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textbook:nrctextbook:chapter7 [2025-04-01 14:52]
Merja Herzig 		textbook:nrctextbook:chapter7 [2025-08-28 21:35] (current)
Merja Herzig
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   * [[textbook:nrctextbook:chapter5#excited_state|excitation]] of nuclei or atoms   * [[textbook:nrctextbook:chapter5#excited_state|excitation]] of nuclei or atoms
   * formation of electromagnetic radiation ([[textbook:nrctextbook:chapter7#bremsstrahlung|bremsstrahlung]], [[textbook:nrctextbook:chapter7#cherenkov_radiation|Cherenkov radiation]])   * formation of electromagnetic radiation ([[textbook:nrctextbook:chapter7#bremsstrahlung|bremsstrahlung]], [[textbook:nrctextbook:chapter7#cherenkov_radiation|Cherenkov radiation]])
-  * absorption into the nucleus – nuclear reaction+  * absorption into the nucleus – [[textbook:nrctextbook:chapter15|nuclear reaction]]
  
 {{anchor:ionization}} {{anchor:ionization}}
 +{{anchor:secondary_ionization}}
 +
 ### ###
-Radiation other than the neutron radiation has a much greater possibility of interacting with the [[textbook:nrctextbook:chapter2#electron|electron cloud]] than with the [[textbook:nrctextbook:chapter2#nucleus|nucleus]] due to the much larger size of the electron cloud compared to nucleus. The removal of electrons from the electron shells of the medium atoms by ionization is the central pattern by which all radiation except neutrons loses their energy when moving in the medium. While the [[textbook:nrctextbook:chapter15#cross_section|cross section]] of the ionization by [[textbook:nrctextbook:chapter2#proton|protons]] or [[textbook:nrctextbook:chapter5#alpha_particle|alpha particles]] can be several hundreds of thousands of barns (for definition, see [[textbook:nrctextbook:chapter15#cross_section|Chapter XV]]) it is only under ten for nuclear scattering and still considerably less for nuclear transformations. //Radiation, which causes ionization, is called ionizing radiation//. The primary result in ionization is the formation of ion pair, electron and positive ion. In most cases, the emitting electrons are so high in energy that they can cause further ionization, //secondary ionization//, which can be an even a larger portion of the overall ionization than the //primary ionization//. The radiation energies generated by [[textbook:nrctextbook:chapter6|radioactive decay]] are typically at least in the keV range. These are high energies compared to energies of atom ionization, which are usually less than 15 eV and those of chemical bonding, which are even lower at 1-5 eV. It is therefore understandable that electrons arising from primary ionization have such a high kinetic energy to cause secondary ionization. Similarly, it is understandable that the primary high energy of a particle or [[textbook:nrctextbook:chapter5#gamma|gamma]] ray does not lose its energy in only one collision with an electron, but several.+Radiation other than the neutron radiation has a much greater possibility of interacting with the [[textbook:nrctextbook:chapter2#electron|electron cloud]] than with the [[textbook:nrctextbook:chapter2#nucleus|nucleus]] due to the much larger size of the electron cloud compared to nucleus. The removal of electrons from the electron shells of the medium atoms by //ionization// is the central pattern by which all radiation except neutrons loses their energy when moving in the medium. While the [[textbook:nrctextbook:chapter15#cross_section|cross section]] of the ionization by [[textbook:nrctextbook:chapter2#proton|protons]] or [[textbook:nrctextbook:chapter5#alpha_particle|alpha particles]] can be several hundreds of thousands of barns (for definition, see [[textbook:nrctextbook:chapter15#cross_section|Chapter XV]]) it is only under ten for nuclear scattering and still considerably less for nuclear transformations. //Radiation, which causes ionization, is called ionizing radiation//. The primary result in ionization is the formation of ion pair, electron and positive ion. In most cases, the emitting electrons are so high in energy that they can cause further ionization, //secondary ionization//, which can be an even a larger portion of the overall ionization than the //primary ionization//. The radiation energies generated by [[textbook:nrctextbook:chapter6|radioactive decay]] are typically at least in the keV range. These are high energies compared to energies of atom ionization, which are usually less than 15 eV and those of chemical bonding, which are even lower at 1-5 eV. It is therefore understandable that electrons arising from primary ionization have such a high kinetic energy to cause secondary ionization. Similarly, it is understandable that the primary high energy of a particle or [[textbook:nrctextbook:chapter5#gamma|gamma]] ray does not lose its energy in only one collision with an electron, but several.
  
