Question

What is the critical mass of a fission reaction? How is that different from the subcritical mass?

Answer 1

@aaronq

Answer 2

http://www.atomicarchive.com/Fission/Fission3.shtml

Critical mass is the mass required for a fission reaction to be self-sustaining.

Sub-critical means below critical mass (sub means under) so it will not be self sustaining under those conditions.

Answer 3

I should clarify critical mass to mean the minimal, or threshold mass needed. Anything at or above critical mass will lead to a self sustaining fission reaction.