How is the radioactivity connected with the atomic nucleus?

How does radioactivity arise and how does it work?

There are many different forms of radiation that humans are exposed to in everyday life - both natural and man-made. This includes light and thermal radiation, but also the radiation emanating from radioactive substances. Many forms of radiation are harmless to health. But above a certain dose it can cause damage.

What is ionizing radiation?

Radiation emanates from a radiation source and transports energy. The energy can be transported in the form of electromagnetic waves, for example with light. However, it can also be transported as a particle stream, for example in the case of alpha and beta radiation emanating from radioactive substances.

The radiation emanating from radioactive substances is often referred to colloquially as "radioactive radiation", but the technical term is ionizing radiation. Radioactivity is the property of the atomic nuclei of certain substances to transform into other nuclei without external influence. This process is known as radioactive decay. Radioactive atoms are called radionuclides.

Ionizing radiation is very energetic. It can change the matter into which it penetrates. In this process, electrons are "knocked out" from the shell of atoms or molecules - the molecule that remains is then electrically positively charged, which is referred to as "ionized". When this radiation hits living cells, it can cause damage to the cells and affected organisms.

As a result of the transformation of atomic nuclei, decay products arise, which in turn can further decay - that is, they can themselves be radioactive. The final result of the decay is stable, non-radioactive nuclei. Radioactive substances emit ionizing radiation until the last radionuclide has decayed.

The duration of these decay processes of radioactive substances can be extremely different. That means: Depending on the substance, the radioactivity decreases at different rates. Therefore half-lives are often mentioned. Half-life is the time that is required to reduce the proportion of radioactive nuclei to about half. The half-lives can be fractions of a second, but for some radionuclides they can be billions of years.

Radioactivity is measured in the unit Becquerel (Bq). The size indicates how many radioactive nuclei decay per second. The Becquerel unit is usually related to area, volume or mass, for example Bq per square meter.

When the atomic nucleus decays, different types of radiation can be produced: alpha, beta, gamma and neutron radiation. Alpha, beta and neutron beams are particles. Alpha rays cannot penetrate human skin. Beta rays, on the other hand, can penetrate a few millimeters into skin or plastic, and even a few centimeters or meters in the air. If radioactive substances get into the body, for example through food, they can damage blood, tissue and other cells there.

Neutrons are released especially when heavy atomic nuclei are fissioned, for example uranium. Neutron radiation has a strong effect on biological tissue, and shielding it is complex. Gamma rays are electromagnetic radiation, similar to light, but with a much higher ability to penetrate matter.

Where does radioactivity occur?

There are various natural and artificial sources of radioactivity that people are exposed to in everyday life.

The noble gas radon (Rn-222, half-life 3.8 days) is one of the natural sources. Radon is present all over the world. It leaks out of the ground or building materials and is inhaled. Natural radionuclides, which come from the decay of the radioactive substances thorium and uranium as well as potassium-40, are also found in food.

Cosmic radiation also contributes to natural radiation exposure. It comes to earth from the sun and from the depths of space. This radiation is much stronger at high altitudes than at low altitudes: it becomes weaker on the way to earth due to the dense atmosphere. There is also terrestrial (terrestrial) radiation. They are mainly caused by natural radioactive substances in soils and rock layers of the earth's crust and in building materials made from them.

In addition to natural radiation, there is radiation from artificial sources. The majority comes from radiation applications in medicine such as X-ray diagnostics, nuclear medicine diagnostics, and radiation and nuclear medicine therapy.

Why is radioactive radiation dangerous to humans?

When radiant energy hits the human body, it is absorbed (absorbed) by the tissue. The energy absorbed can have a variety of effects. Whether and to what extent radiation exposure of an organism leads to damage to health depends on the dose and type of radiation absorbed, as well as on which organ or tissue of the body is mainly affected.

If the radiation dose exceeds a certain threshold, damage to tissues and organs occurs immediately. The reason for this is that body cells are damaged or killed. If too many cells are affected, the affected organs lose their function. Such immediately occurring radiation damage is referred to as deterministic damage.

