Deutsch: Radioaktivität / Español: Radiactividad / Português: Radioatividade / Français: Radioactivitê ©/ Italiano: Radioattività
Radioactive decay, also known as nuclear decay or radioactivity, is the process by which a nucleus of an unstable atom loses energy by emitting ionizing radiation. A material that spontaneously emits this kind of radiation — which includes the emission of alpha particles, beta particles, gamma rays and conversion electrons — is considered radioactive.

In the environmental context, 'radioactive' refers to materials that emit ionizing radiation, which can potentially harm living organisms and the environment. Radioactive materials can come from both natural and human-made sources, and they can be present in air, water, soil, and other environmental media. Here are some examples of radioactive materials in the environment and their sources:

1. Radon: Radon is a radioactive gas that occurs naturally in the environment as a result of the decay of uranium and radium in rocks and soil. Radon can seep into buildings and pose a health risk to occupants, as it can cause lung cancer.

2. Uranium: Uranium is a naturally occurring radioactive element that is found in rocks and soil. Uranium mining and processing can release radioactive materials into the environment, which can contaminate water and soil and pose a risk to human and ecosystem health.

3. Plutonium: Plutonium is a human-made radioactive element that is primarily produced in nuclear reactors and weapons. Plutonium is highly toxic and poses a significant risk to human health and the environment.

4. Cesium-137: Cesium-137 is a radioactive isotope that is produced in nuclear reactions. Cesium-137 can be released into the environment during nuclear accidents, such as the Chernobyl and Fukushima disasters. It can contaminate soil and water and pose a risk to human and ecosystem health.

5. Tritium: Tritium is a radioactive isotope of hydrogen that is produced in nuclear reactions. Tritium can be released into the environment during nuclear power plant operations and nuclear weapons testing. It can contaminate water and pose a risk to human and ecosystem health.

6. Carbon-14: Carbon-14 is a naturally occurring radioactive isotope that is produced in the atmosphere. It is used in carbon dating and can be released into the environment during nuclear power plant operations. Carbon-14 can contaminate air and water and pose a risk to human and ecosystem health.

Overall, radioactive materials can pose significant risks to human and ecosystem health if they are released into the environment or if people are exposed to them. Proper handling, storage, and disposal of radioactive materials are crucial to preventing environmental contamination and protecting public health.