Ch10 nuclear chem

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Ch10 nuclear chem

  1. 1. Nuclear Chemistry Chapter 10 byProf. Geronimo J. Fiedalan Jr., MAT 1
  2. 2. OBJECTIVES• Define nuclear Chemistry• Describe stable, unstable, and very unstable isotopes• Describe the characteristics of the types of radiation• Define half-life• Give uses of radioisotopes• Differentiate nuclear fission from nuclear fusion 2
  3. 3. Nuclear Chemistry• Nuclear Chemistry deals with radioactivity, its origin, nature, properties and characteristics as well as its implication to nature and the physical world. 3
  4. 4. Nuclear Chemistry• Radioactivity is the spontaneous emission of the particles alpha, and beta, or gamma rays through the disintegration of atomic nuclei of radioisotopes.• Radioisotopes are radioactive isotopes. 4
  5. 5. Nuclear Chemistry• Radioactive decay is the disintegration of an unstable atomic nucleus by spontaneous emission of radiation. 5
  6. 6. Nuclear Chemistry• Radiation is the energy emitted by the nucleus (of atom) of an infinitesimal size which travel through space. – Ionizing radiation – Non-ionizing radiation 6
  7. 7. Nuclear Chemistry• Ionizing Radiation – have sufficient energy to ionize an atom – α, β, γ• Non-ionizing Radiation – The energy radiates (i.e., travels outward in straight lines in all directions) from its source. 7
  8. 8. Electromagnetic Radiation• The Electromagnetic Spectrum
  9. 9. DISCOVERY OFRADIOACTIVITY 9
  10. 10. Discovery of Radioactivity• Henri Becquerel (1852 – 1908) found that uranium crystals had the property of “fogging” a photographic plate that had been placed near crystals, which took place even though the photographic plate was wrapped in black paper. 10
  11. 11. Discovery of Radioactivity• Marie Curie and Pierre Curie discovered other radioactive elements (Th, Po, Ra) . They also found that radioactivity of substances was associated with their elements, not with compounds. Marie Curie called the radiation discovered by Becquerel as radioactivity. 11
  12. 12. The Nuclear Atom 12
  13. 13. The Rutherford Experiment 13
  14. 14. • Radioactivity was discovered by Becquerel in 1896.• Radioactive elements spontaneously emit alpha particles (α), beta particles (β) and gamma (γ) rays from their nuclei.• By 1907 Rutherford found that alpha particles emitted by certain radioactive elements 4 were helium nuclei ( 2 He 2 ). 14
  15. 15. Rutherford’s alpha particle scattering experiment. Rutherford in 1911 performed experiments that shot a stream of alpha particles at a gold foil. 155.5
  16. 16. Rutherford’s alpha particle scattering experiment. Most of the alpha particles passed through the foil with little or no deflection. 165.5
  17. 17. Rutherford’s alpha particle scattering experiment. He found that a few were deflected at large angles and some alpha particles even bounced back. 175.5
  18. 18. Rutherford’s alpha particle scattering experiment. An electron with a mass of 1/1837 amu could not have deflected an alpha particle with a mass of 4 amu. 185.5
  19. 19. Rutherford’s alpha particle scattering experiment. Rutherford knew that like charges repel. 195.5
  20. 20. Rutherford’s alpha particle scattering experiment. Rutherford concluded that each gold atom contained a positively charged mass that occupied a tiny volume. He called this mass the nucleus. 205.5
  21. 21. Rutherford’s alpha particle scattering experiment. If a positive alpha particle approached close enough to the positive mass it was deflected. 215.5
  22. 22. Rutherford’s alpha particle scattering experiment. Most of the alpha particles passed through the gold foil. This led Rutherford to conclude that a gold atom was mostly empty space. 225.5
  23. 23. Deflection ScatteringDeflection and scattering of alpha particles by positive gold nuclei. 235.5
  24. 24. Subatomic Particles of the Atom 24
  25. 25. 25
  26. 26. What Makes forNuclear Stability? 26