In addition to direct damage, radiation can cause changes in the genetic material of cells, so-called mutations. The affected cells multiply through the natural process of cell division. This process can lead to the development of cancer or leukemia in body cells years after exposure (here: exposure). Damage to the genetic material is referred to as stochastic radiation effects.

The causes of cancer and leukemia - whether due to radiation or other conceivable causes - cannot be differentiated in terms of clinical appearance. However, even low doses of radiation can increase the likelihood of cancer or leukemia occurring in people who have been exposed to radiation.

Which dose is dangerous?

There is no safe dose value. However, the greater the radiation exposure, the greater the likelihood of health consequences. The lower the exposure, the lower the likelihood of damage.

In order to evaluate and avoid health hazards, limit values ​​for radiation exposure have been set. The limit values ​​mark values ​​below which the probability of the occurrence of health consequences is below a value that is considered to be acceptable.

The Sievert unit of measurement is used to evaluate the radiation exposure of people. It stands for the so-called effective radiation dose. In Germany, the dose limit for people who are occupationally exposed to radioactivity is 20 millisieverts per year. The dose must not exceed 400 millisievert during the entire professional life.

Acute radiation damage - deterministic damage - occurs from a dose threshold value of around 500 millisievert (mSv), in unborn children from around 50 to 100 mSv. These include burn-like symptoms on the skin, hair loss, impaired fertility and anemia. If the extent of cell killing exceeds a certain level in a part of the tissue or in an organ, the function of the affected organ or tissue is impaired.

Such high doses can occur in accidents with radioactive substances. In addition to the reactor accidents in Chernobyl and Fukushima, the radiation accident in Goiâna, Brazil in 1987 is one of them. There, radioactive material was stolen from a former radiation clinic and taken from the security container by the thieves out of ignorance. Four people were killed.

Acute radiation effects such as nausea and vomiting occur within a short time from a threshold dose of 1,000 mSv. An exposure of 3,000 to 4,000 mSv within a short period of time is life-threatening: Without medical intervention, 50 percent of the exposed people die after three to six weeks at this dose.

For comparison: radiation from natural sources, for example from food or cosmic radiation, adds up to an average of 2.1 mSv (effective dose) per person per year in Germany. Depending on where you live, diet and lifestyle, it is between two and three millisieverts, but in exceptional cases it can reach up to ten millisieverts.

The radiation exposure from artificial sources - such as from X-ray examinations or computed tomography (CT) - is around 2.0 mSv per year in Germany. An x-ray of the chest, for example, achieves a maximum of 0.03 mSv; a full body CT scan can result in 10 to 20 mSv. Cosmic radiation also leads to pollution during flights. On a flight from Munich to Japan, values ​​of up to 0.1 mSv are achieved.

What can be done against the dangers of ionizing radiation?

The best protection against health risks from radioactivity is to avoid exposure. Therefore, radiation protection primarily consists of keeping exposure as low as possible. This applies to both exposure to radiation sources outside the body, for example X-rays, and the ingestion of radionuclides with food or breath. For example, mushrooms in various areas of southern Germany are still enriched with Cs-137 from the release after the Chernobyl reactor accident.

Any technical or medical application of ionizing radiation must be justified. There are limit values ​​for radiation doses, compliance with which is monitored. So-called shielding plays an important role in technical applications. Protective suits, protective gloves or respiratory masks can protect against alpha and beta radiation from outside. However, absorption into the body can lead to significant stress. In contrast, heavy materials such as lead and concrete have to be used to shield against gamma radiation. Shielding against neutron radiation is also complex.

After radioactivity is released into the environment, pollution can be reduced, among other things, by removing superficial contamination from radioactive substances. The contamination is called contamination and the removal is called decontamination. For example, after the Chernobyl and Fukushima accidents, buildings and equipment were cleaned and contaminated soil was removed.

Further links on the topic:

Federal Office for Radiation Protection: Ionizing Radiation
http://www.bfs.de/DE/themen/ion/ion_node.html

Federal Environment Ministry: Brief information on radiation protection
http://www.bmu.de/themen/atomenergie-strahlenschutz/strahlenschutz/kurzinfo/

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