 ### ###
 {{anchor:absorption_curve}} {{anchor:absorption_curve}}
 +{{anchor:absorption_range}}
 ===== 7.1. Absorption curve and range ===== ===== 7.1. Absorption curve and range =====
  
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-{{:textbook:nrctextbook:radiation_absorption_curve_determination_system_fig_7_1.png?400|}}+{{:textbook:nrctextbook:radiation_absorption_curve_determination_system.png?400|}}
  
 Figure VII.1 Radiation absorption curve determination system (modified from  Figure VII.1 Radiation absorption curve determination system (modified from 
 https://tap.iop.org/atoms/radioactivity/511/page_47096.html). https://tap.iop.org/atoms/radioactivity/511/page_47096.html).
 {{anchor:figure_72}} {{anchor:figure_72}}
-{{:textbook:nrctextbook:adsorption_curves_of_alpha_veta_and_gamma_neutron_radiation_fig_7_2.png|}}+ 
 +{{:textbook:nrctextbook:absorption_curves_alpha_beta_gamma_l.png?400|}}
  
 Figure VII.2. Absorption curves of [[textbook:nrctextbook:chapter5#alpha|alpha]] (blue), [[textbook:nrctextbook:chapter5#beta|beta]] (grey) and [[textbook:nrctextbook:chapter5#gamma|gamma]]/neutron radiation (orange). Figure VII.2. Absorption curves of [[textbook:nrctextbook:chapter5#alpha|alpha]] (blue), [[textbook:nrctextbook:chapter5#beta|beta]] (grey) and [[textbook:nrctextbook:chapter5#gamma|gamma]]/neutron radiation (orange).
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 {{anchor:absorption_of_alpha_radiation}} {{anchor:absorption_of_alpha_radiation}}
 {{anchor:ionization_alpha_radiation}} {{anchor:ionization_alpha_radiation}}
 +{{anchor:specific_ionization}}
 ===== 7.2. Absorption of alpha radiation ===== ===== 7.2. Absorption of alpha radiation =====
  
 ### ###
 +{{anchor:cloud_chamber}}
 +{{anchor:figure_73}}{{:textbook:nrctextbook:alpha_radiation_tracks_of_226ra_source_in_a_cloud_chamber_fig_7_3.png?400 |}}
 +Figure VII.3. Alpha radiation tracks of a <sup>226</sup>Ra source imaged in a cloud chamber. (https://simple.wikipedia.org/wiki/Cloud_chamber).
 +
 In comparison to other radiation types from radioactive decay, [[textbook:nrctextbook:chapter5#alpha|alpha radiation]] is characterized by the fact that the [[textbook:nrctextbook:chapter5#alpha_particle|alpha particles]] are large and their energies are always high, usually between 4-9 MeV. Due to this, alpha particles do not readily scatter from medium atoms, rather their range is short and path is direct ([[textbook:nrctextbook:chapter7#figure_73|Figure VII.3]]). For example, the 4.8 MeV alpha particles of <sup>226</sup>Ra have a maximum range of 3.3 cm in air and only 0.0033 cm in water. Alpha radiation causes very intense ionization, for example, when traveling in air a 7.7 MeV alpha particle causes 3200 ion pairs/cm. The ion pairs generated in unit length is called specific ionization. [[textbook:nrctextbook:chapter7#figure_74|Figure VII.4]] shows specific ionization of alpha radiation (and of [[textbook:nrctextbook:chapter2#proton|protons]] and electrons) as a function of particle energy. First specific ionization somewhat increases, but at energies higher than 1 MeV specific ionization decreases systematically. The specific ionization of alpha particles is clearly higher than that of protons, let alone electrons. This is due to their larger size and higher electric charge. Most of the electrons produced in primary ionization have a high energy, on average 100 eV, but some even higher than 3 keV and thus they cause strong secondary ionization. In comparison to other radiation types from radioactive decay, [[textbook:nrctextbook:chapter5#alpha|alpha radiation]] is characterized by the fact that the [[textbook:nrctextbook:chapter5#alpha_particle|alpha particles]] are large and their energies are always high, usually between 4-9 MeV. Due to this, alpha particles do not readily scatter from medium atoms, rather their range is short and path is direct ([[textbook:nrctextbook:chapter7#figure_73|Figure VII.3]]). For example, the 4.8 MeV alpha particles of <sup>226</sup>Ra have a maximum range of 3.3 cm in air and only 0.0033 cm in water. Alpha radiation causes very intense ionization, for example, when traveling in air a 7.7 MeV alpha particle causes 3200 ion pairs/cm. The ion pairs generated in unit length is called specific ionization. [[textbook:nrctextbook:chapter7#figure_74|Figure VII.4]] shows specific ionization of alpha radiation (and of [[textbook:nrctextbook:chapter2#proton|protons]] and electrons) as a function of particle energy. First specific ionization somewhat increases, but at energies higher than 1 MeV specific ionization decreases systematically. The specific ionization of alpha particles is clearly higher than that of protons, let alone electrons. This is due to their larger size and higher electric charge. Most of the electrons produced in primary ionization have a high energy, on average 100 eV, but some even higher than 3 keV and thus they cause strong secondary ionization.
 ### ###
-{{anchor:cloud_chamber}} 
-{{anchor:figure_73}} 
  
-{{:textbook:nrctextbook:alpha_radiation_tracks_of_226ra_source_in_a_cloud_chamber_fig_7_3.png|}} 
- 
-Figure VII.3. Alpha radiation tracks of a <sup>226</sup>Ra source imaged in a cloud chamber. (https://simple.wikipedia.org/wiki/Cloud_chamber). 
 {{anchor:figure_74}} {{anchor:figure_74}}
-{{:textbook:nrctextbook:specific_ionization_of_alpha_particles_protons_and_elelctrons_fig_7_4.png|}} 
  
 +{{:textbook:nrctextbook:the_specific_ionization_of_alpha_particles_protons_electrons_l.png?400 |}}
 Figure VII.4. The specific ionization of alpha particles, protons, and electrons (ion pair/mm) in the air as a function of particle energy. Figure VII.4. The specific ionization of alpha particles, protons, and electrons (ion pair/mm) in the air as a function of particle energy.
  
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 ### ###
  
- +{{:textbook:nrctextbook:specific_ionization_of_alpha_proton_as_a_function_of_residual_range_l.png|}}
-{{:textbook:nrctextbook:specific_ionization_of_alpha_particles_and_protons_as_a_function_of_residual_range_fig_7_5.png|}} +
 Figure VII.5. Specific ionization of alpha particles and protons as a function of their residual range. Figure VII.5. Specific ionization of alpha particles and protons as a function of their residual range.
  
