Atomkjerners

Atomkjerners are the compact cores at the centers of atoms. They consist of protons and neutrons, collectively called nucleons, bound together by the strong nuclear force. Their size is about 1 to 2 femtometers, and the nucleus carries a positive charge equal to the number of protons, the atomic number.

Nucleons form different nuclides. Nuclei with the same number of protons but different numbers of neutrons are isotopes. Stability depends on the neutron-to-proton ratio and shell effects; many nuclei are unstable and decay radioactively. The binding energy per nucleon varies, peaking near iron-56; this explains energy release in both fusion and fission. The mass defect equals the difference between the sum of nucleon masses and the actual nuclear mass.

Models used to describe atomkjerners include the liquid drop model for general trends and the nuclear shell model for detailed energy levels. The concept of magic numbers (2, 8, 20, 28, 50, 82, 126) denotes particularly stable configurations.

Nuclear reactions and decay processes involve atomkjerners changing through fusion, fission, or radioactive decay (alpha, beta, gamma). Reactions can be induced in reactors or accelerators, or occur naturally in stars.

Applications span energy production, medical imaging and therapy, dating, and materials analysis. The discovery of the nucleus began with Rutherford's scattering experiments, followed by Chadwick's identification of the neutron in 1932.