Radioactive decay is a random and spontaneous process in which an unstable nucleus becomes more stable by emitting radiation. (p.200)
Alpha decay: AZX → A−4Z−2Y + 42He. (p.200)
Beta decay: a neutron becomes a proton and an electron; AZX → AZ+1Y + 0−1e. (p.201)
Gamma decay: no change in proton or nucleon number; the nucleus loses excess energy. (p.201)
Half-life, T½, is the time taken for a sample of radioactive nuclei to decay to half its initial number. (p.202)
Uranium-238 decays through a series to stable lead-206. (p.202)
The ratio of lead-206 to uranium-238 in rock can be used to estimate the age of rocks and the Earth. (p.203)
Activity of a sample is directly proportional to the number of radioactive nuclei present. (p.204)
N = (½)n N0, where n = t/T½; a shorter half-life means a higher decay rate. (p.205)
Activity after n half-lives: A = (½)n A0. (p.206)
6.2 Nuclear Energy
Nuclear energy is released in radioactive decay, nuclear fission and nuclear fusion. (p.208)
Nuclear fission: a heavy nucleus splits into lighter nuclei, releasing a large amount of energy (e.g. U-235 + neutron → Ba-141 + Kr-92 + 3 neutrons). (p.209)
Nuclear fusion: light nuclei fuse into a heavier nucleus at extremely high temperature and pressure (e.g. deuterium + tritium → helium + neutron). (p.209)
1 amu = 1/12 of the mass of a carbon-12 atom = 1.66 × 10−27 kg. (p.211)
Mass defect is the loss of mass in a nuclear reaction; energy released E = mc2. (p.211)
1 MeV = 1.6 × 10−13 J. (p.211)
Malaysia's TRIGA PUSPATI research reactor is in Bangi; it is not used for electricity generation. (p.213)
Nuclear power station: fission heat boils water, steam turns a turbine, and the generator produces electricity. (p.214)
Chain reaction: neutrons from fission cause further fission of U-235 nuclei. (p.215)
Control: moderator slows neutrons; control rods (boron or cadmium) absorb excess neutrons. Safety: thick concrete walls and water coolant. (p.216)