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   * [[textbook:nrctextbook:chapter7#cherenkov_radiation|Cherenkov radiation]]   * [[textbook:nrctextbook:chapter7#cherenkov_radiation|Cherenkov radiation]]
  
 +
 +{{anchor:figure_75_beta_absorption_processes}} 
 {{ :textbook:nrctextbook:beta_radition_absorption_processes_fig_7_5.png|}} {{ :textbook:nrctextbook:beta_radition_absorption_processes_fig_7_5.png|}}
  
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 {{anchor:excitation_beta}} {{anchor:excitation_beta}}
 ### ###
-As already stated, the beta radiation created in radioactive decay loses its energy in media by essentially two mechanisms: ionizing and excitation. Both processes cause approximately the same fraction of energy loss.  In ionization a beta particle collides with a media electron, removes it from its orbit and proceeds with lower energy and to a direction different from that before the collision. In excitation, collision energy of beta particle is not enough for electron removal from an atom, but  +As already stated, the [[textbook:nrctextbook:chapter5#beta|beta]] radiation created in radioactive decay loses its energy in media by essentially two mechanisms: ionizing and excitation. Both processes cause approximately the same fraction of energy loss.  In ionization a [[textbook:nrctextbook:chapter5#beta_particle|beta particle]] collides with a media [[textbook:nrctextbook:chapter2#electron|electron]], removes it from its orbit and proceeds with lower energy and to a direction different from that before the collision. In excitation, collision energy of beta particle is not enough for electron removal from an atom, but rather moves the electron to a higher energy level, i.e. yields electron excitation.  The result of both processes is the emission of electromagnetic radiation, when an electron hole is filled by an electron from an upper electron shell or when an excitation level relaxes.
-rather moves the electron to a higher energy level, i.e. yields electron excitation.  The result of both processes is the emission of electromagnetic radiation, when an electron hole is filled by an electron from an upper electron shell or when an excitation level relaxes.+
 ### ###
  
 {{anchor:bremsstrahlung}} {{anchor:bremsstrahlung}}
 ### ###
-Bremsstrahlung is the electromagnetic energy that is generated when an electron interacts with the electric field of an atomic nucleus.  The beta particle energy decreases by the amount of energy of the generated photon.  The proportion of energy loss of beta radiation caused by bremsstrahlung is, however, very small.  For example, only 1% of the energy of the 1 MeV beta particles is absorbed in aluminum by bremsstrahlung and the remaining almost exclusively by ionization and excitation.  +Bremsstrahlung is the electromagnetic energy that is generated when an [[textbook:nrctextbook:chapter2#electron|electron]] interacts with the electric field of an atomic [[textbook:nrctextbook:chapter2#nucleus|nucleus]].  The [[textbook:nrctextbook:chapter5#beta_particle|beta particle]] energy decreases by the amount of energy of the generated photon.  The proportion of energy loss of beta radiation caused by bremsstrahlung is, however, very small.  For example, only 1% of the energy of the 1 MeV beta particles is absorbed in aluminum by bremsstrahlung and the remaining almost exclusively by ionization and excitation. At higher beta energies the proportion of energy loss by bremsstrahlung increases. In addition, formation of bremsstrahlung is affected by the [[textbook:nrctextbook:chapter2#proton|atomic number]] of the radiation absorbing material: the higher it is the more bremsstrahlung. For example, in lead already 10% of the energy of 1 MeV energy [[textbook:nrctextbook:chapter5#beta|beta radiation]] is absorbed by formation of bremsstrahlung. Since the electromagnetic radiation of bremsstrahlung is noticeably more penetrating than beta radiation it is sensible to use a lower atomic number than lead as a protective material. One centimeter thick Plexiglas, for example, prevents penetration of high energy beta particles without the fundamental formation of bremsstrahlung like with lead.
-At higher beta energies the proportion of energy loss by bremsstrahlung increases. In addition, formation of bremsstrahlung is affected by the atomic number of the radiation absorbing material: the higher it is the more bremsstrahlung. For example, in lead already 10% of the energy of 1 MeV energy beta radiation is absorbed by formation of bremsstrahlung. Since the electromagnetic radiation of bremsstrahlung is noticeably more penetrating than beta radiation it is sensible to use a lower atomic number than lead as a protective material. One centimeter thick Plexiglas, for example, prevents penetration of high energy beta particles without the fundamental formation of bremsstrahlung like with lead.+
 ### ###
  
