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textbook:nrctextbook:chapter5 [2025-03-18 16:04]
Merja Herzig 		textbook:nrctextbook:chapter5 [2025-08-28 16:31] (current)
Merja Herzig
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 {{anchor:fission}} {{anchor:fission}}
 +{{anchor:spontaneous_fission}}
 +
 ===== 5.1.Fission ===== ===== 5.1.Fission =====
  
 ### ###
-In addition to spontaneous fission, which is one of the radioactive decay modes, induced fission is also shortly discussed here. The reason for the spontaneous fission is that the nucleus is too heavy and it is typical only for the heaviest elements (heavier than uranium). In fission, the nucleus splits into two nuclei of lighter elements, for example:+In addition to spontaneous fission, which is one of the radioactive decay modes, [[textbook:nrctextbook:chapter5#induced_fission|induced fission]] is also shortly discussed here. The reason for the spontaneous fission is that the nucleus is too heavy and it is typical only for the heaviest elements (heavier than uranium). In fission, the nucleus splits into two nuclei of lighter elements, for example:
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-{{:textbook:nrctextbook:spontaneous_fission_fig_5_1.png?400|}}+{{:textbook:nrctextbook:spontaneous_fission_of_heavy_nuclei.png?400|}} 
 + 
 +Figure V.1. Spontaneous fission of a heavy nucleus into two nuclei of lighter elements.
  
-Figure V.1. Spontaneous fission of a heavy nucleus into two nuclei of lighter elements  +{{anchor:induced_fission}}
-(http://physics.nayland.school.nz/VisualPhysics/NZP-physics%20HTML/17_NuclearEnergy/Chapter17a.html).+
  
 ### ###
-In an induced fission a nucleus is bombarded with a particle, such as a neutron, which results in fission, such as+In an induced fission a nucleus is bombarded with a particle, such as a [[textbook:nrctextbook:chapter2#neutron|neutron]], which results in fission, such as
 ### ###
  
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 (http://chemwiki.ucdavis.edu/Physical_Chemistry/Nuclear_Chemistry/Nuclear_Reactions). (http://chemwiki.ucdavis.edu/Physical_Chemistry/Nuclear_Chemistry/Nuclear_Reactions).
  
 +{{anchor:fission_products}}
 ### ###
 In addition to the lighter elements, called fission products, fission yields into emission of 2-3 neutrons and a large amount of energy, the distribution of which is shown in Table V.I. In addition to the lighter elements, called fission products, fission yields into emission of 2-3 neutrons and a large amount of energy, the distribution of which is shown in Table V.I.
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 ^Kinetic energy of neutrinos from beta decays |10 MeV| ^Kinetic energy of neutrinos from beta decays |10 MeV|
  
 +{{anchor:uranium_spontaneous_fission}}
 ### ###
 In the nature, there is only one nuclide, <sup>238</sup>U that decays spontaneously by fission. Fission is, however, not the only decay mode of <sup>238</sup>U and in fact only 0.005% of it undergoes this decay mode while the rest decays by [[textbook:nrctextbook:chapter5#alpha|alpha decay]]. Spontaneous fission of uranium has its own specific decay [[textbook:nrctextbook:chapter6#half_life|half-life]] which is 8·10<sup>15</sup> a. With transuranium and superheavy elements, spontaneous fission is more common but as with uranium, spontaneous fission is mostly a minor decay mode. For example, all plutonium [[textbook:nrctextbook:chapter2#isotope|isotopes]] with a [[textbook:nrctextbook:chapter2#mass_number|mass number]] between 235 and 244 partly decay by spontaneous fission. There are, however, some heavy radionuclides, such as <sup>256</sup>Cf and <sup>250</sup>No, which decay solely by spontaneous fission. In the nature, there is only one nuclide, <sup>238</sup>U that decays spontaneously by fission. Fission is, however, not the only decay mode of <sup>238</sup>U and in fact only 0.005% of it undergoes this decay mode while the rest decays by [[textbook:nrctextbook:chapter5#alpha|alpha decay]]. Spontaneous fission of uranium has its own specific decay [[textbook:nrctextbook:chapter6#half_life|half-life]] which is 8·10<sup>15</sup> a. With transuranium and superheavy elements, spontaneous fission is more common but as with uranium, spontaneous fission is mostly a minor decay mode. For example, all plutonium [[textbook:nrctextbook:chapter2#isotope|isotopes]] with a [[textbook:nrctextbook:chapter2#mass_number|mass number]] between 235 and 244 partly decay by spontaneous fission. There are, however, some heavy radionuclides, such as <sup>256</sup>Cf and <sup>250</sup>No, which decay solely by spontaneous fission.
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 ### ###
-Fission products, the lighter nuclides formed in fission, are radioactive. The heavy elements, such as uranium, have higher neutron to proton ratios compared to elements formed in fission. In the fission, however, only 2-3 neutrons are released and therefore the fission products have too many neutrons for stability. For example, barium isotopes formed in fission have approximately the same neutron to proton ratio as <sup>238</sup>U, 1.59. The stable barium isotopes, however, have neutron to proton  +Fission products, the lighter nuclides formed in fission, are radioactive. The heavy elements, such as uranium, have higher [[textbook:nrctextbook:chapter3#neutron_to_proton_ratio|neutron to proton ratios]] compared to elements formed in fission. In the fission, however, only 2-3 [[textbook:nrctextbook:chapter2#neutron|neutrons]] are released and therefore the fission products have too many neutrons for stability. For example, barium [[textbook:nrctextbook:chapter2#isotope|isotopes]] formed in fission have approximately the same neutron to proton ratio as <sup>238</sup>U, 1.59. The stable barium isotopes, however, have neutron to proton ratio in the range of 1.32-1.46. To obtain stability, the fission products gradually correct their neutron to proton ratio by decaying with [[textbook:nrctextbook:chapter5#beta|beta decay]] (β<sup>-</sup>)  mode, i.e. they transform excess neutrons to [[textbook:nrctextbook:chapter2#proton|protons]] until the nuclide has [[textbook:nrctextbook:chapter3#neutron_to_proton_ratio|neutron to proton ratio]] that enables stability. An example of such decay chain is shown in [[textbook:nrctextbook:chapter5#figure_53|Figure V.3]].
-ratio in the range of 1.32-1.46. To obtain stability, the fission products gradually correct their neutron to proton ratio by decaying with β<sup>-</sup> decay mode, i.e. they transform excess neutrons to protons until the nuclide has [[textbook:nrctextbook:chapter3#neutron_to_proton_ratio|neutron to proton ratio]] that enables stability. An example of such decay chain is shown in [[textbook:nrctextbook:chapter5#figure_53|Figure V.3]].+
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 {{anchor:figure_53}} {{anchor:figure_53}}
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 ### ###
-There is a large number of fission daughter products. They are, however, not evenly formed at various [[textbook:nrctextbook:chapter2#mass_number|mass numbers]]. Instead, they are concentrated to two mass number ranges with mass numbers between 90-105 and 130-140. Graphical presentation of the fission product yields, the percentage of fissions leading to specified mass number, as a function of mass number results in the formation of a double hump curve given in [[textbook:nrctextbook:chapter5#figure_54|Figure V.4]].  The upper mass range is independent of the fissioning nuclide while the lower mass range shifts into higher mass numbers as the mass of the fissioning nuclide increases.+There is a large number of fission daughter products. They are, however, not evenly formed at various [[textbook:nrctextbook:chapter2#mass_number|mass numbers]]. Instead, they are concentrated to two mass number ranges with mass numbers between 90-105 and 130-140. Graphical presentation of the fission product yields, the percentage of fissions leading to specified mass number, as a function of mass number results in the formation of a double hump curve given in [[textbook:nrctextbook:chapter5#figure_54|Figure V.4]].  The upper mass range is independent of the fissioning [[textbook:nrctextbook:chapter2#nuclide|nuclide]] while the lower mass range shifts into higher mass numbers as the mass of the fissioning nuclide increases.
  
