Radium (88Ra) has no stable or nearly stable isotopes, and thus a standard atomic weight 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 34 known isotopes from 201Ra to 234Ra. In the early history of the study of radioactivity, the different natural isotopes of radium were given different names, as it was not until Frederick Soddy's scientific career in the early 1900s that the concept of isotopes was realized. In this scheme, 223Ra was named actinium X (AcX), 224Ra thorium X (ThX), 226Ra radium (Ra), and 228Ra mesothorium 1 (MsTh1). When it was realized that all of these are isotopes of the same element, many of these names fell out of use, and "radium" came to refer to all isotopes, not just 226Ra, though mesothorium 1 in particular was still used for some time, with a footnote explaining that it referred to 228Ra. Some of radium-226's decay products received historical names including "radium", ranging from radium to radium, with the letter indicating approximately how far they were down the chain from their parent 226Ra. In 2013 it was discovered that the nucleus of radium-224 is pear-shaped. This was the first discovery of an asymmetrical nucleus.

List of isotopes

Actinides vs fission products