A concept of Spectroscopy is resonance, which is the quality of sound and the corresponding frequency. Resonance was first used in mechanical systems, like pendulums. Mechanical systems that vibrate or oscillate will experience large amplitude oscillations when they are driven at their resonant frequency. Quantum mechanical systems use resonance as a duo of an atom and an oscillatory source of energy, known as a photon. The photon's frequency can be found with the following equation:
The energy of a photon is related to its frequency. A spectrum of the system response vs. photon frequency peaks at the resonant frequency or energy. Electron and neutrons relationship is comparable to the photon and atom, between their kinetic energy, wavelength, and frequency therefore can also excite resonant interactions.