Uranium-235 (U-235) is fissionable by thermal neutrons due to its low activation energy, which allows for irreversible deformation of the nucleus with minimal energy input. In contrast, Uranium-238 (U-238) requires energy greater than 1.4 MeV for fission, as its activation energy barrier is significantly higher. The semi-empirical mass formula explains this phenomenon, highlighting the interplay between the Coulomb and surface area terms during neutron absorption. Understanding these principles is crucial for nuclear physics and reactor design.
PREREQUISITESNuclear physicists, students studying nuclear engineering, and professionals involved in reactor design and safety analysis will benefit from this discussion.
neu said:235 is fissle as it's activation energy/fissile barrier, the energy required to cause irreversible deformation of the nucleus is very low.
If you look at the semi empirical mass formula the coulomb and surface area terms reduce and increase respectivly (like a harmonic oscillator) when a neutron is absorbed by the nucleus. If the energy is great enough the coulomb term dominates and causes an irreversible deformation which leads to break up of the nucleus.
the activation energy is the energy required to do this
Im studying this currently myself so apologies if I am saying what you already know