  27. 27. Stable and Unstable Nuclides• Stable 12 6 X n=6 p=6 70 32 X n = 38 p = 32 27
  28. 28. Stable and Unstable Nuclides• Unstable 3 1 X n=2 p=1 59 28 X n = 31 p = 28 28
  29. 29. Stable and Unstable Nuclides• Very Unstable 8 n=3 p=5 5 X 58 n = 29 p = 29 29 X 29
  30. 30. Stable and Unstable Nuclides1) Atomic nuclei with even number ofprotons and neutrons are stable. (Of the 264 stable isotopes, 157 haveeven numbers of both protons andneutrons. Only 4 have odd numbers ofprotons and neutrons.) 12 6 C 30
  31. 31. Stable and Unstable Nuclides2) Atomic nuclei with even number ofneutron and odd number of proton, oddnumber of neutrons and even number ofproton, or odd numbers of both neutronsand protons are unstable. 17 8 O 31
  32. 32. Stable and Unstable Nuclides3) “Magic” numbers of either protons or neutrons. (Magic numbers are 2, 8, 20, 50, 82, and 126).4) An atomic number of 83 or less. (All isotopes with atomic numbers greater than 83 are radioactive). 32
  33. 33. Stable and Unstable Nuclides5) There should be no more protons than neutrons in the nucleus, and the ratio of neutrons to protons should be close to 1 if the atomic number is 20 or below. 33
  34. 34. Types of Radiation 34
  35. 35. Types of Radiation1) Background Radiation is the ever-present radiation from cosmic rays and from natural radioactive isotopes in air, water, soil, and rocks. It causes minimal harm.2) Ionizing Radiation is a radiation that produces ions at it passes through matter. It arises from interaction of radiation by knocking electrons from atoms and molecules, converting them into ions. 35
  36. 36. Types of Radiation• Ionizing radiation devastate living cells by interfering with their normal chemical processes – Transformation of water to highly reactive hydrogen peroxide (H2O2). – Affects the bone marrow resulting to low production of RBC leading to anemia, leukemia and cancer. – Change in the molecules of heredity (DNA) in the reproductive cells producing mutations. 36
  37. 37. Types of Radiation3) Medical Irradiation is obtained from exposure to X-rays and LASERS for medical purposes. - Light Amplification by Stimulated Emission of Radiation (LASER)4) Natural Radiation is the type of decay exhibited by radioactive isotopes. 37
  38. 38. Types of Radiation5) Artificial Radiation is the type of decay exhibited by normally non-radioactive light elements through bombardment. -nuclear reactions 38
  39. 39. Types of RadiationProduced by Radioactive Substances 39
  40. 40. Alpha (α) Particles• positively charged.• He nuclei has two protons and two neutrons, thus having a charge of +2. 4 2 He 2• result from radioactive decay of heavy elements such as radium and uranium. 40
  41. 41. Alpha (α) ParticlesA A 4 4 A A 4 4Z X Z 2 Y 2 He Z X Z 2 Y 2 238 4 92 U 2 __ 234 Th 90 212 4 208 84 Po 2 __ 82 Pb 41
  42. 42. Alpha (α) Particles• When an atom emits an alpha particle, its mass number decreases by 4 and its atomic number decreases by 2.• Reason for instability: – Nucleus is too large 42
  43. 43. Beta (β-) Particles• Beta particles are negatively charged.• Beta particles have a charge of negative one (1-)• Beta particles have a very small mass. 43
  44. 44. Beta (β-) Particles• Beta particles are high-speed electrons produced in the nucleus by the transformation of a neutron into a proton and an electron. 1 1 0 1 1 0 0 n 1 p -1 e 0 n 1 H -1 retained emitted in nucleus – The electron is emitted as a beta particle and the proton remains in the nucleus. 44
  45. 45. Beta (β) Particles A A 0 Z X Z 1 Y -1 e 234 234 0 90 Th 91 Pa -132 0 3215 P 1- __ 16 S 14 0 14 6 C 1- __ 7 N 97 0 40 Zr 1- __ 97 41 Nb 45
  46. 46. Beta (β-) Particles• When an atom emits a beta particle, its mass number remains the same, but its atomic number increases by 1.• Reason for instability: – Nucleus has too many neutrons relative to the number of protons. 46
  47. 47. Gamma (γ) Rays• Gamma rays have no charge – not affected by an electrostatic field.• are not particles, so – they have no mass.• are electromagnetic radiation similar to X-rays. 47
