单词	criticality
释义	criticality noun crit·​i·​cal·​i·​ty ˌkri-tə-ˈka-lə-tē  : a critical quality, state, or nature The true criticality of that basic political rationale is being demonstrated in the 1990s. Colin S. Gray But the inspector general of the Department of Homeland Security, in a report released Tuesday, found that the list was not child's play: all these "unusual or out-of-place" sites "whose criticality is not readily apparent" are inexplicably included in the official federal antiterrorism database. Eric Lipton specifically, physics : the state in which a mass of fissionable material sustains or is able to sustain a nuclear chain reaction Criticality can be achieved by increasing mass (adding more plutonium) or … by compressing a barely subcritical mass to increase its density. Daniel J. Lenihan How big is a critical mass? That depends on the proportion of fissile material and on its shape and configuration. Surrounding the mass with a neutron-reflecting substance further reduces the size needed for criticality, by returning neutrons that would otherwise escape. Richard Wolfson Word History First Known Use 1763, in the meaning defined above
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