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  1. 1. Radioactivity Peter Huruma Mammba Department of Physical Science DODOMA POLYTECHNIC OF ENERGY AND EARTH RESOURCES MANAGEMENT (MADINI INSTITUTE) –D
  2. 2. Radioactivity • The nuclei of naturally occurring heavy elements like U, Th, Ra and Po are unstable and keep on emitting spontaneously invisible rays or radiations (α, β, γ -rays) and give more stable elements.
  3. 3. Radioactivity • These heavy elements are called radioactive elements. • The property of emitting these rays is called radioactivity of the elements.
  4. 4. Radioactivity cont…. • It is the nucleus of an atom of an element which spontaneously disintegrates to emit α, β or γ-rays. • The rays emitted by radioactive element are called radioactive rays
  5. 5. Thus radioactivity can be defined as:- The phenomenon in which the nucleus of the atom of an element undergoes spontaneous and uncontrollable disintegration (or decay) and emit α, β or γ-rays.
  6. 6. Also, radioactivity can be defined as:- • Is the Process of spontaneous disintegration of the nuclei of heavy elements with the emission of certain types of radiations.
  7. 7. Radioactivity cont…. The emitted α, β or γ-rays from unstable nuclei are collectively called ionizing radiations. Depending on how the nucleus loses this excess energy either a lower energy atom of the same form will result, or a completely different nucleus and atom can be formed.
  8. 8. Radioactivity cont…. Ionization is the addition or removal of an electron to create an ion. Ionizing radiation is any type of particle (α, β) or electromagnetic wave (γ) that carries enough energy to ionize or remove electrons from an atom. .
  9. 9. Radioactivity cont…. • These radiations are of such high energy that when they interact with materials, they can remove electrons from the atoms in the material. This effect is the reason why ionizing radiation is hazardous to health
  10. 10. • Radioactivity is of the following two types which are: a) Natural radioactivity b)Artificial Radioactivity
  11. 11. Natural Radioactivity is the process of spontaneous (i.e. without external means, by it self) disintegration of the nuclei of heavy elements with the emission of radiation. -these are unstable nuclei found in nature.
  12. 12. Natural radioactivity
  13. 13. Natural radioactivity cont….. • All heavy elements above Z=82 show the phenomenon of radioactivity. the emission of radiation changes the structure of the nucleus and transforms the atom into a lighter atom.
  14. 14. Natural radioactivity cont….. • The heavy element are unstable therefore they disintegrate to acquire a more stable state.
  15. 15. continue • Since radioactivity is practically unaffected by temperature, pressure and other conditions, we conclude that it is a nuclear property. Therefore α,β-particles and γ-rays are emitted from the nucleus. • It may be noted that electrons revolving around the nucleus are not responsible for radioactivity.
  16. 16. Artificial Radioactivity • Is the process in which a stable (non- radioactive) nucleus is changed into an unstable (radioactive) nucleus by bombarding it with appropriate atomic projectiles like α, neutron, proton.
  17. 17. Example of Artificial radioactivity
  18. 18. The differences between natural and artificial radioactivity Natural radioactivity Artificial radioactivity Is spontaneous, since in natural radioactivity, the nuclei of heavy atom disintegrate on their own accord, forming slightly lighter and more stable nuclei and emitting α,β,ᵞ radiations. Is not spontaneous, since in it the nuclei of the atoms have to be bombarded by fast moving particles like α, neutrons, protons, deuterons. Is uncontrolled and hence it can not be slowed down or accelerated by any means. Can be controlled by controlling the speed of the bombarding particles used for bringing about the artificial radioactivity Is usually shown by heavy elements. Can be induced even in light element.
  19. 19. Units of Radioactivity
  20. 20. Equivalent dose Is a dose quantity representing the stochastic health effects of low levels of ionizing radiation on the human body. It is derived from the physical quantity absorbed dose, but also takes into account the biological effectiveness of the radiation, which is dependent on the radiation type and energy. The SI unit of measure is the Sievert (Sv).
  21. 21. Other Common Radiation Units – SI 1. Gray (Gy) • To measure absorbed dose. (the amount of energy actually absorbed in some material) and is used for any type of radiation and any material (does not describe the biological effects of the different radiations) • Gy = J / kg (one joule of energy deposited in one kg of a material)
  22. 22. 2. Roentgen (R) -Is used to measure exposure but only to describe for gamma and X-rays, and only in air. • R = depositing in dry air enough energy to cause 2.58 𝑥10−4 coulombs per kg
  23. 23. 3. Rem (Roentgen Equivalent Man) - to derive equivalent dose related the absorbed dose in human tissue to the effective biological damage of the radiation.
