ATOMIC & NUCLEAR PHYSICS A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z                    HOME ABOUT CATEGORIES SITE MAP COPYRIGHT ADVERTISE CONTACT entire Web this site critical mass 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 4.5 kg, and of 235U about 15 kg. Related category    • ATOMIC AND NUCLEAR PHYSICS Also on this site: Encyclopedia of Alternative Energy & Sustainable Living Encyclopedia of History Transport Concepts & Designs (partner site) BACK TO TOP