  48. 48. Gamma (γ) Rays• often emitted along with alpha or beta particles.• Originate from unstable atoms releasing energy to gain stability. 238 238 * 92 U 92 U• (*) indicates a slightly lower energy 48
  49. 49. Gamma (γ) Rays 99 m 99 Tc 43 43Tcm = indicates metastable (unstable) 49
  50. 50. Gamma (γ) Rays• When an atom emits a gamma ray, there is no change in the atomic number or mass number.• Reason for instability: – Nucleus has excess energy. 50
  51. 51. Other Forms of Radiation 51
  52. 52. Positron (β+) Emission• Positron (β+) is a particle equal in mass but opposite in charge to the electron. It is represented by 0 e. 1 1 p n1 0 e 1 0 1 Neutrino - an elementary particle that usually travels close to the speed of light, is electrically neutral, and is able to pass through ordinary matter almost unaffected 52
  53. 53. • After the positron is 0 0 0 emitted, the original 1 e 1 e 2 0 radioactive nucleus β+ β- has one fewer proton and one more neutron than it has When the emitted before. positron encounters – Therefore, the mass an electron, both number of the particles are product nucleus is annihilated quickly the same, but its resulting to the atomic number has production of two been reduced by 1. gamma photons. 53
  54. 54. Positron (β +) Emission 18 0 18 9 F 1 e __ 8 O 38 38 K 0 __ 18 Ar 19 1• Reason for instability: – Nucleus has too many protons relative to the number of neutrons 54
  55. 55. Electron Capture (EC)• Electron capture (EC) – is a process in which a nucleus absorbs an electron from an inner electron shell, usually the first or the second. Once inside the nucleus, the captured electron combines with a proton to form a neutron. 1 0 1 1 p 1 e 0 n 55
  56. 56. Electron Capture (EC)• When an electron from a higher shell drops to the level vacated by the captured electron, an X-ray is released. 125 0 125 53 I 1 e 52Te• Iodine – 125 is used as medicine to diagnose pancreatic function and intestinal fat absorption, decays by EC. 56
  57. 57. Electron Capture (EC) 37 0 37 18 Ar 1 e __ 17 Cl 55 0 55 26 Fe 1 e __ 25 Mn• Reason for instability: – Nucleus has too many protons relative to the number of neutrons. 57
  58. 58. Radioactive Decay and Nuclear ChangeType of Decay Particle Particle Change in Change in Decay Particle Mass Charge Nucleon Atomic Number Number Alpha α 4 2+ Decrease by 4 Decrease by decay 2 Beta β 0 1- No change Increase by decay 1Gamma γ 0 0 No change No change rayPositron β+ 0 1+ No change Decrease byemission 1Electron e- 0 1- No change Decrease bycapture (absorbed) 1 58
  59. 59. Penetrating andIonizing Power of Radiation 59
  60. 60. Penetrating and Ionizing Power
  61. 61. Penetrating and Ionizing Power– Alpha particles have very low penetrating power and cannot pass through skin. • Can be stopped by skin, Al foil, or paper– have very high ionizing power • Cause more damage than X-rays or gamma radiation • Not harmful to humans or animals as long as they do not get into the body.
  62. 62. Penetrating and Ionizing Power– Beta particles are less damaging to tissue than alpha particles but penetrate farther and so are generally more harmful. • Have slight penetrating power but can be stopped by heavy clothing 62
  63. 63. Penetrating and Ionizing Power– Gamma rays, which can easily penetrate skin, are by far the most dangerous and harmful form of radiation.– causing cellular damage as they travel through the body. 63
  64. 64. Terms and Unit ofMeasurement of Nuclear Radiation 64
  65. 65. Terms and Units of Measurement of Nuclear Radiation The physical unit of radiation is a measure of the number of nuclear disintegrations occurring per second in a radioactive source.• Curie (Ci) - the number of nuclear disintegrations occurring per second in 1 g of Ra. – one Ci = 3.7 x 1010 dps• Becquerel (Bq): equal to one disintegration or nuclear transformation per second.
