PHYSICS & ELECTRONICS / MODERN PHYSICS / PAGE 28 OF 50
Radioactivity and Nuclear Energy
Unstable nuclei, half-life and energy from the nucleus.
Some nuclei are unstable and decay by emitting alpha particles, beta particles or gamma rays. Decay is random for any single nucleus, but a large sample follows a smooth exponential curve, and the time for half of it to decay is the half-life.
Original diagram: radioactivity and nuclear energy
In fission a heavy nucleus splits and in fusion light nuclei join. Both release energy because the total mass drops slightly and the lost mass appears as energy. Radiation needs careful shielding and handling.
- Alpha is stopped by paper, beta by thin metal, gamma needs thick dense shielding.
- Half-life is constant for a given isotope.
- Mass defect gives binding energy.
KEY IDEA
N = N0 (½)^(t / T½) and E = Δm c²Browse all 50 physics and electronics pages | Back to the course index