Moderating a Neutron In a nuclear reactor, neutrons released by nuclear fission

Question

Moderating a Neutron In a nuclear reactor, neutrons released by nuclear fission must be slowed down before they can trigger additional reactions in other nuclei. To see what sort of material is most effective in slowing (or moderating) a neutron, calculate the ratio of a neutron's final kinetic energy to its initial kinetic energy, Kf/Ki, for a head-on elastic collision with each of the following stationary target particles. (Note: The mass of a neutron is m=1.009u, where the atomic mass unit, u, is defined as follows: 1u=1.66×1027kg.) A.) An electron (M=5.49×104u). B.) A proton (M=1.007u).  C.) The nucleus of a lead atom (M=207.2u).

Explanation / Answer

initial KE is Ki

final KE is Kf = (Ki-o.5*m*v^2)

Kf/Ki = (ki-0.5*m*v^2)/ki = 1-(0.5*m*v^2/ki)

more is the mass of the particel then less is the Kf/ki

if Kf/ki is smaller ,then that paricle( more massive particle) will moderate the reaction

among given particles nucleus of lead is more massive than other particles like electron AND proton

So the answer is C) the nucleus of a lead atom

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