Radioactivity explained

What is radioactivity?

Everything in the world is made up of atoms. Some atoms are unstable and change or decay, until they become more stable, emitting their surplus energy as radiation. These atoms are called radionuclides, and radioactivity is the spontaneous emission of radiation from the atomic nucleus.

Where is it?

Radionuclides are in the air we breathe, the water we drink and the food we eat. Even our bodies contain them. Many radionuclides were formed long before our own solar system came into existence, while some are continually created in the Earth's atmosphere by the action of cosmic rays.

How do we use it?

Radioactive materials are used in industry for a variety of purposes, including:

  • measuring the thickness and integrity of structures and materials
  • preserving food
  • diagnosing disease and injury and (in larger doses) treating diseases like cancer
  • defence, in nuclear weapons, submarine propulsion and armour piercing shells
  • power generation.

How do we measure its effects?

The amount of radiation energy absorbed by the body is measured in a quantity called the effective dose. This quantity takes into account the effects of different types of radiation and the sensitivities of different organs and tissues.

The unit of effective dose is the sievert (Sv). One sievert is actually a large quantity, and doses are often reported in units of thousandths of a sievert. So, one thousandth of a sievert is a millisievert (mSv).

What is the breakdown of exposure?

Around 85% of our average annual radiation dose comes from natural sources, with 14% from medical procedures. The remaining 1% comes from a combination of man-made sources (discharges from nuclear sites contribute less than 0.1%). There are internationally agreed procedures for assessing the effects of radiation on human health and for limiting radiation exposures.

What is the UK average dose?

The average dose to members of the public from all sources of radioactivity is estimated by the Health Protection Agency to be 2.6 millisieverts (mSv) per year.

It is important to remember that this is an average exposure. Individual doses may differ widely depending upon age, diet, surroundings, occupation and medical history.

What effect can it have?

When living tissue is exposed to ionising radiation, it will absorb some of the radiation's energy and may become damaged. This may lead to acute and/or chronic health effects such as cancer.