What is radioactivity?

Despite always being exposed to natural radioactivity from stellar radioelements produced billions of years ago, humans were unaware of its existence until 1896 when it was first observed as uranic rays were discovered. Radioactivity has always been an integral part of our environment and is therefore not a human invention.

All matter is made of atoms and at the heart of these atoms is a nucleus that is 100,000 times smaller and normally stable. However, as not all nuclei are stable, it is within these unstable nuclei that radioactivity is produced as a result of a spontaneous transformation.

Since this natural phenomenon was discovered, mankind has searched to define, understand, transform and use it for different ends. In addition to natural ever-present radioactivity that is not a result of human activity, there is therefore also artificial radioactivity produced by man.

Radioactivity is a natural phenomenon and therefore was not invented by man. It was a French physicist, Henri Becquerel, who discovered in 1896 that certain substances such as uranium emit natural radiation known as ionising radiation. Substances that emit ionising radiation are radioactive.

An atom, from the ancient Greek 'that cannot be divided', is a minuscule entity that, with other atoms, forms matter.

The nucleus of an atom is made up of protons and neutrons which themselves make up nucleons.

Electrons circle this nucleus at high speed in an electron cloud.

In nature, all matter and all bodies are made up of atoms.

Isotopes are atoms that have the same number of electrons and protons, but a different number of neutrons (the atomic mass) and identical chemical properties. The proportion of neutrons in a nucleus can make the atom unstable and, in such case, they may be radioactive.

Currently around 325 natural isotopes and 1,200 artificially created isotopes have been recorded.

Most elements are formed naturally out of a mix of isotopes.

A radionuclide or radioisotope is an isotope with an unstable, and therefore radioactive, nucleus. Unstable isotopes always try to regain a stable form through decay.

For example, carbon 14 (14C) is a radioisotope from the element carbon, whose most common isotope (12C) is stable.

Radioisotopes are either natural or artificial in origin. They are mainly used in nuclear medicine, in particular in radiotherapy as a treatment for illnesses such as cancer.

Protons are one of the elements, along with neutrons, that make up the nucleus of an atom. A proton is a subatomic particle that carries a positive electric charge.

Neutrons are one of the elements, along with protons, that make up the nucleus of an atom. A neutron is a subatomic particle that does not carry an electric charge and is therefore neutral.

There are two types of nucleons: protons and neutrons. These two elements form the main part of the nucleus of an atom.

An electron is an elementary particle that has a negative electric charge. Along with neutrons and protons, it is one of the components that make up the atom, albeit the smallest.

Electron clouds are made up of electrons which spin around the nucleus of an atom made up of protons and neutrons at high speed.Le nuage électronique est composé d’électrons qui tournent à vitesse élevée autour du noyau d’un atome composé de protons et de neutrons.

Ionising radiation is a kind of radiation issued by unstable atoms that disintegrate. These reactions take place in the nucleus of the atom.

Different types of radiation are produced:

• Alpha radiation : these are small particles, each made up of two protons and two neutrons;
• Beta radiation : these are small particles of free electrons;
• Gamma radiation : similar to X-rays, but they have greater penetrative capacity and are represented in the form of energy waves.

These forms of radiation differ in their capacity to penetrate the body; gamma radiation can pass through the body completely and damages the organs it passes through.

Ionising radiation that penetrates a living organism can affect the process of cell reproduction by causing abnormal chemical reactions. Some of these reactions cause the cell to die or change.

X-rays, which are used in radiology, are identical in nature to gamma rays and can also affect organs.

Conversely, non-ionising radiation, such as low frequencies, radio frequencies, high frequencies, microwaves or even infra-red and ultraviolet, also exists.

Ionising radiation can be both natural or artificial.

• cosmic radiation ^a;
• radiation from the earth and buildings (construction materials) ^b;
• radiation from the human body ^c;
• soil gas radon ^d;
• medical applications ^e : some radionuclides can be used for examinations (for example X-rays) and medical treatment (for example radiotherapy);
• industrial products ^f : radionuclides produced in nuclear installations and mining.

Radon, a gas from the ground, is the main source of natural radiation exposure.

The main source of artificial exposure is a result of medical applications.

Ionising radiation can be both natural or artificial.

