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Ionising radiation

Environmental Radioactivity - Medicine - Occupational Radiation Protection - Nuclear Hazards Defence

Ionisierende Strahlung

What are the effects of radiation?

Glossary EntryMolecule

A molecule is a group of atoms held together by chemical bonds. A molecule can consist of several atoms of the same chemical element or atoms of different elements.
The hydrogen molecule consists of atoms of the same chemical element: H2 = 2 hydrogen atoms (H: chemical symbol for hydrogen).
The water molecule, in contrast, consists of atoms of different chemical elements: H2O = 2 hydrogen atoms + 1 oxygen atom (O: chemical symbol for oxygen).

When ionising radiation hits a cell, the radiation energy is taken up (absorbed) by the molecules of the cell. This energy has the effect of ejecting electrons from the molecules (ionisation) or breaking bonds in the molecules. The resulting molecule types (radicals) are very reactive chemically and can be electrically charged or electrically neutral. These radicals react with the other molecules inside the cell which may then directly or indirectly lead to cell damage. In most cases, water molecules are affected. However, other substances inside the cell can be affected as well, such as proteins or the DNA (carrier molecules of genetic information).

For the long-term effects on the organism the alterations of the DNA are particularly important.

The effects of radiation on the cell

In general, the cell is able to repair radiation damage which means that no biological effects can be observed. However, if the cell is unable to repair the damage, it usually dies by targeted programmed cell death (apoptosis). In the case of severe damage caused by radiation exposure with very high radiation doses, the cell dies uncontrolled (necrosis). If a faulty or insufficient repair occurs, genetically altered (mutated) cells, which are also able to replicate, may develop.

The effects of radiation on the organism

If and to what extent the radiation exposure leads to health damage depends on the radiation dose absorbed, the type of radiation and the mainly affected organ or body tissue. Radiation damage may also be caused by ionising radiation from natural sources (such as radon).

As a reference: For people living in Germany the dose from natural sources is about 2 to 3 millisieverts per year on average.

A distinction is generally made between deterministic and stochastic radiation effects.

Comparison between deterministic and stochastic radiation effects
Deterministic Radiation EffectsStochastic Radiation Effects
DescriptionDamage to tissues and organs, mostly occurring immediatelyDelayed damage due to cells with damaged DNA (genetic material)
Cause of the DamageKilling or dysfunction of numerous cellsMutations and subsequent replication of individual mutated cells (somatic cells or germ cells)
Dose DependenceThe higher the radiation dose, the more severe the radiation damageThe higher the radiation dose, the higher the probability of radiation damage occurrence
Dose Threshold ValueAbout 500 millisieverts (mSv);
for the unborn child about 50 to 100 mSv
ExamplesSkin reddening, hair loss,
infertility, acute radiation syndrome, malformations and brain maldevelopments in the unborn child
Cancer, leukaemia, hereditary effects

Development of deterministic radiation damage

Deterministic damage is usually the consequence of the massive killing of cells in an organ or tissue system by apoptosis or necrosis. If too many cells in tissue or an organ are killed, the function of the affected organ is impaired. Deterministic radiation damage is caused by high doses of ionising radiation. It always occurs when the dose exceeds a certain threshold value.

Development of stochastic radiation damage

The genetic information of a cell can be altered by a faulty or insufficient repair of the DNA. During the natural process of cell division the altered (mutated) cells replicate. In the case of somatic cells, this procedure can lead to the development of cancer, years after the exposure. The occurrence of radiation-induced hereditary defects has not been observed in humans until now, yet they have been demonstrated in animal studies.

Altering the genetic information in the germ cells produced in the testicles or ovaries can result in hereditary defects in the following generations. The term used with somatic cells as well as germ cells is stochastic radiation damage. It may also occur with low doses of ionising radiation. This means that both low and high doses may induce stochastic damage, but it does not necessarily have to occur. The probability that this type of radiation damage will occur increases, however, with increasing radiation exposure. Between the radiation exposure and the onset of the disease a long period of time may pass (so-called latency period).

Objectives of radiation protection

Radiation protection is aimed at protecting human health. Its objective is to avoid deterministic radiation effects in a reliable manner and to reduce the risk for stochastic effects to a reasonably attainable level.

State of 2017.06.27

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