) for gamma spectrometry for the determination of radionuclides from environmental and radioactive waste samples, for example +  * [[textbook:nrctextbook:chapter9#semiconductor_detectors_gamma|semiconductor detector(s) for gamma spectrometry]] for the determination of radionuclides from environmental and radioactive waste samples, for example 
-  * gamma counter(s) having a solid scintillation detector and a sample changer for the measurement of tracer gamma emitters used in model experiments +  * gamma counter(s) having a [[textbook:nrctextbook:chapter9#solid_scintillators|solid scintillation detector]] and a sample changer for the measurement of tracer gamma emitters used in model experiments 
-  * liquid scintillation counter(s) with alpha-beta discrimination for the measurement of tracer beta and alpha emitters as well as beta and alpha emitters separated from various samples+  * [[textbook:nrctextbook:chapter12|liquid scintillation counter(s)]] with alpha-beta discrimination for the measurement of tracer beta and alpha emitters as well as beta and alpha emitters separated from various samples
   * low background liquid scintillation counter(s) for the measurement of low beta activities   * low background liquid scintillation counter(s) for the measurement of low beta activities
-  * semiconductor alpha detector(s) for the measurement of alpha emitters separated from various samples +  * [[textbook:nrctextbook:chapter11#semiconductor_detectors_alpha|semiconductor alpha detector(s)]] for the measurement of alpha emitters separated from various samples 
-  * gas ionization detector(s) to measure low activity beta emitters separated from various samples+  *[[textbook:nrctextbook:chapter10| gas ionization detector(s)]] to measure low activity beta emitters separated from various samples 
 + 
 +{{anchor:mass_spectrometry}}
  
 ===== 8.6. Measurement of radionuclides with mass spectrometry ===== ===== 8.6. Measurement of radionuclides with mass spectrometry =====
  
 ### ###
-An alternative for radiometric methods for the determination of radionuclide activities is mass spectrometry. Most often inductively-coupled mass spectrometry (ICP-MS) is today used for this purpose. As mentioned, mass spectrometer counts atoms instead of radiation. This makes mass spectrometry particularly suitable for the measurement of long-lived radionuclides for which the detection limit of mass spectrometry is below those obtained by radiometric methods. For example,  +An alternative for radiometric methods for the determination of radionuclide [[textbook:nrctextbook:chapter6#activity|activities]] is mass spectrometry. Most often inductively-coupled mass spectrometry (ICP-MS) is today used for this purpose. As mentioned, mass spectrometer counts atoms instead of radiation. This makes mass spectrometry particularly suitable for the measurement of [[textbook:nrctextbook:chapter6#long_lived_radionuclides|long-lived radionuclides]] for which the detection limit of mass spectrometry is below those obtained by radiometric methods. For example, for <sup>99</sup>Tc (t½ = 211000 y) the detection limit is at best 1 mBq for a [[textbook:nrctextbook:chapter10|gas ionization detector]] and clearly higher in [[textbook:nrctextbook:chapter12|liquid scintillation counting]]. 1 mBq means that there are about four decays in an hour but this [[textbook:nrctextbook:chapter6#activity|activity]] of <sup>99</sup>Tc corresponds to about 100 million atoms. This amount of atoms can be easily detected and counted by mass spectrometry and even as low as a 0.001 mBq detection limit can be  
-for <sup>99</sup>Tc (t½ = 211000 y) the detection limit is at best 1 mBq for a gas ionization detector and clearly higher in liquid scintillation counting. 1 mBq means that there are about four decays in an hour but this activity of <sup>99</sup>Tc corresponds to about 100 million atoms. This amount of atoms can be easily detected and counted by mass spectrometry and even as low as a 0.001 mBq detection limit can be  +achieved by ICP-MS. In principle all radionuclides with [[textbook:nrctextbook:chapter6#half_life|half-lives]] longer than 100 years can be measured by ICP-MS. However, for the radionuclides with half-lives round this limit, radiometric methods are still more sensitive and provide with more accurate results.