  24. 24. 4. Sievert (Sv) • To derive equivalent dose (the absorbed dose in human tissue to the effective biological damage of the radiation). • Sv = Gy x Q (Q = quality factor unique to the type of incident radiation)
  25. 25. 5. Becquerel (Bq) - to measure a radioactivity (the quantity of a radioactive material that have 1 transformations /1s) • Bq = one transformation per second, there are 3.7 x 1010 Bq in one curie.
  26. 26. Detection and Measurement of Radioactivity • The radioactivity of the radioactive substance is detected and measured by instruments like:- Geiger-Muller (G-M) counter Wilson Cloud Chamber. Scintillation Counters. Dosimeter.
  27. 27. Geiger-Muller (G-M) counter
  28. 28. Scintillation Counters
  29. 29. Dosimeters
  30. 30. Types of Radioactive Rays • There are three types of radioactive rays which are:- – Alpha (α) – Beta (β) – Gamma (ᵞ) rays
  31. 31. Alpha ( 4 2He) • An alpha particle is a helium nucleus whose mass number is 4 and nuclear charge (Atomic number) is +2.
  32. 32. Alpha- Particle Decay • For proton- rich heavy nuclei, a possible mode of decay to a more stable is by alpha particle emission.
  33. 33. Alpha decay • Has largest ionizing power Ability to ionize molecules & atoms due to largeness of -particle • has lowest penetrating power Ability to penetrate matter • Skin, even air, protect against -particle radiation
  34. 34. Alpha particle …
  35. 35. X A Z Y A - 4 Z - 2 + He 4 2 Alpha Decay unstable atom more stable atom alpha particle
  36. 36. Alpha Decay Ra 226 88 Rn 222 86 He 4 2
  37. 37. X A Z Y A - 4 Z - 2 + He 4 2 Ra 226 88 Rn 222 86 + He 4 2 Alpha Decay
  38. 38. Rn 222 86 He 4 2 +Po 218 84 He 4 2 Rn 222 86 +Y A Z He 4 2 Alpha Decay
  39. 39. He 4 2 U 234 92 +Th 230 90 He 4 2 X A Z +Th 230 90 He 4 2 Alpha Decay
  40. 40. Th 230 90 +Y A Z He 4 2 Alpha Decay He 4 2 +Ra 226 88 He 4 2 Th 230 90
  41. 41. X A Z +Pb 214 82 He 4 2 Alpha Decay He 4 2 +Pb 214 82 He 4 2 Po 218 84
  42. 42. Beta Decay A beta particle (Denoted by 𝛽) is a fast moving electron which is emitted from the nucleus of an atom undergoing radioactive decay. Beta decay occurs when a neutron changes into a proton and an electron.
  43. 43. Beta Decay • Many neutron-rich radioactive nuclides decay by changing a neutron in the parent nucleus into a proton and emitting an energetic electron.
  44. 44. Beta Decay As a result of beta decay, the nucleus has one less neutron, but one extra proton. The atomic number, Z, increases by 1 and the mass number, A, stays the same.
  45. 45. Beta Decay • Many different names are applied to this decay process: • Electron decay, beta minus decay, negatron decay, negative electron decay, negative beta decay or simply Beta Decay
  46. 46. Beta Decay Po 218 84 b 0 -1 At 218 85
  47. 47. X A Z Y A Z + 1 + b 0 -1 Beta Decay Po 218 84 Rn 218 85 + b 0 -1
  48. 48. Th 234 90 Y A Z + b 0 -1 Beta Decay Th 234 90 Pa 234 91 + b 0 -1
  49. 49. X A Z Pb 210 82 + b 0 -1 Beta Decay Tl 210 81 Pb 210 82 + b 0 -1
  50. 50. Bi 210 83 Y A Z + b 0 -1 Beta Decay Bi 210 83 Po 210 84 + b 0 -1
  51. 51. X A Z Bi 214 83 + b 0 -1 Beta Decay Pb 214 82 Bi 214 83 + b 0 -1
  52. 52. Comparison between a β- particle and electron a) Both the particles are negatively charged which is equal to -1.
  53. 53. Comparison …. b) When an atom lose an electron, a cation of the same element is formed. On the other hand, when the nucleus lose a β –particle a new neutral element is obtained.
