P6 Radioactive Materials Revision

Seite 1

Atomic structure and radiation

Structure of the atom

Atoms contain three sub-atomic particles called protons, neutrons and electrons. The protons and neutrons are found in the nucleus at the centre of the atom. The protons and neutrons are held together in the nucleus by a strong force which balances the repulsive electrostatic force between the protons. The electrons are outside the nucleus.

Radioactive elements give out ionising radiation from their nuclei. This happens all the time, whatever is done to the substance. For example, radiation is still given out if the substance is cooled in a freezer or involved in a chemical reaction.Radioactive elements are found naturally in the environment. The radiation they give off is called background radiation.

If hydrogen nuclei are brought close enough together then they have the ability to fuse. This process is called nuclear fusion. It takes a lot of work to force nuclei together but a lot of energy is released when they fuse.

Isotopes are atoms of an element that have different mass numbers because they have different numbers of neutrons in the nucleus.

E = mc2

Where: E = is the energy produced

M = change in mass

C = speed of light

Radiation can be absorbed by substances in its path. Alpha radiation travels only a few centimetres in air, beta travels tens of centimetres, while gamma radiation travels many metres. All types of radiation become less intense the further they are from the radioactive material, as the particles or rays become more spread out.The thicker the substance, the more the radiation is absorbed. But the three types of radiation penetrate materials in different ways.

Types of Radiation Alpha radiation Alpha radiation is the least penetrating. It can be stopped, or absorbed, by just a sheet of paper.

Beta radiation Beta radiation is able to penetrate air and paper. It can be stopped by a thin sheet of aluminium.

Gamma radiation Gamma radiation is the most penetrating. Even small levels can penetrate air, paper or thin metal. Higher levels can only be stopped by many centimetres of lead, or many metres of concrete.