A sustained uranium fission chain reaction can be successfully initiated and maintained by________________?
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Answer: A. slowing down fast neutrons so that Uz fission continues by slow motion neutrons
Explanation
Slowing down fast neutrons via moderators drastically increases the probability of capturing them for further fissions. Thermal neutrons are much more effective at splitting uranium-235 nuclei than high-speed primary neutrons. Using a moderator bridges the gap between neutron release energy and absorption cross-section peaks. Natural uranium contains a very high proportion of non-fissile uranium-238 which absorbs fast neutrons. Moderators are light atomic materials like graphite or water that scatter and slow down neutrons efficiently. Elastic collisions between neutrons and moderator nuclei transfer kinetic energy away from the neutron particles.
Commercial nuclear reactors rely entirely on moderation to maintain controlled and continuous power generation cycles. Without a proper moderating medium the chain reaction would quickly die out due to insufficient thermal captures. Reactor safety systems depend on moderating characteristics to predict core behavior under various thermal conditions. Accelerating fast neutrons would further decrease their interaction cross-section with uranium-235 nuclei. Absorbing all neutrons would completely shut down the fission process rather than sustain a chain reaction. Enriching uranium increases fissile concentration but still requires moderation to manage neutron velocities effectively.
- Subject
- Engineering
- Category
- Mechanical Engineering
- Topic
- —
- Difficulty
- medium
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