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