Radiation
We are always exposed to a small amount of radiation: it comes from the ground, from space, from food and above all from radon, a gas that rises from the soil. More comes from medical examinations. Here you can see what radiation is, how much we receive and where from.
What it is
Ionising radiation is made of particles or waves with enough energy to knock electrons out of the atoms they pass through. It is released when the nucleus of an unstable, that is radioactive, atom changes. It can damage cells, which is why it is measured and limited. The different kinds pass through matter in very different ways.
- Alpha radiation (α)
- Helium nuclei: two protons and two neutrons. They travel a few centimetres in air; they are dangerous above all when the radioactive substance is breathed in or swallowed, as happens with radon.
- Beta radiation (β)
- Electrons (or positrons) emitted by the nucleus. They travel a few metres in air and a few millimetres in the body.
- Gamma radiation (γ)
- Electromagnetic waves like light, but with much more energy. They pass through the body; the X-rays of medical examinations are of the same kind.
- Neutrons (n)
- Particles without electric charge, released mainly by nuclear fission: in reactors and in nuclear explosions.
- Becquerel (Bq)
- Measures how much radioactivity there is: 1 Bq is one nucleus changing per second. Radon in homes is measured in becquerels per cubic metre of air (Bq/m³).
- Sievert (Sv, mSv)
- Measures the effect of radiation on the body (the effective dose), taking into account the kind of radiation and the organs hit. Usually the millisievert (mSv), a thousandth of a sievert, is used.
How much we receive and where from
In Switzerland each person receives on average about 6 mSv a year, about twice the world average estimated by UNSCEAR. The largest part comes from radon in homes, the second from medical examinations, above all computed tomography (CT).
- Radon
- Food and water
- Ground and building materials
- Cosmic rays
- Air travel
- Medical examinations
- Other (power plants, Chernobyl, nuclear tests)
| Where from | Origin | Switzerland | World |
|---|---|---|---|
| Radon | natural | 3.3 | 1.26 |
| Food and water | natural | 0.4 | 0.29 |
| Ground and building materials | natural | 0.35 | 0.48 |
| Cosmic rays | natural | 0.35 | 0.39 |
| Air travel | natural | 0.05 | not given |
| Medical examinations | artificial | 1.69 | 0.6 |
| Other (power plants, Chernobyl, nuclear tests) | artificial | up to 0.1 | 0.0072 |
| Total | about 6 | 3 |
Values in mSv a year. Switzerland: radon is calculated on an average concentration of 75 Bq/m³; medical examinations are from 2023; “other” is at most 0.1 mSv. World: UNSCEAR values from 2008; the latest report (2024) confirms that natural sources, above all radon, are still the largest part. Sources: FOPH, Radiation exposure of the Swiss population; UNSCEAR 2008, Sources and Effects of Ionizing Radiation, table 1.
The scale of doses
Everyday doses are small and are measured in millisieverts. The scale below is logarithmic: each mark is ten times the previous one. In red, the legal limits in Switzerland.
- 0.005 mSv – Fallout from atmospheric tests, world average per year
- 0.05 mSv – Air travel, Swiss average per year
- 0.35 mSv – Ground and building materials, per year
- 1 mSv – Limit for the public (activities with radiation, excluding medicine and natural sources), per year
- 1.69 mSv – Medical examinations, Swiss average per year
- 2 mSv – Aircrew, per year (more than)
- 2.4 mSv – Natural sources, world average per year
- 3.3 mSv – Radon, Swiss average per year
- 6 mSv – Total, Swiss average per year
- 20 mSv – Limit for people who work with radiation, per year
Sources: UNSCEAR 2008, Sources and Effects of Ionizing Radiation, table 1; FOPH, Radiation exposure of the Swiss population; Radiological Protection Ordinance (RPO, SR 814.501), art. 22; FOPH, Dosimetry of aircrew; FOPH, Dose limits for occupationally exposed persons (RPO, art. 56).
