Masdefekten

Masdefekten, or mass defect, is the difference between the mass of a nucleus and the sum of the masses of its constituent protons and neutrons. This deficit arises because binding energy is released when the nucleus is formed, and, according to E = mc^2, the energy released appears as a small reduction in mass. The concept provides a direct link between mass and energy in nuclear systems.

The mass defect can be expressed mathematically as Δm = Z mp + N mn − Mnucleus, where Z is the number of protons, N the number of neutrons, mp and mn are the masses of the proton and neutron, and Mnucleus is the mass of the nucleus. If atomic masses are used instead of nuclear masses, the formula becomes Δm_atomic = Z mp + N mn + Z me − Matom, with me the electron mass and Matom the atomic mass. The binding energy B of the nucleus is then B = Δm c^2, meaning the mass defect converts into the energy that binds the nucleons together.

In practical terms, the mass defect is a measure of nuclear binding energy. Typical binding energies per nucleon range from about 7 to 8 MeV, with iron-56 near the maximum. For example, the helium-4 nucleus has a mass defect of roughly 0.029 u, corresponding to about 28 MeV of binding energy. Mass defects are determined through high-precision mass measurements and play a central role in nuclear physics, astrophysics, and the understanding of nuclear stability.

Related concepts include the semi-empirical (Weizsäcker) mass formula, nuclear binding energy curves, and processes such as fusion and fission, where changes in mass defect account for the energy released or absorbed.