What is Radioactivity?
Everything in the world is made up of extremely small building blocks called atoms. There are stable and unstable atoms. Unstable atoms change spontaneously to become more stable and during this process energy is released in the form of either particles (alpha and beta) or electromagnetic energy (gamma rays). This process of releasing energy is known as radioactivity while the energy itself is known as ionising radiation.
Figure 1: Illustration of an atom (courtesy NDA)
We are exposed to ionising radiation all of the time from natural sources. This is known as background radiation which includes radiation from rocks containing radioactive elements such as uranium, and cosmic rays from the Sun which enter the Earth’s atmosphere. These levels can be higher in some places than in others. Background radiation can also come from naturally occurring radioactive elements that are present in our food and drink.
How are we exposed to radiation?
The greatest average exposure to ionising radiation that the public receives is from natural radiation and the largest contributor to this dose is radon gas. The greatest average artificial ionising radiation dose that we receive is from medical use in treatment and diagnosis, although the amount of radiation received is dependant on whether a person has undergone certain medical procedures that use ionising radiation.The public also receives small exposures to ionising radiation from consumer products such as smoke detectors, authorised discharges into the environment from hospitals, industrial premises and nuclear power stations, and historic fallout from nuclear weapons testing and nuclear incidents like Chernobyl.
Figure 2: Main routes of human exposure to sources of natural and man-made radiation (Courtesy SEPA)
People receive a radiation dose from many sources, such as eating or breathing in naturally occurring radioactive materials, being exposed to external radiation naturally present in rocks and building materials and cosmic radiation from the sun.
Figure 3: Sources contributing to the average annual UK ionising radiation dose
Types of Ionising Radiation
There are three main types of radiation:
- Alpha (α) radiation can be the most harmful if breathed in or eaten. However, it can only travel a few centimetres in air and can be stopped by a thin layer of material such as paper, clothing or the skin so is less harmful if it is outside the body.
- Beta (β) radiation is less harmful than alpha if breathed in or eaten, but can travel further in air and is more penetrating through material. It passes through paper and needs a few millimetres of aluminium or a thin piece of lead to stop it. Similarly it can pass through the skin from outside the body to affect the internal organs.
- Gamma (γ) radiation can travel a long way through air and is extremely penetrating: several centimetres of lead or metres of concrete are required to stop it. However, it gets weaker as you move away from the source. This means that it can easily pass through the skin into the body and affect internal organs.
Figure 4: Illustration of shielding from radioactivity (redrawn by Bell Design)