  
 ### ###
-When determining the absorption curve for beta radiation, a curve in accordance to Figure VII.6 is obtained by drawing an absorption layer thickness as a function of gross count rate measured from a beta source. After a specific absorber thickness is achieved the count rate levels off. This flat proportion is due to both the background radiation and the bremsstrahlung generated in the absorber.  When their contribution is deducted from the total curve the beta radiation decrease due to the absorber and its maximum range are obtained (In Fig. VII.6 at 300 mg/cm<sup>2</sup>).+When determining the absorption curve for beta radiation, a curve in accordance to [[textbook:nrctextbook:chapter7#figure_76|Figure VII.6]] is obtained by drawing an absorption layer thickness as a function of gross [[textbook:nrctextbook:chapter6#count_rate|count rate]] measured from a beta source. After a specific absorber thickness is achieved the count rate levels off. This flat proportion is due to both the background radiation and the [[textbook:nrctextbook:chapter7#bremsstrahlung|bremsstrahlung]] generated in the absorber.  When their contribution is deducted from the total curve the [[textbook:nrctextbook:chapter5#beta|beta radiation]] decrease due to the absorber and its maximum range are obtained (In Fig. VII.6 at 300 mg/cm<sup>2</sup>).
 ### ###
 +{{anchor:figure_76}}
  
-{{:textbook:nrctextbook:beta_radiation_absorption_curve_background_radiation_and_bremsstrahlung_subtraction_fig_7_6.png|}} +{{:textbook:nrctextbook:beta_radiation_absorption_curve.png?400 |}} 
-VII.6. Beta radiation absorption curve, background radiation and bremsstrahlung subtraction, as well as maximum range determination.+VII.6. [[textbook:nrctextbook:chapter5#beta|Beta radiation]] absorption curve, background radiation and bremsstrahlung subtraction, as well as maximum range determination.
  
 {{anchor:annihilation}} {{anchor:annihilation}}
 ### ###
-Positron particles experience the same interactions in the media as β<sup>-</sup> particles. When a positron has lost its kinetic energy, it combines with its antiparticle electron and they both disappear, annihilate.+[[textbook:nrctextbook:chapter5#positron|Positron particles]] experience the same interactions in the media as β<sup>-</sup> particles. When a positron has lost its kinetic energy, it combines with its antiparticle electron and they both disappear, annihilate.
 ### ###
  
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 {{anchor:cherenkov_radiation}} {{anchor:cherenkov_radiation}}
 ### ###
-Cherenkov radiation is blue light, which is created when a beta particle travels through the medium faster than light.  In water the beta particle energy must be at least 263 keV to exceed the speed of light.  In the absorption of beta radiation energy the formation of Cherenkov radiation forms only a small fraction, less than 0.1%.  Cherenkov radiation may, however, be used to measure high energy (E<sub>max</sub> >700 keV) beta radiation with liquid scintillation counter: this involves direct measurement of the light intensity of Cherenkov radiation without using liquid scintillator agents.+Cherenkov radiation is blue light, which is created when a [[textbook:nrctextbook:chapter5#beta_particle|beta particles]] travels through the medium faster than light.  In water the beta particle energy must be at least 263 keV to exceed the speed of light.  In the absorption of [[textbook:nrctextbook:chapter5#beta|beta radiation]] energy the formation of Cherenkov radiation forms only a small fraction, less than 0.1%.  Cherenkov radiation may, however, be used to measure high energy (E<sub>max</sub> >700 keV) beta radiation with [[textbook:nrctextbook:chapter12|liquid scintillation]] counter: this involves direct measurement of the light intensity of Cherenkov radiation without using liquid scintillator agents.
 ### ###
  
 +{{anchor:absorption_of_gamma_radiation}}
 ===== 7.4. Absorption of gamma radiation ===== ===== 7.4. Absorption of gamma radiation =====
  
