What is radioactivity?

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What is radioactivity?


What is radiation?
What is the unit Becquerel?
What is a radiation dose?

Radioactivity has existed since the beginning of the universe. The earth contained radioactive isotopes long before life started to develop. Even human beings contain radioactive atoms, so-called radioisotopes or radionuclides."Natural radionuclides" either have existed since the beginning of the universe (primordial radionuclides), or are being formed continuously by cosmic radiation (cosmogenic radionuclides). Nuclear energy has created many "artificial radionuclides", which are also detectable in the environment today.

Examples of primordial, cosmogenic, and artificial radionuclides with their half-lives and radiation emitted:

Primordial radionuclides
Nuclide Half-life (years) Radiation emitted
Potassium 40 1,280,000,000 β+- and β-
Rubidium 87 47,000,000,000 β-
Thorium 232 14,100,000,000 α
Uranium 235 704,000,000 α
Uranium 238 4,470,000,000 α
Cosmogenic radionuclides
Nuclide Half-life (years) Radiation emitted
Tritium (3H) 12.3 β-
Beryllium 7 53 Tage Electron aligning and Gamma
Beryllium 10 1,600,000 β-
Kohlenstoff 14 5736 β-
Silicium 32 172 β-
Artificial radionuclides
Nuclide Half-life (years) Radiation emitted
Tritium (3H) 12.3 β-
Cobalt 60 5.3 β- and Gamma
Stronium 90 29 β-
Technetium 99 213,000 β-
Ruthenium 106 1.01 β- and Gamma
Antimon 125 2.77 β- and Gamma
Caesium 134 2.04 β- and Gamma
Caesium 137 30 β- and Gamma
Plutonium 238 87.8 α
Plutonium 239 24,390 α
Plutonium 241 14.9 β-
Americium 241 433 α

Radionuclides are unstable and decay after a certain time. By emitting (radiating) particles from their nucleus, they are transformed into different elements. A characteristic property of each radionuclide is its half-life, which is the time in which one half of its nuclides decays.


The unit of activity is "Becquerel" (symbol: Bq); it has replaced the formerly used unit "Curie". 1 Bq activity means that in a particular substance one nucleus disintegration occurs per second. The activity can also be expressed in relation to a volume of one litre or a mass of one kilogram. In that case you obtain the activity concentration (Bq/l) and specific activity (Bq/kg), respectively. For example, U-238 has a specific activity of 12,400 Bq/g. Prefixes are used to express several orders of magnitude: 

e.g.  1 mBq/l means 0.001 Bq per litre 

        1 kBq/l means 1000 Bq per litre 

        1 MBq/g means 1,000,000 Bq per g 

        1 GBq means 1,000,000,000 Bq (1 billion Bq) 

Radiation dose:

Indication of a substance's activity alone does not say anything about its biological radiation effect. The relation between the activity of a radioactive substance and the radiation dose which is caused by radiation of that substance in an organism is expressed by the so-called dose factor, which has to be determined individually for each radioactive substance. Today, the absorbed radiation dose is computed and indicated mostly as "effective dose equivalent". The unit used is the "Sievert" (Sv). In the past, the unit "rem" (roentgen equivalent man) was used, with 100 rem = 1 Sv. 

Radiation damage:

The lethal (deadly) dose is about 10 Sv (1000 rem), i.e. death occurs within a few days after radiation exposure. At doses of 4 to 6 Sv, the survival rate probability is 50% within the first 4 weeks after exposure. From a dosis of about 500 mSv (=0.5 Sv), so-called "non-stochastic" radiation damage occurs, i.e. direct effects on the human body (e.g. cataracts, changed blood count). Up to about 100 mSv no direct radiation damage occurs but there may be random stochastic effects.

The limit value for professional radiation exposure since 1 August 2001 is 20 mSv per year. The occupational life dose should not exceed 400 mSv (§56 German Radiation Protection Ordinance).

The annual radiation dose of the population in Germany, including internal and external exposure, is about 2.4 mSv. According to the "Strahlenschutzverordnung" (radiation protection regulations), the limit value for environmental emissions from nuclear facilities is max. 0.3 mSv per year for the general population at the "least favourable locations of impact" of the exposure.

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 © 2016 Bundesamt für Seeschifffahrt und Hydrographie Last Update: Apr 19, 2013 6:02:05 PM  
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