Radon
Radon is a radioactive noble gas formed in the ground from the decay of the uranium in rocks. It cannot be seen and has no smell. From the ground it enters buildings, above all cellars and lower floors, and builds up there. Breathed in, it is the most important cause of lung cancer after smoking. In Switzerland the reference value in buildings is 300 Bq/m³; it is measured simply and cheaply with dosimeters.
Worldwide
There is no radon map made with the same method for the whole world. UNSCEAR collected the national surveys of radon in homes of 52 countries: the population-weighted world average is about 39 Bq/m³. The map colours each country by its national mean; click to see the values.
Caution: the surveys date from the 1980s and 1990s and were carried out with different methods (number of homes, season, length of measurement), so countries cannot really be compared with each other. And a national mean says nothing about a single home: even in countries with a low mean there are buildings with a lot of radon, and only a measurement can tell.
- 0–25 Bq/m³
- 25–50 Bq/m³
- 50–75 Bq/m³
- 75–100 Bq/m³
- over 100 Bq/m³
- Geometric mean or maximum only (not comparable)
Radon in homes by country
| Country | Arithmetic mean | Geometric mean | Maximum value |
|---|---|---|---|
| Algeria | 30 | – | 140 |
| Egypt | 9 | – | 24 |
| Ghana | – | – | 340 |
| Canada | 34 | 14 | 1,720 |
| United States | 46 | 25 | – |
| Argentina | 37 | 26 | 211 |
| Chile | 25 | – | 86 |
| Paraguay | 28 | – | 51 |
| People's Republic of China | 24 | 20 | 380 |
| Hong Kong | 41 | – | 140 |
| India | 57 | 42 | 210 |
| Indonesia | 12 | – | 120 |
| Japan | 16 | 13 | 310 |
| Kazakhstan | 10 | – | 6,000 |
| Malaysia | 14 | – | 20 |
| Pakistan | 30 | – | 83 |
| Thailand | 23 | 16 | 480 |
| Armenia | 104 | – | 216 |
| Iran | 82 | – | 3,070 |
| Kuwait | 14 | 6 | 120 |
| Syria | 44 | – | 520 |
| Denmark | 53 | 29 | 600 |
| Estonia | 120 | 92 | 1,390 |
| Finland | 120 | 84 | 20,000 |
| Lithuania | 55 | 22 | 1,860 |
| Norway | 73 | 40 | 50,000 |
| Sweden | 108 | 56 | 85,000 |
| Austria | – | 15 | 190 |
| Belgium | 48 | 38 | 12,000 |
| France | 62 | 41 | 4,690 |
| Germany | 50 | 40 | > 10,000 |
| Ireland | – | 37 | 1,700 |
| Luxembourg | 110 | 70 | 2,500 |
| Netherlands | 23 | 18 | 380 |
| Switzerland | 70 | 50 | 10,000 |
| United Kingdom | 20 | – | 10,000 |
| Bulgaria | – | 22 | 250 |
| Czech Republic | 140 | – | 20,000 |
| Hungary | 107 | 82 | 1,990 |
| Poland | 41 | 32 | 432 |
| Romania | 45 | – | 1,025 |
| Slovakia | 87 | – | 3,750 |
| Albania | 120 | 105 | 270 |
| Croatia | 35 | 32 | 92 |
| Cyprus | 7 | 7 | 78 |
| Greece | 73 | 52 | 490 |
| Italy | 75 | 57 | 1,040 |
| Portugal | 62 | 45 | 2,700 |
| Slovenia | 87 | 60 | 1,330 |
| Spain | 86 | 42 | 15,400 |
| Australia | 11 | 8 | 420 |
| New Zealand | 20 | 18 | 90 |
Values in Bq/m³. Median of the countries: 46 Bq/m³; population-weighted world average: 39 Bq/m³. “–”: value not given. Sources: UNSCEAR 2000, Sources and Effects of Ionizing Radiation, Annex B, table 24.
In Europe
The JRC European Atlas of Natural Radiation brings together measurements from about 38 countries: for each 10 × 10 km cell, the average radon in ground-floor rooms. The data belong to the national bodies and are not public: only the map can be shown.
Sources: European Commission, JRC, European Atlas of Natural Radiation (CC BY 4.0).