The radioactivity that occurs when stable atoms which are not naturally radioactive are bombarded by particles such as protons, neutrons, or alpha particles. It was discovered by Frédéric and Irène Joliot‐Curie in 1934. Radioisotopes produced by artificial radioactivity are far more numerous than all the naturally occurring stable and radioactive isotopes put together; they have been used very extensively in research, industry, and medicine. In chemistry, labelling using radioisotopes has proved very useful in many branches of the subject.