Alpha radiation

An alpha particle corresponds to a helium nucleus and is made up of 2 protons and 2 neutrons. In the air, alpha rays can travel a few centimetres, and only fractions of a millimetre in the human body. Alpha radiation, for example, arises from the decay of radon-222, uranium-238 and plutonium-239.

Beta radiation

Beta decay occurs when an electron is flung out of the decaying nucleus. Beta radiation is more penetrating than alpha radiation. In the air, beta rays can travel several meters, while only a few millimetres in the human body. Beta radiation occurs, for example, when carbon-14, calium-40, strontium-90 or caesium-137 decay.

Cloud phase

Cloud phase denotes the time during which radioactivity is released in a cloud formation, moves away and is constantly diluted. During this phase, there is a particular risk of external radiation through the inhalation of radioactive nuclides suspended in the cloud. Staying indoors, seeking cover in a cellar or protective shelter can reduce external radiation. Taking iodine tablets prevents the enrichment of inhaled radioactivity in the thyroid gland.


Contamination refers to pollution caused by a radioactive substance. The environment may become contaminated due to the deposit of radioactive particles. For humans, external contamination can arise from deposits in the air penetrating the skin or from direct contact with contaminated substances. The inhalation or absorption of contaminated substances causes internal contamination.

Decay (radioactive)

Only around 250 of the currently known 2,000 nuclides are stable. The others have properties that mutate without any external influence, and then decay. These nuclides, called radionuclides, are not stable, but radioactive. It is impossible to delay or influence their decay. When they decay, atoms of another element are formed, which may be stable or radioactive. Radioactive decay results in alpha or beta particles, and often gamma radiation too.


A basic radiation protection measure: the greater the distance from the radiation source, the lower the radiation dose.


The dose is the basis for assessing the risk arising from ionising radiation. The starting point here is the energy released by the radiation to the flesh or to an organ. The energy transferred is a purely physical quantity. The dose, which is given in Sieverts (Sv), also takes into account the different biological effects of various types of radiation. It can either be expressed as an organ dose or a full-body dose (effective dose).

Dose rate

This corresponds to the dose per unit of time. A NADAM station measures the equivalent environmental dose (ambient dose) at a height of 1 metre in nano-Sievert per hour (nSv/h = 10-9 Sv/h)


Negatively charged elementary particle that are small in mass.

External radiation

Radiation which enters the body from outside, for example from a radioactive cloud or radioactive deposits in the soil. The most important protective measure against radiation is to stay indoors (at home, in a cellar, or in a protective shelter) during the cloud phase.

Gamma radiation

Gamma radiation is electromagnetic radiation similar to x-ray radiation, ultraviolet radiation from sunlight or a sun lamp. As a general rule, gamma radiation is more penetrating than alpha or beta radiation. It is only gradually weakened on passing through material. With a high energy level, gamma radiation travels hundreds of metres in the air, and up to around one metre in the human body. Gamma radiation arises, for example, from the beta decay of calium-40 and caesium-137, as well as by alpha decay of uranium-238 and its decay products.

Ground phase

When radioactivity is released, radioactive particles deposit themselves in the soil. This creates a risk of external radiation, albeit much smaller than during the cloud phase. Therefore, during this phase, the majority of measures which were issued during the cloud phase can be either lifted or at least eased. In addition, the deposited radionuclides can enter humans through the food chain (contaminated foodstuffs) and lead to internal radiation. This can be minimised by agricultural measures, such as a ban on harvesting, or the stabling of animals.


Half-life denotes the time it takes for a radioactive substance to decay. Each isotope has its own immutable half-life.

Internal radiation

Internal radiation is caused by the ingestion or inhalation of radioactive materials. For example, taking iodine tablets, switching off the ventilation system in a cellar and measures to prevent the consumption of contaminated foodstuffs aim to minimise internal radiation.


When the atoms of a chemical element can only be differentiated by the number of neutrons in its nucleus, they are called isotopes.


Neutrons are parts of the atomic nucleus. They are heavy particles with no electrical charge.


Nuclide is the general term for nuclei of identical composition. Radioactive nuclei are called radionuclides.

Protection factor

The protection factor defines by what factor the dose is reduced in comparison with an outside, unprotected location.


Protons, like neutrons, are part of an atomic nucleus. They are as heavy as neutrons, but have a positive electrical charge.

Radiation (radioactive)

The body can be affected by both external and internal radiation. External radiation is similar to x-ray radiation. Internal radiation occurs when radioactive substances are inhaled or ingested. Radioactive substances remain in the body until they decay or are excreted.

Radiation protection

There are basic differences between protection from external and from internal radiation. Four factors are decisive for external radiation protection: 1. keeping distance; 2. shielding; 3. reducing time of exposure; 4. time: radioactive substances decay naturally and radiation decreases. For internal radiation, the decisive factors are: breathing protection; avoiding the consumption of contaminated foodstuffs; thyroid protection with iodine tablets.


Radioactive atomic nuclei of identical composition.

Reducing time of exposure

A further protective measure: the shorter the time spent in a place with increased radiation, the smaller the dose and thus the lower the risk of radiation.


The radiation dose can be reduced by a suitable material that is placed between the radiation source and a person’s location. Walls offer good protection; decisive is their thickness and the material used.