A unit of energy equal to one million electronvolts, commonly used in nuclear and particle physics.The MeV (megaelectronvolt) is a unit of energy equal to one million electronvolts. An electronvolt is the energy an electron gains when accelerated through a potential difference of one volt, a tiny amount by everyday standards—about 1.6 × 10⁻¹⁹ joules. The MeV, however, is the natural scale for processes at the level of atomic nuclei and individual particles: nuclear decays, particle collisions, and the energies of photons in gamma-ray bursts. It is the standard currency for describing the masses of particles (via E = mc²), the binding energies of nuclei, and the thresholds for producing new particles in accelerators.
The electronvolt was introduced in the early 20th century as a convenient unit for single-particle energies in atomic physics. The prefix 'mega' (million) became standard in the 1930s as particle accelerators reached energies far beyond the keV scale, making the MeV a natural unit for nuclear physics.
In practice, the MeV is used to quote the kinetic energies of charged particles in accelerators and detectors, the energies of photons in nuclear transitions, and the rest masses of particles like electrons (0.511 MeV) and protons (938 MeV). When a particle with energy in the MeV range interacts with matter, it deposits that energy in a localized way—ionizing atoms and creating measurable signals in detectors. This is why the unit appears across the corpus: from neutrino experiments looking for signals at 17 MeV, to cosmic-ray studies comparing particle energies, to neutron scattering experiments probing nuclear structure.
The MeV is used to calibrate detectors in nuclear medicine (e.g., positron emission tomography), to specify the energies of therapeutic radiation beams in cancer treatment, and to report the energies of particles in high-energy physics experiments.
The energy released by splitting a single uranium-235 nucleus is about 200 MeV—enough to lift a grain of sand by a fraction of a millimeter, yet multiplied by billions of nuclei it powers nuclear reactors.