  54. 54. Gamma Decay Gamma rays are not charged particles like  and b particles. Gamma rays are electromagnetic radiation with high frequency. When atoms decay by emitting  or b particles to form a new atom, the nuclei of the new atom formed may still have too much energy to be completely stable. This excess energy is emitted as gamma rays (gamma ray photons have energies of ~ 1 x 10-12 J).
  55. 55. Absorption of 𝜸 rays • Many nuclides emit 𝛾 rays of more than one wavelength. If 𝛾-rays of a 𝜆 are selected, their absorption is an exponential faction of absorber thickness, i.e. 𝐼 = 𝐼 𝑜 𝑒−𝜇𝑑
  56. 56. Absorption… 𝐼 = 𝐼 𝑜 𝑒−𝜇𝑑 I = the intensity transmitted by a thickness by a thickness d of absorber. 𝐼0 = the intensity of the 𝛾 − rays incident on the absorber 𝜇 = the linear absorption coefficient (or attenuation coefficient) of the absorber (Unit = 𝑚−1 )
  57. 57. • Also hold for x- rays 𝛾 −rays passing through an absorber
  58. 58. Absorption… Note. (i) The absorption of 𝛾-rays increases with the atomic number of the material of the absorber.
  59. 59. Note. (ii) The exponential nature of 𝛾- ray absorption arises because, in most cases, a 𝛾- ray quantum loses all its energy in a single event, and therefore the fractional intensity of the beam falls by a fixed amount each time it traverses any given small thickness of absorber.
  60. 60. Photon Emission Difference Between X-Rays and Gamma Rays 63
  61. 61. X rays • X Rays are electromagnetic waves / photons emitted not from the nucleus, but normally emitted by energy changes in electrons. These energy changes are either in electron orbital shells that surround an atom or in the process of slowing down such as in an X-ray machine.
  62. 62. Properties of α, β and ᵞ rays
  63. 63. Radiation Penetration Ability
  64. 64. Other important particles
  65. 65. Positron Decay • Nuclei that have too many protons for stability often decay by changing a proton into a neutron. • In this decay mechanism an anti-electron or positron 𝛽+ or 1 0 𝑒, and a neutrino 𝜐 are emitted.
  66. 66. Positron Decay • The 𝛽+ decay reaction is written as 𝑍 𝐴 𝑃 → 𝑧 −1 𝐴 𝐷 + +1 𝑜 𝑒 + 𝜐 The positron has the same physical properties as an electron, except that it has one unit of positive charge.
  67. 67. Neutron Decay • A few neutron-rich nuclides decay by emitting a neutron producing a different isotope of the same parent element. • Generally, the daughter nucleus is left in an excited state which subsequently emits gamma photons as it returns to its ground state.
  68. 68. Neutron Decay • This decay reaction is 𝑍 𝐴 𝑃 → 𝑧 𝐴−1 𝑃∗ + 0 1 𝑛 An example of such neutron decay reaction is;- 54 138 𝑋𝑒 → 54 137 𝑋𝑒∗ + n
  69. 69. Proton Decay • A few proton-rich radionuclides decay by emission of a proton. • In such decays, the daughter atom has an extra electron (i.e., it is a singly charged negative ion)
  70. 70. Proton Decay • This extra electron is subsequently ejected from the atom’s electron cloud to the surroundings and the daughter returns to an electrically neutral atom.
  71. 71. Proton Decay • The proton decay reaction is thus;- 𝑍 𝐴 𝑃 → 𝑧−1 𝐴−1 𝐷∗ − + 1 1 𝑝 • In this reaction P and D refer to atoms of the parent and daughter.
  72. 72. Electron Capture • In the quantum mechanical model of an atom, the orbital electrons have a finite (but small) probability of spending some time inside the nucleus, the innermost K-shell electrons having the greatest probability.
  73. 73. Electron Capture • It is possible for an orbital electron, while inside the nucleus, to be captured by a proton, which is thus transformed into a neutron.
  74. 74. Electron Capture • Conceptually, we can visualize this transformation of the proton as 𝑝 + −1 0 𝑒 → 𝑛 + 𝜐, Where the neutrino is again needed to conserve the energy and momentum.
  75. 75. Electron Capture • The general electron capture (EC) decay reaction is written as 𝑍 𝐴 𝑃 → 𝑍−1 𝐴 𝐷∗ + 𝑣 Where the daughter is generally left in an excited nuclear state with energy E above a ground level.