 ### ###
-Since gamma radiation is weightless and uncharged, it rarely interacts in media.  That is why it is penetratable and has a long range. Specific ionization of gamma radiation is small compared to beta radiation, let alone alpha radiation.  For example, a 1 MeV gamma photon causes only one ion pair per centimeter in the air, compared to many tens by beta radiation and several tens of thousands by alpha radiation.+Since [[textbook:nrctextbook:chapter5#gamma|gamma radiation]] is weightless and uncharged, it rarely interacts in media.  That is why it is penetratable and has a long range. Specific ionization of gamma radiation is small compared to [[textbook:nrctextbook:chapter5#beta|beta radiation]], let alone [[textbook:nrctextbook:chapter5#alpha|alpha radiation]].  For example, a 1 MeV gamma photon causes only one [[textbook:nrctextbook:chapter7#ionization|ion pair]] per centimeter in the air, compared to many tens by beta radiation and several tens of thousands by alpha radiation.
 ### ###
  
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 ^Type of radiation ^Specific ionization in air (ion pair/cm) ^Range in the air ^Interaction process ^ ^Type of radiation ^Specific ionization in air (ion pair/cm) ^Range in the air ^Interaction process ^
-|Alfa radiation| tens of thousands| a few centimeters|• [[textbook:nrctextbook:chapter7#ionization|ionization]] \\ • [[textbook:nrctextbook:chapter5#excited_state|excitation]]|+|Alfa radiation| tens of thousands| a few centimeters|• [[textbook:nrctextbook:chapter7#ionization|ionization]] \\ • excitation|
 |Beta radiation| tens to hundreds| a few meters|• [[textbook:nrctextbook:chapter7#ionization_beta|ionization]] \\ • [[textbook:nrctextbook:chapter7#excitation_beta|excitation]] \\ • [[textbook:nrctextbook:chapter7#bremsstrahlung|bremsstrahlung formation]] \\ • [[textbook:nrctextbook:chapter7#annihilation|positron annihilation]] \\ • [[textbook:nrctextbook:chapter7#cherenkov_radiation|Cherenkov radiation]]| |Beta radiation| tens to hundreds| a few meters|• [[textbook:nrctextbook:chapter7#ionization_beta|ionization]] \\ • [[textbook:nrctextbook:chapter7#excitation_beta|excitation]] \\ • [[textbook:nrctextbook:chapter7#bremsstrahlung|bremsstrahlung formation]] \\ • [[textbook:nrctextbook:chapter7#annihilation|positron annihilation]] \\ • [[textbook:nrctextbook:chapter7#cherenkov_radiation|Cherenkov radiation]]|
 |Gamma radiation| few| exponential attenuation, “range” meters, tens of meters| • [[textbook:nrctextbook:chapter7#coherent_scattering|coherent scattering]] \\ • [[textbook:nrctextbook:chapter7#photoelectric_effect|photoelectric effect]] \\ • [[textbook:nrctextbook:chapter7#compton_scattering|Compton scattering]] \\ • [[textbook:nrctextbook:chapter7#pair_formation|pair formation]] \\ • [[textbook:nrctextbook:chapter15|photonuclear reaction]]| |Gamma radiation| few| exponential attenuation, “range” meters, tens of meters| • [[textbook:nrctextbook:chapter7#coherent_scattering|coherent scattering]] \\ • [[textbook:nrctextbook:chapter7#photoelectric_effect|photoelectric effect]] \\ • [[textbook:nrctextbook:chapter7#compton_scattering|Compton scattering]] \\ • [[textbook:nrctextbook:chapter7#pair_formation|pair formation]] \\ • [[textbook:nrctextbook:chapter15|photonuclear reaction]]|
  
  
textbook/nrctextbook/chapter7.1743511948.txt.gz · Last modified: 2025-04-01 14:52 by Merja Herzig

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