The main natural sources of radiation are:

• cosmic radiation ^a : this comes from space and increases significantly with altitude (the dose received by a mountain dweller at an altitude of 1,000 metres is 20% higher than that received by someone living by the seaside);
• terrrestrial or telluric radiation ^b : the human body is constantly exposed to this radiation that appeared during the formation of the earth. It originates from the ground and is also found in construction materials for buildings obtained from materials extracted from the ground;
• soil gas radon, Rn ^d : this natural radioactive gas (odourless, colourless and tasteless) is the main source of natural exposure following the disintegration of uranium that occurs naturally in the earth's strata (earth, rocks and water);
• mineral water and foods ^b : radiation from the ground and cosmic radiation also affect plants, animals and water, so the food and water we ingest is naturally mildly radioactive;
• radiation from the human body ^c : at around 120 Bq/kg (or 8,400 Bq for an individual weighing 70 kg), this is the result of consuming foods that naturally contain radioactive elements.

Radon is the main source of natural radiation exposure. This natural radioactive gas comes from the soil and human and animal exposure to this natural radiation can vary greatly due to geographical differences. In some places in the world, local geology can cause radiation exposure to vary.

Radon can also be emitted by some construction materials that use naturally radioactive rocks such as some types of granite, gneiss and basalt. Radon is also present in some houses.

In Luxembourg, the average concentration of radon in homes is 50 Becquerels/m3 (Bq/m3) in the south of the country, and 150 Becquerels/m3 (Bq/m3) in the north. The European reference value is 400 Bq/m3 for old homes and 200 Bq/m3 for new builds.

The Becquerel (Bq) is the unit that quantifies radioactivity and measures the activity of an object: one piece of granite weighing 125 grammes has an activity of 1000 Bq, coal ash has an activity of 2000 Bq (per kg), fruit has an activity of 40 to 90 Bq (per kg), while a man or woman weighing 70 kg has an activity of 8000 Bq.

The human body is naturally radioactive because people eat, drink and inhale radioactive substances that are naturally present in the environment.

These substances are continually absorbed by the human body and integrate into its tissues, organs and bones.

A human body typically contains approximately 40 grammes of potassium.

Around 1/1000 of the 40 g is potassium-40, a radioactive isotope of potassium.

Radioactive radiation in the human body is around 120 Bq/kg (about 8,400 Bq for an individual weighing 70 kg).

Ionising radiation can be both natural or artificial.

The main artificial sources of radiation are:

• medical ^e : the main areas of medical use are radiology (mammograms, X-rays and scans), nuclear medicine (diagnosis or treatment using radioisotopes) and radiotherapy (cancer treatment);
• industrial ^f : the nuclear industry is obviously the biggest user of radioactive sources (fuel extraction, production, use and reprocessing, the storage and treatment of waste), but many other industrial activities use them too (for example for evaluating faults in the homogeneity of metal and in particular in welding chords, measuring the humidity and density of various soils, monitoring the fill level in a container and measuring basis weight). Industrial applications make up only 1% of the average individual dose;
• X-rays ^e : produced using electricity and used both in medicine and industry, they have a similar effect to gamma radiation.

Alpha radiation is a specific kind of ionising radiation. It occurs when the alpha particle, a small positively charged nucleus made up of two protons and two neutrons, is emitted.

It has a weak penetrative capacity : it does not pass through 50 mm of air or a sheet of paper.

Outside of the organism, the substances that issue alpha rays are mainly harmless. If these substances enter an organism they can be harmful to the organs with which they come into contact.

Beta radiation is a specific kind of ionising radiation. This radiation is issued when a neutron transforms into a proton by emitting an electron.

It has an average penetrative capacity : it can be stopped by a few millimetres of aluminium.

The substances that emit beta rays can be dangerous for external tissues as the rays can pass through 1 to 2 cm of tissue. If these substances enter an organism they can be harmful to the organs with which they come into contact.

Gamma radiation is a particular type of ionising radiation. A high-energy electromagnetic wave is issued that does not emit particles.

Gamma radiation has the greatest penetrative capacity: it carries very high levels of energy, from tens of thousands of electron-volts to several millions.

Passing through a lead or concrete plate, however, reduces its strength considerably.

A half-life, sometimes called the radioactive period, is the time required for half of the nuclei of a radioactive isotope to decay naturally. Depending on the isotope, decay can vary from several fractions of a second to many billions of years.

The principle of a half-life is the half of the half of the half, etc.

