Question

the phenomenon of radioactivity is

Answer 1

Matter is composed of atoms, most often assembled in molecules. At the heart of these atoms, is found the nucleus, 10 000 to 100 000 smaller than the atom itself. Radioactivity is a phenomenon which is produced deep within the atom, in this very same nucleus. This phenomenon is very difficult to observe : it was only in 1896 that the first radiation of unknown origin was observed, emitted by uranium salts.

Certain unstable atom nuclei are the source of radiation, designated by the first three letters of the Greek alphabet : alpha (α), beta (β) and gamma (γ). This radiation is composed of particles emitted by high energy nuclei. Alpha radiation is composed of light helium nuclei, β radiation of posititve or negative electrons and γ radiation of high energy photons.

What distinguishes a radioactive atom from an ordinary atom, is this unique moment when it turns into another kind while emitting radiation. This emission occurs after after very variable times, up to billions of years. Apart from this moment a radioactive atom behaves exactly like an ordinary atom. with the same physical, chemical or biological properties. Throughout its existence it is no more harmful nor mobile than its non-radioactive homologues.
Marie Curie and Ernest Rutherford
Marie Curie and Ernest Rutherford discovered, with others, radioactivity and the nucleus of the atom in the early twentieth century.

Answer 2

the activities of elements in the presence of light or radiation. .is radioactivity