  66. 66. Terms and Unit of Measurement of Nuclear Radiation• Roentgen (R): a measure of the energy delivered by a radiation source. – A unit of radiation applied to X-rays and gamma rays only – the amount of radiation that produces ions having 2.58 x 10-4 coulomb/kg; 66
  67. 67. Terms and Units of Measurement of Nuclear Radiation• Radiation absorbed dose (Rad) - total amount of ionizing radiation absorbed by tissue that has been radiated; the SI unit is the gray (Gy) – 1 rad = 100 ergs of energy absorbed/gram of tissue – Gray (Gy): one Gy = 1 joule/kilogram (1 J/kg)• Roentgen-equivalent-man (Rem): a measure of the effect of the radiation when one roentgen is absorbed by a person; the SI unit is the sievert (Sv) where one Sv = 1 J/kg 67
  68. 68. Difference BetweenChemical and Nuclear Reactions 68
  69. 69. Chemical Reactions Nuclear ReactionsAtoms retain their identity Atoms change from one element to anotherReactions involve only Reactions mainly involve protonselectrons and usually only and neutrons.outermost electrons.Reactions rates can be Reactions rates are unaffected byspeeded up by raising the changes in temperature.temperature.Energy absorbed or given Reactions sometimes involveoff in reactions is enormous changes in energy.comparatively small.Mass is conserved. Huge changes in energy are accompanied by measurable 69 changes in mass (E=mc2).
  70. 70. HALF – LIFE 70
  71. 71. Half - life• Half-life – is the amount of time required for one-half the radioactive nuclei in a sample to decay. – The fraction of the original isotope that remains after a given number of half-lives passed is calculated from the relationship 1 fraction remaining = 2n where –n is the number of half - lives 71
  72. 72. Half – life• The amount left after a radioactive atom underwent decay can be calculated by t 1 A A orig 2 – where • t is the number of half-lives that passed 72
  73. 73. Problem 1: Cobalt – 60 has a half-life of 5.25years. If you have a 400-mg sample of Co-60,how much remains after 15.75 years? • Solution: 1 1 1 Fraction remaining 2n 23 8 1 A 400 mg 8 A 50 mg 73
  74. 74. Problem 1: Cobalt – 60 has a half-life of 5.25years. If you have a 400-mg sample of Co-60,how much remains after 15.75 years?• Solution: no. of years 15.75 yrst half - life 5.25 yrs 1 t A A orig 2t 3 1 3 400 mg 2 A 50 mg 74
  75. 75. 234Problem 2: Starting with a 2-gram sample of Th 90, how much remains at the end of 48 days? Thehalf-life of Th-234 is 24 days?Problem 3. Krypton-81 m is used for lungventilation studies. Its half-life is 13 seconds.How long does it take the activity of this isotopeto reach one-quarter of its original value?a) 0.5 g b) 26 s 75
  76. 76. N ame Half-life RadiationHydrogen-3 (tritium) 12.26 y BetaCarb on -14 5730 y BetaPh os phoru s-28 0.28 s PositronPh os phoru s-32 14.3 d BetaPotass iu m-40 1.28 x 109 y Beta + gammaScandium-42 0.68 s PositronCob alt-60 5.2 y GammaStrontium-90 28.1 y BetaTech netium-99m 6.0 h GammaIndiu m-116 14 s BetaIod ine-131 8d Beta + gammaMercury-197 65 h GammaPolonium-210 138 d Alp haRadon-205 2.8 m Alp haRadon-222 3.8 d Alp haUraniu m-235 4 x 109 y Alp ha
  77. 77. Half-life of Some Common RadioisotopesRadioisotopes Half-life Uses Tc-99m 6 hr Imaging of brain, liver, lung, bone marrow, kidney Fe-59 45 days Detection of anemia Ra-226 1600 yr Radiation therapy for cancer I-131 8 days Thyroid therapy P-32 14.3 days Detection of skin cancer Co-60 5.3 yr Radiation cancer therapy C-11 20.3 min Brain scans H-3 12.3 yr Determining total body water Ga-67 78 hr Scan for lung tumors Cr-51 27.8 days Blood volume determination Na-24 15 hr Locating obstruction in blood flow 77 Ir-192 74 days Breast cancer therapy
  78. 78. USES ofRADIOISOTOPES 78
  79. 79. Uses of Radioisotopes1. Tracers2. Nuclear Medicine3. Food Irradiation4. Radioisotopic Dating5. Warfare6. Power Generation 79
  80. 80. Tracers• Tracers are radioactive isotopes used to trace movement or locate the sites of radioactivity in physical, chemical, and biological systems. 80
  81. 81. Nuclear Medicine• Nuclear Medicine involves two distinct uses of radioisotopes – therapeutic and diagnostics. – Therapeutic involves the use of radiation therapy to treat or cure diseases. – Diagnostic involves the use of radioisotopes to obtain information about the state of a patient’s health. 81
