Typical designed operational lifetimes for many nuclear power plants are in the 30–40 year range.

Six alpha emissions reduce A by 24 and Z by 12; four beta emissions increase Z by 4, net ΔA = -24 and net ΔZ = -8; a common resulting stable lead isotope is Z=82, A=212.

Deuterium commonly refers to the hydrogen-2 atom, while triton refers to the nucleus of tritium, so atom and nucleus of hydrogen.

The reciprocal of the decay constant is the mean life τ = 1/λ, not the half-life.

Characteristic X-rays arise when electrons in the target atom drop from higher to lower energy levels, emitting photons of specific energies.

Neutrons have no charge so they interact less with electrons and can penetrate deeply into matter compared with charged particles.

Mean life τ = 1/λ and half-life T1/2 = ln2/λ so τ/T1/2 = 1/ln2 ≈ 1.4427, i.e. 1.44.

The symmetric (bosonic) eigenstate under particle exchange is the normalized sum (1/√2)[ψ(1,2)+ψ(2,1)], which is option D.

Nuclear fusion requires extremely high temperatures and pressures to overcome Coulomb repulsion, so option A is correct.

Helium nuclei (alpha particles) are produced when hydrogen nuclei fuse together in nuclear fusion processes.