By international agreement, they defined the atomic mass unit (symbol: amu or u) as precisely one-twelfth the mass of an electrically neutron carbon-12 atom (12 6C). Therefore, one atomic mass unit is equivalent to 1.6605 × 10−27 kg. While this new unit of mass provides a convenient description of the average mass of a nucleon, it is still a bit cumbersome. Enter Albert Einstein (1879–1955) and his famous energy-mass equivalence equation that emerged from special relativity. The rest mass equivalent energy (E0) of an atomic mass unit is determined from equation 4.3 as follows: E0 = (∆m0) c2
where (∆m0) is change in mass of an object with no kinetic energy (therefore at rest) and c is the speed of light. After paying careful attention to unit conversions and mathematical calculations, we discover that one atomic mass unit has the energy equivalence of 931.5 million electron volts (MeV). In other words, the transformation of just a small fraction of the mass of a nucleon accounts for the enormous amounts of energy released in fission, fusion, or radioactive decay. The energy equivalent of an electron is approximately 0.51 MeV
Atomic and Nuclear Structure
