(a) ³²P has a half-life of 14.3 days. Find its decay constant and mean life. (b) A ³²P sample's activity drops from 8000 Bq to 1000 Bq. How much time passed? Solution: (a) λ = 0.693/14.3 d = 0.0485 d⁻¹ = 5.61×10⁻⁷ s⁻¹. τ = 1/λ = 14.3/0.693 ≈ 20.6 days. (b) 8000 → 1000 is a factor of 8 = 2³, so 3 half-lives passed: t = 3 × 14.3 = 42.9 days.