How is nuclear stability related to radioactive decay?
An unstable nucleus tries to become more stable by decaying into another nucleus.
During radioactive decay, an unstable nucleus emits alpha particles, beta particles, positrons, or gamma rays.
An alpha particle is a helium nucleus. The heavier elements usually decay by alpha emission. For example,
₉₂²³⁸U → ₉₀²³⁴Th + ₂⁴He
A beta particle is an electron. The emission of an electron changes a neutron into a proton, and the nucleus becomes more stable, For example,
₁₅³²P → ₁₆³²S + ₋₁⁰e
Nuclei that have too many protons can decay by converting a proton to a neutron and emitting a positron. For example,
₅⁸B → ₄⁸Be + ₁⁰e
Gamma rays are high-energy photons. When a nucleus emits an alpha or beta particle, the new nucleus has excess energy. It can release this excess energy by emitting gamma rays.
Thus, thorium-234 becomes more stable by releasing gamma rays and a beta particle.
₉₀²³⁴Th → ₉₁²³⁴Pa +₋₁⁰e