Actinides are radioactive because their atomic nuclei are unstable. Here’s why :
- Large number of protons: Actinides have very high atomic numbers (from 89 to 103). More protons mean strong repulsion between positively charged protons in the nucleus.
- Insufficient nuclear binding: Although neutrons help hold the nucleus together, in actinides, the number of neutrons is often not enough to fully balance the proton repulsion, making the nucleus unstable.
- Energy release through decay: To reach a more stable state, the nucleus spontaneously emits radiation in the form of alpha particles, beta particles, or gamma rays. This process is called radioactive decay.
- All actinides beyond thorium are mostly unstable: This is why many actinides, like uranium, plutonium, and americium, are naturally or artificially radioactive.
In short: Actinides are radioactive because their large, heavy nuclei cannot stay stable and release energy to become more stable.