-achieved by ICP-MS. In principle all radionuclides with half-lives longer than 100 years can be measured by ICP-MS. However, for the radionuclides with half-lives round this limit, radiometric  methods are still more sensitive and provide with more accurate results.+
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-The components of an ICP-MS are presented in Figure VIII.6. The sample solution is introduced into the system by a nebulizer which turns the solution into a fine mist (aerosol). This is transferred with argon flow into the torch where plasma is created with the help of radiofrequency. Plasma atomizes the sample, ionizes the atoms and the ions are directed into a mass analyzer for the separation of ions based on their mass to charge ratio (//m/z//).+The components of an ICP-MS are presented in [[textbook:nrctextbook:chapter8#figure_86|Figure VIII.6]]. The sample solution is introduced into the system by a nebulizer which turns the solution into a fine mist (aerosol). This is transferred with argon flow into the torch where plasma is created with the help of radiofrequency. Plasma atomizes the sample, ionizes the atoms and the ions are directed into a mass analyzer for the separation of ions based on their mass to charge ratio (//m/z//).
 ### ###
 +{{anchor:figure_86}}
  
 {{:textbook:nrctextbook:components_of_an_icpms_system_fig_8_6.png|}} {{:textbook:nrctextbook:components_of_an_icpms_system_fig_8_6.png|}}
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-The mass analyzer is either quadrupole or double focusing system. The former is smaller, cheaper and easier to operate. The latter, however, is much more sensitive yielding to lower detection limits and to more accurate isotopic ratios. A quadrupole consists of four metallic rods aligned in a parallel diamond pattern. By placing a direct current field on one pair of opposite rods and a radio frequency field on the other pair, an ion of a selected mass and charge ratio (//m/z//) is allowed to pass +The mass analyzer is either quadrupole or double focusing system. The former is smaller, cheaper and easier to operate. The latter, however, is much more sensitive yielding to lower detection limits and to more accurate [[textbook:nrctextbook:chapter2#isotope|isotopic ratios]]. A quadrupole consists of four metallic rods aligned in a parallel diamond pattern. By placing a direct current field on one pair of opposite rods and a radio frequency field on the other pair, an ion of a selected mass and charge ratio (//m/z//) is allowed to pass 
 through the rods to the detector while the others are forced out of this path. By varying the combinations of voltages and frequency, an array of different //m/z// ratio ions can be scanned in a very short time. The high-resolution double focusing system in turn consists of an electromagnet and an electrostatic analyzer in series. After mass separation the ions are detected and counted. through the rods to the detector while the others are forced out of this path. By varying the combinations of voltages and frequency, an array of different //m/z// ratio ions can be scanned in a very short time. The high-resolution double focusing system in turn consists of an electromagnet and an electrostatic analyzer in series. After mass separation the ions are detected and counted.
