Radioactivity is the spontaneous emission of ionizing radiation as a consequence of a nuclear reaction or directly from the breakdown of an unstable nucleus. Radioactive nuclei are unstable and decay by emitting energetic particles such as photons, electrons, neutrinos, protons, neutrons, or alphas. The degree of radioactivity depends on the fraction of unstable nuclei and how frequently those nuclei decay. The effect of radioactivity also depends on the type and energy of the particles produced during nuclear decay. Some of these particles are known as ionizing particles, which are particles with enough energy to knock electrons off atoms or molecules. The following are key points about radioactivity:

• Types of radiation: There are six types of radiation produced during radioactivity: alpha particle (α), beta particle (β), gamma radiation (γ), positron emission (β+ decay), electron capture, and nuclear fission.

• Radioactive decay: An unstable nucleus will decompose spontaneously, or decay, into a more stable configuration but will do so only in a few specific ways by emitting certain particles or certain forms of electromagnetic energy.

• Measurement: Radioactivity is a physical phenomenon that can be measured by counting how many atoms are spontaneously decaying each second. This can be done with instruments designed to detect the particular type of radiation emitted with each "decay" or disintegration.

• Uses: Radioactivity is used as a source of heat for satellites, for medical imaging, for targeted cancer treatments, for radiometric dating, and for research into the laws of nature and the origin of matter.

Radioactivity can cause damage in materials and in plant, animal, and human tissue. Although radioactivity is observed as a natural occurring process, it can also be artificially induced typically via the bombarding atoms of a specific element by radiating particles, thus creating new atoms/Nuclear_Chemistry/Radioactivity).