Highly effective neutron moderators are generally materials characterized by containing____________________?
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Answer: A. light weight atoms
Explanation
Effective neutron moderators need lightweight atoms to maximize the transfer of kinetic energy. When fast neutrons collide with similarly sized light nuclei, they lose speed very rapidly. This efficient slowing down process creates thermal neutrons capable of sustaining further fissions. Elastic scattering is the primary physical mechanism by which moderators slow down high-speed neutrons. Common moderator materials include heavy water, ordinary light water, and high-purity reactor graphite. Hydrogen and deuterium atoms possess masses very close to that of a single neutron.
Thermal nuclear reactors require these moderators to maintain efficient fuel consumption and power output. Selecting appropriate lightweight materials prevents unnecessary neutron capture while slowing them effectively. Graphite and water moderators have historically powered numerous commercial and research nuclear reactors worldwide. Option B is wrong because heavy weight atoms would cause neutrons to bounce off without losing speed. Option C is incorrect because critical atoms refer to fissionability rather than moderating efficiency properties. Option D and E are invalid because mass ratio is the fundamental physical criterion for moderation.
- Subject
- Engineering
- Category
- Mechanical Engineering
- Topic
- —
- Difficulty
- medium
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