The positively charged, high-energy, particles emitted from the nucleus of a radioactive atom.

They consist of two neutrons and two protons and so they are identical to the nucleus of a helium atom and are one of the products of the spontaneous disintegration of radioactive elements; such as, radium and thorium.

The process of emission, alpha decay, transforms one element into another, decreasing the atomic (or proton) number by two and the atomic mass (or nucleon number) by four.

It is a product of disintegration of various isotopes of both natural and artificial radioactive elements.