Alpha particle
A heavy, positively charged particle made of two protons and two neutrons: the same thing as a helium nucleus. It is thrown out by radioactive substances.
In 1899 Ernest Rutherford divided the radiation from radioactive substances into "alpha rays" and "beta rays" according to how easily they pass through matter. In 1909 Rutherford and Thomas Royds collected alpha particles in a thin glass vessel and saw the spectral lines of helium appear inside, showing that alpha particles are helium[1].
Rutherford went on to use alpha particles as bullets for probing atoms. Because alpha particles fired at gold foil were occasionally thrown back sharply, he concluded in 1911 that the charge of an atom is concentrated in a tiny region at its centre[2].
Alpha particles are also produced in D-T fusion, where they stay in the plasma and heat the fuel.
Related terms
- Atomic nucleusThe tiny, heavy core at the centre of an atom, made of protons and neutrons and carrying a positive charge.
- Bohr modelThe 1913 model in which electrons circle only on certain orbits and emit light of definite energy when jumping between them.
- D-T fusionThe fusion of deuterium (D) and tritium (T) into a helium-4 nucleus and a neutron. Almost every fusion reactor now under development is built around this reaction.