Alphanreaktioner

Alphanreaktioner, also known as alpha reactions, refer to nuclear processes in which an alpha particle (a helium‑4 nucleus consisting of two protons and two neutrons) is either emitted from or absorbed by a nucleus. In an alpha emission, a heavy nucleus releases an alpha particle to reach a more stable configuration, often accompanied by a shift to a lower atomic mass. In an alpha absorption or capture reaction, the incoming alpha particle unites with the target nucleus, resulting in an excited compound nucleus that subsequently releases energy, often by emitting neutrons or gamma rays.

These reactions are distinguished by their relatively large mass and charge of the projectile, which creates significant Coulomb repulsion with the target nucleus. As a result, alpha particles require higher kinetic energies or quantum tunneling to overcome the Coulomb barrier. Cross sections for alpha reactions are typically lower compared to neutron or proton reactions at the same energy, making them less probable but still important in certain astrophysical and industrial contexts.

Alpha decay is one of the most common forms of spontaneous radioactivity and is integral to the decay chains of heavy elements such as uranium, thorium, and radium. The energy released in these decays—ranging from a few to several million electronvolts—can be directly measured and used to determine the age of rocks and minerals in radiometric dating methods. In contrast, alpha capture reactions play a key role in stellar nucleosynthesis, contributing to the creation of heavier elements in supernova environments where high temperatures and densities facilitate the penetration of alpha particles into atomic nuclei.

The first experimental observation of alpha radiation was made by Ernest Rutherford in 1899, who identified it as a distinct type of ionizing radiation. Since then, research in alpha reactions has expanded to include applications such as cancer therapy, where alpha-emitting radionuclides are targeted to destroy malignant cells with minimal damage to surrounding tissue. Industrial irradiation processes also employ alpha sources for surface analysis and material defect detection.