  76. 76. Electron Capture • The following nuclear reactions are electron capture reactions. 26 55 𝐹𝑒29 + −1 0 𝑒 → 25 55 𝑀𝑛30 + 𝑣 56 131 𝐵𝑎75 + −1 0 𝑒 → 55 131 𝑀𝑛76 + 𝑣
  77. 77. Some important particles
  78. 78. Some important particles contin...
  79. 79. Example 1 • 90 234 𝑇ℎ disintegrates give 82 206 𝑃𝑏 as the final product. How many alpha and beta particles are emitted during this process?
  80. 80. Solution • If the number of ∝, 𝛽 particles which are emitted from 90 234 𝑇ℎ is x and y respectively, then the formation of 82 206 𝑃𝑏 can be represented as; 90 234 𝑇ℎ −𝑥2 4 𝐻𝑒 → . 90−2𝑥 234−4𝑥 𝐴 −𝑦−1 0 𝑒 → . 90−2𝑥+𝑦 234−4𝑥 𝑃𝑏 = 82 206 𝑃𝑏
  81. 81. Solution 234 - 4x = 206 or x = 7 and 90 - 2x + y = 82 90 - 14 + y = 82 y = 6 Thus 7𝛼 and 6𝛽 particles are emitted
  82. 82. Exercise 1 • In the following natural radioactive series where only the first and last elements are given, calculate the number of ∝, 𝛽- particles emitted in each case.
  83. 83. Exercise 1 (a) 92 238 𝑈 → 82 206 𝑃𝑏 (b) 90 232 𝑇ℎ → 82 208 𝑃𝑏 (c) 92 235 𝑈 → 82 207 𝑃𝑏
  84. 84. Exercise 2 • The Uranium atom 92 238 𝑈 emits an 𝛼 - particle to become thorium, which then emits a 𝛽- particle to become protactinium. What are the atomic and mass numbers of protactinium?
  85. 85. Exercise 3 • Radon has an atomic number of 86 and a mass number of 220. it emits an 𝛼 − particle to become Thorium A (polonium), which emits another 𝛼 − particle to become Thorium B (radioactive lead). Thorium B then emits a 𝛽 − particle to become Thorium C (bismuth). What is (a) the atomic number and (b) the mass number of Thorium C?
  86. 86. Exercise 4 • Radioactive Uranium 92 238 𝑈 emits an 𝛼 − particle to become Thorium. Thorium emits a 𝛽 − particle to become Protactinium which then emits another 𝛽 − particle. What is the atomic number, mass number and name of the final atom produced?
  87. 87. Exercise 5 • In each of the nuclear reactions listed below, what is the atomic number, mass number and name of the particle produced? • Boron 5 10 𝐵 bombarded with a neutron gives Lithium 3 7 𝐿𝑖 + particle. • Aluminum 13 27 𝐴𝑙 bombarded with an 𝛼 − particle gives Silicon 14 30 𝑆𝑖 + particle. • Sodium 11 23 𝑁𝑎 bombarded with an 𝛼 − particle gives Aluminum 13 26 𝐴𝑙 + particle.
  88. 88. Disintegration constant or Decay Constant (K)
  89. 89. Decay Constant (K) • Suppose a radioactive element A (i.e. at t = 0 be 𝑁0) disintegrates into another substance B. • Now as the time passes, the element A disintegrates and hence the amount of A goes on decreasing while that of B goes on increasing.
  90. 90. Decay Constant (K) • Suppose that after t time, the amount of A left undisintegrated is N. • ( 𝑁0 - N ) is the amount of A that gets disintegrated into B after time t.
  91. 91. Decay Constant (K) • Now if a small amount, 𝑑𝑁 of A gets disintegrated into B in a small time 𝑑𝑡, then the rate of a disintegration (i.e. rate of decrease) of A into B is equal to − 𝑑𝑁 𝑑𝑡 which is proportional to the amount of A left undisintegrated (N).
