Isotopes of radium

Radium (Ra) has no stable or nearly stable isotopes, and thus a standard atomic mass cannot be given. The longest lived, and most common, isotope of radium is ²²⁶Ra with a half-life of 1,600 years. ²²⁶Ra occurs in the decay chain of ²³⁸U (often referred to as the radium series.) Radium has 33 known isotopes from ²⁰²Ra to ²³⁴Ra.