Mass and energy are equivalent, linked byΔE = c2Δm so a mass can be written as an energy divided by c2. In particle physics, masses are usually given in MeV/c2 or GeV/c2. A particle of mass 1 MeV/c2 has a rest energy of 1 MeV.Converting to kilograms:
1 MeV/c2 = 1.6 × 10-13 J / (3.0 × 108 m s-1)2 = 1.78 × 10-30 kgUseful values:
• electron: 0.511 MeV/c2
• proton: 938.3 MeV/c2
• neutron: 939.6 MeV/c2The advantage of these units is that masses and energies can be compared directly. To create a particle of mass 938 MeV/c2, at least 938 MeV of energy must be available; a particle of mass 500 MeV/c2 has a rest energy of 500 MeV.Worked example: convert the proton mass to kg.
m = 938 × 1.78 × 10-30 = 1.67 × 10-27 kg
Going the other way for the electron: E = mc2 = 9.11 × 10-31 × (3.0 × 108)2 = 8.2 × 10-14 J, and 8.2 × 10-14 / 1.6 × 10-13 = 0.51 MeV, so the mass is 0.51 MeV/c2.
1 MeV/c2 = 1.6 × 10-13 J / (3.0 × 108 m s-1)2 = 1.78 × 10-30 kgUseful values:
• electron: 0.511 MeV/c2
• proton: 938.3 MeV/c2
• neutron: 939.6 MeV/c2The advantage of these units is that masses and energies can be compared directly. To create a particle of mass 938 MeV/c2, at least 938 MeV of energy must be available; a particle of mass 500 MeV/c2 has a rest energy of 500 MeV.Worked example: convert the proton mass to kg.
m = 938 × 1.78 × 10-30 = 1.67 × 10-27 kg
Going the other way for the electron: E = mc2 = 9.11 × 10-31 × (3.0 × 108)2 = 8.2 × 10-14 J, and 8.2 × 10-14 / 1.6 × 10-13 = 0.51 MeV, so the mass is 0.51 MeV/c2.