This study explores neutron energy attenuation in reactors using helium as a coolant. Helium’s interaction with neutrons is pivotal, reducing their energy and assimilating them into the background system. Unlike typical Maxwell-Boltzmann behavior, neutron scattering off helium results in a distinct nonthermal distribution, characterized by deviations in energy components defined as nonthermal energy. This paper highlights the significance of entropy in these interactions, noting that components with nonthermal energy exhibit higher entropy levels even at constant temperatures. Nonthermal energy not only prompts an immediate rise in temperature, but can also be directly measured through precise experiments. This phenomenon holds both scientific intrigue and substantial engineering relevance, offering insights into neutron dynamics within helium-cooled systems. A thorough analysis of nonthermal energy elucidates its accumulation within the system and its impact on energy balance, advancing our understanding of neutron interactions in such environments.