| English | Radioactive decay |
|---|---|
| Bahasa Melayu | Reputan radioaktif |
| 中文 | 放射性衰变 |
Definition
The random process by which an unstable nucleus loses energy by emitting radiation and changes into a more stable nucleus.
In exam terms
Radioactive decay is the random process by which an unstable nucleus loses energy by emitting radiation and changes into a more stable nucleus. It is random because it is impossible to predict which nucleus will decay next, and spontaneous because it is not affected by external conditions.
Decay is described by a nuclear equation in which the nucleon numbers and proton numbers on each side must balance.
A correct sentence: "In alpha decay, ²³⁸₉₂U decays to ²³⁴₉₀Th by emitting a ⁴₂He nucleus." The activity is measured in becquerel (Bq).
Do not confuse it with…
Do not confuse radioactive decay with nuclear fission. In decay, a nucleus spontaneously emits a small particle (alpha or beta) or gamma ray and becomes slightly lighter; in fission, a heavy nucleus is split into two much lighter nuclei, usually after absorbing a neutron.
Also distinguish decay from radioactivity, which is the general phenomenon rather than the individual event.
In Paper 2 you may be asked to define radioactive decay, state that it is random and spontaneous, or complete and balance a decay equation.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)