4.4 Radioactivity

Nuclear Reaction - involves change in nucleus Radioactivity – substances spontaneously emit radiation. Element can change into another element. Occurs because nucleus becomes unstable. Unstable atoms gain stability by losing energy. Energy lost by emitting radiation. Chemical Reaction: change of 1 or more substances into new substances. atoms are rearranged nucleus is unchanged

Nuclear vs. Chemical Reactions Nucleus is changed: Atoms are rearranged:

Types of Radiation Type Nature 4 2He +2 Sheet of Paper Beta β -1e 0* Symbol Mass Charge Nature Penetra- tion Alpha 4 2He +2 Helium Nucleus Sheet of Paper Beta β -1e 0* 1/1840 -1 From nucleus High speed electrons Aluminum Foil Gamma 0 Electro- Magnetic Radiation Lead Shielding

Penetration of Radiation:

Nuclear Equations – Mass numbers & atomic numbers must be conserved. Alpha emission: 226Ra  222Rn + 4He 88 86 2 alpha particle Mass # and Atomic # Conserved: 226  222 + 4 88  86 + 2

Beta Emission: Ex. Carbon-14 decays to produce a beta particle. 14C  14N + 0β 6 7 -1 beta

Gamma Emission – accounts for most of energy lost during radioactive decay. Usually accompanies alpha & beta. 238U  234Th + 4He + 0 92 90 2 0

Nuclear stability – primarily determined by: Ratio of neutrons to protons. Size of nucleus. Atoms with atomic # greater than 83 (Bismuth) are unstable. Atoms eventually decay to form stable, nonradioactive atoms.

Radioactive Decay Series

Nuclear Fission (Splitting) Unstable atoms break apart into smaller ones. Releases tremendous amounts of energy. Nuclear power plants (U-235)

Nuclear Fusion (Uniting) Fusing together smaller elements to make larger ones. Produces all elements larger than He Fusion releases tremendous amounts of energy. (Greater than fission) Occurs on the Sun (and stars) Cleaner method but no current technology for power plants.

Nuclear Energy (Fission) Pros: Cons: Does not cause air pollution (no CO2 emissions, etc.) Doesn’t use up fossil fuel (coal) Less global warming, acid rain Limited amount of nuclear fuel (Ex. U-235) Spent fuel is radioactive Transportation & storage problems! Water used in cooling process may cause problems when released to environment.

Coal vs. Nuclear Power

Pro Con Coal waste has more radiation than spent fuel! Except for Chernobyl, minimal releases of radiation. High cost of nuclear power (due to government regulations).

15% power by nuclear 52% by coal power

The End Chain Reaction: Neutrons released start new reactions: