This is the standard atomic weight, which is the weighted average of the atomic masses of all naturally occurring isotopes of radium.

It's important to note that this is an estimated value because:

* Radium is radioactive and decays over time, meaning its isotopic composition changes.

* There are multiple isotopes of radium, each with slightly different atomic masses.

Therefore, the atomic weight of radium is not a fixed number but rather an approximation based on the known isotopic abundances and their atomic masses.