A radioactive atom is like a ticking clock that can change at any moment. The nucleus contains protons and neutrons that are not perfectly stable. When the balance is off, the nucleus will decay – it emits particles or energy to become more stable. This process is spontaneous – it happens without any external trigger. It is also random – you cannot predict exactly when a particular atom will decay, only the probability of it happening.
Imagine a bag filled with marbles that can pop out at any time. You cannot see which marble will pop next, but you know that after a certain amount of time, about half of the marbles will have popped. This is similar to radioactive decay: each atom is a marble, and the “popping” is the emission of radiation.
The number of undecayed nuclei \$N(t)\$ after time \$t\$ follows:
\$ N(t) = N_0 e^{-\lambda t} \$
where \$N_0\$ is the initial number of nuclei. This exponential decay law shows how the population decreases over time.
| Isotope | Half‑life | Decay Mode |
|---|---|---|
| ¹⁴C (Carbon‑14) | ≈ 5,730 years | β⁻ decay |
| ²³⁸U (Uranium‑238) | ≈ 4.5 × 10⁹ years | α decay |
| ¹⁰⁶Ru (Ruthenium‑106) | ≈ 374 days | β⁻ decay |
Because each atom decays independently, the total number of decays in a large sample follows a Poisson distribution. This means that even though the process is random, the overall behaviour is predictable when many atoms are involved. This principle underpins techniques like radiocarbon dating and nuclear medicine.
Answer Key
- Radioactive decay is a spontaneous, random process.
- Each nucleus behaves independently, but large numbers give predictable patterns.
- The half‑life and decay constant are key parameters that describe how quickly a substance decays.
- Understanding these concepts helps us use radioactivity safely in science and technology.