Critical Mass

Name:
Critical Mass
Detailed information:
The minimum mass of a fissionable material (²³⁵U or ²³⁹Pu) that will initiate an uncontrolled chain reaction as in an atomic bomb. The critical mass of pure ²³⁹Pu is about 10 lb, and of ²³⁵U about 33 lb. This phenomenon was unknown before 1940.