Practice question

**Stability** belt of stability N≈Z for light, N>Z for heavy due to Coulomb, beyond leads to alpha decay, fission, stability requires balance, nuclear force saturated explains constant density and BE/A. Density = (mass/volume) , Volume = (4/3) π R³ . R³ = (2.0 × 10⁻¹⁵)³ = 8.0 × 10⁻⁴⁵ m³ . Volume = (4/3) × 3.14 × 8.0 × 10⁻⁴⁵ ≈ 3.35 × 10⁻⁴⁴ m³ . Density = (3.67 × 10⁻²⁷/3.35 × 10⁻⁴⁴) ≈ 1.10 × 10¹⁷ kg/m³ . Using E_n = -13.6/n² eV, r_n = n² a₀, L = n h/2π, R = R₀ A^¹/³, BE = Δm c² and 1 u = 931.5