| English | Alpha particle |
|---|---|
| Bahasa Melayu | Zarah alfa |
| 中文 | α粒子 |
Definition
A particle made of two protons and two neutrons (a helium nucleus) emitted by some radioactive nuclei; it has a positive charge and low penetrating power.
In exam terms
An alpha particle is made of two protons and two neutrons, that is, a helium nucleus (⁴₂He), emitted by some radioactive nuclei. It carries a charge of +2 and is relatively heavy, so it is strongly ionising but has low penetrating power, it is stopped by a sheet of paper or a few centimetres of air.
A correct sentence: "Alpha particles cause the most ionisation because of their large charge and mass." In a nuclear equation, emitting an alpha particle reduces the nucleon number by 4 and the proton number by 2.
Do not confuse it with…
Do not confuse an alpha particle with a beta particle. Alpha is a heavy, +2 helium nucleus that is highly ionising but weakly penetrating; beta is a light, −1 fast electron that is less ionising but more penetrating.
Alpha is deflected less in a magnetic field because of its greater mass.
In Paper 2 you may be asked to state the nature and charge of an alpha particle, compare its penetrating power with beta and gamma, or complete a decay equation showing the change in A and Z.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)