Which statement about neutrons is true?

• A. Neutrons are charged particles
• B. Fast neutrons have high kinetic energy compared to surrounding material
• C. Thermal neutrons have the same kinetic energy as the surrounding material
• D. Neutrons cannot cause fission

Answer: (B)

Neutrons move through matter with energies that determine how they interact. Fast neutrons carry high kinetic energy, typically in the MeV range, which means they are moving much faster than the surrounding material, whose particles have thermal energies around 0.025 eV at room temperature. Because of this energy difference, fast neutrons interact differently (for example, they’re less readily captured per collision) and can initiate fission in certain nuclei. This makes the statement about fast neutrons having high kinetic energy relative to the environment true. The other statements aren’t correct: neutrons are neutral particles, not charged; thermal neutrons have energies tied to the material’s temperature but aren’t strictly the same exact energy as every surrounding particle; and neutrons can indeed cause fission in suitable nuclei.