A [[neutron]] (with a lower kinetic energy level of a few hundredths eV to an upper energy of about 100 eV) which has been slowed down in the moderation process from a high kinetic energy level of about 100 keV. The energy level of an epithermal neutron is just above that of a[[ thermal neutron]] (about 0.025 eV). See [[neutron]] and [[neutron log]]. Compare [[thermal neutron]].