Answer the following question given this paragraph: 

Not every neutron produced by fission induces fission. Some neutrons escape the fissionable material, while others interact with a nucleus without making it fission. We can enhance the number of fissions produced by neutrons by having a large amount of fissionable material. The minimum amount necessary for self-sustained fission of a given nuclide is called its critical mass.


Q: The minimum amount necessary for self-sustained fission of a given nuclide is called what?

 Choices:

- its half-life

- its molar mass

- its activation energy

- its critical mass

A:
its critical mass
