NRF reactions are the result of nuclear absorption and subsequent emission of high-energy photons (gamma rays). As a gamma ray strikes the nucleus, the nucleus becomes excited (that is, the nuclear system as a quantum mechanical ensemble is put into a state with a higher energy). Much like electronic excitation, the nucleus will decay toward its ground state, releasing a high-energy photon at a number of possible, discrete energies. Thus, NRF can be quantified using spectroscopy. Nuclei can be identified by the distinct pattern of NRF emission peaks, although NRF analysis is much less straightforward than typical electronic emissions.