Understanding radioactivity

What is radioactivity?

To understand radioactivity, it is important to know that all matter is made up of atoms. Atoms are composed of electrons that revolve around a nucleus, which is itself composed of protons and neutron.

In most atoms, the nucleus is stable and remains unchanged over time. In some atoms, though, the nucleus is unstable.

Unstable nuclei will try to stabilise themselves by transforming their structure. They will spontaneously decay and, as they do so, they release ionising radiation (in the form of alpha, beta or gamma radiation, or X-rays). This phenomenon is known as radioactivity.

When an unstable nucleus emits ionising radiation, it is said to decay. When an atom's nucleus decays, the atom is transformed into another element, which itself might be stable or also radioactive. If it is radioactive, it will also emit radiation, and so on until the decay process results in a stable nucleus.

For example, as uranium nuclei successively decay into other elements, they eventually become lead nuclei.

There are different types of ionising radiation.

• Alpha radiation:
  which consists of small particles, each of which is made up of two protons and two neutrons;
• Beta radiation:
  which consists of small particles of free electrons;
• Gamma radiation:
  gamma radiation is similar to X-rays, but is more penetrating, and exists in the form of high-energy waves.
• X-rays:
  This is electromagnetic radiation, used in medical radiology, among other applications.

How can we protect ourselves against radioactivity?

There are 3 golden rules when it comes to protecting ourselves from radioactivity. The effects of radiation are reduced with:

• distance: the further away the source of radiation, the lower the dose received;
• use of a protective screen: in the event of a nuclear accident, for example, sheltering in a house acts as a protective screen against ionising radiation;
• the duration of exposure: the shorter the period of exposure, the smaller the dose received.

What are the units used to measured radioactivity?

Quantities of radioactive substances and doses of ionising radiation are measured using 3 different units:

• the Becquerel (Bq) is the number of disintegrations per second.
• the Gray (Gy) expresses the dose that is physically absorbed, i.e. the quantity of ionising radiation absorbed by the tissues of the human body or by an object. The Gray is the unit typically used in nuclear medicine.
• the Sievert (Sv) expresses the effective dose, i.e. the biological effect of the type of ionising radiation (α, β, γ) concerned.