• $summary_{type}$: concept
• $word_{count}$: 180

Three primary decay modes exist. Alpha decay: emission of He-4 (2p + 2n), reducing Z by 2 and A by 4. Alpha particles are monoenergetic (discrete spectrum). By momentum conservation, $KE_{alpha}$ = Q x $\frac{A-4}{A}$. Beta-minus decay: neutron converts to proton, emitting electron + antineutrino. Z increases by 1, A unchanged. The beta spectrum is continuous because the neutrino carries variable energy (this continuous spectrum led Pauli to predict the neutrino in 1930). Beta-plus decay: proton converts to neutron, emitting positron + neutrino. Requires parent to be 2$m_e$*$c^2$ = 1.022 MeV heavier than daughter. Gamma decay: excited nucleus emits a photon, changing neither Z nor A. Gamma energies are discrete (like atomic spectral lines but at MeV scale). Ionizing power: alpha > beta > gamma (reverse of penetrating power). Alpha stopped by paper, beta by mm of aluminum, gamma by cm of lead. JEE problems often require tracking Z and A through successive alpha and beta decays.