Gamma ray
After emitting an alpha or beta particle, the nucleus will often still be ‘excited’ and will need to lose energy.
It does this by emitting a high energy electromagnetic wave called a gamma ray.
Gamma radiation does not consist of particles but as short wavelength, high energy electromagnetic radiation emitted from unstable nuclei.
It is normally emitted alongside alpha or beta radiation.
Gamma ray emission causes no change in the number of particles in the nucleus meaning both the atomic number and mass number remain the same.
It can be written as γ or \(_{0}^{0}\textrm{γ}\)
Gamma decay
\(_{X}^{A}\textrm{X}\rightarrow_{Z}^{A}\textrm{Y}+_{0}^{0}\textrm{γ}\) (or γ).
Example
Beta and gamma decay of cobalt-60
(2760ٱٰǰٲǷɳ2860ٱٰ+-10ٱٰ+00ٱٰγ)
Properties of nuclear radiations
The different types of radiation are often compared in terms of their The power of the radiation that demonstrates how far into a material the radiation will go., their To ionise is to convert an uncharged atom or molecule into a charged particle by adding or removing electrons. and how far they can travel in the air.
| Symbol | Penetrating power | Ionising power | Range in air | |
| Alpha | α | Skin/paper | High | < 5 centimetre (cm) |
| Beta | β | 3 mm aluminium foil | Low | ≈ 1 metre (m) |
| Gamma | γ | Lead/concrete | Very low | > 1 kilometre (km) |
| Alpha | |
|---|---|
| Symbol | α |
| Penetrating power | Skin/paper |
| Ionising power | High |
| Range in air | < 5 centimetre (cm) |
| Beta | |
|---|---|
| Symbol | β |
| Penetrating power | 3 mm aluminium foil |
| Ionising power | Low |
| Range in air | ≈ 1 metre (m) |
| Gamma | |
|---|---|
| Symbol | γ |
| Penetrating power | Lead/concrete |
| Ionising power | Very low |
| Range in air | > 1 kilometre (km) |
All types of radioactive decay can be detected by a Geiger-Muller tube, or G-M tube. The radiations ionise the gas inside the G-M tube and the resulting charged particles move across the chamber and get counted as charges rather like an ammeter.
Key points - alpha radiation
- alpha particles are helium nuclei consisting of two protons and two neutrons emitted from unstable nuclei;
- alpha radiation is stopped by a few centimetres of air or a thin sheet of paper;
- alpha decay:\(_{Z}^{A}\textrm{X}\rightarrow_{Z-2}^{A-4}\textrm{Y}+_{2}^{4}\textrm{He}\) (or\(_{2}^{4}\textrm{α}\))
- Alpha particles are relatively heavy and so produce the most ionisation.
Key points: beta radiation
- beta particles are fast moving electrons emitted from the nucleus of an unstable atom;
- beta radiation is stopped by several metres of air or a thin sheet of aluminium;
- beta decay:\(_{X}^{A}\textrm{X}\rightarrow_{Z+1}^{A}\textrm{Y}+_{-1}^{0}\textrm{e}\) or (\(_{-1}^{~0}\beta\))
- beta particles are much lighter than alpha particles and so produce a great deal less ionisation.
Key points: gamma radiation
- gamma radiation is high energy electromagnetic waves emitted from unstable nuclei;
- gamma radiation easily passes through air, paper, skin and aluminium but can be partly blocked by thick lead or concrete;
- leaves mass number and atomic number unchanged;
- gamma rays produce the least ionization.