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Nuclear Chemistry
 

Nuclear Chemistry

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    Nuclear Chemistry Nuclear Chemistry Presentation Transcript

    • Nuclear Chemistry
    • Radioactivity – spontaneous emission of particles and or radiation
      (proposed by Marie Curie)
      • Three types of ray are produced by the decay, or breakdown, of radioactive
      substances
      A. Alpha rays ( α ) – consist of positively charged particles called alpha particles and therefore are deflected by the positively charged plate.
      B. Beta rays ( β ) – or beta particles – are electrons and deflected by negatively charged plate
      C. Gamma rays ( γ ) – have no charged and are not affected by an external electric field or magnetic field
    • Lead block
      Radioactive substance

      a
      g
      b
      +
    • Lead block

      +
    • Lead block
      Radioactive substance

      a
      +
    • Lead block
      Radioactive substance

      b
      +
    • Lead block
      g
      Radioactive substance

      +
    • Lead block
      Radioactive substance

      a
      g
      b
      +
    • A
      X
      Mass Number
      Element Symbol
      Z
      Atomic Number
      a particle
      proton
      neutron
      electron
      positron
      or
      or
      1p
      1H
      0b
      0e
      or
      1
      1
      +1
      1n
      0e
      +1
      0b
      0
      -1
      -1
      4a
      4He
      or
      2
      2
      Atomic number (Z) = number of protons in nucleus
      Mass number (A) = number of protons + number of neutrons
      = atomic number (Z) + number of neutrons
      A
      1
      1
      0
      0
      4
      1
      0
      -1
      +1
      2
      Z
      23.1
    • +
      +
      + 2
      +
      +
      + 2
      1n
      1n
      1n
      1n
      96
      96
      0
      0
      0
      0
      Rb
      Rb
      37
      37
      235
      138
      235
      138
      U
      Cs
      U
      Cs
      92
      55
      92
      55
      Balancing Nuclear Equations
      Conserve mass number (A).
      The sum of protons plus neutrons in the products must equal the sum of protons plus neutrons in the reactants.
      235 + 1 = 138 + 96 + 2x1
      Conserve atomic number (Z) or nuclear charge.
      The sum of nuclear charges in the products must equal the sum of nuclear charges in the reactants.
      92 + 0 = 55 + 37 + 2x0
      23.1
    • or
      alpha particle -
      212Po 4He + AX
      2
      Z
      84
      212Po 4He + 208Pb
      2
      82
      84
      4a
      4He
      2
      2
      212Po decays by alpha emission. Write the balanced nuclear equation for the decay of 212Po.
      212 = 4 + A
      A = 208
      84 = 2 + Z
      Z = 82
      23.1
    • 23.1
    • I. Nuclear Stability and Radioactive Decay
    • X
      Y
      n/p too large
      beta decay
      n/p too small
      positron decay or electron capture
      23.2
    • Predicting the mode of decay
      High n/p ratio (too many neutrons; lie above band of stability) --- undergoes beta decay
      Low n/p ratio (neutron poor; lie below band of stability) --- positron decay or electron capture
      Heavy nuclides ( Z > 83) --- alpha decay
    • II. Nuclear Transmutations
      • Nuclear reactions that are induced in a way that nucleus is struck by a neutron or by another nucleus (nuclear bombardment)
      Positive ion bombardment
      - alpha particle is the most commonly used positive ion
      - uses accelerators
      Examples:
      147 N + 42 He -> 178 O + 11H
      94Be + 42 He -> 126 C + 10n
      Neutron bombardment
      - neutron is bombarded to a nucleus to form a new nucleus
      - most commonly used in the transmutation to form synthetic isotopes because neutron are neutral, they are not repelled by nucleus
      Example:
      5826 Fe + 10 n -> 5926 Fe -> 5927 Co + 0-1 e
    • 5
      +
      +
      +
      +
      + 0-1 e
      +
      +
      4He
      1n
      1n
      0e
      14N
      1n
      2
      0
      -1
      7
      0
      0
      239
      242
      238
      239
      239
      239
      238
      247
      Pu
      Cm
      U
      U
      Pu
      Np
      U
      Es
      94
      96
      92
      92
      94
      93
      92
      99
      Transuranium elements
      • Element with atomic numbers above 92
      • Produced using artificial transmutations, either by:
      alpha bombardment
      neutron bombardment
      bombardment from other nuclei
      Examples:
      a.
      b.
      c.
    • III. Nuclear Energy
      Recall:
      Nucleus is composed of proton and neutron
      Then, is the mass of an atom equal to the total mass of all the proton plus the total mass of all the neutron?
      Example for a He atom:
      Total mass of the subatomic particles
      = mass of 2 p+ + mass of 2n0
      = 2 ( 1.00728 amu ) + 2 (1.00867 amu)
      = 4.03190 amu
      And atomic weight of He-4 is 4.00150
