Radioactive decay is a random process by which unstable nuclei lose energy by emitting radiation. The amount of substance decreases exponentially over time, described by the decay law.

Key Formulas:

• N = N₀ × e^-λt
• λ = ln(2) / t½
• t½ = ln(2) / λ
• t = (1/λ) × ln(N₀/N)

Units:

• Time: s, min, h, d, y
• Amount: g, mol, atoms

Applications:

• Radiometric dating (carbon-14, uranium-lead)
• Medical imaging and therapy
• Nuclear power and safety