Does radium have a critical mass?

BEGIN EDIT (in reply to your update).

There are a number of different types of radioactive decay (e.g. alpha decay, beta decay).

Fission is just one type of decay - where a large nucleus splits apart (into fission fragments) either spontaneously or because it first absorbs a free neutron which makes the nucleus unstable anf then split (induced fission).

But in beta decay for example, a neutron turns to a proton and a beta particles (and also an antineutrino, though this is not taught at an introductory level). This is a form of radioactive decay - but it has nothing whatsoever to do with fission.

E.g. see link.

END EDIT

_____________________________________________

No. Critical mass only applies to fissile isotopes (ones that are able to undergo fission). Radium has no fissile isotopes.

Radium Mass