Alpha particles are made up of two protons and neutrons bound together into a particle. They are produced mainly during alpha decay but can be produced in other ways. The mass of an alpha particle is 6.644 x 10-27 kilograms with an electric charge of 2e. Alpha particles are identical to helium nuclei and therefore sometimes they are interchanged.
Alpha particles have zero new spin on them. However they generally have a kinetic energy of about MeV and a velocity of about 5% the speed of light. They are highly ionizing from particle radiation but have low penetration depth. They stop within a few centimeters in the air or by the skin. Therefore, alpha particles are not harmful to humans.
Alpha particles are emitted by all larger radioactive nuclei. These large radioactive nuclei include uranium, thorium, actinium, radium and the transuranic elements. The alpha decay process must have a minimum-size atomic nucleus that can support it. Element 52, tellurium, is the lightest element that is capable of alpha emission. The process of emitting alpha particles from a nucleus leaves it in an excited state.
Alpha particles are useful in many aspects of our everyday life. They are used in smoke detectors, they are used to power space probes and artificial heart pacemakers, static eliminators and in certain types of radiation cancer therapy.