### Radiological Protection Institute of Ireland

Physics
This lesson describes the various kinds of radiation associated with radioactivity and outlines what we can do to minimise our exposure to ionising radiation.

Contains the full lesson along with a supporting toolkit, including teachers’ notes.

### Lesson excerpt

You’ve probably heard that heat travels in three different ways: by conduction, convection and radiation. Transfer of heat in solids is by conduction; for example, if you put a metal spoon into a cup of boiling water heat travels from the hot part to the colder part. Heat transfer in fluids (liquids and gases) is mainly by convection — the heated part generally becomes less dense and so convection currents are set up. In this case heat is transferred by bulk movement of the fluid. Heat transfer by radiation involves the emission of electromagnetic waves by a hot source; such waves do not require a medium and so can travel through empty space. The light and heat we get from the sun is of this kind.

The electromagnetic radiation generally associated with heat transfer is known as infrare radiation. Some other kinds of electromagnetic radiation can break the bonds that hold molecules together or knock electrons off them forming ions; this is known as ionising radiation. The minimum energy required to break the bonds in molecules or to produce ions is of the order of 5 x 10−19 J. The energy of electromagnetic waves is a function of their wavelength; the shorter the wavelength the greater the energy.

### True or False?

1. Heat can be transferred through a vacuum. true
2. All electromagnetic radiation is ionising. false
3. Gamma ray photons have higher energy than UV photons. true
4. Electrons can be emitted from some atomic nuclei. true
5. The speed of beta particles is about 1000 km/hour false
6. Most of the ionising radiation that Irish people are subjected to comes from radon. true
7. If all materials are radioactive then all atoms are radioactive. false
8. There is only one form of radon. false
9. Alpha particles can travel through sheets of lead. false
10. Cosmic rays are mostly high energy protons. true
11. Uranium 238 (238U) is very radioactive. false

alpha particle
beta particle
building slab
conduction
convection