Despite always being exposed to natural radioactivity from stellar radioelements produced billions of years ago, humans were unaware of its existence until 1896 when it was first observed as uranic rays were discovered. Radioactivity has always been an integral part of our environment and is therefore not a human invention.
All matter is made of atoms and at the heart of these atoms is a nucleus that is 100,000 times smaller and normally stable. However, as not all nuclei are stable, it is within these unstable nuclei that radioactivity is produced as a result of a spontaneous transformation.
Since this natural phenomenon was discovered, mankind has searched to define, understand, transform and use it for different ends. In addition to natural ever-present radioactivity that is not a result of human activity, there is therefore also artificial radioactivity produced by man.