radioactivity, nuclear energy, solar energy introduction – part 1 nuclear energy or fission –...
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RADIOACTIVITY, NUCLEAR ENERGY, SOLAR ENERGY
Introduction – Part 1
Nuclear Energy or Fission – Part 2
Solar Energy or Fusion – Part 3
Nuclear Chemistry
• The study of the properties and changes (rxns) that take place in atomic nuclei.
• Isotopes have the same Z but different # of neutrons; i.e. different mass number
• Carbon has 13 isotopes
• C-12 has 6 p+, 6 n0 and 6 e-; stable
• C-13 has 6 p+, 7 n0 and 6 e- ; stable
• C-14 has 6 p+, 8 n0 and 6 e- ; unstable
Radioactive Elements
• Elements that are unstable and that decompose spontaneously.
• All elements have at least one radioactive isotope. Elements with Z > 83 are radioactive.
• The decomposition products are – other elements - stable or radioactive– high energy particles – alpha, beta, gamma
• During these decompositions, mass and charge must be conserved.
Alpha Particles (α)
• Review definition of isotope, Z, mass number, structure of atom
• α = nucleus of He or 42He with charge = +2
and mass number = 4 = 2 n0 + 2 p+
• Ex 17.2a 23994Pu 235
92U + 42He
• Ex 17.2c 17979Au 175
77Ir + 42He
• State Z (#p+), #n0 for each species in eqn.
• Note that Z of product element decreases
Beta Particles (β)
• β = electron with charge = -1 and negligible mass
• Produced when neutron splits– neutron proton + electron
• Ex 17.3a 146C 14
7N + 0-1e
• Ex 17.3c 9942Mo 99
43Tc + 0-1e
• State Z (#p+), #n0, #e-1
• Note that Z of product element increases
Gamma Emission (γ)
• γ = gamma ray = light or photon with no mass and no charge
• High energy photons
Summary
Particle Symbol Change in Z
Change in mass number
Change in #n0
Alpha α, 42He -2 -4 -2
Beta β, 0-1e +1 0 -1
Gamma γ, 00γ 0 0 0
What α, β, γ Emissions Do
• These radioactive byproducts are emitted at very high energies.
• These energies can be high enough to– break chemical bonds and ionize atoms and
molecules.– produce free radicals that can damage DNA, proteins– damage tissue if the radioactive element is ingested– cause cell mutations– kill cells
Radioactive Decay
• As mentioned before,radioactive atoms are unstable and decay spontaneously.
• Some atoms decay over a long period of time (billions of years) and others over a short period of time (fractions of seconds)
• One radioactive atom may decay to another which then decays to another (Fig 17.5)
Radioisotope Half-Life, τ1/2
• Half-life is the time it takes for half of the atoms in a radioactive sample to decay.
• The longer the half-life, the longer the radioactive isotope exists and the longer its potential danger exists.
• Prob 17-43: After 6 hr, 25 mg remain. After 12 hr, 12.5 mg remain. After 18 hr, 6.25 mg remain. After 24 hr, 3.125 mg remain. After 48 hr, 0.20 mg remain.
• Fig 17.4
Uses of Radioisotopes
Radio isotope
Symbol Prod Half-life Use
Tritium 31H β 12.33 yr Biochem tracer
C-14 146C β 5730 yr C-dating
P-32 3215P β 14 dy Leukemia
therapy
Co-60 6027Co β 5.27 yr Cancer therapy
I-123 12753I γ 13.27 hr Thyroid therapy
Nuclear and Chemical RxnsA Comparison
Reactant atoms ≠ product atoms
Conservation of atom identities
Diff isotopes may have diff nuclear properties
Diff isotopes may have @same chem properties
Rate of nuclear rxn ≠ f(T, P, catalyst)
Rate of chem rxn = f(T, P, catalyst)
Nuclear rxn ≠ f(atom’s environment, phase)
Chem rxn = f(atom’s environment, phase)
Energy changes: 1 g U-235 releases 8.2E+7 kJ
1 g methane burns to produce 56 kJ
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