  92. 92. Decay Constant (K) − 𝑑𝑁 𝑑𝑡 ∝ N or − 𝑑𝑁 𝑑𝑡 = KN Where K = is amount of proportionality which is called disintegration or decay constant - 𝑑𝑁 𝑁 = 𝐾. 𝑑𝑡 ………….. (i)
  93. 93. Decay Constant (K) • Decay Constant (K) Can be defined as the fraction of the total amount of the radioactive substance 𝑑𝑁 𝑁 which disintegrates in unit time. K is expressed in 𝑡𝑖𝑚𝑒−1 units i.e. in 𝑠−1 , 𝑚𝑖𝑛−1 , ℎ𝑟𝑠−1 , 𝑑𝑎𝑦𝑠−1 , 𝑦𝑟𝑠−1
  94. 94. Decay Constant (K) • Integrating equation (i) over limit 𝑁0 and N (for the left hand side) and 0 and t (for the right hand side), we get; 𝑁0 𝑁 𝑑𝑁 𝑁 = - 0 𝑡 𝐾𝑑𝑡 𝐼𝑛 𝑁 𝑁0 = - Kt …………………… (ii)
  95. 95. Decay Constant (K) 𝑁 𝑁0 = 𝑒−𝐾𝑡 𝑵 = 𝑵 𝟎 𝒆−𝑲𝒕
  96. 96. Radioactive Decays 99 Variation of N as a function of time t N No t N = No e - t Also A = Ao e - t Radioactive Decay Kinetics - plot Number of radioactive nuclei decrease exponentially with time as indicated by the graph here. As a result, the radioactivity vary in the same manner. Note  N = A  No = Ao
  97. 97. Radioactive Decays 100 Decay Constant and Half-life Variation of N as a function of time t N No t N = No e - t Also A = Ao e - t Be able to apply these equations! N = No e– t A = Ao e – t ln N = ln No –  t ln A = ln Ao –  t Determine half life, t½ Ln(N or A) t ln N1 – ln N2  = ––––––––––– t1 – t2 t½ *  = ln 2
  98. 98. HALF-LIFE (𝑇1 2 )
  99. 99. Half-Life • The half-life of a radioactive nuclide – Is the time taken for half the nuclei present to disintegrate. If the half-life is represented by 𝑻 𝟏 𝟐 , then when t = 𝑻 𝟏 𝟐 , 𝑁 = 𝑁 𝑜 2, and therefore by equation 𝑁 = 𝑁0 𝑒−𝐾𝑡 𝑁0 2= 𝑁0 𝑒 −𝐾𝑇1 2 ∴ 𝑇1 2 = 0.693 𝐾
  100. 100. Half-life • Most radioactive materials decay in a series of reactions. • Radon gas comes from the decay of uranium in the soil. • Uranium (U-238) decays to radon-222 (Ra-222).
  101. 101. Radioactive Decays 104 The Decay Path of 4n + 2 or 238 U Family 238 U234 U 234 Pa 234 Th230 Th 226 Ra 222 Rn 218 At 218 Po214 Po 214 Bi 214 Pb 210 Po 210 Bi 206 Pb 210 Pb 206 Tl 210 Tl 206 Hg Minor route Major route  decay b decay Radioactivity - 238U radioactive decay series
  102. 102. Decay Constant for some Elements
  103. 103. ACTIVITY
  104. 104. ACTIVITY • Activity is the rate of disintegration in a radioactive substance. Activity of a substance, A = - 𝑑𝑁 𝑑𝑡 The minus sign shows that the activity decreases with the passage of time.
  105. 105. ACTIVITY • According to decay law, the rate of disintegration is directly proportion to the number of atoms present. i.e. − 𝑑𝑁 𝑑𝑡 ∝ 𝑁 − 𝑑𝑁 𝑑𝑡 = 𝐾𝑁 ∴ 𝐴𝑐𝑡𝑖𝑣𝑖𝑡𝑦, 𝐴 = 𝐾𝑁
  106. 106. Examples
  107. 107. Examples… 4. A sample of radioactive material contains 1018 atoms. The half-life of the material is 2000 days. Calculate;- (i) The fraction remaining after 5000 days (ii) The activity of the sample after 5000 days.
  108. 108. Exercise 6 • Half-file of . 210 𝑃 is 140 days. Calculate the number of days after which 1 4g of . 210 𝑃 will be left undisintegrated from 1g of the isotope.
  109. 109. Exercise 6 The mass number of radium is 226. It is observed that 3.67 𝑥 1010 ∝ − particles are emitted per second from 1g of radium. Calculate the half-life of radium.
  110. 110. Exercise 7 The count rate meter is used to measure the activity of a given amount of a radioactive element. At one instant, the meter shows 475 count/ minutes. Exactly 5 minutes later, it shows 270 counts/minutes. Find (i) The decay constant (K) (ii) Mean life (iii)The half life of the element.
  111. 111. Exercise 8 • The half-life of radium is 1500 years. After how many years will 1 g of pure radium (i) reduce to 1 centigram (ii) lose 1 mg?
