Alfahajoamiset

Alfahajoamiset, or alpha decay, are a form of radioactive decay in which an atomic nucleus emits an alpha particle, consisting of two protons and two neutrons (a helium-4 nucleus). The parent nucleus is transformed into a lighter daughter nucleus with its atomic number reduced by 2 and its mass number reduced by 4.

The process is governed by quantum tunneling through the Coulomb barrier rather than simple particle emission. Alpha decay typically occurs in heavy nuclei where the strong binding energy cannot sustain a large alpha cluster. The energy released, the Q-value, is usually in the range of about 4 to 8 MeV. Because the decay is a tunneling event, the half-life can vary enormously—from microseconds to billions of years depending on the isotope.

Alpha emissions deposit a large amount of energy locally and are highly ionizing, but alphas have very limited penetration: they are stopped by a sheet of paper or a few centimeters of air, making external exposure relatively low but dangerous if alpha-emitting material is ingested or inhaled. Detection relies on radiation detectors and alpha spectroscopy; the decay rate is often described by the Geiger–Nuttall law, which relates the half-life to the Q-value.

Natural alpha emitters include isotopes in the uranium and thorium decay series, such as uranium-238 (which decays to thorium-234 via alpha emission) and thorium-232 (to radium-228). Common alpha emitters also include radium-226, radon-222, polonium-210, and manufactured americium-241, used in smoke detectors. Alfahajoamiset are important in nuclear dating methods (e.g., uranium–lead dating) and in various applications requiring alpha spectroscopy.