![]() ![]() A fission bomb is in a race with itself: to successfully fission most of the material in the bomb before it blows itself apart. Two conditions must be met before fission can be used to create powerful explosions: 1) the number of neutrons lost to fission (from non-fission producing neutron captures, or escape from the fissionable mass) must be kept low, and 2) the speed with which the chain reaction proceeds must be very fast. If on average *more* than one neutron from each fission triggers another fission, then the number of neutrons and the rate of energy production will increase exponentially with time. ![]() If on average one neutron from each fission is captured and successfully produces fission then a self-sustaining chain reaction is produced. The nuclei of these isotopes are just barely stable and the addition of a small amount of energy to one by an outside neutron will cause it to promptly split into two roughly equal pieces, with the release of a great deal of energy (180 MeV of immediately available energy) and several new neutrons (an average of 2.52 for U-235, and 2.95 for Pu-239). Nuclear fission occurs when the nuclei of certain isotopes of very heavy elements, isotopes of uranium and plutonium for example, capture neutrons. 2.2.2 Basic Principles of Fusion Weapon Design.2.1.4 Basic Principles of Fission Weapon Design.2.1.3 Time Scale of the Fission Reaction.2.1.1 The Nature Of The Fission Process.Section 4 deals with the design and engineering of nuclear weapons in more detail, and the physics discussions there can be considered a continuation of Section 2. In this section I set forth the basic principles behind all nuclear weapons, although some familiarity with physics is assumed. The only authorized host site for the NWFAQ in English is the Nuclear Weapon Archive ()īack to Main Index 2.0 Introduction to Nuclear Weapon Physics and Designĭiscussions of physical principle, particularly nuclear physics, is unavoidable in most of the sections of this FAQ. Unauthorized host sites are expressly forbidden. Only authorized host sites may make this document publicly available on the Internet through the World Wide Web, anonymous FTP, or This material may be excerpted, quoted, or distributed freely provided that attribution to the author (Carey Sublette), theĭocument name (Nuclear Weapons Frequently Asked Questions) and this copyright notice is clearly preserved, and the URL of this website is included: Introduction to Nuclear Weapon Physics and Design Section 2.0 Introduction to Nuclear Weapon Physics and Design Nuclear Weapons Frequently Asked Questions ![]()
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