  112. 112. Exercise 9 • A sample of radioactive material has an activity of 9 𝑥 1012 𝐵𝑞. The material has a half-life of 80 s. How long will it take for the activity to fall to 2 𝑥 1012 𝐵𝑞?
  113. 113. Exercise 10 • Biologically useful technetium nuclei (with atomic weight 99) have a half life of six hours. A solution containing 10−12 g of this is injected into the bladder of a patient. • Find its activity in the beginning and after one hour.
  114. 114. Exercise 11 • An isotope (36 87 𝐾𝑟) has a half-life of 78 minutes. Calculate the Activity of 10 𝜇𝑔 of 36 87 𝐾𝑟. The (Avogadro's constant, 𝑁𝐴 = 6.0 𝑥 1023 𝑚𝑜𝑙−1 )
  115. 115. Exercise 12 • Carbon-14, 6 14 𝐶, is a radioactive isotope of carbon that has a half-life of 5730 years. If you start with a sample of 1000 carbon-14 nuclei, how many will still be around in 22920 years?
  116. 116. Exercise 13 • The half-life of the radioactive nucleus 88 226 𝑅𝑎 is 1.6 𝑥 103 𝑦𝑒𝑎𝑟𝑠. If a sample contains 3 𝑥 1016 such nuclei, determine the activity of this time.
  117. 117. Exercise 14 • A radioactive sample contains 3.50 𝜇𝑔 of pure 6 11 𝐶, which has a half-life of 20.4 min. (a) Determine the number of nuclei present initially.
  118. 118. Exercise 15 • A sample of the Isotope 53 131 𝐼, which has a half-life of 8.04 days, has a measured activity of 5 𝑚𝐶𝑖 at the time of shipment. Upon receipt in a medical laboratory, the activity is measured to be 4.2 𝑚𝐶𝑖. How much time has elapsed between the two measurements?
  119. 119. Exercise 16 • A piece of charcoal of mass 25 g is found in some ruins of a ancient city. The sample shows a 6 14 𝐶 activity of 250 decays/min. How long has the tree that this charcoal came from been deed?
  120. 120. Exercise 17 • Why are heavy nuclei unstable?
  121. 121. Exercise 18 • If a nucleus has a half-life of 1 year, does this mean that it will be completely decayed after 2 years? Explain
  122. 122. Exercise 19 • What do you understand by mass defect of an atom. • Distinguish between binding energy of an atom and binding energy of the nucleus. Give the expressions for binding energy in MeV and binding energy in Joules (J)
  123. 123. Exercise 20 • What is the difference between a neutrino and photon?
  124. 124. Exercise 21 • Explain why many heavy nuclei undergo alpha decay but not spontaneously emit neutrons or protons. • Pick any beta decay process and show that the neutrino must have zero charge.
  125. 125. Isotopes
  126. 126. Isotopes Isotope are the atoms of the same elements which have the same atomic number (Z) or the same number of protons (p) but different mass number s(A). For example (A = 2,Z =1), (A = 1, Z= 1), these are isotopes of hydrogen. Isotopes of chlorine 35Cl 37Cl 17 17 chlorine - 35 chlorine - 37 129
  127. 127. Isotopes + + + + + + Nucleus Electrons Nucleus Neutron Proton Carbon-12 Neutrons 6 Protons 6 Electrons 6 Nucleus Electrons Carbon-14 Neutrons 8 Protons 6 Electrons 6 + + + + + + Nucleus Neutron Proton
  128. 128. 3 p+ 3 n0 2e– 1e– 3 p+ 4 n0 2e– 1e– 6Li 7Li + + +Nucleus Electrons Nucleus Neutron Proton Lithium-6 Neutrons 3 Protons 3 Electrons 3 Nucleus Electrons Nucleus Neutron Proton Lithium-7 Neutrons 4 Protons 3 Electrons 3 + + +
  129. 129. Mass Spectrophotometer electron beam magnetic field gas stream of ions of different masses lightest ions heaviest ions Dorin, Demmin, Gabel, Chemistry The Study of Matter 3rd Edition, page 138
  130. 130. . • mass spectrometry is used to experimentally determine isotopic masses and abundances • interpreting mass spectra • average atomic weights - computed from isotopic masses and abundances - significant figures of tabulated atomic weights gives some idea of natural variation in isotopic abundances Weighing atoms gas sample enters here filament current ionizes the gas ions accelerate towards charged slit magnetic field deflects lightest ions most ions separated by mass expose film The first mass spectrograph was built in 1919 by F. W. Aston, who received the 1922 Nobel Prize for this accomplishment
  131. 131. Natural uranium, atomic weight = 238.029 g/mol Density is 19 g/cm3. Melting point 1000oC. Two main isotopes: U 238 92 U 235 92 99.3% 0.7% Because isotopes are chemically identical (same electronic structure), they cannot be separated by chemistry. So Physics separates them by diffusion or centrifuge Separation of Isotopes (238 amu) x (0.993) + (235 amu) x (0.007) 236.334 amu + 1.645 amu 237.979 amu U 238 92
  132. 132. Characteristics of Isotopes i. Since the atomic number of the isotopes are the same, they contain the same number of protons in the nucleus and the same number of electrons revolving around the nucleus
  133. 133. Characteristics of Isotopes ii. Since the mass number of isotopes are different, the sum of protons and neutrons in the nucleus is also different.
