Electron excitation is the transfer of a bound electron to a more energetic, but still bound state. This can be done by photoexcitation (PE), where the electron absorbs a photon and gains all its energy or by electrical excitation (EE), where the electron receives energy from another, energetic electron. Within a semiconductor crystal lattice, thermal excitation is a process where lattice vibrations provide enough energy to transfer electrons to a higher energy band. When an excited electron falls back to a state of lower energy, it undergoes electron relaxation. This is accompanied by the emission of a photon (radiative relaxation) or by a transfer of energy to another particle. The energy released is equal to the difference in energy levels between the electron energy states. But, because Noble gas atoms have a relatively high first ionization energy and the electrons don't carry enough energy to cause excitation therefore ionization and excitation of the atoms are unlikely and the probability of elastic scattering over all angles is approximately equal to the probability of collision. Ramseur and Townsend effect is somehow familiar in this case.