Radioactive decay
![Alpha decay is one type of radioactive decay, in which an atomic nucleus emits an alpha particle, and thereby transforms (or](/Images/godic/202502/05/Alpha_Decay.svg1959.png")
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![Pierre and Marie Curie in their Paris laboratory, before 1907](/Images/godic/202502/05/Pierre_and_Marie_Curie2000.jpg")
![Taking an X-ray image with early Crookes tube apparatus in 1896. The Crookes tube is visible in the centre. The standing man is viewing his hand with a fluoroscope screen; this was a common way of setting up the tube. No precautions against radiation exposure are being taken; its hazards were not known at the time.](/Images/godic/202502/05/Crookes_tube_xray_experiment2000.jpg")
Radioactive decay, also known as nuclear decay or radioactivity, is the process by which the nucleus of an unstable atom loses energy by emitting radiation, including alpha particles, beta particles, gamma rays and conversion electrons. A material that spontaneously emits such radiation is considered radioactive.