  134. 134. Characteristics of Isotopes iii. Since isotopes of a given element have different number of neutrons, they show different physical properties (e.g.. 𝜌, MP, BP etc..). • Since isotopes have the same atomic number, they have the same electronic configurations and hence have the same chemical properties.
  135. 135. Characteristics of Isotopes iv. Isotopes have different radioactive properties, since the composition of their nuclei is different.
  136. 136. Characteristics of Isotopes v. All the isotopes are placed in the same group of the periodic table, since they have the same atomic number.
  137. 137. Types of isotopes Radioactive (unstable) as well as non-radioactive (stable) elements give two types of isotopes as follows:- I. Radioactive or Unstable isotopes II. Non-radioactive or stable isotopes
  138. 138. Radioactive or Unstable isotopes
  139. 139. Non-radioactive or Stable isotopes
  140. 140. Production of an isotopes by the emission of one α and two β-particles
  141. 141. Uses of Radioactive Isotopes In Medical Field (i) In order to find out if blood is circulating to a wound or not, a radiotracers is introduced in to the body and after suitable time, some quantity of blood is taken from the wound and its radioactivity is measured by means of a Geiger-Muller Counter.
  142. 142. (i) • The Geiger-Muller Counter detect the exact position where the blood clot in that human body.
  143. 143. In Medical Field conti… • Diagnosis of diseases. Isotopes with a short half-life give off lots of energy (γ-rays) in a short time has been used to detect the exact position of the tumour in the human body. Therefore, Isotopes are useful in medical imaging.
  144. 144. Single-photon emission computed tomography (PET)
  145. 145. Image produced by PET scanner during diagnosis
  146. 146. Image produced by PET scanner during diagnosis PECT can be used for nuclear cardiology SPECT modality can be used to assess cerebral perfusion.
  147. 147. In Medical Field conti… • The isotopes with high energy γ rays has been used for the treatment of cancer. The treatment of diseases by the use of radioactive isotopes is called Radiotherapy
  148. 148. The use of linear Accelerator for the treatment of different kinds of Cancer
  149. 149. Treatment of Cervical Cancer using High Dose Rate Intracavitary Brachytherapy (HDR-ICBT)
  150. 150. Treatment of Prostate Cancer using High Dose Rare Interstitial Brachytherapy
  151. 151. In Medical Field conti… Sterilization and irradiation • Syringes, dressings, surgical gloves and instruments, and heart valves can be sterilized after packaging by using radiation. • Radiation sterilization can be used where more traditional methods, such as heat treatment, cannot be used, such as in the sterilization of powders and ointments and in biological preparations like tissue grafts.
  152. 152. Medical Sterilization Machines
  153. 153. In Agriculture • In agriculture, radioactive materials are used to improve food crops, preserve food, and control insect pests. • They are also used to measure soil moisture content, erosion rates, salinity, and the efficiency of fertilizer uptake in the soil.
  154. 154. Application of radiation during protection of Agricultural materials
  155. 155. Environment • Radioactive materials are used as tracers to measure environmental processes, including the monitoring of silt, water and pollutants. • They are used to measure and map effluent and pollution discharges from factories and sewerage plants, and the movement of sand around harbours, rivers and bays. Radioactive materials used for such purposes have short half- lives and decay to background levels within days.
  156. 156. In Industry • Radioactive materials are used in industrial radiography, civil engineering, materials analysis, measuring devices, process control in factories, oil and mineral exploration, and checking oil and gas pipelines for leaks and weaknesses.
  157. 157. In industry… • Examples on the uses of industrial measuring devices which containing radioactive materials are:- (i) They are used for testing the moisture content of soils during road construction.