      Why does the mass differ if the atomic mass = number of protons + number of neutrons?
    • Mass defect
      -mass difference due to the release of energy
      -this mass can be calculated using Einstein’s equation E =mc2
      2 11 H + 2 20 H -> 42 He + energy
      Therefore:
      -energy is released upon the formation of a nucleus from the constituent protons and neutrons
      -the nucleus is lower in energy than the component parts.
      -The energy released is a measure of the stability of the nucleus. Taking the reverse of the equation:
      42He + energy -> 2 11 H + 2 20 n
    • Therefore,
      -energy is released to break up the nucleus into its component parts. This is called the nuclear binding energy.
      -the higher the binding energy, the stable the nuclei.
      -isotopes with high binding energy and most stable are those in the mass range 50-60.
    • Nuclear binding energy per nucleon vs Mass number
      nuclear binding energy
      nucleon
      nuclear stability
      23.2
    • -The plot shows the use of nuclear reactions as source of energy.
      -energy is released in a process which goes from a higher energy state (less stable, low binding energy) to a low energy state (more stable, high binding energy).
      -Using the plot, there are two ways in which energy can be released in nuclear reactions:
      a. Fission – splitting of a heavy nucleus into smaller nuclei
      b. Fusion – combining of two light nuclei to form a heavier, more stable nucleus.
    • BE + 19F 91p + 101n
      0
      9
      1
      binding energy per nucleon =
      binding energy
      number of nucleons
      2.37 x 10-11 J
      19 nucleons
      =
      Nuclear binding energy (BE) is the energy required to break up a nucleus into its component protons and neutrons.
      E = mc2
      BE = 9 x (p mass) + 10 x (n mass) – 19F mass
      BE (amu) = 9 x 1.007825 + 10 x 1.008665 – 18.9984
      BE = 0.1587 amu
      1 amu = 1.49 x 10-10 J
      BE = 2.37 x 10-11J
      = 1.25 x 10-12 J
      23.2
    • 23.3
    • 14N + 1n 14C + 1H
      0
      7
      1
      6
      14C 14N + 0b + n
      6
      7
      -1
      238U 206Pb + 8 4a + 6 0b
      92
      -1
      82
      2
      Radiocarbon Dating
      t½ = 5730 years
      Uranium-238 Dating
      t½ = 4.51 x 109 years
      23.3
    • 14N + 4a17O + 1p
      7
      2
      1
      8
      27Al + 4a30P + 1n
      13
      2
      0
      15
      14N + 1p 11C + 4a
      7
      1
      2
      6
      Cyclotron Particle Accelerator
      Nuclear Transmutation
      23.4
    • Nuclear Transmutation
      23.4
    • 235U + 1n 90Sr + 143Xe + 31n + Energy
      38
      0
      0
      54
      92
      Nuclear Fission
      Energy = [mass 235U + mass n – (mass 90Sr + mass 143Xe + 3 x mass n )] x c2
      Energy = 3.3 x 10-11J per 235U
      = 2.0 x 1013 J per mole 235U
      Combustion of 1 ton of coal = 5 x 107 J
      23.5
    • 235U + 1n 90Sr + 143Xe + 31n + Energy
      38
      0
      0
      54
      92
      Nuclear Fission
      Representative fission reaction
      23.5
    • Non-critical
      Critical
      Nuclear Fission
      Nuclear chain reaction is a self-sustaining sequence of nuclear fission reactions.
      The minimum mass of fissionable material required to generate a self-sustaining nuclear chain reaction is the critical mass.
      23.5
    • Nuclear Fission
      Schematic diagram of a nuclear fission reactor
      23.5
    • 35,000 tons SO2
      4.5 x 106 tons CO2
      70 ft3 vitrified waste
      3.5 x 106
      ft3 ash
      1,000 MW coal-fired
      power plant
      1,000 MW nuclear
      power plant
      Nuclear Fission
      Annual Waste Production
      23.5
    • Nuclear Fission
      Hazards of the radioactivities in spent fuel compared to uranium ore
      23.5
      From “Science, Society and America’s Nuclear Waste,” DOE/RW-0361 TG
    • 2H + 2H 3H + 1H
      1
      1
      1
      1
      2H + 3H 4He + 1n
      2
      1
      0
      1
      6Li + 2H 2 4He
      2
      3
      1
      Nuclear Fusion
      Fusion Reaction
      Energy Released
      6.3 x 10-13 J
      2.8 x 10-12 J
      3.6 x 10-12 J
      Tokamak magnetic plasma confinement
      23.6
    • Radioisotopes in Medicine
      • 1 out of every 3 hospital patients will undergo a nuclear medicine procedure
      • 24Na, t½ = 14.8 hr, b emitter, blood-flow tracer
      • 131I, t½ = 14.8 hr, b emitter, thyroid gland activity
      • 123I, t½ = 13.3 hr, g-ray emitter, brain imaging
      • 18F, t½ = 1.8 hr, b+ emitter, positron emission tomography
      • 99mTc, t½ = 6 hr, g-ray emitter, imaging agent
      Brain images with 123I-labeled compound
      23.7
    • Geiger-Müller Counter
      23.7
    • Biological Effects of Radiation
      Radiation absorbed dose (rad)
      1 rad = 1 x 10-5 J/g of material
      Roentgen equivalent for man (rem)
      1 rem = 1 rad x Q
      Quality Factor
      g-ray = 1
      b = 1
      a = 20
      23.8
    • Chemistry In Action: Food Irradiation