  82. 82. Nuclear Medicine• Therapeutic – Iodine-131and Iodine-123 – treatment of thyroid conditions – Cobalt-60 and Cobalt-57 – for treatment of many different types of cancer – Gold-198 – treatment of pleural and peritoneal metastases (spreading disease from original sites). – X-ray therapy – uses Ra or Co-60. X-rays can be used for treatment of superficial skin conditions, deep-seated malignancies and many different types of cancer. 82
  83. 83. Nuclear Medicine• Diagnostic – Technetium–99m – used for many types of scans and measuring blood volume – Krypton-79 – for evaluation of cardiovascular system – Selenium-75 – for determination and size of the pancreas – Mercury-197 – for evaluation of spleen function and for brain scans. 83
  84. 84. Nuclear Medicine• Diagnostic – PET (Positron Emission tomography) Scan – is a technique that uses radioisotopes to get three dimensional pictures showing function processes occurring in the human body. This technique is used to trace gamma rays sent forth by positron producing radionuclide. 84
  85. 85. Nuclear Medicine• Diagnostic – MRI (Magnetic Resonance Imaging) – is a noninvasive (nonsurgical) method of following biochemical reactions in both cells and entire organs under normal physical conditions. 85
  86. 86. Nuclear Medicine• MRI (Magnetic Resonance Imaging) MRI doesn’t involve ionizing radiation, as do X-rays and CT scans. MRI takes advantage of something you have plenty of in your body: 86 water.
  87. 87. Nuclear Medicine• Diagnostic – X-ray - radiation similar to visible light but of much higher energy and much more penetrating. 87
  88. 88. Nuclear Medicine• Radioisotopes have two main uses in medicine; diagnosis and therapy
  89. 89. Food Irradiation• Food Irradiation consists of exposing food to some of ionizing radiation, such as gamma rays or X-rays to kills insects and microorganisms and also to halt the ripening of fruits. Co-60 is used for this purpose. Irradiation lengthens the shelf life of food and reduces the need for preservatives, some of which have toxic effects. 89
  90. 90. Radioisotopic Dating• Radioisotopic Dating is used in determining the age of objects. – Carbon-14 dating – a technique for determining the age of artifacts based on the half-life of C-14. Ex. Shroud of Turin 90
  91. 91. Radioisotopic Dating• Radioisotopic Dating is used in determining the age of objects. – Tritium dating (H-3) – is useful for dating items up to about 100 years old, i.e. beverages, wine. – Tritium has a half-life of 12.43 years. 91
  92. 92. Radioisotopic Dating• Radioisotopic Dating is used in determining the age of objects. – Uranium dating – uses U-238 to determine the age of the earth and other heavenly bodies. 92
  93. 93. Warfare• Warfare – involves construction of nuclear bombs and nuclear weapons. 93
  94. 94. Warfare and Power Generation• Power Generation – involves production of electricity using nuclear energy from nuclear fission of radioactive material, i.e., U-235 in nuclear reactors. 94
  95. 95. ArtificialTransmutation 95
  96. 96. Artificial Transmutation• Artificial Transmutation is the changing of one element into another.• In order to accomplish transmutation, one must alter the stable nucleus by bombarding it with – Alpha particle - Electrons – Neutrons -Deuterons (Hydrogen-2) – Protons – Other particles 96
  97. 97. Artificial Transmutation 14 4 17 1 7 N 2 He 8 O 1 H• The hydrogen nucleus is simply a proton, 1 hence the alternative symbol 1 H for the proton. 39 1 36 19 K 0 n 17 Cl ?• Answer: 4 He 2 97
  98. 98. Artificial Transmutation 7 1 3 Li 1 H 2 4 He 240 1 1 4018 Ar 1 H __ 0 n 19 K114 2 1 115 48 Cd 1 H __ 1 H 48 Cd238 12 1 92 U 6 C __ 60 n 244 Cf 9814 1 1 6 C 0 n __ 1 H 14 C 627 4 113 Al 2 __ 0 n 30 P 15 98
  99. 99. Artificial Transmutation• When chlorine–37 is bombarded with a neutron, a proton is ejected. What new element is formed? 37 1 37 1 17 Cl 0 n 16 S 1 p 37 1 37 1 17 Cl 0 n 16 S 1 H 99
  100. 100. Nuclear Reaction 100
  101. 101. Nuclear Reaction Nuclear Reaction is the process by which one type of nucleus changes into another. Types of Nuclear Reaction1. Nuclear Fission2. Nuclear Fusion 101
  102. 102. Nuclear Fission• Nuclear Fission – is a process by which certain heavy nuclei split into lighter nuclei when they absorb slow moving neutrons. 102
  103. 103. Nuclear Fission1 235 145 88 10 n 92 U 56 Ba 36 Kr 3 n 0 energy • When uranium- 235 is bombarded with neutron, it is broken into two smaller elements. 103
  104. 104. Nuclear Fission1 235 145 88 10 n 92 U 56 Ba 36 Kr 3 n 0 energy – The products have less mass than the starting materials. – The mass decrease in fission is converted into energy. – This form of energy is called atomic energy.