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-{{:textbook:nrctextbook:beta_decays_on_isobaric_line_fig_5_8.png?400|}}+{{:textbook:nrctextbook:beta_decay_on_isobaric_line_2.png?400|}}
  
 Figure V.8. Beta decays on isobaric line A=12. Figure V.8. Beta decays on isobaric line A=12.
  
-==== 5.3.1. Beta decay ==== 
 {{anchor:beta_decay}} {{anchor:beta_decay}}
 +==== 5.3.1. Beta decay ====
 +
  
 ### ###
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 [V.V] [V.V]
 ;;# ;;#
 +{{anchor:beta_spectrum_fig}}
 {{anchor:figure_59}} {{anchor:figure_59}}
  
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 {{anchor:pure_positron_emitters}} {{anchor:pure_positron_emitters}}
 +
 ### ###
 As in [[#5.3.1._beta_decay|beta minus decay]], also positron decay often takes place via the [[textbook:nrctextbook:chapter5#excited_state|excited states]] of the daughter nuclide and the excitation energy is relaxed by [[textbook:nrctextbook:chapter5#internal_transition|internal transition]]. There are, however, some radionuclides, particularly within light positron emitters, that decay solely to ground state. Examples of //pure positron emitter nuclides// are <sup>11</sup>C, <sup>13</sup>N, <sup>15</sup>O, <sup>18</sup>F. [[textbook:nrctextbook:chapter5#figure_511|Figure V.11]] shows examples of both: a pure positron emitter (<sup>18</sup>F) and a nuclide with excited states (<sup>22</sup>Na). As in [[#5.3.1._beta_decay|beta minus decay]], also positron decay often takes place via the [[textbook:nrctextbook:chapter5#excited_state|excited states]] of the daughter nuclide and the excitation energy is relaxed by [[textbook:nrctextbook:chapter5#internal_transition|internal transition]]. There are, however, some radionuclides, particularly within light positron emitters, that decay solely to ground state. Examples of //pure positron emitter nuclides// are <sup>11</sup>C, <sup>13</sup>N, <sup>15</sup>O, <sup>18</sup>F. [[textbook:nrctextbook:chapter5#figure_511|Figure V.11]] shows examples of both: a pure positron emitter (<sup>18</sup>F) and a nuclide with excited states (<sup>22</sup>Na).
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-{{:textbook:nrctextbook:positron_emission_and_positron_annihilation_fig_5_12.png?400|}}+{{:textbook:nrctextbook:positron_emission_and_annihilation.png?400|}}
  
 Figure V.12. Positron emission and positron annihilation. Figure V.12. Positron emission and positron annihilation.
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 Figure V.22. Decay scheme of <sup>137</sup>Cs (Radionuclide Transformations, Annals of the ICRP, ICRP Publication 38, Pergamon Press, 1983). Figure V.22. Decay scheme of <sup>137</sup>Cs (Radionuclide Transformations, Annals of the ICRP, ICRP Publication 38, Pergamon Press, 1983).
  
 +{{anchor:particles_and_rays_in_decay_processes}}
 ===== 5.5. Particles and rays in radioactive decay processes ===== ===== 5.5. Particles and rays in radioactive decay processes =====
  
textbook/nrctextbook/chapter5.1742310258.txt.gz · Last modified: 2025-03-18 16:04 by Merja Herzig

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