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-Some radionuclides, such as uranium, can be measured from natural waters directly with ICP-MS without chemical separation of interfering elements. Most radionuclides, however, need to be separated into a pure form prior to measurement. The separation requirements may essentially differ from those used in radiochemical separations for radiometric measurements. For example, if plutonium is measured by alpha spectrometry 1% of uranium activity in the counting source does not result in a large error. In mass, however, this 1% activity means about 2000-times excess of <sup>238</sup>U  +Some [[textbook:nrctextbook:chapter4|radionuclides]], such as uranium, can be measured from natural waters directly with ICP-MS without chemical separation of interfering elements. Most radionuclides, however, need to be separated into a pure form prior to measurement. The separation requirements may essentially differ from those used in radiochemical separations for radiometric measurements. For example, if plutonium is measured by [[textbook:nrctextbook:chapter11|alpha spectrometry]] 1% of uranium [[textbook:nrctextbook:chapter6#activity|activity]] in the counting source does not result in a large error. In mass, however, this 1% activity means about 2000-times excess of <sup>238</sup>U compared to <sup>239</sup>Pu which would prevent the measurement of plutonium. In mass spectrometry there are three types of interferences that need to be taken into account when measuring radionuclides. First, the [[textbook:nrctextbook:chapter2#isobar|isobars]] with approximately same mass cause interference, for example<sup> 129</sup>Xe in <sup>129</sup>I measurement and <sup>135</sup>Ba in <sup>135</sup>Cs measurement. Second, in the plasma there are not only single atoms formed but also polyatomic ions such as <sup>204</sup>Hg<sup>35</sup>Cl or <sup>238</sup>UH which interfere with the measurement of <sup>239</sup>Pu having approximately the same mass. Even though only a small fraction of the total elemental concentrations forms these polyatomic ions <sup>204</sup>Hg<sup>35</sup>Cl or <sup>238</sup>UH their concentrations are 
-compared to <sup>239</sup>Pu which would prevent the measurement of plutonium. In mass spectrometry there are three types of interferences that need to be taken into account when measuring radionuclides. First, the isobars with approximately same mass cause interference, for example<sup> 129</sup>Xe in <sup>129</sup>I measurement and <sup>135</sup>Ba in <sup>135</sup>Cs measurement. Second, in the plasma there are not only single atoms formed but also polyatomic ions such as <sup>204</sup>Hg<sup>35</sup>Cl or <sup>238</sup>UH which interfere with the measurement of <sup>239</sup>Pu having approximately the same mass. Even though only a small fraction of the total elemental concentrations forms these polyatomic ions <sup>204</sup>Hg<sup>35</sup>Cl or <sup>238</sup>UH their concentrations are +
 nevertheless much higher than that of plutonium due to the greater abundances of the polyatomic ion forming elements, in this case Hg, Cl and U. Therefore, chemical separations are needed to enable measurement of radionuclides at very low concentrations. Third type of interference comes from broadening the neighbor mass peaks at higher concentration. Due to this, for example, <sup>238</sup>U at  nevertheless much higher than that of plutonium due to the greater abundances of the polyatomic ion forming elements, in this case Hg, Cl and U. Therefore, chemical separations are needed to enable measurement of radionuclides at very low concentrations. Third type of interference comes from broadening the neighbor mass peaks at higher concentration. Due to this, for example, <sup>238</sup>U at 
 much higher concentrations compared to plutonium causes extra counts to the mass peak of <sup>239</sup>Pu. much higher concentrations compared to plutonium causes extra counts to the mass peak of <sup>239</sup>Pu.
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-ICP-MS is increasingly used for the measurement of long-lived radionuclides, especially actinides. For neptunium it is clearly superior to radiometric methods due to its low specific activity. In plutonium measurement, mass spectrometry also offers a change to measure individually <sup>239</sup>Pu and <sup>240</sup>Pu which cannot be separated from each other in alpha spectrometry. In turn, <sup>238</sup>Pu cannot be +ICP-MS is increasingly used for the measurement of [[textbook:nrctextbook:chapter6#long_lived_radionuclides|long-lived radionuclides]], especially actinides. For neptunium it is clearly superior to radiometric methods due to its low [[textbook:nrctextbook:chapter6#specific_activity|specific activity]]. In plutonium measurement, mass spectrometry also offers a change to measure individually <sup>239</sup>Pu and <sup>240</sup>Pu which cannot be separated from each other in [[textbook:nrctextbook:chapter11|alpha spectrometry]]. In turn, <sup>238</sup>Pu cannot be measured by mass spectrometry due to interference of uranium. Thus, to determine all relevant plutonium isotopes both mass and alpha spectrometry are needed.
-measured by mass spectrometry due to interference of uranium. Thus, to determine all relevant plutonium isotopes both mass and alpha spectrometry are needed.+
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textbook/nrctextbook/chapter8.1744804651.txt.gz · Last modified: 2025-04-16 13:57 by Merja Herzig

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