The becquerel (Bq) is the unit that expresses the activity of a radioactive substance and enables radioactivity to be quantified. This unit measures the amount of radiation emitted.

A Bq corresponds to one decay per second within a radioactive substance. It is a very small unit, which is why multiples of becquerels are often used, for example:

• the kilobecquerel (1 kBq = 1000 Bq);
• the megabecquerel (1 MBq = 1,000,000 Bq);
• the terabecquerel (1 TBq = 100,000,000,000 Bq).

One piece of granite weighing 125 grammes has an activity of 1000 Bq, coal ash has an activity of 2,000 Bq (per kg), fruit has an activity of 40 to 90 Bq (per kg), while a person weighing 70 kg has an activity of 8,400 Bq.

The becquerel carries the name of the French physicist Henri Becquerel who discovered radioactivity.

The Sievert (Sv) is a unit of measurement that enables the effect or impact of ionising radiation on the human body or on any other living organism to be evaluated from a biological point of view.

This is a large unit, which is why

• millisieverts (1 mSv = 0.001 Sv)
• or even microsieverts (1 mSv = 0.000001 Sv),

are often used.

When a person is exposed to radioactivity, they are said to be 'receiving a dose of X millisieverts'.

In Luxembourg, annual exposure to natural radioactivity is 2 millisieverts per year, while one single pulmonary X-ray exposes a patient to a dose of 0.2 millisieverts, the equivalent to around 3 days' worth of natural exposure.

The Sievert gets its name from the Swedish radiobiologist Rolf Sievert.

The Gray (Gy) measures the dose physically absorbed, i.e. the quantity of ionising radiation absorbed by the tissues in the human body or by an object.

The Gray is a unit typically used in nuclear medicine (for treating cancer).

The Gray gets its name from the English physicist Harold Gray.

No, radioactivity is odourless, colourless, tasteless and invisible.

It can only be detected and measured using specially designed devices.

Although some of those devices are easy to use to detect a radiation source, the data gathered during an accident situation must be interpreted by specialists.

Radioactivity cannot be seen. Specialised equipment is required to measure it.

The Geiger-Müller (or G-M counter) is a very sensitive instrument for detecting and measuring ionising radiation. Designed by Hans Geiger in 1913 and updated by Walther Müller in 1928, it is also used to find uranium ore, a radioactive heavy metal that is the main raw material used in the nuclear industry.

In Luxembourg, ambient (environmental) radioactivity, both natural and artificial, has been continually measured since 1983 by the Radiation Physics Laboratory of the Department for Radiation Protection at the National Health Directorate using a network of measurements and automatic alerts.

These measurements are published via the Department for Radiation Protection's website. A large number of samples are taken each year in different biological environments and in the food chain. The national network for measurements and automatic alerts provides over 19,000 measurements of ambient radioactivity per month, which are then the subject of monthly public reports.

These tests enable changes in residual artificial radioactivity to be monitored, as was the case after the accident in Chernobyl in 1986, and also the exposure of the Luxembourg population to be analysed.

The aim of Luxembourg's national network for measurements and automatic alerts is to:

• continually monitor ambient radioactivity and natural background radiation;
• detect uncontrolled and accidental releases from nuclear installations in neighbouring countries;
• alert national authorities in the event of a nuclear emergency;
• enable an overview of the radiological situation to be rapidly established.

This network is entirely automated and alerts the authorities when radiation that exceeds the levels of natural background radiation is detected.

Two programmes were set up to monitor the Luxembourg population  and the environment for exposure to radiation, namely:

• monitoring radioactivity within the environment;
• monitoring radioactivity in the food chain.

These two programmes go hand in hand as any increase in radioactivity in the different biological environments causes an unavoidable increase in radioactivity in foodstuffs.

In the event of an accident leading to radioactive release into the environment, there are systems in place to ensure that information can be communicated continuously between the managers of the power plant in question and the authorities, and between the authorities and the population.

The national network for measuring radioactivity in the air and raising the alarm continually sends its results to the Department for Radiation Protection and, in the event of a nuclear emergency, the Crisis Cell. These results are made available to the population accompanied by the necessary explanations. The population is also informed of the degree of exposure to radioactivity measured in specific places in the country.

Our body is subjected to invisible radioactivity on a daily basis, emitted by both the earth and the universe.

This radiation is generally harmless as the dose is very low. However, exposure to a large quantity of radiation can cause several illnesses, including different types of cancer.