  105. 105. Nuclear Fission• Nuclear fission is a chain reaction Chain Reaction is a self-sustaining reaction which once started, steadily provides energy and matter needed to continue the reaction.
  106. 106. Nuclear Fission• Nuclear reactions do not obey the law of conservation of mass. They obey the combined Law of Conservation of Mass and Energy which states that the amount of mass that disappears is converted into an equivalent amount of energy.• This can be calculated by using Einstein’s equation E = mc2. 106
  107. 107. Nuclear Fission 1 235 145 88 1 0 n 92 U 56 Ba 36 Kr 30 n energy(kg) 1.0087 234.9934 93.9154 138.9179 3(1.0087) Total mass of reactants = 236.0021 kg Total mass of products = 235.8594 kg Loss in mass = 0.1427 kg • Using Einstein’s equation, E=mc2, we find E mc 2 8 2 0.1427 kg 3 x 10 m/s 16 E 1.28 x 10 J 107
  108. 108. Nuclear Fission• Nuclear reactors use U3O8 (a compound enriched with scarce fissionable U-235).• Because the supply of U-235 is limited breeder reactor has been developed.• Breeder reactors use neutrons to convert non-fissionable isotopes such as U-238 or Th-232 to fissionable isotopes , Pu-239 or U-233. 108
  109. 109. Nuclear Fission • Breeder reactors1 238 239 239 2390 n 92 U 92 U 93 Np 94 Pu1 232 233 233 2330 n 90 Th 90 Th 91 Pa 92 U • Atomic bomb uses Pu-2391 238 239 239 2390 n 92 U 92 U 93 Np 94 Pu 109
  110. 110. Nuclear Fusion• Nuclear Fusion is the process whereby nuclei of light atoms combine to form a heavier nucleus with the release of energy. The sun provides us with energy through nuclear fusion. 110
  111. 111. Nuclear Fusion in the Sun 1 1 2 0Step 1 : H 1 1 H 1 H 1 e energy 2 1 3Step 2 : H 1 1 H 2 He energy (occurstwice) 3 3 4 1Step 3 : He 2 2 He 2 He 2 H energy 1• The reaction that takes place in the Sun is called thermonuclear reactions because very high temperatures (million of degrees) are required in order to initiate them. The fusion of only 1 g of H releases an amount of energy equivalent to the burning of nearly 20 tons of coal. 111
  112. 112. PROTECTION FROM RADIATION 112
  113. 113. Protection from Radiation• Shielding, distance, and limiting exposure are the only effective preventive methods against radiation exposure.• Exposure to external radiation can be controlled by increasing distance between the body and the source of the radiation. The amount of radiation received varies inversely as the square of the distance. 113
  114. 114. Problem: A nurse receives an exposure of 20 mrem when standing 3 ft from a radioactive source. What will be the exposure at a distance of (a) 6 ft? 1 rem = 1 R 2 rem = amount ofexposure at distance1 d2 ionizing radiation,exposure at distance 2 2 d1 that when absorbed by human, has an 2 20 mrem 6 ft effect equal to the x 2 absorption of 1 R. 3 ft mrem is a smaller x 5 mrem unit. 114
  115. 115. 115

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