1. Uranium: properties, uses and distribution in nature

1.1 Uranium element (symbol U)

Uranium is the last chemical element in the periodic table of natural elements, with 92 protons in its atomic nucleus, making it the "heaviest". In its natural state, it is composed of two isotopes:

• uranium 238, denoted ²³⁸ U, whose nucleus contains 146 neutrons, in a mass proportion of 99.29% ;

• uranium 235, denoted ²³⁵ U, whose nucleus contains 143 neutrons, in a mass proportion of 0.711%.

These two main isotopes are unstable, but with extremely long half-lives (4.46 billion years for ²³⁸ U and 704 million...