Law of radioactive decay
Radioactivity · Physics
Bohr atom
Interactive 3DElectrons orbit the nucleus in shells — switch element to see H, He and Li fill their shells.
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A sample contains 8.0 × 10²⁰ nuclei of ¹³¹I (half-life 8.0 days). (a) Find λ in s⁻¹. (b) How many nuclei remain after 24 days? (c) What is the initial activity in Bq? Solution: (a) λ = ln2/T₁/₂ = 0.693/(8.0 × 86400 s) ≈ 1.00 × 10⁻⁶ s⁻¹. (b) 24 days = 3 half-lives → N = N₀/2³ = 8.0×10²⁰/8 = 1.0 × 10²⁰ nuclei. (c) A₀ = λN₀ = 1.00×10⁻⁶ × 8.0×10²⁰ = 8.0 × 10¹⁴ Bq.