Ionisation

The radiation on passing through the material causes electrons to be stripped from some of the atoms in the absorbing material. The process is called ionisation.

Energy is transferred to the absorber during the ionisation process. For a given thickness of absorber, alpha radiation produces most ionisation, beta next and gamma least.

Safety and radiation dose

Safety precautions are necessary when working with radioactive sources. Radioactive sources should be kept away from the body and never brought close to the eyes. Sources should be shielded from the body and handled using tongs so that the source is kept away from the body.

The radiation that a person receives can be monitored using film badges. The film in the badge is developed once the badge has been worn for a certain length of time. The amount of blackening that is produced on the film is a measure of the dose received by the person wearing the badge. Film badges are checked regularly to ensure that the dose received by the person does not exceed safety limits.

The radiation dose received by body tissue depends on the type of radiation absorbed by the tissue eg whether the radiation is alpha, beta, gamma or some other type of radiation such as X-rays. The radiation dose received also depends on the energy of the radiation.

A way of expressing the radiation dose received from different sources is in terms of a quantity called equivalent dose. Equivalent dose is measured in sieverts (Sv). A dose of one sievert from an alpha radiation source, for example, is equivalent to a dose of one sievert from a beta radiation source or any other source of radiation.

The risk of damage to body tissue from a dose of radiation depends on the size of the dose. The risk of damage also depends on the type of body tissue absorbing the radiation. Some tissues of the body are more susceptible to harm from radiation than others. This is taken into account when estimating the dose of radiation a person has effectively received.