  158. 158. In industry…. (ii) The are used to measure the thickness of paper and plastics during manufacturing. (iii) To checking the height of fluid when filling bottles in factories. NB: Radioactive materials are even used in devices designed to detect explosives.
  159. 159. In Our Homes One of the most common uses of radioactive materials in the home is in smoke detectors. Most of these life-saving devices contain tiny amounts of radioactive material which make the detectors sensitive to smoke. The radiation dose to the occupants of the house is very much less than that from background radiation.
  160. 160. Smoke detectors
  161. 161. Other Applications of radioactive isotopes • Many satellites use radioactive decay from isotopes with long half-lives for power because energy can be produced for a long time without refueling. • The isotope carbon-14 is used by archeologists to determine age. • Radioactive isotopes are used to detect the leakage or crack in the underground oil pipes, gas pipes and water
  162. 162. Exercise 22 • Explain in detail how you can determine the age of a sample using the technique of carbon dating. • Why is carbon dating unable to provide accurate estimates of very old material?
  163. 163. Nuclear stability • It has been observed that some isotopes are stable while others are unstable. Stable nuclides are not undergo spontaneous disintegration. This is due to the stability of their nuclides of an atom called nuclear stability.
  164. 164. Factors Affecting Nuclear stability i. Even and Odd number of protons and neutrons. ii. Neutron-to-proton ratio. iii. Packing fraction. iv. Binding energy. v. Magic numbers.
  165. 165. Exercise 23 Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms. 12C 13C 14C 6 6 6 #P _______ _______ _______ #N _______ _______ _______ #E _______ _______ _______ LecturePLUS Timberlake 168
  166. 166. Nuclear reactions • These are the reactions in which one element is converted into the other either by emitting α or β particles (spontaneous disintegration) or by bombarding it with suitable bombarding particle(artificial transmutation of element).
  167. 167. Differences between chemical reaction and Nuclear reaction
  168. 168. Nuclear Fission • Is a nuclear reaction in which a heavy nucleus, when bombarded with slow moving neutrons, split into two nuclei of near equal mass with the release of anomalous amount of energy.
  169. 169. Example of nuclear fission A B C D Where A = Thermal neutron B = Fission C = Fission product D = Huge amount of energy
  170. 170. Types of fission reaction • We have two types of nuclear fission reaction. These are :- a. Uncontrolled or explosive fission reaction b. Controlled or artificial fission reaction
  171. 171. Uncontrolled or explosive fission reaction
  172. 172. Nuclear Reactor or Atomic Reactor • Is a kind of furnace in which controlled fission of a radioactive material like U-235 takes place and a manageable amount of nuclear energy (atomic energy) is produced at a steady slow rate.
  173. 173. Uses of a Nuclear Reactor (i) Radioactive isotopes of various elements are produced (ii) Heat energy produced in the fussion of u-235 nucleus by slow neutrons taking place in the atomic reactor has been used to generate electricity
  174. 174. Uses of a Nuclear Reactor iii. It produces fissionable material like plutonium which is used in atomic bomb. iv. It is also used for the production of fast neutrons that are needed for nuclear bombardment
  175. 175. The Uses of Nuclear reactor for the production of electricity
  176. 176. Nuclear Fusion Also called Atomic Fusion • Is the nuclear reaction in which lighter nuclei combine together to form a single heavy and more stable nucleus and large amount of energy is released.
  177. 177. Example of nuclear fusion reaction A B C D E A= Deuterium B= Tritium C = α- Particle D= Neutron E = Anomalous amount of energy
  178. 178. Nuclear fusion
  179. 179. Our sun undergos nuclear fusion
  180. 180. Differences between Nuclear fusion and Nuclear fission
  181. 181. Exercise 24 • Distinguish between nuclear fission and nuclear fusion. Give some equations to support your answer.
  182. 182. Atomic Bomb in Japan
  183. 183. Atomic Bomb in Japan cont..
  184. 184. Atomic Bomb in Japan cont..
  185. 185. The after-effects of atomic bomb
  186. 186. Now days in Japan
  187. 187. Now days in Japan cont…
  188. 188. Now days in Japan cont…
  189. 189. Thank you for your attention
  190. 190. 1. Can a single nucleus emit 𝛼-particle, 𝛽- particle or 𝛾-ray together? (1 Mark) 2. When does 𝛼-decay occur? (1 Mark) 3. The half-life of radium is 1600 Years. After how much time 1 20 𝑡ℎ part of radium will remain undisintegrated in the sample. (3 Marks)