Radiation
If an atomic The central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. The plural of nucleus is nuclei. does not change or break down, we say that it is stable. Most Nuclei is the plural of nucleus. The nucleus is the central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. are stable. However, some atomic nuclei are unstable and may change or break down. When this happens, they emit particles or rays, including:
- Subatomic particle comprising two protons and two neutrons (the same as a helium nucleus).
- An electron emitted from a radioactive atom.
- Uncharged subatomic particle, with a mass of 1 relative to a proton. The relative charge of a neutron is 0.
- Energy travelling as waves in the form of changing electrical and magnetic fields. as The shortest wavelength and highest energy part of the EM spectrum. Produced by radioactive materials.
Substances containing unstable The smallest part of an element that can exist. are described as When unstable atoms give off particles that can be harmful to humans.. The particles or rays they give off are types of radiation.
Types of radiation
The table shows some features of the four main types of radiation:
| Type of radiation | Nature | Symbol in a nuclear equation | Electric charge |
| alpha, 伪 | Two protons and two neutrons bound together (identical to a helium nucleus) | \(_{2}^{4}\alpha\) | +2 |
| beta, 尾 | A fast-moving electron from a nucleus | \(_{-1}^{0}\beta\) | -1 |
| neutron, n | A neutral subatomic particle from a nucleus | \(_{0}^{1}n\) | 0 |
| gamma, 纬 | Electromagnetic radiation | \(_{0}^{0}\gamma\) | 0 |
| Type of radiation | alpha, 伪 |
|---|---|
| Nature | Two protons and two neutrons bound together (identical to a helium nucleus) |
| Symbol in a nuclear equation | \(_{2}^{4}\alpha\) |
| Electric charge | +2 |
| Type of radiation | beta, 尾 |
|---|---|
| Nature | A fast-moving electron from a nucleus |
| Symbol in a nuclear equation | \(_{-1}^{0}\beta\) |
| Electric charge | -1 |
| Type of radiation | neutron, n |
|---|---|
| Nature | A neutral subatomic particle from a nucleus |
| Symbol in a nuclear equation | \(_{0}^{1}n\) |
| Electric charge | 0 |
| Type of radiation | gamma, 纬 |
|---|---|
| Nature | Electromagnetic radiation |
| Symbol in a nuclear equation | \(_{0}^{0}\gamma\) |
| Electric charge | 0 |
Penetrating properties
Radiation can be absorbed by substances in its path. For example, alpha radiation travels only a few centimetres in air, Radiation caused by beta particles (high-energy electrons). A beta particle is an electron ejected from a nucleus when a neutron becomes a proton. travels tens of centimetres in air, and gamma radiation travels very large distances.
All types of radiation become less intense as they travel further away from the radioactive material. This is because the particles or rays become more spread out. The thicker the substance, the more the radiation is absorbed.
Alpha, beta and gamma radiations penetrate materials in different ways.
Alpha radiation
Alpha radiation is the least penetrating. It can be stopped (or absorbed) by a sheet of paper or a human hand.
Beta radiation
Beta radiation can penetrate air and paper. It can be stopped by a thin sheet of aluminium.
Gamma radiation
Gamma radiation is the most penetrating. It can penetrate air, paper or thin metal. It may only be stopped by many centimetres of lead or many metres of concrete.