Isotopes of radium
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, which is in the decay chain of 238U.
Radium now 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 work in the 1900s and 1910s that the concept of isotopes was employed. In this scheme, Ra was named actinium X, Ra thorium X, Ra radium, and Ra mesothorium 1. 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 Ra, though mesothorium 1 in particular was still used for some time, with a footnote explaining that it referred to Ra. The known decay products of radium-226 received historical names including "radium", starting with radium emanation and then ranging from radium A to radium G, with the letter indicating approximately how far they were down the chain from their parent.
In 2013 it was discovered that the nucleus of radium-224 is pear-shaped. This was the first discovery of an asymmetrical nucleus.