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单词 critical mass
释义
critical mass

Physics
  • The minimum mass of fissile material that will sustain a nuclear chain reaction. For example, when a nucleus of uranium–235 disintegrates two or three neutrons are released in the process, each of which is capable of causing another nucleus to disintegrate, so creating a chain reaction. However, in a mass of U–235 less than the critical mass, too many neutrons escape from the surface of the material for the chain reaction to proceed. In the atom bomb, therefore, two or more subcritical masses have to be brought together to make a mass in excess of the critical mass before the bomb will explode.


Chemical Engineering
  • The smallest amount of a fissile material required to sustain a nuclear fission chain reaction. In a nuclear reactor, the chain reaction is controlled in order to produce thermal energy, which raises steam used to produce electricity. The fissionable material of an atomic bomb is divided into portions, each less than the combined critical mass. When they are brought together at the moment of detonation, their combined mass exceeds the critical mass.


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